design and fabrication of parabolic trough solar …scbaghdad.edu.iq/library/physics/phd/2011/design...

Republic of Iraq

Ministry of Higher Education

& Scientific Research

University of Baghdad

College of Science

Design and Fabrication of Parabolic

Trough Solar Collector for Thermal

Energy Applications

A Thesis Submitted to the

College of Science / University of Baghdad

In Partial Fulfillment of the Requirements for the Degree of

Doctor of Philosophy in Physics

BY

Falah Abd Alhasan Mutlak (M.Sc. 2002)

Supervised By Prof. Dr. Baha T. Chiad

Chief of Researchers Dr. Naseer .K. Kasim

March 2011 1432

Supervisor Certification

We certify that this thesis was prepared under our supervision at the

Physics Department, College of Science, University of Baghdad, as a partial

requirement for the degree of doctor of philosophy in Physics / Laser

Signature :

Name : Dr. Baha T. Chiad Title : Professor Address : Vice-president of Baghdad University Date : / / 2011 Signature :

Name : Dr. Nasser K. Kasim Title : Chief Researcher Address : Center of Renewable Energy, Ministry of Electricity Date : / / 2011 In view of the available recommendations, forward this thesis for

debated by the examination committee.

Signature :

Name : Prof. Dr. Raad A. Rudhi Title : Chairman of Physics Department Address : College of Science, University of Baghdad Date : / / 2011

Examination Committee Certification

We certify that we have read the thesis entitled" Design and Fabrication of Parabolic Trough Solar Collector for Thermal Energy Applications" and examined the student," Falah Abd Alhasan Mutlak" in its content ,and that in our opinion it is adequate for the Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Physics .

Approval by the Deanship of Department of physics in collage of science, University of Baghdad

Signature:

Name : Dr. Saleh Mahdi Ali Title : Professor Address : Dean of the College of Science University of Baghdad Date: / / 2011

Signature:

Name: Dr.Abass J.H.Al-Wattar Title : Professor Address: Dept. of Physics College of Science University of Baghdad (Chairman)

Signature:

Name:Dr.Raad M.S.Al-Haddad Title : Professor Address: Dept. of Physics College of Science University of Baghdad (Member)

Signature:

Name : Dr. Manal M.Abdullah Title : Assist. Professor Address: Dept .of Physics College of Science University of Baghdad (Member)

Signature:

Name : Dr. Ali H. Al-Hamadani Title : Assist. Professor Address: Energy and Fuel Center University of Technology (Member) Signature:

Name: Dr.Nasser K. Kasim Title : Chief Researcher Address: Center of Renewable Energy, Ministry of Electricity ( Supervisor)

Signature:

Name:Dr.Abdul-Hussain K.Iltaif Title : Chief Researcher Address: Center of Applied Physics, Ministry of Science & Technology (Member)

Signature:

Name: Dr. Baha T. Chiad Title : Professor Address: Dept. of Physics College of Science University of Baghdad (Supervisor)

DEDICATION

To my first teacher who gave me strength …. My father.

To her who planted love in my heart ………. My mother.

To the symbols of love and fait fullness …. My brothers and sisters

To noble spirit for my dear life partner Dr. Ala and my child Saif

ACKNOWLEDGMENTS

Thanks to God the Compassionate, the Merciful and my God bestow peace on

Prophet Mohammed, member of his family and his followers.

I would like to express my deep gratitude to my supervisors Prof. Dr.Bahaa T. Chiad and Dr. Nasser K. Kasim, who suggested this project and generously gave guidance throughout this work.

My gratitude is due to the head and staff of the Physics Department in the College of Science for their assistant and support during the years of my study and research.

I would like to express my deepest gratitude to my colleagues and staff of Thermal Solar Energy Department, especially, Dr. Falah Ibrahim, Eng. Aed Ibrahim, Eng. Rasim Ahmed, Eng. Salah Abd, Eng. Hamza Jabbar, Eng. Khalil, Eng. Hazim, Mr.Tarik and Mr.Alla for supporting me along the experimental work,

I feel grateful to Dr. Mohammed A. Saleh , Dr. Jaber O. Dahloos, Dr. Qusay Adnan, Dr. Udai M. Naief and Mr.Saleh S. Abbas for the valuable advice.

Finally, my thanks go to the members of my family for help and encouragement for various kinds of assistance, and to anyone who helped in one way or another in bringing out this work.

My God bestow health and happiness to all of them.

Falah A-H Mutlak

University of Baghdad College of science Department of Physics Name: Falah Abdalhasan Mutlak Title of Thesis: "Design and Fabrication of Parabolic Trough Solar Collector for Thermal Energy Applications" Supervisor: Dr. Baha T. Chiad Supervisor: Dr. Nasser K. Kasim Abstract

This work presents the design, construction and investigation of experimental study of a Parabolic Trough Solar Collector (PTSC). It is a construction of a matrix of mirrors to form the parabolic reflector (1.8 2.8 m). They are aligned by a laser beam. Solar tracker has been constructed (using two-axis) to track PTSC according to the direction of solar radiation. Synthetic oil is used as a heat transfer medium because of its capability to have load of high temperature (400 oC). The storage tank has been fabricated of stainless steel of size 50 liter with two loads: the first load is designed as a solar cooker and the second one for space heating. Three types of experimental tests have been achieved using non-coated metallic, coated metallic and evacuated glass receiver. The experimental tests have been carried out in Baghdad with climatic conditions (33.3o N, 44.4o E) during selected days of the months of October, November and December. The performance of PTSC is evaluated by using outdoor experimental measurements including the useful heat gain, the thermal instantaneous efficiency and the energy gained by the storage tank fluid. The value of each of these parameters is observed to be maximum, whenever evacuation is used. The storage tank fluid temperature is increased from 30 oC at 9:30 am to be 135 oC at 13:30 pm without drawing-off heat transfer fluid (HTF), when the maximum HTF outlet temperature from evacuated receiver was 150 oC in typical December days. The heat loss coefficient of the evacuated receiver has been found 7.5 W/oCm2, while the heat loss coefficients were 18.3 W/oCm2 and 20.6 W/oCm2 for non-coated and coated metallic receivers, respectively, and the most heat losses occur through storage tank. The average thermal efficiency for the collector is approximately 61% when evacuated receiver is used. The heat losses which occurred at high temperatures which, decreased the average thermal efficiencies to 51% and 40%, are respectively the selectively coated and non-coated metallic receivers. It was also found that the obtained characteristic curve of the tested collector is considerably higher than that of a typical collector which can be attributed to the lower thermal losses of the evacuated glass envelope. Generally, the performance results of this collector which is fairly acceptable, considering that it is the first attempt to fabricate such collector locally and evaluated in Iraq environment. The final results establish the technical feasibility of using PTSC for applications requiring thermal energy at temperatures up to 150 oC for solar irradiance about 400-500 W/m2.

I

Abstract

This work presents the design, construction and investigation of experimental study of a Parabolic Trough Solar Collector (PTSC). It is a construction of a matrix of mirrors to form the parabolic reflector (1.8 2.8 m). They are aligned by a laser beam. Solar tracker has been constructed (using two-axis) to track PTSC according to the direction of solar radiation. Synthetic oil is used as a heat transfer medium because of its capability to have load of high temperature (400 oC). The storage tank has been fabricated of stainless steel of size 50 liter with two loads: the first load is designed as a solar cooker and the second one for space heating. Three types of experimental tests have been achieved using non-coated metallic, coated metallic and evacuated glass receiver. The experimental tests have been carried out in Baghdad with climatic conditions (33.3o N, 44.4o E) during selected days of the months of October, November and December. The performance of PTSC is evaluated by using outdoor experimental measurements including the useful heat gain, the thermal instantaneous efficiency and the energy gained by the storage tank fluid. The value of each of these parameters is observed to be maximum, whenever evacuation is used. The storage tank fluid temperature is increased from 30 oC at 9:30 am to be 135 oC at 13:30 pm without drawing-off heat transfer fluid (HTF), when the maximum HTF outlet temperature from evacuated receiver was 150 oC in typical December days. The heat loss coefficient of the evacuated receiver has been found 7.5 W/oCm2, while the heat loss coefficients were 18.3 W/oCm2 and 20.6 W/oCm2 for non-coated and coated metallic receivers, respectively, and the most heat losses occur through storage tank. The average thermal efficiency for the collector is approximately 61% when evacuated receiver is used. The heat losses which occurred at high temperatures which, decreased the average thermal efficiencies to 51% and 40%, are respectively the selectively coated and non-coated metallic receivers. It was also found that the obtained characteristic curve of the tested collector is considerably higher than that of a typical collector which can be attributed to the lower thermal losses of the evacuated glass envelope. Generally, the performance results of this collector which is fairly acceptable, considering that it is the first attempt to fabricate such collector locally and evaluated in Iraq environment. The final results establish the technical feasibility of using PTSC for applications requiring thermal energy at temperatures up to 150 oC for solar irradiance about 400-500 W/m2.

V

Symbol Description Unit i Incidence angle of solar radiation Degree

Optical efficiency -------

Thermal efficiency of the system -------

Emissivity -------

Stefan –Boltzmann Constant W/m2.K4

Wind speed m/s

Altitude angle ,absorptivity Degree,----

Declination angle Degree

Transmissivity --------

Dynamic viscosity Kg/m.s

Kinematic viscosity m2/s

a Acceptance half angle Degree

Unit Description Symbol m2 Aperture area Aa

m2 Receiver area Ar ……. Air mass AM

J/Kg. K Specific heat at constant pressure Cp …… Geometric concentration ratio Cr

…… Days number from year dn Km Distance between the sun and the earth D Km Mean distance between the sun and the earth Ds-e

minute Equation of time ET W/m2.K Radiation heat transfer coefficient W/m2.K Convection heat transfer coefficient Degree Hour angle hs W/m2 Beam solar radiation Ib

W/m2 Diffuse solar radiation Id W/m. K Thermal conductivity

Kg Mass m W/m2 Absorbed solar radiation

W Heat loss W Useful heat gain s Time t

oC Temperature W/m2.K Heat loss coefficient UL

Latin Symbols

Greek Symbols

VI

Symbol Description Equation

Rayliegh number

Modified Grashof number

Nusselt number h. Dh/

Prandtl number

Reynolds number Dh/

Symbol Description

Aperture amb Ambient

Inner glass

Outer glass

Convection

Conduction

Radiation

Mean inst. instantaneous

Beam radiation

Diffuse radiation out outlet in Inlet

Initial

Final

Average

Dimensionless Group

Subscript

VII

Symbol Description ETR Evacuated Tube Receiver PV Photovoltaic

PTSC Parabolic Trough Solar Collector HCE Heat Collection Element ETR Extraterrestrial Solar Radiation HTF Heat Transfer Fluid

Abbreviations

V

Unit Description Symbol m2 Aperture area Aa

m2 Receiver area Ar

m Altitude of location above mean sea level AL ……. Air mass AM

J/Kg. K Specific heat at constant pressure Cp …… Geometric concentration ratio Cr

…… Days number from year dn Km Distance between the sun and the earth D Km Mean distance between the sun and the earth Ds-e

m Diameter of glass envelope Dg m Diameter of receiver Dr

minute Equation of time ET m Focal length f Friction factor ff

W/m2.K Radiation heat transfer coefficient hr W/m2.K Convection heat transfer coefficient hw

Degree Hour angle hs W/m2 Beam solar radiation Ib

W/m2 Diffuse solar radiation Id W/m2 Extraterrestrial solar radiation Io W/m2 Solar constant Isc

Degree Incidence angle modifier K(θi) Degree Latitude angle L Degree Standard meridian Lst W/m. K Thermal conductivity K

Kg Mass m W/m2 Absorbed solar radiation

W Heat loss W Useful heat gain m Parabolic radius r

sec Time t oC Temperature

W/m2.K Overall Heat loss coefficient UL

m Aperture width W Degree End losses XEND

Symbol Description Unit a Acceptance half-angle Degree

i Incidence angle of solar radiation Degree

r Rim angle Degree

s Sun's subtend angle Degree

z Zenith angle Degree z Solar azimuth angle Degree

Latin Symbols

Greek Symbols

VI

s Solar altitude angle Degree

Optical efficiency -------

Thermal efficiency of the system -------

Emissivity -------

Stefan –Boltzmann Constant W/m2.K4

Wind speed m/s

Altitude angle ,absorptivity Degree,----

s Sun's Declination angle Degree

Transmissivity --------

Dynamic viscosity Kg/m.s

Kinematic viscosity m2/s

a Mirror reflectance -------

Symbol Description Equation

Rayliegh number

Modified Grashof number

Nusselt number h. Dh/

Prandtl number

Reynolds number Dh/

Symbol Description

Aperture amb Ambient

Inner glass

Outer glass

Convection

Conduction

Radiation

Mean inst. instantaneous

Beam radiation

Dimensionless Group

Subscript

VII

Diffuse radiation out outlet in Inlet

Initial

Final

Average

Symbol Description CIMAT Centro de investigaciones Energeticas

Medioambientales Tecnologicas ET Euro Trough

ETR Extraterrestrial Solar Radiation HTF Heat Transfer Fluid HCE Heat Collection Element LST Local Standard Time NIR Near Infrared PSA Plataforma Solar de Almeria

PTSC Parabolic Trough Solar Collector PV Photovoltaic

SEGS Solar Electric Generating System UV Ultraviolet

Abbreviations

II

Page ITEM I Abstract II Table of Contents

V Nomenclature CHAPTER ONE: Theoretical Part

1 1.1 Introduction 2 1.2 Basics of Solar Thermal/Concentrating Solar Power 3 1.3 Solar Potential in Iraq 3 1.3.1 The Intensity of Solar Radiation 5 1.3.2 Solar Energy Exposure 5 1.3.3 Solar Energy Applications 6 1.4 Fundamental of Solar Radiation / Solar Geometry 6 1.4.1 Sun Earth Geometrical Relationship 7 1.4.2 Basic Earth-Sun Angles 8 1.4.3 Derived Sun-Earth Angles

10 1.5 Solar Radiation 10 1.5.1 Extraterrestrial Solar Radiation 11 1.5.2 Terrestrial Solar Radiation 12 1.5.3 Spectral Distribution of Solar Radiation 14 1.6 Geometry of Parabolic Trough Solar Collector 16 1.7 Optical Performance for PTSC 16 1.7.1 Incidence Angle Modifier 17 1.7.2 End Effect Correction 18 1.7.3 Optical Efficiency of the PTSC 18 1.8 Thermal Performance and Losses of PTSC 18 1.8.1 Overall Heat Loss Coefficient 20 1.8.2 Heat Transfer to Fluid 21 1.8.3 Overall Heat Transfer Coefficient and Factors 22 1.8.4 Thermal Efficiency of a PTSC 24 1.9 Heat Collection Element (HCE) 25 1.9.1 Heat Transfer Fluids fo PTSC 26 1.10 Storage of Thermal Energy 26 1.10.1 Sensible Heat Storage 26 1.10.2 Latent Heat Storage 27 1.11 Sun Tracking System 28 1.12 Literature Review

34 1.13 Aim of the WorkCHAPTER TWO: Experimental Part

35 2.1 Introduction

35 2.2 Description of Parabolic Trough Solar Collector

Table of Contents

III

36 2.3 Design Concepts for the Mechanical Unit 36 2.3.1 Stationary Base Assembly 37 2.3.2 Moving Assembly 37 2.3.2.1 Tilting Motion 37 2.3.2.2 Axial Motion 38 2.3.2.3 Two Groups Assembly 38 2.4 Design Concepts for Reflecting Parts Assembly 39 2.4.1 The First Way for Design Reflecting Parts Assembly 40 2.4.2 The Second Way for Design Reflecting Parts Assembly 42 2.5 Assembly of the Trough Parts 42 2.5.1 Trough Reflector Assembly 44 2.5.2 Mechanical Unit 46 2.6 Comparison between Two Fabricated 47 2.7 Heat Collecting Elements 48 2.7.1 Thermal Metallic Receiver 49 2.7.2 Optical Efficiency of the Receivers 50 2.7.3 Evacuated Glass Receiver 53 2.8 Tracking and Control System 56 2.9 Design Concepts of the Thermal Storage 58 2.10 Apparatus and Instrumentation 61 2.11 Experimental Setup and Procedure

CHAPTER THREE: Results and Discussion

63 3.1 Introduction

63 3.2 Solar Calculations 65 3.3 Geometry Analysis of the PTSC 67 3.4 Total Solar Radiation and Temperatures for a Non-Coating

Metallic Receiver 70 3.5 Total Solar Radiation and Temperatures for Coating

Metallic Receiver 72 3.6 Total Solar Radiation and Temperatures for an Evacuated

Glass Receiver 74 3.7 Thermal Stratification in the Storage Tank without HTF

Draw-off 75 3.8 Performance Analysis of PTSC 75 3.8.1 Useful Heat Gain

77 3.8.2 Effect of Beam Solar Flux on the Useful Energy Gain

79 3.8.2 The Instantaneous Thermal Efficiency

80 3.8.3 Energy Gained by the Storage Tank

83 3.9 Performance Curve of the PTSC

IV

83 3.9.1 Non – coating metallic receiver

85 3.9.2 Coating metallic receiver

86 3.9.3 Evacuated – glass receiver

87 3.9.3 Comparison of the results

88 3.10 Effect of the HTF Inlet Temperature on the Thermal Efficiency of the Collector

90 3.11 Heat Loss Coefficient for the Storage Tank 91 3.12 Heat losses for the PTSC without Draw-off 93 3.13 Conclusions 94 3.14 Future Works

REFERENCES

95-101 References

APPENDICES 102 Appendix (A) Solar Calculations

104 Appendix (B) Heat transfer equations rate for the receiver

105 Appendix (C -Tables) 109 Appendix (D -Tables) 113 Appendix (E-Tables) 117 Appendix (F) Intercept factor calculations 119 Appendix (G) Optical efficiency of the receivers 120 Appendix (H)Thermal losses calculations for Connecting tube 122 Appendix (I) Design Calculations of Storage Tank 128 Appendix (J) Design Drawings of the PTSC

CHAPTER ONE

Theoretical Part

Chapter One Theoretical Part

1

1.1 Introduction

The contemporary trends of energy focus on modern permanent

renewed and alternative unlimited sources which have less polluted

remain in order to avoid probable drain of other sources. The solar energy

source has taken up priority over other sources because of its ability to be

achieving human needs of energy, moreover it has a large active

contribution in future since it has no pollution harm or damage and it is

able to transform into other kinds of energy such as: electrical,

mechanical and thermal energy. Recently, the researches of energy of

solar system has witnessed rapid expansion in applications in most world

regions including the Arab countries, concentrating on ways which leads

to increase and developed its efficiency of solar system applications.

There is no doubt that the regions that has suitable moderate climate with

high temperature, have got many opportunities and ability to obtain the

maximum energy of solar system with high efficiency. Iraq is one of that

countries, it can receive solar rays with approximate time of 4000 hours

per year in convenient places of solar energy. When dealing with solar

energy, there are two basic choices, the first is photovoltaic, which is

direct energy conversion that converts solar radiation to electricity. The

second is solar thermal systems, in which the solar radiation is used to

provide heat to a thermodynamic system, thus creating mechanical energy

that can be converted to electricity. Photovoltaic systems, efficiencies are

of the order of 10 to 20 percent, where in a solar thermal system,

efficiencies as high as 30 percent are achievable [1]. In this study we have

worked on thermal utilization of solar intensity. Atypical thermal solar

utilization system consists of one or more solar collectors, connected to a

storage and distribution system. A solar collector is advice that utilizes

the solar radiation to heat a fluid, which can then be used for suitable


2

applications [2]. There are basically three types of thermal solar

collectors: flat-plate, evacuated tube and concentrators.

1.2 Basics of Solar Thermal Collection / Concentrating Solar

Power

The basic principle of solar thermal collection is that when solar

radiation is incident on a surface (such as that of a black – body) part of

this radiation is absorbed, thus increasing the temperature of the surface.

As the temperature of the body increases, the surface loses heat at an

increasing rate to the surroundings. Steady – state is reached when the

rate of the solar heat gain is balanced by the rate of heat loss to the

ambient surroundings [3]. Solar concentrators increase the amount of

incident energy on the absorber surface as compared to that on the

concentrator aperture. The increase is achieved by the use of reflecting

surfaces or other optical means which concentrate the incident radiation

onto a suitable absorber / receiver. Therefore, a solar concentrator

generally consists mainly of (i) a focusing device, (ii) an absorber /

receiver provided with or without a transparent cover, and (iii) a tracking

device for continuously following the sun. Concentrating Solar Power

(CSP) technologies are usually categorized in three different concepts, as

shown in figure (1-1). They work as follows [4]:

Troughs: parabolic trough – shaped mirror reflectors linearly

concentrate sunlight onto receiver tubes, heating a thermal

transfer fluid which is then used to produce superheated

steam.

Dishes: parabolic dish – shaped reflectors perfectly

concentrate sunlight in two dimensions and run a small

engine or turbine at the focal point.


3

Towers: central receivers use numerous heliostats to

concentrate sunlight onto a central receiver on the top of a

tower.

The solar flux concentration ratio typically obtained is at the level of

30 – 100, 100 – 1000, and 1000 – 10000 for trough, tower and dish

systems, respectively [5].

1.3 Solar Potential in Iraq

The available solar activities for investment in Iraq depend on

many factors such as:

1.3.1 The Intensity of Solar Radiation

Theoretically Iraq is considered at the second level of solar

exposure radiation as shown in figure (1-2). The daily averaged solar

insolation contour map of Iraq as shown in figure (1-3) have established

that almost all of Iraq has the potential areas for establishing large – scale

solar utilities. In Iraq, the annual average of energy received daily from

the sun ranges between 4.5 – 5.4 kWh/m2. Figure (1-3) shows the daily

average for solar exposure in Iraq which is high degree thus; Iraq is

among the most suitable countries for solar applications [6].

Figure (1-1) Schematic diagrams of the three CSP systems (Tower, Dish, and Trough) [5]


4

Figure (1-2) Classification of solar radiation exposure [7].

38 39 40 41 42 43 44 45 46 47 48 4928

29

30

31

32

33

34

35

36

37

38

4.44.454.54.554.64.654.74.754.84.854.94.9555.055.15.155.25.255.35.355.45.45

Figure (1-3) Daily-averaged solar insolation for different locations in Iraq [6].


5

1-3-2 Solar Energy Exposure

Solar energy exposure period in Iraq is available for a long period

as shown below:-

Table (1-1) Solar exposure period in Iraq [6]

1-3-3 Solar Energy Applications

Technically, Iraq's weather is convenient for all solar applications

but from the economic aspect there are some factors must be taken in to

consideration while choosing the application.

First the Iraqi environment has particular weather conditions such as dust

spread for a long period each year. The thermal solar energy utilization is

less affected in accordance to this type of environment than the utilization

of solar energy in direct generation of electricity by using photovoltaic

(PV) technology. Because the PV absorb the visible part and little from

NIR part of solar spectrum (range 400-1100 nm) the visible part intensity

is influenced obviously by dust atmosphere while the thermal system

works mainly on long wave-length infrared of spectrum which is less

affected by dust. Second the Iraqi family's needs of energy is distributed

between (65-70%) for heating and cooling equipments per a year and

30% for lighting and other electrical sets, so there is a need for thermal

Solar Exposure period ِِِQuantity

4100 hours Sunny hours

333.6 days Sunny days

31.4 days cloudy days


6

system that has efficiency of conversion the solar energy to thermal about

(60-70%). Third the cost of electrical production of PV system is about

20 Cent/kWh while it cost 10 Cent/kWh with thermal system. Fourth the

storage of energy of thermal system is better in quantity, cost and age

than PV system.

1.4 Fundamentals of Solar Radiation /Solar Geometry

In order to track the sun throughout the day for every day of the

year, there are geometric relationships for the position of the collector

with respect to the time that is needed to be known.

1.4.1 Sun Earth Geometrical Relationship

The earth revolves around the sun every 365.25 day in an elliptical

orbital called eclliptic plane, and it completes a full rotation about its axis

every 24 hours. The earth – sun distance is smallest on December 21

(perihelion, 1.47 1011 m) and highest on June 21 (aphelion, 1.52 1011

m) [8]. The axis of rotation of the earth is tilted at an angle of 23.45° with

respect to its orbital plane, as shown in figure (1.4). This tilt remains

fixed and is the cause for the seasons throughout the year [9].

Figure (1-4) Motion of the earth about the sun [10].


7

1.4.2 Basic Earth – Sun Angles

The position of a point P as shown in figure (1-5) on the earth

surface with respect to the sun's ray is known at any instant by the

following angles [11].

The Latitude angle (L): is the angular distance of the point p north or

south of the equator. It is the angle between the radius vector op and its

projection on the equator.

The Hour angle (hs): is the angle measured in the earth's equatorial plane

between the projection of op and the projection of a line from the center

of the sun to center of the earth. The hour angle can be written as follows:

)12(15 SThs Degree ……………… (1-1)

Where ST is solar time in hours, as a result of the earth's rotation hs varies

at the rate of 15o per hour, that hs = 0 at solar noon [12]. The conversion

between solar time and local time requires knowledge of the location

Figure (1-5) Basic earth – sun angles [11].


8

(longitude), the day of the year, and local standard meridian as in the

following equation [12]:

ETLLLSTST locst )(4 ………….. (1-2)

Where LST is the local standard time, Lst is the standard meridian for

local time zone (45o for Baghdad), Lloc is the longitude of location (44o

for Baghdad), and ET is the equation of time in minutes and equal to:

BSinBCosBSinET 5.135.7287.9 …… (1-3)

Where B, in degree is defined as:

364/)81(360 ndB …………………… (1-4)

Where dn is the day number during the year (1 dn 365). The values of

the hour angle east due south (morning) are negative; and the values west

of due south (afternoon) are positive [12].

The Sun's declination angle s is the angular distance of a sun's ray

north (or south) of the equator. It’s the angle between a line extending

from the center of the sun to the center of the earth and the projection of

this line upon the earth's equatorial plane. The angle of declination s

is estimated by use the following equation [13].

365

28436045.23 no

s

dSin Degree ……… (1-5)

1.4.3 Derived Sun – Earth Angles

In addition to the three basic angles hour, latitude and sun's

declination angles, several other angles are used to define the sun's

position in relation to the surface as shown in figure (1-6) [14]:


9

Zenith angle (z): is the angle QOV between the sun's rays and a line

perpendicular to horizontal surface at O.

Solar altitude angle (s): is the angle QOH on a vertical plane between

the sun's ray and its projection on the horizontal plane, i.e. the

complement of the zenith angle. It follows that:

090 zs ……………………………………………….. (1-6)

As can be calculated by use of the following [15].

ssss hCosCosLCosSinLSinSin …… (1-7)

Solar azimuth angle (z): is the angle HOS it is the angular displacement

from south to the horizontal projection of the sun's rays. The azimuth

angle is found by using the following equation [16].

LCosCos

SinLSinSinCos

s

ssz

…………………… (1-8)

Figure (1-6) Derived sun – earth angles [14].


10

1.5 Solar Radiation

The sun is a spherical source of about 1.39 million Km diameter.

Due to its immense, but finite size, it has an angular diameter of 0.53o

(32') as shown in figure (1-7). The solar radiation is a flow of energy

outward from the sun constantly and simultaneously in all directions. The

solar radiation can be divided into two types, extraterrestrial and

terrestrial [17].

1.5.1 Extraterrestrial Solar Radiation

Solar radiation outside the earth's atmosphere is called

extraterrestrial solar radiation (ETR) (Io). The ETR on top of the earth's

surface depends on many factors such as the distance and orientation.

ETR at the mean sun earth distance, Dm is called the solar constant, Isc

was first introduced by the French scientist Pouillet in 1837 [17] and

current accepted value from NASA is said to be 1353 W/m2 , and the

mean earth sun distance is 1.4961011m. Because of the variation in

seasonal solar due to elliptical orbit of the earth about the sun, the earth

sun distance has a variation of 1.7 percent. Io varies by the inverse square

law, as shown in the following equation [15].

Solar constant =1353 W/m2

Distance =1.495x1011 m

Figure (1-7) Sun-earth relationship [17].


11

2

se

msco D

DII ………………………… (1-9)

Where De-s is the distance between the earth and the sun. The value of Io

for a given day of the year is approximated by the following empirical

equation [17].

25.365

360034.01 n

sco

dCosII ……… (1-10)

1.5.2 Terrestrial Solar Radiation

The amount of solar radiation that actually reaches the earth's

surface is reduced through reflection, absorption and scattering of light by

gas molecules located in the atmosphere. The total radiation incident on a

surface (at earth's surface) is comprised of two forms: the first, beam

radiation, Ib is solar radiation on a surface that has passed through the

atmosphere without being appreciable scattered [17]. The second, diffuse

radiation, Id is that which reaches the surface after being significantly

scattered by the atmosphere [17]. The sum of the beam and diffuse

radiation is referred to as global (total) radiation or terrestrial solar

radiation [18]. A simple clear day model by Hottel [19] for predication

the beam solar radiation at normal incidence, Ib, is given Shah [20]:

kAMoob eaaII 1 ……………….. (1-11)

Parameters ao, a1 and k are empirical constants, and given by Duffie and

Beckman [17].

])6(00821.04237.0[94.0 2ALao ………… (1-12)

])5.6(00595.05055.0[98.0 21 ALa ……….. (1-13)


12

])5.2(01858.02711.0[02.1 2ALk ………… (1-14)

Where AM is the air mass (which equal to 1/cosz or 1/sins) and AL, is

the altitude of location above mean sea level (km).

For tilted surface the beam radiation received is related to incident

angle,θi given by [17]:

ibbt CosII ………………………. (1-15)

The diffused solar irradiance on a horizontal surface may be calculated by

using the following equation [12]:

)](2939.02710.0[ )(1

kAMozod eaaCosII ………. (1-16)

The diffused radiation has no effect on the design of the concentrating

collector calculation, while the fraction of direct radiation is particularly

important to the performance of focusing or concentrator collector.

1.5.3 Spectral distribution of Solar Radiation

The wavelength of the spectral distribution of solar radiation

beyond the atmosphere ranges between 0.2 - 50m. This range is reduced

to 0.3 – 3m, when reaching the earth surface because of two

phenomena. The first, scattering of the radiation as it passes through the

atmosphere which caused by interaction of the radiation with air

molecules, water (vapor and droplets) and dust as shown in figure (1-8).

The degree of the scattering which occurs is a function of number of

particles through which is the radiation must pass, and of the size of the

particles relative to the wavelength of the solar radiation, and scattering is

occurs in accordance with the theory of Rayleigh (i.e., Rayleigh

scattering depends on wavelength to the negative fourth power -4 ).


13

Rayleigh scattering is significant only at short wavelengths smaller than

0.6m [21].

Absorption of radiation in atmosphere for solar energy spectrum is due

largely to ozone for the ultraviolet (UV) (short wave radiation below

0.29m), water vapor and carbon dioxide in the infrared (IR) bands.

Water vapor absorbs strongly in bands centered 1.0, 1.4 and 1.8 m.

beyond 2.5m. The spectral distribution of solar radiation as a function of

wavelength can be listed in Table (1-2). It can be seen from this table that

the solar radiation contains about 47% of visible range and this ratio

decreased by dust effect especially for Iraq environment.

Table (1-2) The spectral distribution of solar radiation [21].

Range Wavelength (nm) Percentage% Solar radiationW/m2

UV 0-380 7 95

Visible 380-780 47.29 640

IR 780-3000 45.71 618

Figure (1-8) Spectral distribution of solar radiation [21].


14

1.6 Geometry of Parabolic Trough Solar Collector

Parabolic Trough Solar Collector (PTSC) which is also called

cylindrical parabolic collector employs linear imaging concentration.

These collectors are comprised of a cylindrical concentrator of parabolic

cross – sectional shape, and a circular cylindrical receiver located along

the focal line of the parabola. A section of a PTSC is shown in figure (1-

9).

Basically it consists of (i) a parabolic reflector of about 1-6 m

aperture width, (ii) an absorber (receiver) tube made of steel or copper

with diameter 1.5-5 cm and coated with selective coating, and (iii) a

concentric tubular glass cover surrounding receiver with a gap of about 1-

2 cm which is evacuated [22].

The cylindrical parabolic reflector focuses all the incident sunlight

onto a metallic tubular or flat receiver placed along its length in the focal

plane. The heat transfer fluid is allowed to flow through the receiver. The

parabolic reflector is defined by its aperture diameter (W), rim angle (r),

and receiver shape and size.

Figure (1-9) Cross-sectional view of PTSC [22].


15

The radius of parabola at an arbitrary location is defined by r, and is

called the "mirror radius". The maximum mirror radius occurs at its outer

rim and is fittingly called "rim radius" or parabolic radius. The rim angle,

r, corresponds to beam radiation reflected from the outer rim of the

concentrator. The focal length, f, is related to rim angle, and aperture

width, W, as [23]:

2tan4 rfW

…………………………… (1-17)

The size of a reflected solar image at the focal point depends upon the

mirror radius at the point of incident of the beam radiation. A simple

equation for the image width Wim was developed by Jeter [24].

sim rW ………………………………… (1-18)

Where s represents the angular width of the incident beam radiation of

0.53o ( 0.00925 rad), acceptance half – angle a of 0.267o, and the

reflected beam path length is equal to the parabolic radius, r. So, for near

normal incidence, occurring more frequently in the summer months,

equation (1-18) can be rewritten as:

rWim 00925.0 ………………………………. (1-19)

The geometric concentration ratio is given as [22]:

LD

LDW

areatubeceiver

araeaperatureEffectiveC

or

or

,

,

Re

……….. (1-20)

The concentration ratio (C) is related to θr can also be defined as [22]:

a

r

Sin

SinC

……………………………………(1-21)


16

The size of the receiver to intercept the entire solar image can be

calculated. The diameter Dr of a cylindrical receiver is [17]:

rar Sin

WSinrSinD

267.0

2 …………………………. (1-22)

For a flat receiver in the focal plane of the parabola the width Wf is [17]:

267.0

267.0

267.0

2

rrr

af CosSin

WSin

Cos

rSinW

……… (1-23)

1.7 Optical Performance for PTSC

The optical analysis of solar collectors with parabolic reflector

must take into account many different effects, such as optical properties

of materials, relative size of receiver and concentrator and the type of

tracking and corresponding losses.

1.7.1 Incidence Angle Modifier

In addition to losses due to the angle of incidence, there are other

losses from the collector that can be correlated to the angle of incidence.

The effects of errors in the concentrating collector, tracking errors, and

errors in displacement of receiver from the focus all lead to enlarged or

shifted images and affect the intercept factor. These errors can be

accounted for by using incidence angle modifier K(i) is given as an

empirical fit to experimental data for a given collector type. The

incidence angle modifier for the LS-3 collector is [24,25].

200005369.0000884.0 iiii CosK ………… (1-24)

Where i, the incidence angle, is provided in degrees.


17

1.7.2 End Effect Correction

End losses occur at the ends of the receiver where, for a nonzero

incidence angle, some length of receiver tube is not illuminated by solar

radiation reflected from the mirrors. Figure (1-10) depicts the occurrence

of end losses for an absorber with a nonzero angle of incidence [26].

These end – effects are typically insignificant for long collector strings,

so, in this study for shorter strings the end losses may be negligible

because of the two - axis solar tracking system is used.

The end losses XEND are a function of the focal length of the collector, the

length of the collector L, and the incidence angle given by [25].

iEND L

fX tan1 …………………………………(1-25)

Therefore, two-axis solar tracking is used to eliminate the end losses in

our work.

Figure (1-10) End losses from the receiver tube


18

1.7.3 Optical Efficiency of the PTSC

The optical efficiency, o is the fraction of solar radiation incident

on the aperture of the collector which is absorbed at the surface of the

receiver tube [26].

bI

S0 …………………………………………… (1-26)

With all of the modifiers taken into account, the absorbed radiation, S, or

the actual amount of radiation on the receiver is calculated by [28,29]:

ENDrgab XKIS ……………………….. (1-27)

Optical efficiency of PTSC embodies many important concentrators'

optical properties including mirror surface reflectance, a, receiver (glass)

transmittance, g, receiver surface absorption, r, and intercept factor,

which represents the fraction of reflected radiation which intercept the

receiver.

1.8 Thermal Performance and Losses of PTSC

In a thermal conversion system a working fluid is used to extract

energy from the receiver. The thermal performance of PTSC is

determined by their thermal efficiency which is defined as the ratio of the

useful energy delivered to the energy incident at the concentrator

aperture. The thermal losses for a PTSC are from convection and

radiation from the receiver tube to ambient [22,28].

1.8.1 Overall Heat Loss Coefficient (UL)

The overall loss coefficient (UL) combines the thermal losses into

one coefficient. For the assumption that the area between the cover


19

(glass) and the receiver (absorber) tube is a stagnant quantity of air, UL is

one of the most important parameters and can be found out from the

following equation [30].

1

,,,

1

grrambgrambgcg

rL hhhA

AU ……………………… (1-28)

Where: Ar area of the receiver (absorber) tube and Ag area of glass cover.

hc,g-amb= convection heat transfer coefficient between glass and ambient

air which is due to wind [28,30].

g

aUawambgc D

kNhh , ……………………….................. (1-29)

Nusselt number (NUa) of air can be defined by two equations [28]:

10001.054.04.0 53.0 eaeaUa RforRN …………………. (1-29a)

5000010003.0 6.0 eaeaUa RforRN ……………………… (1-29b)

Reynolds number (Rea) of air is calculated by following equation [31]:

a

gaaea

DR

……………………………………………. (1-29c)

Where ka, a, a and a are thermal conductivity, density, velocity and

viscosity of air, respectively. Dg is cover (glass) diameter.

hr,g-amb = radiation heat transfer coefficient between glass and the ambient.

22, ambgambggambgr TTTTh ………………………… (1-30)

hr,r-g = radiation heat transfer coefficient between receiver tube and glass

tube.


20

111

22

,

gg

r

r

grgrgrr

A

A

TTTTh

…………………………….. (1-31)

Where Tr is temperature of the receiver, Tg is the temperature of the glass,

r is emittance of receiver, g is emmitance of glass and is Stefan

Boltzman constant which 5.6710-8 W/m2k4.

1.8.2 Heat Transfer to Fluid

The heat transfer from the receiver tube to the fluid (HTF) must be

characterized by turbulent or laminar flow conditions accordingly, the

evaluates the Reynolds number, Ref of the fluid [32].

firf D

m

,

.4Re ...................................................................... (1-32)

Nusselt number of the fluid Nuf for laminar flow is given by equation (1-

33) and for turbulent flow by equation (1-34).

If Ref 2200

7.3fNu ……………………………………………… (1-33)

If Ref 2200

]1[Pr8/7.1207.1

PrRe8/3/2

ff

ffff

f

fNu ………………….. (1-34)

Friction factor, ff , for smooth pipes is given by:

264.1Reln79.0 fff


21

The heat transfer coefficient, hf, to the fluid is then evaluated [32]:

ir

fff D

kNuh

,

…………………………………………. (1-35)

Where m., f, kf, and Prf are mass flow rate, viscosity, thermal

conductivity and Prandlt number of the fluid, respectively. Dr,i is reciver

inner diameter.

1.8.3 Overall Heat Transfer Coefficient and Factors

The overall heat transfer coefficient (Uo) is the coefficient for heat

transfer from the surroundings to the fluid, based on the outer diameter of

the receiver tube Dr,o, this is given by following equation [30,33]:

1

,

,,

,

,

2

ln1

K

D

DD

Dh

D

UU

ir

oror

irf

or

Lo …………………….. (1-36)

Where: K is the thermal conductivity of receiver tube material.

It is convenient to define a collector efficiency factor (F') as: the ratio of

actual useful energy collected to the useful energy collected if the entire

absorber surface is at the mean fluid temperature.

L

o

U

UF '

…………………………………………….. (1-37)

Now eq. 1-36 can be re-written in the following form [33]:

K

DDD

Dh

D

U

UF

iroror

irf

or

L

L

2

)/ln(1

/1

,,,

,

,

'

………………… (1-38)


22

The heat removal factor or correction factor, FR, having a value between

0FR1, can be interpreted as the ratio of the actual useful energy

collected to that which would be collected if the entire absorbed surface is

at the temperature of the fluid entering the collector. FR is a measure of

the efficiency of the receiver when viewed as a heat exchanger, that is,

the effectiveness with which the absorber radiation energy is transferred

to the working fluid. Its value is governed by the working fluid flow rate

and its properties as well as the thermal properties of the receiver material

[34].

pf

Lr

Lr

pfR cm

FUA

UA

cmF

.

'.

exp1 ……………………… (1-39)

Where: cp is the specific heat of the fluid.

The collector flow factor F" is then described in following equation:

'

"

F

FF R

pf

Lr

Lr

pf

cm

FUA

FUA

cm.

'

'

.

exp1 ………………… (1-40)

1.8.4 Thermal Efficiency of a PTSC

The instantaneous thermal efficiency th of a solar concentrator

may be calculated from an energy balance on the receiver. The useful

heat gain, Qu, delivered by the receiver can be written in terms of optical

and thermal losses, where optical losses are represented by the optical

efficiency, o [22,35].

rambrLabou ATTUAIQ ………………………. (1-41)


23

Where Aa is the aperture area, since the receiver surface temperature is

difficult to determine, it is convenient to express the Qu in terms of the

inlet fluid temperature by means of heat removal factor FR as [36]:

C

TTUSFAQ ambifL

Rau,

………………………….. (1-42)

The useful heat is related to the flow rate can also be defined on the base

of fluid difference temperature as [22]:

ifofpu TTcmQ ,,. ………………………………… (1-43)

Where: Tf,i, Tf,o and Tamb represent the inlet fluid, exit fluid and ambient

temperatures, respectively.

The thermal efficiency of the solar thermal collector can also be

simplified and defined as the ratio of useful heat Qu, delivered per Aa, and

the insolation, Ib, which is incident on the aperture.

ba

uth IA

Q ………………………………………….. (1-44)

The thermal efficiency of the collector can now be re-written from eq. 1-

42 and eq. 1-44 as follow [36,37]:

CI

TTUF

b

ambifLoRth

, ………………………….. (1-45)

The thermal efficiency depends upon two types of quantities namely the

concentrator design parameters and the parameters characterizing the

operating conditions. The optical efficiency, heat loss coefficient and heat

removal factor are the design dependent parameters while the solar flux,

inlet fluid temperature and the ambient temperature define the operating

conditions [22].


24

The exit fluid temperature, Tf,o the temperature rise, (Tf,o-Tf,i) and the

efficiency can be calculated using the following equation [22,37].

ab

ifofpth AI

TTcm )( ,,.

……………………………… (1-46)

1.9 Heat Collection Element (HCE)

HCE or PTSC's receiver tube, as shown in figure (1-11) is located

at the focus line of parabolic reflector surface, with means of transferring

the absorbed solar energy to a fluid. The HCE consists of receiver tube

that is surrounded by a glass envelope. The receiver is typically a

stainless steel or copper tube coated with selective coating; this coating

has high absorption of short length solar radiation and low emissivity for

long wave energy spectrum to reduce thermal radiation losses [38,39].

The glass envelope is typically made from Pyrex, which maintains good

strength and transmittance under high temperatures. The outside glass

envelope is transparent to solar radiation over the solar absorbed surface

that reduces convection and radiation losses to atmosphere; the annulus

gap between receiver and glass envelope is under vacuum to reduce

thermal losses [40-42].

Figure (1-11) Heat collection element [40].


25

1.9.1 Heat Transfer Fluid for PTSC

Heat transfer fluids carry heat from HCE to the heat storage tanks

in solar heating (and cooling) systems. The fluids most commonly used

are water, hydrocarbons oil, glycol and air. When selecting a transfer

fluid, the following criteria should be considered: the coefficient of

expansion, viscosity, thermal capacity, freezing point and boiling point.

The following are some of the most commonly used heat transfer fluids

and their properties.

Air will not freeze or boil, and is non-corrosive. However, it has a

very low heat capacity, and tends to leak out of collectors, ducts

and dampers.

Water is non-toxic and inexpensive. It has a high specific heat and

a very low viscosity, making it easy to pump. Unfortunately, water

has a relatively low boiling point and high freezing point. It can

also be corrosive if the PH (acidity / alkalinity level) is not

maintained at a neutral level.

Hydrocarbon oils have a high viscosity and lower specific heat

than water; they require more energy to pump. These oils are

relatively inexpensive and have a low freezing point.

Refrigerants/phase change fluids, these are commonly used as

the heat transfer fluid in refrigerators, air conditioners, and heat

pumps. They generally have a low boiling point and a high heat

capacity. Heat absorption occurs when the refrigerant boils

(changes phase from liquid to gas) in the solar collector.

Chlorofluorocarbon (CFC) refrigerants, such as Freon, were the

primary fluids used by refrigerator, air –conditioner, and heat pump


26

manufactures because they are nonflammable, low in toxicity,

stable, non-corrosive, and do not freeze [22,43].

1.10 Storage of Thermal Energy

Thermal energy may be stored in the forms of: 1) sensible heat, 2)

latent heat. These methods differ in the amount of heat that can be stored

per unit weight or volume of storage media and operating temperatures

[44].

1.10.1 Sensible Heat Storage

In sensible heat storage, the thermal energy is stored by changing

the temperature of the storage medium. The amount of energy required to

rise the temperature of one unit of a material one degree is its specific

heat (heat capacity), however the amount of heat stored depends on the

heat capacity of the media being used, the temperature change, and the

amount of storage media. Water and pebbles are the most common

materials used for low temperature energy storage and hydrocarbon oil

have been proposed for high temperature [21,45].

1.10.2 Latent Heat Storage

In latent heat storage, thermal energy is stored by means of a

reversible change of state (phase change) in the media. Solid-liquid

transformations are most commonly

utilized. Liquid-gas and solid-gas phase changes involve the most

energy of the possible latent heat storage methods. A common media

used for latent heat storage in solar thermal system is molten salt [46].


27

1.11 Sun Tracking Systems

Sun tracking is the continuous positioning of the reflector toward

the sun. As the sun's position changes hourly, the solar power device

should be adjusted to produce the maximum output power. Regarding

movement capability, two main types of sun tracker exist [47,48]:

1- One axis tracker

2- Two axes trackers

The main difference among them is the ability to reduce the pointing

error, increasing the daily irradiation incident to increase the energy

output.

Regarding control units the main types of solar trackers are [49]:

1- Passive

2- Microprocessors

3- Electro – optical controlled units

The first one doesn't use any electronic control devices or motors. The

second type use mathematical formula to predict the sun's movement

while the third type use information of some type of sensors to estimate

the sun position [47,50].

Regarding control strategy the main types of solar trackers are:

1- Closed Loop

2- Open Loop

3- Hybrid System


28

The main difference among them is time dependency and processing data

flow. The first type is time independent it depends on determination of

the movement error aided by solar sensor and feed the sensor reading

back to the actuators to correct the movement. The second type is time

dependent; it uses the time and mathematical formulas to predict the sun

orientation. The hybrid system is the newest tracking system, it is a

combination of the other two types, also the new algorithms i.e. Fuzzy

logic, Neural Network and neuro-fuzzy are listed under this category

[51,52].

1.12 Literature Review

The following is a summary of the previous experimental and

theoretical work related to the present research in the field of solar

concentrator. Parabolic trough technology is nowadays the most extended

solar system for electricity production or steam generation for industrial

processes.

Records date as far back as 1774 for attempts to harness the sun's energy

for power production [53]. One furnace designed by the French chemist

Lavoisier, attained the remarkable temperature of 1750 oC. The furnace

used a 1.32m lens plus a secondary 0.2m lens to concentrating the rays of

the sun on a test tube [54].

Between 1907 and 1913, the American engineer F. Shuman and C.V.

Boys built a large solar engine, of over 50hp; with a 1200m2 array of

parabolic troughs for pumping irrigation water from the Nile near Cairo,

Egypt. It was shutdown during WWI [55,56].


29

Interest in solar concentrator began to rise again in the 1960s, a

technique for optimizing the design of focusing solar collectors was

developed through a detailed study of the energy balances for a

parabolic-cylindrical reflector with tubular receivers of different

diameters, was studied by G.Lof 1962 [57]. The result of this

investigation shows that the increase of the size of the receiver leads to

increase thermal losses and the intercept factor, defined as "the fraction

of radiation specularly reflected from the reflector which is intercepted

by the receiver".

Later, Lof 1963 [58] studied an analysis of factor and methods

involved in design optimization, and a set of graphical relationships

which may be used in designing focusing solar-collectors system of

maximum efficiency and minimum size depending on width ratio "the

fraction of width of receiver to the parabolic cylinder reflector aperture".

The result of the analysis states both maximum energy delivery and

intercept factor where width ratio is (0.02-0.025). The influence of target

geometry on maximum concentration has been theoretically studied by

Edward and Cherng 1976 [59]. The results show that the elliptic

cylindrical target and flat plate will achieve a maximum concentration as

the optimum target for the same value aperture.

Parmpal and Cheema 1976 [60] investigated an analysis of the

performance of a cylindrical-parabola collector regarding the amount of

energy collected, optimization of its various parameters and that the use

of aperture of a cylindrical-parabola collector as a characteristics

dimension seems to be more logical than the use of the focal length. The

heat balance on the absorber showed that the dimensionless temperature

(ratio of the absorber temperature to the stagnation temperature)


30

completely predicts the performance of the collector. The maximum

temperature attained by the absorber for zero energy extraction, called

stagnation temperature.

Ramsey and Gupta 1977 [61] evaluated the performance of the PTSC

by using three different absorbers; a black painted tube designed to

operate near ambient temp, a heat pipe which had a selective solar

absorber coating applied to its surface, and a heat pipe which had it

surface coated with nonselective black paint. The peak efficiency for the

collector in the absence of heat losses is approximately 62% when the

incoming solar energy is normal to the collector aperture. The losses

which occurred at elevated temperatures (300oC) decreased the peak

efficiencies to 50% and 30%, respectively, for the selectively coated and

black painted tubes.

Derrick 1979 [62] analyzed and compared between the compound

parabolic and simple parabolic solar collectors for their ability to accept

non-direct radiation and for their respective reflector arc-lengths. For

concentration ratios greater than about 10, the simple parabolic

concentrator has the advantage, because the compound parabolic reflector

cost is more than 4.4 times as expensive. However, the simple parabolic

trough may be more cost effective than the compound parabolic

concentrator.

Clark 1982 [63] studied the principle design factors that influence the

performance of a PTSC. Factors such as spectral directional reflectivity

of the mirror system, the mirror-receiver tube intercept factor, the

incident angle modifier, the end loss, effect of tracking errors and

receiver tube misalignment were considered for analysis.


31

Jeter 1983 [64] studied geometrical effects on the performance of

PTSC, it concentrated on end-effect. The results show the significance of

end-effects particularly increases when short troughs are considered and

elimination of this effect is important in obtaining test results.

The American company Luz International Ltd ., founded in 1979,

designed three generation of PTSC, called LS-1 , LS-2 and LS-3 ,

installed in Solar Electric Generating System (SEGS) plants. The first

two generations of collectors, LS-1 and LS-2, consisted of similar

assemblies, mounted on a structure of similar length, but the aperture

width of the LS-2 collector was twice that of the LS-1 collector. The

structure is based on a rigid structural support tube, called the torque tube,

which supports the steel profiles to which the parabolic mirrors are

attached. In the LS-3, the torque tube is replaced by a metal lattice

framework, the aperture width is 14% wider than the LS-2 and collector

length is doubled [65].

Thomas 1994 [66] developed a sample structure of PTSC to study its

deflection and optical characteristics under various load conditions. In the

absence wind tunnel facilities, the test gives sufficient information about

the effect of wind load on the optical performance of a PTSC.

Odeh et al. 1998 [67] carried out the performance analysis of PTSC

with synthetic oil and water as working fluids. The formulations for

efficiency of solar parabolic trough collectors have been developed based

on absorber wall temperature to predict the performance of the system

with any working fluid. The thermal losses from the trough collector have

been described in terms absorber, emissivity, wind speed, absorber wall

temperature and radiation level.


32

The researcher Volker and Franz 2001 [68] processed an experimental

and theoretical study of solar power plants in southern California working

with concentrator of PTSC (Solar Electrical Generating System) (SEGS)

where these concentrators are competent in the production of thermal

energy crisis of the work of electrical system, and considered plants

(SEGS) as one of the most profitable plants in terms of economy where

the price of kWh during peak hours over 100 USA-cents.

A group of researcher from European countries Rafael et al. 2002 [69]

developed a new design of PTSC called (Euro Trough) through the

development of a generation of solar concentrators and reduce cost. The

manufacture of two types of concentrates (ET 100 & ET 150), was

designed and developed to utilize it to generate steam required for the

applications of solar thermal electric power generation. As electric power

generation system in California could complement the use of these

models has been the rehabilitation of this plant is actually in the years

(2000-2002) and use the same materials in the manufacture of models,

but the difference between the lengths of PTSC in the area and the

number of absorber tubes, with a length of the form (ET150)

(148.5m)area (817.5m2) either the model (ET 100) was long (99.5m) and

area (545m2).

Balbir and Fuaziah 2003 [70] investigated the performance of a PTSC

and the use of processed data to design a simulated model using the same

meteoro- logical data. The results indicated that there would be an

equilibrium achieved between the increasing thermal losses with the

increasing aperture area, and the increasing optical losses with the

decreasing aperture area.


33

Thomas and Michael 2005 [71] developed a PTSC similar in size to

smaller-scale commercial modules for use in a South African solar

thermal research program. The collector length is 5m, aperture width is

1.5m and rim angle is 82o. Two receivers were fabricated for comparative

testing, including one enclosed in an evacuated glass cover. Peak

efficiencies of 55.2% and 53.8% were obtained with the unshielded and

glass-shielded receivers respectively.

Umamaheswaran 2005 [72] presented study details of the

construction, testing and analysis of PTSC for small scale domestic

purpose water distillation application. Ground water is heated by the solar

radiation as it circulates along the solar collector within an absorber pipe

in order to generate steam directly into the absorber pipe.

Miguel and Javier 2006 [73] developed the design of a PTSC called

(SENER) and the aim of the research was to reduce cost of construction

of the concentrators. Two prototype modules of SENER trough have been

mounted and tested at the CIEMAT-PSA facilities. A first prototype of

SENER parabolic collector was mounted and tested in CIEMAT-RSA

facilities in October 2005. The purpose was to get mounting experience

and to have a general idea of the operational behavior comparing it

against other collectors. This first prototype was composed of a torque

tube and cantilever arms made of welded tube profiles. The 28 cantilever

arms were assembled to the torque tube using a manual jeg. A second

prototype of SENER parabolic collector is mounted in February 2006.

This second design includes the optimal solution for the cantilever arms.

The experience acquired with the first prototype in mounting procedures

is applied to this second prototype. The same optical and thermal tests are

performed, these tests have shown that this model more an accurate

structure has resulted to further improve performance and addition of


34

these stamped cantilever arms reduce the possible errors in the position

of the mirror support points.

Valan and Samuel 2006 [74] developed a new PTSC for hot water

generation. The variation of collector water outlet temperature and the

storage tank water temperature is increased from 36 oC to 73 oC.

Kassem 2007 [75] predicted natural convection heat transfer in an

annular space between a circular receiver tube and a glass envelope of a

PTSC.

Dirk et al. 2008 [76] investigated the solar thermal parabolic trough

collectors called solitem PTC-1800 to provide heat for desalination,

cooling and electricity generation. The results showed that thermal testing

of the collector has revealed comparably low thermal losses and still

significant optical losses. Altogether the collector is well applicable for

medium temperature applications in the range of 150° to 190°C.

1.13 Aim of the Work

The aim of this work can be summarized in the following points:

1- Design and fabrication of a parabolic trough solar collector of total

aperture area (5.04 m2) to convert the incident solar energy to thermal

energy to achieve some important applications in using thermal solar

energy.

2- Theoretical and experimental study to evaluate the performance of the

system in Baghdad environment.

CHAPTER TWO

Experimental Part

Chapter Two Experimental Part

٣٥

2.1 Introduction

This work focuses on the design and fabrication of PTSC system for

converting incoming solar radiation to thermal energy. This chapter

contains a description of Parabolic Trough Solar Collector (PTSC) and a

detailed explanation of how the individual components of the system

work. The design, implementation and testing of the system were

conducted at solar energy center located on the roof of the Ministry of

Science and Technology in Jadaria, Baghdad.

2.2 Description of the Parabolic Trough Solar Collector

A small scale model has been designed, constructed and tested in

the open area of the Solar Energy Center. This model consisted of the

mechanical unit (metal support frame), reflecting parts assembly, heat

collection element, tracking and control system as shown in figure (2-1).

The newly developed PTSC specifications are given in Table (2-1).

Table (2-1) PTSC system specifications

ITEM Value/Type

Collector aperture area 5.04 m2

Aperture width 2.8 m

Length-to-Aperture ratio 0.64

Rim angle 67.8o

Receiver diameter 48 mm

Tracking mechanism type Electro-optical

Mode of tracking Two- axis

Concentration ratio 35


٣٦

Figure (2-1) The schematic of PTSC 1) Axial Motion Guide Ass. 2) Tilting Motion

Base 3) Tilting Motion Ass. 4) Reflecting Ass. 5) Thermal Receiver Ass. 6) Heat

Receiver Support 7) DC actuator motor 8) Side Support Angle 9) Bracate 50.

2-3 Design Concepts for the Mechanical Unit

Mechanical unit (metal support frame) consists of two mechanical

assemblies: stationary base assembly and the other moving assembly.

2-3-1 Stationary Base Assembly

The idea of the fixed base design has been put in order to undergo

the hard weather conditions, achieve the bearing and supporting

requirement through the solar energy system operation and to satisfy the

functional specifications that is to be used by the moving assembly and

support this important assembly. The selection of the part materials is

confirmed in order to meet the above requirements as declared: The

materials Steel U – channels, Steel angles, and Steel tubes. So they have

been used because they have higher maximum bending stress and

maximum shearing stress to which the system will exposed to them, as

shown below by the formulas:

Max. Bending stress I

MC ………………………. (2-1)


٣٧

64

4DI

For shaft

64

44io DD

I

For cylindrical tube

Max. Bending stress for tube is more than that for shaft, so that it is better

to select from the shaft. Besides this good bearing resistance they have

light weight which makes the system easy for handling and transporting

from place to other as required.

2-3-2 The Moving Assembly

The system has two motions, so it has two groups of the moving

assembly.

2-3-2-1 Tilting Motion

The first group is the moving assembly for the tilting motion

containing two electrical actuators, the axel, two bearing brackets, two

ball bearing, plates from carbon steel, U – channels, steel angles

rectangular tubes and tilting motion base. The resulted mechanism will

satisfy the tilting motion within 90o. All the mentioned parts were

supported by the base, must lead to perform the function of the assembly

(tilting motion) properly and successfully. The materials of the parts are to

be selected carefully to withstand the hard working conditions i.e.

environment conditions, bending stress, torsion stress, etc.

2-3-2-2 Axial Motion

The second group is the moving assembly for the axial motion

containing: rotational or axial motion guide assembly with two types of

discs, one stationary disc to be welded with the whole system base and the


٣٨

other rotational disc to be connected with the rotational parts, which must

rotate by the worm gear motor.

2-3-2-3 Two Groups Assembly

The first group is to be connected with the second group by four

fixtures the final assembly will containing two electrical D-C motors, one

is used for the axial motion and the other, is used for tilting motion.

2-4 Design Concepts for Reflecting Parts Assembly

The reflector is designed to set the focal length (f) 1.04 m from the

vertex (V) the aperture width of the system (W) is 2.8 m so the equation of

the designed system will be

yx 16.42 ……………………………… (2-2)

The plot of this equation gives the surface illustrated in the figure (2-2)

Figure (2-2) Designed parabola.

Focal point


٣٩

This figure shows the designed dimension, focus point (f) is 1.04 m

distance from the V, arc length of the parabola 3 m and the maximum

height at the end of the parabola is 0.47 m.

There are two situations have been followed for to fabricate the reflecting

assembly.

2-4-1 The First Way for Design Reflecting Parts Assembly

The whole assembly consists of two secondary assemblies as

below:

A- The Parabolic Base Assembly: it is made of steel tubes which

takes a parabolic form, exactly the same as the reflecting form.

This assembly must be made by accurate procedure i.e. to make

reference templet made of wood, then using accurate profile

machine to fabricate the required parabolic form depending on the

wooden reference.

B- The Reflecting Assembly: the function of this assembly is to

reflect and concentrate the parallel solar rays on the receiver to

achieve the focus line finally. It is made of steel plate with

thickness of 1 mm. The steel has been selected because it has good

reflectivity, uncorrosive, not expensive, available and easily to

perform as shown in figure (2-3). The steel plate must be supported

by the parabolic base assembly and takes its form exactly, but

because of the fabrication difficulties which occurs through making

this assembly by this way, therefore the second way has been

followed as bellow:


٤٠

Figure (2-3) Stainless steel plate reflector.

2-4-2 The Second Way (Alternative Way)

As mentioned in the first way the assembly consists of two

secondary assemblies

A- The Parabolic Base Assembly: it is made of several pieces of flat

steel bar. This material is elastic and soft that is easily to perform

and to make the reflector profile depending upon the concerned

design drawing. The resulted form must be supported by steel

hollow bar (tube) which is carried by the moving assembly. To

obtain the parabolic shape characterized in figure (2-2), steel tubes

with different lengths are fixed in the back – structure (figure 2-4).

The distance between one and another is 0.15 m and the length of

the tubes will be as shown in figure (2-5).


٤١

Figure( 2-4) Steel tubes welded in the back – structure

Figure( 2-5) schematic of reflecting base parts (1) steel tubes (2) steel flat bar

B- The Reflecting Assembly: consists of several segment or pieces of

mirrors with width of 5 cm. These mirrors must be fixed by sticky

material on the designed parabolic structure form of the flat bar so

the resulting form will be a profile of glass mirror. Technically, this

parabola is very difficult to form locally because the curved mirrors

are not available. The parabolic shape can be formed by taking

each 0.05 m as one piece. This will minimize the mirrors width to

0.05 m straight plates as show in figure (2-6), so that no need to

form the concave mirrors. Although, this solution will increase the

radiation losses due to the miss reflective rays and increase the

unreflective areas between the mirrors bisections, but it is a

reasonable assumption specially that the focus will not be point but


٤٢

it is cylinder of 0.05 m diameter. Obviously, the shape of parabolic

surface will not deflect the reflected rays out of focus.

Figure (2-6) Parabolic reflector mirror

2-5 Assembly of the Trough Parts

2-5-1 Trough Reflector Assembly

1- Building the Mirrors Supporting

The drawing of the trough form at the same scale requires fixing the

reflector on a big desk by sticker and steel flat bar accurately on the

drawing and then fix them by steel tubes (1 inch) according to the

required dimensions to keep the arc of the trough within the right

measurements. This operation will be done frequently in four times as

shown in figure (2-7).


٤٣

Figure (2-7) Welding reflector base parts

2- The Alignment of the mirrors by laser beam

The shape of the required parabola obtained in previous operation

was tested with the help of a laser as shown in Figure (2-8).

Figure (2-8) Apparatus for characterizing slope error of parabolic

reflector mirrors.

An inspection base is used to insure that the laser pointer source can move

gently along a horizontal axis parallel with the structure to fix the focus at

the certain place. The mirrors were fixed by silicon sticker on parabolic

surface to ensure the reflected laser beam was collected at the focus. The

second part is to be done by the same way as shown in figure (2-9).


٤٤

Figure (2-9) The final form of reflecting parts assembly

2-5-2 Mechanical Unit

The Mechanical unit consists of the following assemblies:

1- The Stationary Main Base Assembly

The main base of the solar collector was fixed on concrete ground

base by anchor bolt, this main base consists of cast iron tube with

diameter (160 mm) fixed on mechanical structure loader.

2- The Axial Motion Guide Assembly

It consist of rolling tray that has two parts: the lower is a fixed part

standing on the main base tube and the upper is a rotating part, to insure

the axial movement and make it smooth in order to reduce the load on the

moving part. The axial motion assembly which is in charge of the

horizontal movement was fixed on the main base tube and this was a

worm gear box and will move by dc motor as shown in figure (2-10).


٤٥

Figure (2-10) Axial motion assembly with main base

3- Tilting Motion Assembly

The lower base of the flexible structure was fixed on the rotating part of the rolling tray with four stands. The flexible top side and the moving lower side was connected by two electrical dc motors, which allow moving in the y-axis from (10o to 90o). The flexible point consists of two brackets with diameter (50 mm) as shown in figure (2-11).

Figure (2-11) DC actuator motor for tilting motion and main base


٤٦

4- The Final Form of the Trough

The two structures, trough reflector structure and the flexible basement structure were fixed by screws and a stand rots as figure (2-12).

Figure (2-12): The final form of the trough system

2-6 Comparison between Two Fabricated Troughs

The base, moving parts and the reflecting parts have been fabricated according to the design drawings: The first design method is shown in figure (2-13) and the second design method is shown in figure (2-14). However, the first way some deformation occurred on the reflecting parts. The Manufacturing and assembling was affecting the accuracy of the resulted parabolic assembly. So it was necessary to follow the second way which is simple in fabrication and thus is more effective in final testing. The first method gave deformation because of the method of fabrication, used welding operation for assembling the parts; in other words it caused the deformation because this operation needs high accuracy otherwise the results will be rejected. The Second method will be the best to follow for fabrication and the result will be as required, the reflecting part would be group of segments of mirrors which do not need welding operation for fixing but need sticky material which are easier to use and don’t cause deformation in the parabolic structure as happened in the first method.


٤٧

2-7 Heat Collecting Elements (HCE)

In order to achieve the required design, there must be certain procedure to be followed as below:

- Using a suitable shape for the receiver that receives the reflected sun's rays successfully producing focal line.

- Selecting suitable material which has high absorptivity and conductivity as high as possible and the heat emissivity as low as possible, some times using special coating to decrease it.

- Selecting suitable heat transfer medium which transforms the absorbed heat easily with low heat loss.

After previous procedure, the resulting are two HCEs, or receivers, are tested: one an unshielded tube (metallic tube) and the other was shielded with evacuated glass tube.

Figure (2-13): Photograph of Trough system according to first method

Figure (2-14): Photograph of Trough system according to second method


٤٨

2-7-1 Thermal Metallic Receiver

It is a mechanical structure used for collecting the concentrated solar rays in limited line which is called focal line, so the receiver must be designed to receive and absorb that concentrated rays. It consists of the parts: receiver jacket, receiver tube, support plate and insulator. The parts are made of the materials; carbon steel and glass wool, there are several objects considered for selection of those materials, such as their availability, cost and easy to manufacture as well as the suitable thermal specifications. The receiver tube is a rectangle carbon steel, 180 cm – long

with cross section (84) cm. Figure (2-15) shows a cross – sectional view of a metallic receiver. This tube has been insulated by a glass wool with thickness 2 cm in three faces. The forth face has a section of 8 cm has no insulation, because it will be the focus side of the parabolic reflector.

Figure (2-15): Cross – sectional view of metallic receiver

Carbon steel material has good conductivity and absorptivity, but the high emissivity cause high heat loss, so the coating for the receiver is the best way to overcome this problem. The outer tube surface could be coated with a special black paint (selective surface) which increases the absorptance of the incident solar irradiance and reduces, simultaneously the reflectance as shown in figure (2-16).


٤٩

2.7.2 Optical efficiency of the receivers

The optical efficiency of the receivers has been determined experimentally. As illustrated in previous section, so the optical efficiency can be determined by using Eq. (1-27). The products of the transmittance – absorbance of the receiver and the reflectance of the aperture, according to the specification of the collector. The optical efficiency of the

evacuated glass receiver (0.920.930.940.85) is then 0.683. While, the optical efficiency of coated metallic receiver to be 0.63, by using Cellulose Nitrate as a coated black paint have absorbance 0.78 as illustrated in figure (2-16).

Figure (2-16) Absorbance of the thermal paint (Cellulose Nitrate)


٥٠

Figure (2-17): A schematic of the metallic receiver

2-7-3 Evacuated Glass Receiver

Evacuated thermal receiver consists of evacuated tube, bushings, O-ring and support plate. Evacuated tube is composed of two coaxial borosilicate glass tubes figure (2-17) with one open end for inlet and outlet and the another end sealed; the outer of 58mm diameter (1800mm) length (cover tube) and the inner 47mm diameter and (1720mm) length (absorbing tube). The thickness of the inner tube and outer tube is 1.6mm. The inner tube exterior is coated by selective coating (Aluminum Nitrite) in order to increase the absorptivity. The space between the two tubes is evacuated from the air to prevent the heat losses which resulted from the convection and conduction. Thus the absorbed solar energy is converted to heat and transmitted to fluid. Evacuated glass specifications are given in Table (2-2).

Figure (2-18): Schematic diagram of the Evacuated tube elements


٥١

Table (2-2): Evacuated tube specifications

ITEM Value

Receiver length 1800mm

Cover diameter 58mm

Absorber diameter 47mm

Cover Transmittance 0.91

Coated surface absorptance 0.93

Emissivity 0.08

Pressure of vacuum space 510-3 Pa

The modification on evacuated tube is illustrated in the figure (2-18). Some changing on the tube by use of two iron adapters, one in each side, one of them is used only for close the end of the tube by using a bushing of Teflon inside the iron adapter with o-ring made of rubber on a groove, and the other side also using a bushing of Teflon inside the iron

Figure (2-19): A cross - section schematic diagram of evacuated glass receiver.

adapter with busing made of rubber have cone shape to match the end of the tube. Moreover, at the end of the tube it has two openings for the two copper tubes to put them inside the evacuated tube, one of them goes to the end of it as shown in figure (2-19).


٥٢

Figure (2-20) Schematic diagram of evacuated glass receiver

However, the receiver of a PTSC is that element of the system where solar radiation is absorbed and converted primarily into heat. It includes the absorber tube through which the heat transfer fluid flows. Figure (2-20) shows two receivers used in this work.

Figure (2-21): Photographic of two receivers in the lab.


٥٣

2-8 Tracking and Control System

A parabolic trough solar collector with automatic two-axis solar tracking system was constructed, operated and tested to overcome the need for frequent manual tracking. This procedure causes an increase in the out put power of the PTSC by making the solar angle of incidence between the beam of the solar radiation and the normal on the surface of the trough equal to zero (the geometrical losses becomes zero). The system consists of position sensing detectors by using; four photodiodes (PIN silicon photodiodes) of technical specifications listed in table (2-3). This sensor is aimed to keep the solar radiation beam as near as possible to the (0,0) position for both two-axis [ azimuth (x-axis) and altitude (y-axis)], which make the trough perpendicular to solar beam. The PS sends the error signals of each axis (x and y) to the controller which actuates the motors to track the sun. This sensor is connected to an electronic card. Practically if the PS is not aligned with sun's rays then it can switch the motor on until it is once again aligned. When the PS is aligned, with the sun, the motor will be in still position. However, as the sun is moving across the sky and is not in proper alignment with PS, the motor moves the trough to get perfectly aligned with sun's rays.

Table (2-3): Specifications of PIN silicon photodiode

ITEM Value

Active area 33 mm2

Spectral response 700 – 1100 nm

Max. response wavelength 950 nm

Max Responsivity 0.6 A/W

Dark current at (10 mV) 10 nA


٥٤

The second part of the system is the control part represented as electronic card, which consists of principle parts such as x-direction comparison unit used to correct the horizontal deviation by receiving the electric error signal from two horizontal detectors (x+ , x-) of sensor which give the amplified error signal to the relay in order to energize the horizontal motor and make the correct position of PTSC in X-direction relative to the new position of the sun. Similarly, the y-direction comparison unit is used to correct the vertical deviation by receiving the electric error signal from the vertical detectors of sensor (y+ , y-) and give the amplified error signal to the relay in order to energize the vertical motor and make the correction of the vertical position of the trough relative to the new position of the sun. Moreover, there is an electronic regulating device used to protect the circuit and to control the battery and works as an amplifier to amplify the signals delivered from light sensor and to convert them into voltage values. The electronic block diagram of the tracking system is shown in figure (2-21).

Figure (2-22): Block diagram of two – axis tracker

The third part of the system represent, the mechanical part and consists of three drivers as shown in figure (2-22). The first one uses the driving motor for the axial motion of the system from east to west to track the


٥٥

solar azimuth angle; the second and third use driving motors for the tilting movement to the zenith angle.

Figure (2-23): The experimental set-up of the tracker

The applied voltage of the motors is 12 Vdc supply for the purpose of driving the system. These motors are attached to the frame with mechanical arms to ensure the movement of the PTSC due to the signal received from a control unit as shown in figure (2-23).

Figure (2-24): Photograph of the drivers attached to the frame

The forth part of the system is the power supply which consists of two batteries (12V, 100 Ah) and a charging unit connected to the solar panel of 100 W power.


٥٦

2-9 Design Concepts of the Thermal Storage Tank

The design drawings for at the storage tank of the project included two cases:

First case: when the load is solar cooker as shown in figure (2-24) and as declared below:

- The inner container which is made of carbon steel with thickness of 2.5 mm used for saving the storage media.

- The outer container which is made of carbon steel used for fixing the insulator around the inner container.

- The glass wool with thickness of 15 cm was used as insulator in order to save the required working temperature and to decrease the losses storage thermal energy as low as possible.

- Electrical heater to be used as auxiliary energy for heating the storage media.

- The temperature of the storage must be measured and thus a thermometer is used.

- The oil is used as a heat transfer fluid must be transferred from or to the load and from or to the collector through the outer and inner tubes.

Second case: when using the trough for space heating as a load as shown in figure (2-25), there is a heat exchanger used for transferring the heat from the oil to the water then to the load for space heating of houses. It is made of copper with 1.25 cm diameter and length of 3 m.


٥٧

Figure (2-25): A Schematic of storage tank illustrated the load A.

Figure (2-26): ASchematic of storage tank illustrated load B.


٥٨

2.10 Apparatus and Instrumentation

The experimental instruments, which have been used to investigate the performance of PTSC, can be classified into:

1- Thermocouples

Thermocouples are used to measure temperature at several locations in the system as shown in figure (2-26) according to their purpose:

A- Two of the thermocouples type K (1 and 2) in the metallic receiver were placed at inlet and outlet of the heat element flow for measuring HTF temperatures.

B- Two thermocouples type K (3 and 4) were inserted in the open end of evacuated receiver to measure the inlet and outlet temperatures.

C- Two thermocouples type K (5 and 6) to measure the upper and lower temperatures of the storage tank.

D- One thermocouple type K was used to measure the temperature of evacuated tube to calculated heat loss coefficient of tube.

The thermocouples are connected to electrical digital reader. The thermocouples were calibrated according to the company that manufactured these thermocouples and the errors are found to be 0.4o C for K-type.

2- Data logger

Data logger system (2000 series) from Spectrum Technologies Inc. has been used in all the required measurements in combination with the software PC208W. The accurate logger measurement sampling interval is 10 seconds. Five minutes averages are stored in the logger. Data logger is connected to PC in order to record and save the solar radiation, ambient temperature, wind speed. It is located near the collector as shown in figure (2-27).

3- Pump

The recycling of the HTF (Mobitherm Light) from the tank to the system requires a pump capable of withstanding high temperatures due to


٥٩

the high oil temperature; a regulated oil pump is used and located on the underside of the PTSC as shown in figure (2-28). The pump has a small

motor having dimensions of 120mm 105mm 70mm, and the controller,

50mm40mm20mm. the pump has a maximum flow rate 1.2 LPM. The pump runs off of 220 volt ac, with a maximum power usage of 180 Watt. The pump is designed for longevity having an absence of moving parts within the motor, with only a short single shaft inside the pump.

Figure (2-27): Positions of thermocouples


٦٠

Figure (2-28): Data logger (2000) series system

Figure (2-29): A Photograph of Pump located on underside of the PTSC

4- Power Supply

Although the system is designed to produce power, some power consumed in order to do so. Power was needed for the tracker actuators for positioning of the PTSC, as well as for operation of the pump. This power was provided by two 12 volt batteries. The batteries were wired in parallel for control of the tracking. The batteries were kept constantly charged by use of two photovoltaic panels. Because the actuators and tracking modules operate on DC current, they were able to function directly from the battery bank. The pump, however, is operated on AC power. In order to supply the type of current needed, a DC to AC power inverter was used. The inverted power used, shown in figure (2-29) was capable of operating at 1000 watts.


٦١

Figure (2-30): Two batteries with power inverter

2-10 Experimental Setup and Procedure

The experimental setup used for testing the fabricated PTSC is shown schematically in figure (2-30) and as a photo in figure (2-31). It consists of the constructed (1) PTSC, (2) a 50 liter storage tank, (3) a circulating pump, with maximum mass flow rate of 0.02 kg/sec and (4) control system. The pump is driven by a 180 W AC motor. In the current experiment, the oil circulation is a closed one. The collecting tank is filled up from the main oil supply. At the edge of the receiving pipes, a flexible tube is used for conveyance of the heat transfer fluid. The pump circulates oil from the collecting tank through the receiver tube of the solar collector back to the collecting tank. The oil temperatures at inlet and outlet of the receiver tube, upper and lower of the storage tank, and solar radiation intensity are continuously measured during the experiment.


٦٢

Figure (2-31): A schematic diagram of the experimental setup

(1) PTSC with tracking system; (2) Storage tank; (3) Pump; (4) Control system

Figure (2-32): A Photograph of PTSC setup

4

CHAPTER THREE

Results and Discussion

Appendices

Chapter Three Results and Discussion

٦٣

3.1 Introduction

In this chapter, the effects of various parameters on the

performance of the PTSC are analyzed. The results were obtained from

outdoor experimental tests through the selected clear-sky days for the

months of October, November and December without draw-off HTF. The

performance of the PTSC was evaluated using three different receivers; a

metallic receiver of non-coated surface, coated metallic receiver and the

evacuated glass receiver.

3.2 Solar Calculations

The characteristics and the nature of solar radiation incident upon

the earth surface are considered as the essential requirements for

designing solar energy systems. This system requires information about

the amount of the solar radiation falling on the collector and the position

of the sun relative to the location of the collector. The location of the

PTSC in Al-Jaderiyha – Baghdad with latitude of 33.3o North, longitude

of 44.4o East, and a standard time meridian of 45o. The calculations in

this section are performed for a single day, October 10th (dn is number of

day, equal 283), at solar noon, in which the hour angle is at 0 degree. Full

calculations for particular days mentioned in appendix A. The solar

declination angle, s, is the angle between the earth-sun line and the plane

through the equator (refer to Fig. 1-4), is needed to perform calculations

for the position of the sun. The declination angle is measured by using

equation (1-5). The declination angle was found to be -7.724o. The

position of the sun can be described at any time by two different angles,

the solar altitude angle, αs, and the solar azimuth angle, γs, (refer Eq. 1-7

and Eq. 1-8). The solar altitude angle is 49.89o, and since the calculations

are for solar noon, the solar azimuth angle is zero. Figure (3-1) shows the


٦٤

solar altitude and azimuth angle for the entire day. However, they need to

be related to fundamental angular quantities, as the sunrise and sunset

hour angles, latitude and declination angle. The hour angles for Al-

Jaderiyha on October 10th were ±84.89o; negative for morning and

positive for afternoon and the time from solar noon is calculated to be 5

hours 39 minutes and 33 seconds. However, due to the irregularity of the

earth's motion about the sun, a correction factor is 13.8 minutes which is

given by the equation of time (refer Eq. 1-3). Appling the equation of

time correction factor, the sunrise and sunset local standard times are 6:21

AM and 17:39 PM, respectively, and resulting a day length of 11 hours

and 19

minutes.

Figure (3-1): Variation of solar angles and solar radiation versus

solar time for October 10th

By having a collector which tracks the position of the sun, an optimum

amount of solar radiation can be collected. At solar noon, the beam solar

radiation falling on the PTSC was measured to be approximately 633

W/m2. However, only beam (direct) insolation can be utilized due to the

type of collector, approximately, 540 W/m2 of solar radiation.


٦٥

3.3 Geometry Analysis of the PTSC

Measurements of the PTSC were taken to calculate the equation to

describe the shape. The trough is considered to be that of a parabolic

concentrator with aperture width, W of 2.8 m and a depth hc, of 0.47 m as

shown in figure 3-2.

Figure (3-2): Geometric dimensions of the trough

The focal length, f, can be computed using the following equation:

)13(04.116

2

mfh

Wf

c

The arc length of the parabolic curve, Sp, can be computed as follows

[31]:

)23(144

ln214

2

22

W

h

W

hf

W

hWS ccc

p

The arc length is found to be 3 m and is used to determine the reflective

surface area, As, by the following equation:


٦٦

)33( LSA ps

for a parabolic trough length L, 1.8 m. The rim angle θR, corresponds to

beam radiation reflected from the outer rim of the concentrator, which is

calculated by the following equation [31]:

)43(1

21

5.0

2 1

21

22

1

R

fCos

hfW

fCos

c

R

The simulated results for the focal length (f), the parabolic radius of curvature (R), the height of the parabolic curve (hc), the arc length of the parabolic curve (Sp), and the surface area of the concentrator (As) of PTSC for following rim angles 00000000 150115,90,75,60,45,30,15 and are

show in figure (3-3).

Figure (3-3) A Geometrical dimension of a PTSC versus rim angle with

common aperture width 2.8 m.


٦٧

This figure shows the effect of various rim angles on the geometric dimensions of PTSC. As the rim angle increases the focal length decreases. The parabolic radius decreases as the rim angle increases, however, at rim angle of 900, it starts increasing progressively within the investigation range of 1500. The height of the curve increases with increase of the rim angle. The surface area of the parabolic increases with increase of rim angle and the arc length increases progressively with increase of rim angle. Figure (3-4) shows that the thermal efficiency has a small change at a smaller rim angle until the rim angle reached 90o. It stars decreasing progressively within the range of 1500. However, the rim angle of 700 exhibited the maximum thermal efficiency of 0.672.

Figure (3-4) Thermal efficiency of PTSC versus rim angle

The rim angle is found to be 67.7o, which is considered appropriate in our measurements. Moreover, the parabolic radius R, is calculated to be 1.51 m. The resulting surface area of the concentrator is 5.4 m2.

3.4 Total Solar Radiation and Temperatures for a Non-

Selective Coated Metallic Receiver

A period of four clear sky days (10th, 13th, 17th, 25th October 2010)

have been selected for measuring all necessary data for analysis of the

performance of the PTSC by using a non-coated metallic receiver. A

typical data obtained in these days are showing in figure (3-5.a-d), in


٦٨

which the flow rate of the HTF is 0.02 kg/s. Ta, Ts, Tin, Tout and Itotal stand

for the ambient temperature, storage tank temperature, the inlet and outlet

temperatures of HTF and total solar radiation, respectively. The necessary

data for describing the PTSC are shown in appendix (C). Which figures

show the ambient temperature measured at the site during the test hours

for the four days of the experimental part, higher temperatures were

observed during the day time occurring between 12:30 pm and 13:30 pm.

The total solar radiation was measured during the test period exhibited,

higher values of total solar radiation between 11:30 am and 12:30 pm

with a peak occurring at about 12:00 o'clock. an increase in outlet HTF

temperature was noticed during early hours of the day until it reaches

maximum values around mid noon when total solar radiation values are

the highest. After that, outlet HTF temperature decreases due to the after

noon. The HTF temperature inside the receiver reached 157oC in clear

October day, where the maximum registered ambient temperature was

36oC. It was noticed that the HTF temperature inside the receiver

increases when the ambient temperatures is higher or when the solar

intensity is abundant. It is noticed that the lower temperature of the

storage tank is equal to inlet HTF temperature, approximately. The

temperature of the fluid in storage tank will be raised and thus, by

convection. This rising is, proportional with that of incident solar

radiation until solar noon, then temperature of storage tank leaves the

storage to the inlet of the receiver. Temperature will continuously

increase due to the fact the temperature of HTF in storage tank is

proportional directly with useful heat energy, this energy will increase

continuously with time whenever, the solar radiation is available. The

average maximum storage tank HTF temperature has been measured as

136oC, when no energy is withdrawn from the tank to the load during the

collection period.


٦٩

Figure (3-5,a,b,c&d): show variation of total solar radiation, ambient

temperature, lower and upper storage temperature, inlet and outlet

temperature of a non-selective coated metallic receiver with local time

for different clear October days.


٧٠

3.5 Total Solar Radiation and Temperatures for a Selective

Coating Metallic Receiver

A period of four clear sky days (2nd, 7th, 10th and 15th November)

has been selected for measuring all required data, as was mentioned

previously for analysis of the performance of the PTSC by using a coated

metallic receiver as shown in figure (3-6.a-d). The required data for

describing the PTSC performance with coated metallic receiver are

demonstrated in appendix D. as we have seen in figure (3-5) that the

performance of the PTSC is high, the collector's performance is also good

for November days, although the solar radiation and ambient temperature

is lower than those of the October days. The ambient temperature is in the

range 22-27oC, while the total solar radiation is 480 W/m2 at 9:30 am

reaching about 645 W/m2 at solar noon then decreases after solar noon

gradually. From figure (3-6), it can be found that the outlet HTF

temperature rises from 56oC at 9:30 am to 150oC at 12:30 pm. This rising

can be attributed to the selective surface (special black paint) for the

receiver which is a combination of high absorptance for solar radiation

with a low emittance for the temperature range in which the surface emits

radiation. It can be also seen that the storage temperature is 37oC in the

morning reaching 133oC at 13:30 pm, tacking 2nd of the November as a

sample.


٧١

Figure (3-6,a,b,c&d): show variation of total solar radiation, ambient

temperature, lower and upper storage temperature, inlet and outlet

temperature of a selective coated metallic receiver with local time for

different clear November days.


٧٢

3.6 Total Solar Radiation and Temperatures for an Evacuated

Glass Receiver

The experiments on the constructed PTSC with evacuated glass

receiver were carried out during four days through November and

December 2010, (23th, 29th November and 2nd, 6th December). A typical

data obtained in these days are shown in figure (3-7.a-d), where the total

solar irradiance on the PTSC, the ambient temperature, the storage

temperature, the inlet and outlet temperature of the receiver are shown.

The experiments have been conducted from 9:30 am to 13:30 pm with a

total solar radiation in the range of 400-520 W/m2 and a ambient

temperature in the range 17-24oC. Analyzing figure (3-7a), it can be

found that the outlet HTF temperature and storage temperature increase

from 47 to 150oC and from 30 to 134oC, respectively, when the solar

radiation intensity and local time are varied from 400 to 520 W/m2 and

from 9:30 am to 13:30 pm, respectively. Therefore, at any instant, the

receiver HTF temperature is greater than the storage tank fluid

temperature. This behavior is the same for the selected days of outdoor

test, see appendix E for details. The big difference in performance is due

to using different types of receivers. In this process, the absorber tube is

contained with glass envelope transparent to solar radiation over the solar

absorber surface that reduces convection and radiation losses to the

atmosphere. However, the primary function of the evacuated receiver is

to absorb and transfer the concentrated energy to the fluid follow through

it, and its temperature will become considerably higher than that of

metallic receiver.


٧٣

Figure (3-7,a,b,c&d):The total solar radiation, ambient temperature,

lower and upper storage temperature, inlet and outlet temperature of a

evacuated glass receiver with local time for different clear November

and December days.


٧٤

3.7 Thermal Stratification in the Storage Tank without HTF

Draw-off

In the present work, thermal storage tank operates with a

significant degree of thermal stratification when the fluid temperature

increases from the bottom to the top of tank. This phenomena

demonstrate the heat transfer mode of fluid when it is classified as not

mixed thermal layers, and this is in contrast to that obtained in a well-

mixed tank (storage) in which the fluid temperature is uniform

throughout. Figures (3-5), (3-6) and (3-7) show the temperature

distribution of the storage tank at different time of the day for several

days. It is clear that the temperature difference of the thermal layers is

rather high in storage tank, at the morning reaching 10oC, then drop

slowly after solar noon. Thus, the result shows the thermal stratifications

tend toward the well-mixed situation, especially at the end of each day of

operation. So the stratification mainly depends on the inlet and outlet of

the entering and leaving streams and the volume of the tank. It is obvious,

that the temperature difference between upper and lower layers in the

storage tank tends towards the well-mixed condition, due to smaller

storage tank volume.


٧٥

3.8 Performance Analysis of PTSC

The performance of the PTSC according to the previously

mentioned tests is determined by obtaining values of the useful heat gain,

Qu, the collector instantaneous thermal efficiency, th, the energy gained

Qs, by the storage tank and the overall efficiency, s, for different

parameters of operation; incident radiation, ambient temperature and inlet

HTF temperature.

3.8.1 Useful Heat Gain (Qu)

The useful heat gain is calculated from the measurements of the

inlet and outlet HTF temperatures and mass flow rate as demonstrated in

equation (1-43). Figures (3-8), (3-9) and (3-10) show the relation between

the variation of beam solar radiation, Ib, and the useful heat gain for a non

coated, coated metallic receiver and evacuated glass receiver,

respectively. The experiments were carried out from 9:30 am to 13:30 pm

for several days. It is clear that the Qu varies from 1 kW to 1.4 kW when

the beam radiation varied from 470 W/m2 to 654 W/m2 for 10 Oct. by

using a non coated metallic receiver. While, the value of Qu increases to

1.55 kW, although there is a drop in Ib for 2 Nov. when using a coated

metallic receiver. On the other hand, there is a small change in Qu

reaching about 1.45 kW, while the value of Ib decreases sharply, for 23rd

Nov. by using evacuated glass receiver. However, the useful heat gain

first increases, reach a peak value around noon and then decreases. This is

due to the fact that the useful heat gain is strongly influenced by the

incident beam radiation and therefore follows its variation.


٧٦

Figure (3-8): Variation of Ib and Qu with time for non coated receiver

Figure (3-9):Variation of Ib and Qu with time for coated metallic receiver

Figure (3-10): Variation of Ib and Qu with time for evacuated receiver


٧٧

3.8.2 Effect of Beam Solar Flux on the Useful Energy Gain

The influence of beam solar flux on the useful energy gain of the

PTSC are plotted in figures (3-11), (3-12) and (3-13) for non-coated

metallic, coated metallic and evacuated glass receiver, respectively. The

fluid mean temperature of the whole collector and the ambient

temperature essentially determine the losses from the collector. Hence, if

these quantities are constant and the beam solar flux increases, the useful

energy gain must increase. It can be found that the useful energy gain is

varied from 665 kJ to 1175 kJ when the solar flux varied from 915 kJ/m2

to 1350 kJ/m2 by using a non-coated metallic receiver. While, the value

of useful energy gain increases to 1400 kJ, although the values of solar

flux had been dropped from 945 kJ/m2 to 1170 kJ/m2 by using coated

metallic receiver. Typical results are shown in figure (3-13) for useful

energy gain during a solar flux changes from 720 kJ/m2 to 930 kJ/m2

when evacuated glass receiver used. As mentioned before the evacuated

glass receiver have relative low heat loss compared to metallic receiver.

Thus the decrease in useful energy gain over the solar flux range is small.


٧٨

Figure (3-11) Useful energy gain as a function of solar flux for non-coated metallic

receiver.

Figure (3-12) Useful energy gain as a function of solar flux for coated metallic rec.

Figure (3-13) Useful energy gain as a function of solar flux for evacuated rec.


٧٩

3.8.3 The Instantaneous Thermal Efficiency

Data for the beam solar radiation and useful heat gain by the

collector was obtained previously to determine the instantaneous

efficiency, th. The collector instantaneous thermal efficiency is

computed from equation (1-46). The efficiency th, of the collector

operating with each of the three previously described receivers is plotted

in figure (3-14) against the local time from 9:30 am to 13:30 pm for

different days. This figure shows that the collector efficiency of a non-

coated and coated metallic receiver is varied from 0.32 to 0.42 and from

0.39 to 0.55, respectively, when the beam solar radiation is varied from

460 to 650 W/m2 and from 410 to 560 W/m2, respectively. This variation

is related to the improvement in receiver and decreasing of heat losses

due to using a special black paint. Also, the collector efficiency of

evacuated glass receiver is improved and varies from 0.55 to 0.68, while

the value of Ib decreases sharply. This shows that rising of th, for

evacuated receiver is mainly attributed to the less thermal loss

(convection and radiation) due to using glass envelope and high

absorbtivity of selective coating.

Generally, it will be noted that the general pattern of variation of

efficiency over day is the same as that of the useful heat gain because the

value of efficiency depends on both the incident beam radiation and the

useful heat gain.


٨٠

Figure (3-14): Variation of collector instantaneous efficiency with time

for a non coated, coated metallic and evacuated receivers

3.8.3 Energy Gained by the Storage Tank

The accumulation of the energy gained, Qs, by the storage tank

fluid each 15 minutes is computed using previous receivers. Figures (3-

15), (3-16) and (3-17) show the energy gained and average storage

temperature above initial temperature with time by using non-coated,

coated metallic receiver and evacuated glass receiver, respectively. It can

be found that the average storage temperature above initial increase with

time. It is mainly because the solar radiation incident on the collector

goes up with time. It is noteworthy that the average storage temperature

above initial temperature has a small decrease from 12:30 am to 13:30

pm. A possible reason is the little increase of solar radiation. This


٨١

behavior is the same for the three previous receivers. On the other hand, it

can be seen that there is a relationship between energy gained and the

average storage above the initial. It can be found that the energy gained

by using non-coated and coated metallic receiver is increased from 1000

kJ to 10000 kJ and from 1000 kJ to 11937 kJ, respectively, when the

average storage temperature above the initial temperature is increased

from 8 oC to 80 oC and from 8 oC to 95.5 oC, respectively. As also seen

from figure (3-17), that Qs, and average storage temperature above the

initial by using evacuated receiver are increased sharply, at 12:30 pm

reaching about 12937 KJ for a 103.5 oC temperature difference between

average storage and the initial temperature. However, the energy gained

per quarter hour, by the storage tank fluid increases, reaching a peak

value around noon. This effect is due to the fact that the energy gained by

the storage tank is directly proportional to the average storage above

initial temperature across the collector with time. The hourly collected

load energy, QL, is plotted in figure (3-18), against the local time. It is

found that the QL are varied from 0.27 kWh to 2.78 kWh and from 0.27

kWh to 3.31 kWh, respectively, when used non-coating and coating

metallic receiver, respectively. While, the highest value of QL is noted by

using evacuated receiver, reaching about 3.6 kWh. By comparison of the

results, it was found that the difference among them due to their various

energy gained, and the maximum QL equal to 3.6 kWh which is optimum

for the thermal applications.


٨٢

Figure (3-15): Variation of QS and average storage temerp.using non coaed

metallic reeiver.

Figure (3-16): Variation of QS and average storage temperature using coated

metallic receiver.

Figure (3-17): Variation of QS and average storage temperature using evacuated

receiver.


٨٣

Figure (3-18): Variation load energy with time using different receivers

3.9 The Performance Curve of the PTSC

The thermal efficiency of a PTSC can be described by ASHRAE

Standard 93 (1986) [77] as demonstrated in Eq.(1-45). If the thermal

efficiency from Eq. (1-45) is plotted against bambin ITT / a straight line

will result provided UL is constant. The intercept is FRo and the slope is

FRUL /C. The performance curve of the PTSC, is derived from a series of

tests conducted by the use of three receivers.

3.9.1 Non-coated metallic receiver

Five tests were conducted to generate the thermal efficiency curve

of the PTSC, which is shown in figure (3-19).


٨٤

Figure (3-19): Thermal efficiency curve with non-coating receiver

The best fit curve in figure (3-19) is obtained which is shown as a solid

line. This yielded equation (3-5), the thermal performance equation for

the collector with non-coated receiver.

)53(5387.04468.0

b

ambinth I

TT

From equation (3-5), (ArULFR /Aa) = 0.5387 W/ocm2 and FRo =0.4468.

For a geometric concentration ratio (Aa/Ar) of 35 the gradient of equation

3-5 gives ULFR =18.854 W/ocm2. The optical efficiency can be calculated

from equation 1-26, from which o =0.407, this result gives in a heat

removal factor (FR) of 0.913. The heat removal factor represents the ratio

of actual useful energy gain of the collector to the useful gain if the whole

receiver were at the fluid inlet temperature. This in turn yields an overall

heat loss coefficient (UL) of 20.65 W/ocm2.


٨٥

3.9.2 Coated metallic receiver

The test programme for coated metallic receiver has been predicted

based on the measured data which was collected through five tests. These

tests were conducted to determine the thermal efficiency curve, which is

shown in figure (3-20)

Figure (3-20): Thermal efficiency curve with coated metallic receiver

The following performance equation for the collector with coated

metallic receiver:

)63(4907.06012.0

b

ambinth I

TT

From equation 3-6, (ArULFR /Aa) = 0.4907 W/ocm2 and FRo = 0.6012. for

a concentration ratio of 35, the gradient of equation 3-6 gives ULFR =

17.17 W/ocm2. as with non-coated receiver, the optical efficiency can be


٨٦

calculated from equation (1-26). The presence of the selective coating

increases o from 0.40 to 0.63, this result in a heat removal factor (FR) for

coating metallic receiver of 0.94 and an overall heat loss coefficient (UL)

of 18.29 W/ocm2.

3.9.3 Evacuated – glass receiver

The performance curve of the PTSC with evacuated receiver, as

derived from five tests conducted is shown in figure (3-21).

Figure (3-21): Thermal efficiency curve with evacuated glass receiver

An equation for the curve is obtained using standard technique of

the best fit. The intercept is equal 0.6737 and the slope is 0.37. Therefore,

the collector thermal efficiency equation for PTSC with evacuated

receiver can be written as:


٨٧

)73(37.06737.0

b

ambinth I

TT

The optical efficiency, o of the collector is determined as 0.683 and a

concentration ratio of 20.16. The calculation was done as was described

in the previous section, heat removal factor for the evacuated receiver of

0.985 and an overall heat loss coefficient of 7.56 W/ocm2.

3.9.4 Comparison of the results

Data is obtained from three sets of thermal efficiency tests for non-

coated, coated metallic receiver and evacuated receiver, as were

demonstrated previously. It is noted clearly, that the thermal efficiency

using non-coated and coated metallic receiver is varied from 0.46 to 0.34

and from 0.625 to 0.44, respectively, when receiver temperature above

ambient is varied from 29.5 to 106 oC and from 21.5 to 111.5 oC,

respectively. The thermal efficiency using evacuated receiver increasing

steadily compared with those previous results. Thus, thermal efficiency

and receiver temperature above ambient are varied from 0.68 to 0.53 and

from 17 to 114 oC. These results indicate a beneficial effect when the

receiver is painted black. Moreover, using glass cover protective

apparently proved benefit to the overall performance. The efficiency

equation using evacuated receiver compares well with the other reported

research works as presented in Table (3-1).


٨٨

Table (3-1): Comparison of collector efficiency equations for evacuated receiver.

Efficiency equation Reference

bambinth ITT /233.066.0 Murphy and Keneth,1982 [78]

bambinth ITT /441.0642.0 Kalogirou, 1994 [79]

bambinth ITT /387.0638.0 Kalogirou et al, 1996 [35]

bambinth ITT /39.069.0 Valan and Samuel, 2006 [80]

bambinth ITT /37.06737.0 This work

3.10 Effect of the HTF Inlet Temperature on the Thermal

Efficiency of the Collector

The HTF inlet temperature is an operational parameter which

strongly influences the performance of the PTSC. Figures (3- 22) and (3-

23) show that the thermal efficiency decreases slightly with increasing

values of HTF inlet temperature for non-coated and coated metallic

receiver. The values of thermal efficiency for no-coated and coated

metallic receiver have dropped from 0.46 to 0.33 and from 0.62 to 0.44,

respectively, as HTF inlet temperature increases from 50 to 124 oC and

from 31 to 120 oC respectively. This decrease in thermal efficiency occurs

because of the higher temperature level at which the collector as a whole

operates when the fluid inlet temperature increase. A possible reason for

the temperature difference with the surroundings increases, and then the

heat loss increases, so the efficiency decreases. The experimental results

are obtained of the fluid inlet temperature for evacuated receiver as

shown in figure (3-24). It can be found that the fluid inlet temperature

rises from 23 to 122 oC, while, thermal efficiency varies from 0.68 to

0.54. As mentioned before the evacuated receiver has relatively low heat


٨٩

loss comparison with other receiver. Thus the decrease in thermal

efficiency over the measured temperature range is small.

Figure (3-22): Variation of thermal efficiency of the collector with

HTF inlet temperature for non-coated metallic receiver


HTF inlet temperature for coated metallic receiver


٩٠


HTF inlet temperature for evacuated glass receiver

3.11 Heat Loss Coefficient for the Storage Tank

The heat loss (UA)s for the storage tank has been determined

experimentally. A cool-down test was done to determine (UA)s after

reaching average storage temperature of 130 oC. The temperature

decrease over two days was recorded without draw-off. The oil

temperature is determined by averaging the readings of two

thermocouples K-type placed at upper and lower positions inside the

tank. The ambient temperature was also monitored by data logger which

was positioned near the storage tank. The heat loss coefficient for the

tank was then calculated over 2 days test periods based on the following

correlation (ISO9459-2, 1995) [81].

avTT

avTT

t

CVUA

ambsf

ambsipsf ln

………………….. (3-8)

where f is oil density at that particular temperature range (kg/m3), Cp is

the specific heat of oil (kJ/kg oC), Vs is the volume of the storage tank


٩١

(m3), t is the period of averaging (sec), Tsi and Tsf are oil temperature at

the start and at the end of the measuring respectively, Ta(av) is the average

ambient temperature over the period of test. The average heat loss

coefficient of the storage tank (UA)s was found to be 1.82 W/oC as shown

in Table (3-2).

3-12 Heat Losses for the PTSC without Draw-off

The thermal losses through the PTSC are changed in different ways

depending on the receiver configuration and operational conditions.

Figure (3-25a,b,and c) show the heat losses with receiver operating

temperature representing the non-coated, coated metallic and evacuated

receiver, respectively. The experiments were done under the condition of

the wind velocity of about 1m/s, and the ambient temperature in the range

of 18-36 oC. Analyzing figure (3-25), it can be found that linear loss of

heat depends on the receiver operating temperature. The heat losses from

non-coated receiver and storage tank have an increase from 174 W to 625

W and from 43.5 W to 181 W, when receiver operating temperature

increases from 29.5 oC to 106 oC. it can be also seen from figure (3-20b)

that the heat loss from coated metallic receiver was low and had a

decrease of 10% from 21.5 oC to 111 oC compared with previous

receiver. A reason is that the outer pipe surface with a black paint which

(UA)s

W/oC

Ta)final

(oc)

Ta)initial

(oc)

Tupper)final

(oc)

Tupper)initial

(oc)

Tlow )final

(oc)

Tlow )initial

(oc)

Duration

(hour)

Test no.

0.95 18 20 93 132 90 130 14.5 1

1.07 21 20 82 132 80 130 19 2

1.89 20 20 36 132 35 130 33.5 3

2.84 23 20 28 132 28 130 38 4

Table (3-2): Heat loss coefficient for the storage tank


٩٢

reduced the heat loss, while the heat loss from storage tank is

approximately the same. Also, seen in figure (3-20c), the heat loss from

evacuated receiver is drastically lower than those of the metallic receiver.

The heat losses were about 213 W for a 114 oC temperature difference

between the receiver temperature and the ambient temperature. The

thermal loss reduction is due to adding glass envelope to the collector

receiver. However, the reason for the higher thermal loss with sun is that

solar flux heats the solar collector to a higher temperature, which is

related to grater thermal losses.


٩٣

Figure (3-25 a,b&c): heat losses versus the receiver operating

temperature using non-coated, coated metallic and evacuated receivers,

respectively

3-13 Conclusions

The following conclusions have been obtained:

1- Solar tracking system of two-axis has proved the reception of a

higher energy gain and improved collector operating efficiency.

2- Practical results have shown that the maximum thermal efficiency

of the PTSC are 44%, 59% and 67% using non-coating, coating

metallic and evacuated receivers, respectively.

3- The evacuated receiver is suitable for obtaining high temperature

about 130-140 oC, and its cylindrical shape leads to receive

reflected and deflected radiations from the focus.

4- The use of glass envelope has shown that the collector can offer

significant reductions in the overall system heat loss.


٩٤

5- The PTSC that has been performed is suitable for space heating

and hot water loads, because of high temperature of storage that

reaches 135 oC.

3.13 Future Works

1- Optical design and fabrication of solar concentrator for photovoltaic.

2- The PTSC can be analyzed with several types of operation fluids as a

working fluid.

3- Design and fabrication of a new trough, possibly made from

composite materials, to make lighter and more durable.

4- Parallel to the experimental work, a numerical analysis can be used to

compare the results of both theoretical and experimental investigation to

optimize the collector design.

Appendix F

The Intercept Factor Calculation (γ)

Figure (F.1) Cross section for metallic receiver

)1()( 43 FqqATTUAIQ rambrLabou

Let Qu=q1 , UL(Tr – Tamb)Ar=q2, oIbAa=q

q=q1+q2+q3+q4

Now we can be calculated: q1, q2, q3 and q4

q1=m.Cpdt

m.=0.02 kg/s Cp=2.5 kJ/kg.K dt=20 oC

q1=1 kW

Where: q3, radiation heat loss from the surface (focus), q4, convection heat loss from the surface.

q2= UL(Tr – Tamb)Ar

)2(11

111

11

,,

,,

F

AhAhAk

x

AhUA

verrverhorrhor

insrins

ins

extrf

Ar,ext=(20.04+20.08) 1.8=0.43 m2 ,internal area of receiver

Ar,int=(20.04+0.08) 1.8=0.28 m2 , external area of receiver

Ar,hor= area of horizontal sides for the receiver

Ar,ver= area of vertical sides for the receiver

Ar,hor= 2(0.041.8)= 0.144 m2

Ar,ver= (0.081.8)=0.144 m2

hver=1.77(T)1/4 =1.77(Ts-Tamb)1/4 =3.4 W/oCm2

hhor=2.5(T)1/4 =4.9 W/oCm2

11

144.09.4

11

144.04.3

11

288.0038.0

02.0

43.07.8

1

UA

(UAr) = 0.35 W/oC

q2= 0.35 (120-35) = 30 W, thermal losses from insulator sides

q3= hfocal Ar,focal T

hfocal =1.77 (200-35)1/4, Ar,focal =0.81.8=0.144 m2

q3=21 W

WTTAq skysurfsurfacerr 248)( 44,4

q=1000+30+21+248=1300 W

o Ib Aa =0.5 6005.04=1512 W

Therefore, can be calculating the intercept factor, to be 0.85.

Appendix G

Optical efficiency of the receivers

The optical efficiency of the receivers has been determined experimentally. As illustrated in previous section, so the optical efficiency can be determined by using Eq. (1-27). The products of the transmittance – absorbance of the receiver and the reflectance of the aperture, according to the specification of the collector. The optical efficiency of the evacuated

glass receiver (0.920.930.940.85) is then 0.683. While, the optical efficiency of coated metallic receiver to be 0.63, by using Cellulose Nitrate as a coated black paint have absorbtance 0.78 as illustrated in figure (G1).

Figure (G1) Absorbtance of the thermal paint (Cellulose Nitrate)

Appendix H

Thermal losses Calculation for the connecting tube

At the edge the receiving tubes, a flexible tube is used for the conveyance of the HTF. The thermal losses for connecting tube are estimated by:

Ti = temperature of liquid inside tube ( K )

T0= temperature of liquid outside tube ( K )

Di = diameter of tube (m) = 0.015 m

D0 = diameter of tube + insulator (m) = 0.045 m

If Ti = 150 oC , T0 = 30 oC

L = 5 m

Figure (H.1) Cross section of the connecting tube

Mobitherm Light (Temperature 250 C0)

at T = 93 C0 [From Table]

ρ = 935 Kg/m 3 , µ = 1.6 g/m.s, cp = 2.5 KJ/Kg.K,

K = 0.116 W/moC, Pr = 27.9, m0 = 1 liter/min = 0.0166 Kg/sec,

din = 0.0155 m, dout = 0.045 m, Kins. = glass – wool = 0.04 W/moC

32

106.14

)015.0(

015.0016.0

A

dmR in

o

e

Re=1020.42300 [Laminar flow]

At laminar, Nu = 3

WhhK

hdN

ins

outu 66.2

045.0

04.03

Tin = 150 oC, Tout = 30 oC, L = 5 m

66.250225.014.32

1

504.014.32

)0075.00225.0(

2

1

2

)(

n

LhrLK

rrnR

oins

ioth

Rth = 0.09 / 1.256 + 1 / 1.836

Rth = 0.071 + 0.54 = 0.61 oC/W

qloss = ∆T / Rth

∆T = ( 150 – 30 ) C0

qloss = 120 / 0.61 = 196.7 W

Appendix I

Design Calculations of the Storage Tank

A: load without heat exchanger:

From collector

Required load

1. Calculation of the volume for the storage tank:

Storage media :‐ oil

Cp = 2.5 KJ/Kg.K

qst / Vst = ρs CPs ∆T ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ (1)

The total energy required for charging storage per m3

For & time = 4 hour.

From 1:

2. Calculation of the heat losses for the

storage tank:

Insulation :- glass wool (15 cm)

Ambient temperature Ta= 25

Heat transfer coefficient (h) for

Inner radius

Outer radius

Kins=0.038 W/moC

Li = 0.52 m Lt = Li + (2 * 0.15)

Lt = 0.25 + 0.3 = 0.82 m

Heat transfer resistance of the cylindrical part

due to convection & conduction

Ln (0.32/0.17) 1

Rth = ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ + ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

2π (0.038 * 0.82) 2π (0.032 * 0.82) (4)

= 3.23 + 0.15 = 3.38 oC/W

Heat transfer resistance for the flat part

tins

io

oth hK

rr

rR

1

2

12

42.65.5

1

038.0

17.032.0

)32.0(14.32

12

thR oC/W

∆T = Ts – Ta = 200 – 25 = 175 C0

Total rate of heat loss, UA

Tqloss /1

(1/UA=thermal resistance)

79642.6

175

38.3

175lossq W

qloss=0.079 kJ/s

The highest energy losses in the storage tank at temp. 200C0

3. USEFUL STORAGE ENERGY FOR THE LOAD

qloss = 0.079 KJ/s

quseful = m cp ∆T (∆T = 200 – 100)

quseful = ρ Vs cp ∆T

quseful = 940 * 0.05 * 2.5 * 100

quseful = 11750 KJ Useful energy gain

4. TIME FOR PARTIAL CHARGING WITH THE USEFUL ENERGY

qu = 1.8 Kw

qloss = 0.079 KJ/s qL = 0

qst = (qu – qloss) * t * 3600 t = hour

qst = (1.8– 0.079) * t * 3600

6195.6 t = 11750

utehourthourtt min53&189.16.6195

11750

5. TIME FOR LOSSING THE USEFUL ENERGY WITH NO LOAD

hourtq

qt

loss

useful 3.41079.0

11750

6. TIME FOR SUPPLYING THE LOAD

q s. useful = 11750 KJ q L = 1 KJ/s

utehourthourtskJ

Jk

q

qt

L

useful min15&326.3/36001

/11750

B. LOAD WITH HEAT EXCHANGER

TO determine the length (L) of the heat exchanger coil

=h(

From the Table (for water):

mcminchdskgm

pmKkWkmNsKkgkJcmkgow

r

0125.025.15.0,/03.0

54.3,/10648.0,/102.549,./17.4,/1.988 3263

(Turbulent flow)

L = 1.0 is the length of heat exchanger

If the, of the heat exchanger is 50%

Then V = 50 liter = 0.05 m3

*L

Re=

No. of Turns

dcoil =0.2 m

coil=0.62 mm Length of the heat exh. = 2 m

coil (no. of turns)

The Length of the heat exch. Is :

L = 2.5 m + 0.5 m

Lt

Ts

= 200 C0

F-1

Appendix F

The Intercept Factor Calculation (γ)

Figure (F.1) Cross section for metallic receiver

)1()( 43 FqqATTUAIQ rambrLabou

Let Qu=q1 , UL(Tr – Tamb)Ar=q2, oIbAa=q

q=q1+q2+q3+q4

Now we can be calculated: q1, q2, q3 and q4

q1=m.Cpdt

m.=0.02 kg/s Cp=2.5 kJ/kg.K dt=20 oC

q1=1 kW

Where: q3, radiation heat loss from the surface (focus), q4, convection heat loss from the surface.

q2= UL(Tr – Tamb)Ar

)2(11

111

11

,,

,,

F

AhAhAk

x

AhUA

verrverhorrhor

insrins

ins

extrf

Ar,ext=(20.04+20.08) 1.8=0.43 m2 ,internal area of receiver

Ar,int=(20.04+0.08) 1.8=0.28 m2 , external area of receiver

102

APPENDIX A

Solar Calculations

Calculations performed for Baghdad, where L is the local latitude, Llocal is the local longitudes and Lst is the standard meridian for the local time zone.[Duffie,1991]

L= 33.3 deg, LLocal=44.4, Lst=45o

Julian Day (n) n=1, 2, 3 …………. 365

Declination angle

deg])365

284360sin[(.deg45.23

ns

1deg012.23 nifs

At solar noon hs=0

The solar altitude is thus

Sin(αs)=cos(L).cos(δs). cos(hs) + sin(L). sin(δ)

αs= asin[Cos(L). Cos(δs(n)).cos(hs)+sin(L).sin(δs(n))]

αs= 36.608 deg.

and the solar azimuth angle is ])cos(

)sin()).(sin[cos(

sss a

hsna

γs=0

At solar noon the altitude can also solved by

αs=90deg-(L-s(n))

αs=36.608deg

Sunrise/Sunset Angle

hss(n)=a cos[-tan(L). tan(s(n)]

hss(n)=73.80 deg

note: sunset and sunrise angle are the same (+/-)

103

time from solar noon

time- from- solar- noon(n)= hss(n).4 deg

min

time- from- solar- noon(n)=295.2 min

use Equation at time to convert the solar time for sun rise and sunset to local times.

364

81deg360)(

dnnB

deg121.79)( nB

E(n)=(9.87sin(2B(n)-7.53Cos(B(n))-1.5 sin(B(n))

E(n)=-3.607 min

Local standard time (LST)

LST=solar-time-ET+4(Lst-LLcoal)

)(4 LocalLLstET

)4445(4)()( nETn

min007.6)( n

LST=solar-time + )(n

The length of the day can also be calculated by the following method

hr

nhssnLengthday

deg15

)(*2)(

9:50:24 hhmmss

104

Appendix (B)

Heat transfer equations rate for the Receiver and storage tank

Heat Name

Heat Transfer

type

From To Heat Calculation Equation reference

Qsun-

concentrator

………… Sun light concentrator Qsun-

concentrator=

Rabl,Ari,1985 [82]

Qsun- receiver ……….. Sun light Receiver Qsun-receiver=ταAconcentrator

sin2( half)σTr4

Rabl,Ari,1985 [82]

Qreceiver-amb Radiation receiver Ambient Qreceiver-Amb=ξrArσTr4 Rabl,Ari,1985 [82]

Q°conv,rec-air convection Outer surface of

receiver Ambient air Qconv,rec-air=hAr(Tr-Ta) Holman,1976 [83]

Q°rad,rec-sky Radiation Outer surface of

receiver sky Qrad,rec-sky=σξrAr[Tr

4-T4

sky] Holman,1976 [83]

Q°cond,rec conduction Inner surface of

receiver Outer surface of receiver

Qcond=

Holman,1976 [83]

Ustorage-tank conduction Inner surface of tank

Outer surface of tank

Us=

Budihardjo,et,al,2002 [81]

QLoss conduction Inner surface of tank


QLoss=

F-2

Ar,hor= area of horizontal sides for the receiver

Ar,ver= area of vertical sides for the receiver

Ar,hor= 2(0.041.8)= 0.144 m2

Ar,ver= (0.081.8)=0.144 m2

hver=1.77(T)1/4 =1.77(Ts-Tamb)1/4 =3.4 W/oCm2

hhor=2.5(T)1/4 =4.9 W/oCm2

11

144.09.4

11

144.04.3

11

288.0038.0

02.0

43.07.8

1

UA

(UAr) = 0.35 W/oC

q2= 0.35 (120-35) = 30 W, thermal losses from insulator sides

q3= hfocal Ar,focal T

hfocal =1.77 (200-35)1/4, Ar,focal =0.81.8=0.144 m2

q3=21 W

WTTAq skysurfsurfacerr 248)( 44,4

q=1000+30+21+248=1300 W

o Ib Aa =0.5 6005.04=1512 W

Therefore, can be calculating the intercept factor, to be 0.85.

A-2



min



364

81deg360)(

dnnB

deg121.79)( nB


E(n)=-3.607 min



)(4 LocalLLstET

)4445(4)()( nETn

min007.6)( n



hr

nhssnLengthday

deg15

)(*2)(

9:50:24 hhmmss

B-1

Appendix (B)


Heat Name

Heat Transfer

type


Qsun-

concentrator


concentrator=

Rabl, 1985 [82]


sin2( half)σTr4

Rabl, 1985 [82]

Qreceiver-amb Radiation receiver Ambient Qreceiver-Amb=ξrArσTr4 Rabl, 1985 [82]





4-T4




Qcond=

Holman,1976 [83]



Us=




QLoss=

G-1

Appendix G

Optical efficiency of the receivers

The optical efficiency of the receivers has been determined experimentally. As illustrated in previous section, so the optical efficiency can be determined by using Eq. (1-27). The products of the transmittance – absorbance of the receiver and the reflectance of the aperture, according to the specification of the collector. The optical efficiency of the evacuated

glass receiver (0.920.930.940.85) is then 0.683. While, the optical efficiency of coated metallic receiver to be 0.63, by using Cellulose Nitrate as a coated black paint have absorbtance 0.78 as illustrated in figure (G1).

Figure (G1) Absorbance of the thermal paint (Cellulose Nitrate)

H-1

Appendix H

Thermal losses Calculation for the connecting tube

At the edge the receiving tubes, a flexible tube is used for the conveyance of the HTF. The thermal losses for connecting tube are estimated by:

Ti = temperature of liquid inside tube ( K )

T0= temperature of liquid outside tube ( K )

Di = diameter of tube (m) = 0.015 m

D0 = diameter of tube + insulator (m) = 0.045 m

If Ti = 150 oC , T0 = 30 oC

L = 5 m

Figure (H.1) Cross section of the connecting tube

Mobitherm Light (Temperature 250 C0)

at T = 93 C0 [From Table]

ρ = 935 Kg/m 3 , µ = 1.6 g/m.s, cp = 2.5 KJ/Kg.K,

K = 0.116 W/moC, Pr = 27.9, m0 = 1 liter/min = 0.0166 Kg/sec,

din = 0.0155 m, dout = 0.045 m, Kins. = glass – wool = 0.04 W/moC

32

106.14

)015.0(

015.0016.0

A

dmR in

o

e

H-2

Re=1020.42300 [Laminar flow]

At laminar, Nu = 3

WhhK

hdN

ins

outu 66.2

045.0

04.03

Tin = 150 oC, Tout = 30 oC, L = 5 m

66.250225.014.32

1

504.014.32

)0075.00225.0(

2

1

2

)(

n

LhrLK

rrnR

oins

ioth

Rth = 0.09 / 1.256 + 1 / 1.836

Rth = 0.071 + 0.54 = 0.61 oC/W

qloss = ∆T / Rth

∆T = ( 150 – 30 ) C0

qloss = 120 / 0.61 = 196.7 W

Appendix I

Design Calculations for the Storage Tank

A: load without heat exchanger:

From collector

Required load

1. Calculation of the volume for the storage tank:

Storage media :‐ oil

Cp = 2.5 KJ/Kg.K

qst / Vst = ρs CPs ∆T ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ (1)

The total energy required for charging storage per m3

For & time = 4 hour.

From 1:

2. Calculation of the heat losses for the

storage tank:

Insulation :- glass wool (15 cm)

Ambient temperature Ta= 25

Heat transfer coefficient (h) for

Inner radius

Outer radius

Kins=0.038 W/moC

Li = 0.52 m Lt = Li + (2 * 0.15)

Lt = 0.25 + 0.3 = 0.82 m

Heat transfer resistance of the cylindrical part

due to convection & conduction

Ln (0.32/0.17) 1

Rth = ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ + ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

2π (0.038 * 0.82) 2π (0.032 * 0.82) (4)

= 3.23 + 0.15 = 3.38 oC/W

Heat transfer resistance for the flat part

tins

io

oth hK

rr

rR

1

2

12

42.65.5

1

038.0

17.032.0

)32.0(14.32

12

thR oC/W

∆T = Ts – Ta = 200 – 25 = 175 C0

Total rate of heat loss, UA

Tqloss /1

(1/UA=thermal resistance)

79642.6

175

38.3

175lossq W

qloss=0.079 kJ/s

The highest energy losses in the storage tank at temp. 200C0

3. USEFUL STORAGE ENERGY FOR THE LOAD

qloss = 0.079 KJ/s

quseful = m cp ∆T (∆T = 200 – 100)

quseful = ρ Vs cp ∆T

quseful = 940 * 0.05 * 2.5 * 100

quseful = 11750 KJ Useful energy gain

4. TIME FOR PARTIAL CHARGING WITH THE USEFUL ENERGY

qu = 1.8 Kw

qloss = 0.079 KJ/s qL = 0

qst = (qu – qloss) * t * 3600 t = hour

qst = (1.8– 0.079) * t * 3600

6195.6 t = 11750

utehourthourtt min53&189.16.6195

11750

5. TIME FOR LOSSING THE USEFUL ENERGY WITH NO LOAD

hourtq

qt

loss

useful 3.41079.0

11750

6. TIME FOR SUPPLYING THE LOAD

q s. useful = 11750 KJ q L = 1 KJ/s

utehourthourtskJ

Jk

q

qt

L

useful min15&326.3/36001

/11750

B. LOAD WITH HEAT EXCHANGER

TO determine the length (L) of the heat exchanger coil

=h(

From the Table (for water):

mcminchdskgm

pmKkWkmNsKkgkJcmkgow

r

0125.025.15.0,/03.0

54.3,/10648.0,/102.549,./17.4,/1.988 3263

(Turbulent flow)

L = 1.0 is the length of heat exchanger

If the, of the heat exchanger is 50%

Then V = 50 liter = 0.05 m3

*L

Re=

No. of Turns

dcoil =0.2 m

coil=0.62 mm Length of the heat exh. = 2 m

coil (no. of turns)

The Length of the heat exch. Is :

L = 2.5 m + 0.5 m

J-4

Figure (J.4) Dimensioned diagram of tilting movement base

J-5

Figure (J.5) Dimensioned diagram of the tilting motion assembly

J-1

Appendix J Design Drawings of PTSC

Fig

ure

(J.

1) T

otal

ass

embl

y of

the

para

boli

c tr

ough

sol

ar c

olle

ctor

Appendix J Design Drawings of PTSC

J-9

Fig

ure

(J.

9) D

imen

sion

ed d

iagr

am o

f th

e ev

acu

ated

rec

eive

r

J-6

Fig

ure

(J.

6) D

imen

sion

ed d

iagr

am o

f th

e re

flec

tin

g pa

rts

asse

mbl

y

J-2

Figure (J.2) Dimensioned diagram of the axial motion guide assembly

J-3

Figure (J.3) Dimensioned diagram of the axial motion assembly

J-7

Fig

ure

(J.

7) D

imen

sion

ed d

iagr

am o

f th

e re

flec

tin

g ba

se p

arts

J-8

Fig

ure

(J.

8) D

imen

sion

ed d

iagr

am o

f th

e m

etal

lic

rece

iver

APPENDIX A

Solar Calculations

Calculations performed for Baghdad, where L is the local latitude, Llocal is the local longitudes and Lst is the standard meridian for the local time zone.[Duffie,1991]

L= 33.3 deg, LLocal=44.4, Lst=45o

Julian Day (n) n=1, 2, 3 …………. 365

Declination angle

deg])365

284360sin[(.deg45.23

ns

1deg012.23 nifs

At solar noon hs=0

The solar altitude is thus

Sin(αs)=cos(L).cos(δs). cos(hs) + sin(L). sin(δ)

αs= asin[Cos(L). Cos(δs(n)).cos(hs)+sin(L).sin(δs(n))]

αs= 36.608 deg.

and the solar azimuth angle is ])cos(

)sin()).(sin[cos(

sss a

hsna

γs=0

At solar noon the altitude can also solved by

αs=90deg-(L-s(n))

αs=36.608deg

Sunrise/Sunset Angle

hss(n)=a cos[-tan(L). tan(s(n)]

hss(n)=73.80 deg

note: sunset and sunrise angle are the same (+/-)



min



364

81deg360)(

dnnB

deg121.79)( nB


E(n)=-3.607 min



)(4 LocalLLstET

)4445(4)()( nETn

min007.6)( n



hr

nhssnLengthday

deg15

)(*2)(

9:50:24 hhmmss

Appendix (B)


Heat Name

Heat Transfer

type


Qsun-

concentrator


concentrator=

Rabl,Ari,1985 [82]


sin2( half)σTr4

Rabl,Ari,1985 [82]

Qreceiver-amb Radiation receiver Ambient Qreceiver-Amb=ξrArσTr4 Rabl,Ari,1985 [82]





4-T4




Qcond=

Holman,1976 [83]



Us=




QLoss=

Appendix (C -Tables) No. of day =22 δ=-19.92 =33.33o β=45o

Table C-1: Experimental data for evacuated tube collector during 22nd January 2009

105

Qloss(tank)

W sys (%)

Qstorage(tank)

kJ Qloss(rec)

W th

(%)

Qu

W өz

degree

αs

degree

Windm/sec

Isc W/m2

Id

W/m2

Ib

W/m2 Itotal

W/m2

Tamb oC

Tupper oC

Tlower oC

Tout oC

Tin oC

Time (hour)

43.6 174.05 46 1000 54.1 35.9 0.27 1360 77.5 467 545 31.5 59 52 72 50 9:30

57.69 44 1000 210.63 40 1050 51.8 38.2 2 1360 80.1 509 590 31.8 68 59 78 57 9:45

71.89 43 2000 262.55 43 1070 49.7 40.3 2 1360 82.1 517 600 32 76 67 88 65 10:00

85.17 39 2937 299.72 36 1100 47.7 42.3 2 1360 83.8 555 639 32.2 83 75 93 73 10:15

99.37 38 3937 351.64 42 1150 46 44 0.27 1360 85.2 574 660 32.4 91 83 104 80 10:30

114.29 37 5062 400.02 36 1200 44.4 45.6 1.15 1360 86.4 593 680 33.2 100 92 112 90 10:45

127.94 36 6062 438.37 33 1211 43.1 46.9 0.27 1360 87.4 610 698 33.7 108 100 118 98 11:00

141.59 35 7062 482.62 32 1224 42.1 47.9 1 1360 88.1 626 715 34.2 115 109 126 106 11:15

152.8 34 8000 542.21 38 1250 41.3 48.7 1 1360 88.6 639 728 34.6 123 116 139 114 11:30

167.25 33 8875 591.77 40 1300 40.8 49.2 0.27 1360 88.9 641 730 34.7 129 124 148 122 11:45

176.9 32 9562 638.38 42 1400 40.7 49.3 0.27 1360 89 654 743 34.8 133 131 157 129 12:00

180.1 30 9812 634.25 35 1200 40.8 49.2 0.27 1360 88.6 640 730 35 135 133 154 131 12:15

182.5 29 10000 630.12 32 1150 41.3 48.7 0.27 1360 88.1 621 710 35.2 136 135 152 132 12:30

183.8 28 10000 630.12 31 1050 42.1 47.9 0.27 1360 87.4 601 690 35.7 136 135 152 133 12:45

182 27 10000 625.99 31 1000 43.1 46.9 0.27 1360 87.4 582 670 35.9 136 135 151 133 13:00

181.1 27 10000 625.4 32 900 44.4 45.6 0.27 1360 86.4 543 630 36 136 135 151 133 13:15

181.1 27 10000 625.4 32 900 46 44 0.27 1360 85.2 514 600 36 136 135 151 133 13:30

Appendix (C -Tables) No. of day =290 δ=-10.33o L=33.33o Lloc=44.4o

Table C-3: Experimental data for non-coating metallic receiver during 17th October 2010

107

Qloss(tank)

W sys (%)

Qstorage(tank)

kJ Qloss(rec)

W th

(%)

Qu

W өz

degree

αs

degree

Windm/sec

Isc W/m2

Id

W/m2

Ib

W/m2 Itotal

W/m2

Tamb oC

Tupper oC

Tlower oC

Tout oC

Tin oC

Time (hour)

39.494 151.63 43 1000 56.1 33.9 0.27 1365 75.8 459 535 34.3 60 52 70 50 9:30

52.234 44 1062 192.93 39 950 53.9 36.1 0.27 1365 78.2 481 560 34.8 67 60 77 58 9:45

69.16 43 2125 247.8 37 900 51.9 38.1 0.27 1365 80.3 489 570 35 76 70 86 68 10:00

78.98801 41 2875 291.46 41 1100 50 40 0.8 1365 82.1 517 600 35.6 82 76 96 74 10:15

95.368 37 4000 341.61 38 1050 48.3 41.7 0.27 1365 83.6 536 620 35.6 91 85 104 83 10:30

107.562 38 4812 381.14 40 1100 46.8 43.2 0.27 1365 84.8 555 640 35.4 97 92 111 89 10:45

121.758 37 5812 433.06 40 1200 45.6 44.4 0.27 1365 85.8 574 660 35.6 105 100 121 97 11:00

129.948 35 6437 462.56 39 1150 44.6 45.4 0.8 1365 86.6 580 667 36.1 110 105 126 103 11:15

138.502 35.5 7062 496.19 41 1250 43.9 46.1 0.8 1365 87.1 582 670 36.4 115 110 133 108 11:30

146.692 32 7625 528.64 43 1300 43.4 46.6 0.8 1365 87.6 582 670 36.4 119 115 139 113 11:45

151.242 30 7937 537.49 38 1150 43.3 46.7 0.8 1365 87.7 584 672 36.4 121 118 139 116 12:00

154.336 29.5 8250 544.57 37 1050 43.4 46.6 0.8 1365 87.7 566 654 37.2 123 121 140 119 12:15

156.338 28 8375 548.11 35 1000 43.9 46.1 0.8 1365 87.1 557 645 37.1 124 122 140 120 12:30

157.066 26 8437 547.52 36 1000 44.6 45.4 0.8 1365 86.6 553 640 37.2 124 123 140 120 12:45

156.52 26 8537 545.75 35 900 45.6 44.4 0.8 1365 85.8 509 595 37.5 124 123 139 121 13:00

156.338 25 8437 542.21 34 850 46.8 43.2 2.1 1365 84.8 490 575 37.6 124 123 138 121 13:15

156.338 24 8437 542.21 35 850 48.3 41.7 2.1 1365 83.6 476 560 37.6 124 123 138 121 13:30

Appendix (D -Tables) No. of day =313 δ=-17.65o L=33.33o Lloc=44.4o

Table D-3: Experimental data for coating metallic receiver during 10th November 2010

111

Qloss(tank)

W sys (%)

Qstorage(tank)

kJ Qloss(rec)

W th

(%)

Qu

W өz

degree

αs

degree

Windm/sec

Isc W/m2

Id

W/m2

Ib

W/m2 Itotal

W/m2

Tamb oC

Tupper oC

Tlower oC

Tout oC

Tin oC

Time (hour)

25.29 106.08 60 1250 62 28 1 1380 69 411 480 24.1 42 34 57 32 9:30

39.494 50 1000 141.44 58 1150 60 30 1.2 1380 71 428 500 24.3 50 42 63 40 9:45

53.326 50 2000 178.36 57 1100 58.1 31.9 1 1380 72 457 530 24.7 58 50 70 48 10:00

69.706 47 3437 227.76 55 1100 56.5 33.5 1 1380 76 473 550 25.2 67 60 80 58 10:15

84.994 49 4312 263.64 54 1050 55 35 1.2 1380 77 502 580 25.8 77 68 87 66 10:30

102.648 46 5500 319.28 55 1200 53.7 36.3 1 1380 79 510 590 25.6 87 77 99 75 10:45

112.294 44 6250 357.24 56 1300 52.6 37.4 1 1380 80.5 519 600 26.3 92 84 108 82 11:00

125.216 44 7250 399.36 58 1400 51.7 38.3 1.2 1380 81.3 528 610 27.2 99 93 118 90 11:15

136.682 43 8125 437.32 59 1500 51.1 38.9 1 1380 82 530 612 27.9 106 100 127 97 11:30

147.42 42 8875 478.4 61 1550 50.7 39.3 1 1380 82.3 532 615 28 112 106 136 104 11:45

154.882 40 9437 499.72 62 1560 50.6 39.4 1 1380 82.4 522 605 28.4 116 111 140 109 12:00

164.528 40 10125 522.08 58 1500 50.7 39.3 1.5 1380 82.3 517 600 28.6 121 117 144 114 12:15

169.988 40 10875 532.48 55 1350 51.1 38.9 1.2 1380 82 508 590 28.6 124 120 144 118 12:30

177.086 37 11000 542.36 54 1100 51.7 38.3 1 1380 81.3 499 585 28.7 127 125 144 122 12:45

179.088 37 11125 548.08 51 1000 52.6 37.4 1 1380 80.5 489 580 28.6 128 126 144 124 13:00

179.816 36 11250 547.56 49 900 53.7 36.3 1.2 1380 79.4 480 560 28.7 128 127 143 125 13:15

179.634 36 11250 547.04 48 900 55 35 1 1380 77.9 470 543 28.8 128 127 143 125 13:30


Table D-1: Experimental data for coating metallic receiver during 2nd November 2010

109

Qloss(tank)

W sys (%)

Qstorage(tank)

kJ Qloss(rec)

W th

(%)

Qu

W өz

degree

αs

degree

Windm/sec

Isc W/m2

Id

W/m2

Ib

W/m2 Itotal

W/m2

Tamb oC

Tupper oC

Tlower oC

Tout oC

Tin oC

Time (hour)

27.3 111.8 62.5 1250 59.9 30.1 0.27 1375 71.7 408 480 22 40 34 56 31 9:30

41.496 52 1080 147.16 60 1150 57.8 32.2 1.15 1375 74.3 425 500 22.2 49 41 62 39 9:45

57.33 50 2088 195 57 1100 55.9 34.1 0.27 1375 76.6 443 520 22.5 57 51 71 49 10:00

72.254 52 3186 229.84 56 1100 54.2 35.8 0.27 1375 78.5 456 535 22.8 67 58 78 56 10:15

89.362 52 4320 289.12 54 1000 52.6 37.4 0.27 1375 80.1 469 550 23.4 77 68 89 69 10:30

106.288 50 5400 329.68 53 1000 51.2 38.8 0.27 1375 81.5 498 580 24.6 87 79 98 78 10:45

124.124 48 6480 393.64 55 1250 50.1 39.9 0.27 1375 82.6 507 590 24.8 96 90 113 88 11:00

141.05 48 8127 452.4 58 1400 49.2 40.8 0.27 1375 83.4 536 620 25 105 100 126 98 11:15

153.244 47 9072 489.84 59 1500 48.5 41.5 0.27 1375 84 546 630 25.8 113 107 135 105 11:30

162.162 43 9801 520.52 61 1550 48.1 41.9 0.27 1375 84.3 550 635 26.4 118 113 143 110 11:45

168.168 41 10260 550.68 6 1560 48 42 0.27 1375 84.4 555 640 26.6 121 117 150 115 12:00

175.266 40 10890 560.56 57 1540 48.1 41.9 0.27 1375 84.3 560 645 26.7 125 121 150 119 12:15

183.092 38 11340 567.32 55 1350 48.5 41.5 0.85 1375 84 559 643 27.4 130 126 150 123 12:30

189.098 38 11817 576.68 50 1150 48.2 41.8 0.27 1375 83.4 531 615 27.6 133 130 150 127 12:45

189.826 37.7 11970 578.76 47 1000 50.1 39.9 0.27 1375 82.6 507 590 27.7 133 131 149 129 13:00

190.554 38 11880 578.24 45 900 51.2 38.8 0.27 1375 81.5 478 560 27.8 133 132 148 130 13:15

190.918 37.5 11952 579.28 43 900 52.6 37.4 0.27 1375 80.1 459 540 27.6 133 132 148 130 13:30


Table C-2: Experimental data for non-coating metallic receiver during 13rd October 2010

106

Qloss(tank)

W sys (%)

Qstorage(tank)

kJ Qloss(rec)

W th

(%)

Qu

W өz

degree

αs

degree

Windm/sec

Isc W/m2

Id

W/m2

Ib

W/m2 Itotal

W/m2

Tamb oC

Tupper oC

Tlower oC

Tout oC

Tin oC

Time (hour)

50.96 194.7 42 1000 55 35 1.15 1362 76 465 542 27 58 52 70 50 9:30

65.33801 44 1062 235.41 36 900 52.7 37.3 0.85 1362 79 493 573 27.6 67 60 77 58 9:45

76.44 40 1875 274.35 34 900 50.6 39.4 0.85 1362 81 518 600 28 73 67 84 65 10:00

88.816 36 2750 308.57 33 950 48.7 41.3 1.15 1362 83 556 640 28.2 80 74 89 72 10:15

104.832 37 3875 360.49 30 850 47 43 1.7 1362 84 575 660 28.4 90 82 99 80 10:30

118.664 37 4875 414.18 0.37 1100 45.5 44.5 1.15 1362 85,7 584 670 28.8 98 90 110 88 10:45

137.228 38 6125 480.26 39 1200 44.2 45.8 1.7 1362 86.7 593 680 28.6 108 100 122 98 11:00

150.878 37 7187 539.26 42 1300 43.2 46.8 1.15 1362 87.5 602 690 29.6 115 110 134 108 11:15

159.796 35 7875 571.12 41 1300 42.4 47.6 0.85 1362 88.1 611 702 30.2 120 116 140 114 11:30

163.072 32 8125 578.79 40 1250 42 48 2.5 1362 88.3 621 710 30.4 122 118 141 116 11:45

164.892 29 8312 584.69 37 1200 41.8 48.2 3.1 1362 88.4 625 714 30.9 123 120 142 118 12:00

166.712 28 8437 587.64 38 1150 42 48 3.1 1362 88.1 590 697 30.9 124 121 142 119 12:15

168.532 27 8562 590.59 37 1100 42.4 47.6 0.85 1362 88 581 670 30.9 125 122 142 120 12:30

170.352 26.5 8687 590.59 35 1000 43.2 46.8 0.85 1362 87.5 562 650 30.9 126 123 141 121 12:45

171.262 25 8750 590.59 33 900 44.2 44.8 0.85 1362 86.7 553 640 30.9 126 124 140 122 13:00

170.898 24 8750 586.46 31 850 45.5 44.5 0.85 1362 85.7 534 620 31.1 126 124 139 122 13:15

169.624 24 8750 582.33 33 850 47 43 0.85 1362 84.5 502 580 31.8 126 124 139 122 13:30



112

Qloss(tank)

W sys (%)

Qstorage(tank)

kJ Qloss(rec)

W th

(%)

Qu

W өz

degree

αs

degree

Windm/sec

Isc W/m2

Id

W/m2

Ib

W/m2 Itotal

W/m2

Tamb oC

Tupper oC

Tlower oC

Tout oC

Tin oC

Time (hour)

24.57 98.8 60 1200 63 27 2.5 1383 67 412 480 23 41 32 54 30 9:30

36.946 50 938 126.36 56 1150 61.1 28.9 2.5 1383 70 419 490 23.2 49 38 59 36 9:45

48.958 48 1812 163.28 55 1100 59.2 30.8 3 1383 72 437 510 23.6 55 46 66 44 10:00

62.426 44 2750 204.36 54 1100 57.6 32.4 2.5 1383 75 460 540 23.7 62 54 74 52 10:15

76.44 43 3750 241.8 52 1050 56.1 33.9 2.8 1383 76 488 565 24 70 62 81 60 10:30

90.636 43 4750 284.96 53 1050 54.9 35.1 2.5 1383 78 496 575 24.2 78 70 90 68 10:45

104.468 42.5 5750 329.68 54 1200 53.8 36.2 3 1383 79.4 510 590 24.6 86 78 100 76 11:00

120.484 42 6875 380.64 54 1300 53 37 2.5 1383 80.3 519 600 24.8 95 87 111 85 11:15

135.408 42 7937 431.08 56 1400 52.4 37.6 2.5 1383 80.9 524 605 25.1 103 96 122 94 11:30

151.424 43 9062 471.64 57 1400 52 38 2.8 1383 81.3 527 610 25.3 112 105 130 102 11:45

158.886 42 9625 490.36 58 1300 51.9 38.1 2.5 1383 81.3 518 600 25.7 116 110 133 107 12:00

162.708 40 9937 501.28 55 1150 52 38 3 1383 81.4 520 595 26.1 118 113 134 111 12:15

167.622 38 10312 512.72 52 1000 52.4 37.6 2.5 1383 80.9 509 590 26.4 120 117 135 115 12:30

169.806 38 10500 516.36 48 900 53 37 2.8 1383 80.3 491 572 26.7 121 119 135 117 12:45

170.17 36 10625 517.4 46 850 53.8 36.2 2.5 1383 79.4 470 550 27 121 120 135 118 13:00

170.17 35.5 10625 514.8 45 800 54.9 35.1 2.5 1383 78.2 456 535 27 121 120 134 118 13:15

169.624 34 10625 513.24 44 800 56.1 33.9 2.5 1383 76.8 448 525 27.3 121 120 134 118 13:30

Appendix (E -Tables) No. of day =339 δ=-18.54o L=33.33o Lloc=44.4o

Table E-4: Experimental data for evacuated glass receiver during 6th December 2010

116

Qloss(tank)

W sys (%)

Qstorage(tank)

kJ Qloss(rec)

W th

(%)

Qu

W өz

degree

αs

degree

Windm/sec

Isc W/m2

Id

W/m2

Ib

W/m2 Itotal

W/m2

Tamb oC

Tupper oC

Tlower oC

Tout oC

Tin oC

Time (hour)

22.75 32.4 67 1100 66.1

23.9 0.27 1393 63

325 388 16 32 25 45 23 9:30

35.126 66 1000 44.64 67 1150 64.2 25.8 0.8 1393 66 330 396 16.7 40 32 53 30 9:45

49.504 63 2062 57.06 64 1100 62.5 27.5 0.27 1393 68 348 416 17.3 49 40 60 38 10:00

64.246 62.5 3125 73.44 63.5 1150 60.9 29.1 0.27 1393 71 360 431 17.7 58 48 70 47 10:15

79.352 61 4250 87.48 62.8 1200 59.5 30.5 1.15 1393 73 380 453 18.4 67 57 79 55 10:30

95.368 60 5437 105.12 62 1250 58.4 31.6 0.8 1393 74 395 469 19.1 76 67 90 65 10:45

109.564 60 6500 120.06 61 1250 57.4 32.6 0.8 1393 75 405 480 19.8 84 76 99 74 11:00

127.4 59 7812 137.7 63 1300 56.6 33.4 1.15 1393 76 420 496 20.5 95 86 110 84 11:15

141.96 57 8875 154.8 64.5 1400 56 34 0.27 1393 77 422 499 21 103 95 121 93 11:30

154.882 56 9812 168.48 66 1400 55.7 34.3 0.8 1393 77 428 505 21.4 110 103 129 101 11:45

165.438 53 9937 178.92 63 1300 55.5 34.5 0.27 1393 78 426 504 21.6 115 110 134 108 12:00

171.99 53 11062 185.4 62 1200 55.7 34.3 0.27 1393 77 412 489 22 118 115 137 113 12:15

175.812 53 11375 188.28 61 1100 56 34 0.8 1393 77 392 469 22.4 120 118 138 116 12:30

177.45 52 11562 189 58 1000 56.6 33.4 0.27 1393 76 375 451 23 121 120 138 118 12:45

176.358 50 11562 187.02 56 950 57.4 32.6 0.8 1393 75 360 435 23.6 121 120 137 118 13:00

175.63 49 11562 185.4 54 900 58.4 31.6 0.27 1393 74 350 424 24 121 120 136 118 13:15

175.63 48 11562 184.5 53 850 59.5 30.5 0.27 1393 73 340 413 24 121 120 135 118 13:30


Table E-3: Experimental data for evacuated glass receiver during 2nd December 2010

115

Qloss(tank)

W sys (%)

Qstorage(tank)

kJ Qloss(rec)

W th

(%)

Qu

W өz

degree

αs

degree

Windm/sec

Isc W/m2

Id

W/m2

Ib

W/m2 Itotal

W/m2

Tamb oC

Tupper oC

Tlower oC

Tout oC

Tin oC

Time (hour)

19.11 29.7 67.5 1150 65.7 24.3 2 1391 63 340 403 16 30 23 44 21 9:30

34.034 63 1000 41.76 65 1150 63.8 26.2 2 1391 66 350 416 16.8 40 31 51 29 9:45

47.32 60 2000 54.9 63 1100 62.1 27.9 1.5 1391 69 365 434 17.5 48 39 59 37 10:00

58.786 60 3000 67.14 62 1100 60.5 29.5 2 1391 71 380 451 18.7 55 47 67 45 10:15

70.252 54 3875 77.57 58 1200 59.1 30.9 1.5 1391 73 404 477 19.4 62 54 73 52 10:30

86.45 54.6 5062 95.4 59 1200 57.9 32.1 2 1391 75 410 485 20 71 64 85 61 10:45

100.464 54.2 6187 110.16 60 1250 56.9 33.1 2 1391 76 422 498 21.3 80 73 95 70 11:00

119.21 54.2 7500 127.8 62 1250 56.1 33.9 1.8 1391 77 435 512 21.5 91 83 105 80 11:15

134.498 54 8562 144.72 64 1300 55.5 34.5 2 1391 77 440 517 21.6 100 91 115 89 11:30

148.512 54 9625 161.28 67 1400 55.2 34.8 1.5 1391 78 440 518 22.4 108 100 126 98 11:45

161.07 54 10562 172.8 64 1300 55.1 34.9 1.8 1391 78 430 508 23 115 108 132 106 12:00

168.532 53.2 11125 181.08 61 1200 55.2 34.8 1.8 1391 78 422 500 23.4 118 114 136 112 12:15

174.538 53 11562 186.12 58 1100 55.5 34.5 2 1391 77 417 494 23.6 121 118 138 116 12:30

177.45 50 11750 188.1 56 1000 56.1 33.9 1.5 1391 77 401 478 23.5 122 120 138 118 12:45

176.904 48 11750 186.66 55 950 56.9 33.1 2 1391 76 389 465 23.8 122 120 137 118 13:00

177.45 47.3 11812 186.3 53 950 57.9 32.1 1.5 1391 75 367 442 24 122 121 137 118 13:15

176.54 46 11812 184.5 53 900 59.1 30.9 2 1391 84 356 440 24.5 122 121 136 118 13:30


Table E-1: Experimental data for evacuated glass receiver during 23rd November 2010

113

Qloss(tank)

W sys (%)

Qstorage(tank)

kJ Qloss(rec)

W th

(%)

Qu

W өz

degree

αs

degree

Windm/sec

Isc W/m2

Id

W/m2

Ib

W/m2 Itotal

W/m2

Tamb oC

Tupper oC

Tlower oC

Tout oC

Tin oC

Time (hour)

20.74 30.6 68 1100 64.4 25.6 0.27 1387

68 350 418 18 34 25 47 23 9:30

34.9 65 1062 43.92 67 1150 62.5 27.5 0.27 1387 40 360 400 18.6 43 34 54 32 9:45

46.22 63 2000 58.14 65 1170 60.8 29.2 0.27 1387 53 367 420 19.2 50 42 63 40 10:00

61.15 62 3125 72.18 65 1200 59.2 30.8 0.27 1387 68 377 445 20.4 59 51 72 49 10:15

80.9 62 4500 88.92 63 1250 57.7 32.3 0.27 1387 76 389 465 21.6 70 62 83 59 10:30

95.55 61.8 5562 103.86 62 1270 56.5 33.5 0.27 1387 77 398 475 21.8 79 70 92 67 10:45

108.47 58 6500 119.7 64 1300 55.5 34.5 0.27 1387 78 417 495 22 86 78 101 76 11:00

125.76 58 7812 137.7 66 1350 54.7 35.3 0.27 1387 79 426 505 22.5 97 88 112 86 11:15

143.23 58.3 9062 156.06 68 1400 54.1 35.9 0.27 1387 80 430 510 23.3 107 98 124 96 11:30

159.43 57 10125 170.46 66 1450 53.7 36.3 0.27 1387 80 436 516 23.8 115 107 133 104 11:45

166.53 54 10812 180.54 65 1400 53.6 36.4 0.27 1387 80 444 524 24.2 120 113 138 111 12:00

176.9 54 11562 188.1 63 1350 53.7 36.3 0.27 1387 80 425 505 25 125 120 142 117 12:15

184 52.6 12062 194.76 61 1250 54.1 35.9 0.85 1387 80 420 500 25.3 129 124 145 122 12:30

190 52 12500 200.88 6 1150 54.7 35.3 0.85 1387 79 406 485 25.4 132 128 148 126 12:45

194.3 52 12875 207.72 58 1100 55.5 34.5 0.27 1387 78 387 465 25.6 134 132 152 130 13:00

194.74 50 12937 205.2 56 1050 56.5 33.5 0.85 1387 77 373 450 26 134 133 150 130 13:15

195.65 49 12937 204.48 55 1000 57.3 32.7 0.27 1387 76 364 440 26.4 134 133 150 130 13:30


Table C-4: Experimental data for non-coating metallic receiver during 25th October 2010

108

Qloss(tank)

W sys (%)

Qstorage(tank)

kJ Qloss(rec)

W th

(%)

Qu

W өz

degree

αs

degree

Windm/sec

Isc W/m2

Id

W/m2

Ib

W/m2 Itotal

W/m2

Tamb oC

Tupper oC

Tlower oC

Tout oC

Tin oC

Time (hour)

46.228 167.56 42 800 58.3 31.7 0.27 1371 73.4 396 470 29.6 58 52 66 50 9:30

56.966 40 750 199.42 36 750 56.2 33.8 2.5 1371 76 420 500 29.7 64 58 71 56 9:45

68.796 39 1625 231.87 34 750 54.2 35.8 0.27 1371 78.2 446 525 30.2 72 64 77 62 10:00

79.716 38 2437 282.02 37 850 52.4 37.6 1 1371 80.1 459 540 30.7 77 72 87 70 10:15

95.186 40 3500 323.32 32 750 50.8 39.2 1 1371 81.6 478 560 30.7 86 80 93 78 10:30

107.198 38 4375 371.11 41 1000 49.4 40.6 0.5 1371 82.9 487 570 31.1 94 86 104 84 10:45

118.664 40 5187 411.23 41 1000 48.2 41.8 2.5 1371 84 506 590 31.3 100 93 111 91 11:00

128.674 38 5875 455.48 42 1100 47.3 42.7 1.15 1371 84.8 555 640 31.8 105 100 120 98 11:15

135.772 33 6375 481.44 41 1100 46.6 43.4 2.5 1371 85.4 540 625 31.4 108 104 124 102 11:30

144.872 32 7000 507.99 39 1050 46.2 43.8 0.27 1371 85.7 542 628 31.4 113 109 128 107 11:45

150.878 31 7500 524.51 39 1050 46.1 43.9 1.7 1371 85.8 544 630 32.1 117 113 131 111 12:00

154.518 30 7750 539.26 37 1000 46.2 43.8 2.25 1371 85.7 534 620 32.6 119 116 134 114 12:15

156.884 29 8000 549.88 38 1000 46.6 43.4 0.85 1371 84.4 529 615 32.8 120 118 136 116 12:30

157.612 28 8125 546.34 36 900 47.3 42.7 0.85 1371 84.4 505 590 33.4 121 119 135 117 12:45

157.43 27.5 8187 542.8 33 800 48.2 41.8 1.7 1371 84 491 575 34 121 120 134 118 13:00

156.156 26 8187 538.67 35 800 49.4 40.6 0.85 1371 82.9 453 536 34.7 121 120 134 118 13:15

156.702 25 8187 540.44 35 800 50.8 39.2 0.85 1371 81.6 440 522 34.4 121 120 134 118 13:30



110

Qloss(tank)

W sys (%)

Qstorage(tank)

kJ Qloss(rec)

W th

(%)

Qu

W өz

degree

αs

degree

Windm/sec

Isc W/m2

Id

W/m2

Ib

W/m2 Itotal

W/m2

Tamb oC

Tupper oC

Tlower oC

Tout oC

Tin oC

Time (hour)

24.752 101.92 61 1200 61.1 28.9 3 1378 70 419 490 22.4 40 32 54 30 9:30

38.948 50 990 137.28 56 1100 59.1 30.9 3 1378 72 447 520 22.6 48 40 60 38 9:45

50.96 45 1872 169 55 1050 57.2 32.8 3.5 1378 75 464 540 23 55 47 66 45 10:00

64.064 42 2808 203.84 53 1050 55.5 34.5 3 1378 77 497 570 23.3 62 55 73 52 10:15

77.35 40 3600 241.8 51 1000 54 36 3.2 1378 78 501 580 23.5 70 62 80 60 10:30

93.184 43 4725 297.44 53 1100 52.6 37.4 3 1378 80 509 590 23.8 78 72 92 70 10:45

107.38 41 5832 343.2 54 1200 51.5 38.5 3.1 1378 81 523 605 24 86 80 102 78 11:00

119.756 41 6741 383.76 57 1300 50.6 39.4 3 1378 82 527 610 24.2 93 87 111 85 11:15

131.768 40 7560 412.88 62 1300 50 40 2.8 1378 83 537 620 24.6 100 94 117 91 11:30

140.14 36 8181 442 60 1400 49.6 40.4 3.1 1378 83.2 561 645 25 105 99 124 96 11:45

145.054 35 8550 461.24 55 1400 49.5 40.5 3 1378 83.3 551 635 25.3 108 102 128 100 12:00

154.154 35 9306 476.84 54 1250 49.6 40.4 3 1378 83.2 556 640 25.8 113 108 130 105 12:15

157.976 33 9720 487.76 53 1100 50 40 2.8 1378 82.8 547 630 26.2 115 111 131 109 12:30

162.89 34 9945 494 47 900 50.6 39.4 3 1378 82.2 527 610 27 118 115 131 113 12:45

168.532 30 10458 504.92 45 750 51.5 38.5 3.1 1378 81.4 523 605 27.4 121 119 132 117 13:00

169.078 30 9450 506.48 44 700 52.6 37.4 3 1378 80.3 509 590 27.6 121 120 132 118 13:15

168.35 30 10080 504.4 43 700 54 36 3 1378 78.9 481 560 28 121 120 132 118 13:30


Table E-2: Experimental data for evacuated glass receiver during 29th November 2010

114

Qloss(tank)

W sys (%)

Qstorage(tank)

kJ Qloss(rec)

W th

(%)

Qu

W өz

degree

αs

degree

Windm/sec

Isc W/m2

Id

W/m2

Ib

W/m2 Itotal

W/m2

Tamb oC

Tupper oC

Tlower oC

Tout oC

Tin oC

Time (hour)

24.57 35.1 68 1200 65.3 24.7 1 1390 64 360 424 16.5 34 26 48 24 9:30

39.494 63.8 1062 48.96 66 1200 63.4 26.6 1 1390 67 368 435 16.8 43 34 56 32 9:45

52.234 59 2000 61.56 65 1150 61.7 28.3 1.2 1390 70 375 445 17.3 50 42 63 40 10:00

65.52 55 3000 73.8 64 1100 60.1 29.9 1 1390 72 390 462 18 58 50 70 48 10:15

80.8 55 4187 88.93 62 1100 58.7 31.3 1.4 1390 74 400 474 19.1 67 60 79 58 10:30

101.01 58 5625 108.9 61 1200 57.5 32.5 1.6 1390 75 410 485 19.5 80 70 92 68 10:45

113.568 57 6500 123.12 64 1200 56.5 33.5 1 1390 76 420 496 19.6 86 78 100 76 11:00

131.04 56.6 7750 140.4 66 1300 55.7 34.3 1 1390 77 432 509 20 96 88 111 85 11:15

146.692 56 8875 159.48 67 1400 55.1 34.9 1.2 1390 78 436 514 20.4 105 97 123 95 11:30

160.342 55 9937 174.78 68 1450 54.7 35.3 0.8 1390 78 440 518 21.4 113 106 133 104 11:45

172.9 57 10937 184.5 69 1300 54.6 35.4 1.2 1390 78 420 498 22.5 121 114 138 112 12:00

180.18 56 11625 192.6 65 1200 54.7 35.3 1 1390 78 411 489 23 124 120 142 118 12:15

184.548 55 11875 196.92 62 1100 55.1 34.9 1 1390 78 390 468 23.6 126 124 144 122 12:30

187.824 51 12125 198.36 58 1000 55.7 34.3 1.4 1390 77 375 452 23.8 128 126 144 124 12:45

186.914 50 12125 197.46 56 1000 56.5 33.5 1 1390 76 365 441 24.3 128 126 144 124 13:00

186.186 50 12125 196.74 55 1000 57.5 32.5 1.2 1390 76 350 426 24.7 128 126 144 124 13:15

185.64 49.5 12125 196.2 54 1000 58.7 31.3 1 1390 74 350 424 25 128 126 144 124 13:30

Papers published from this thesis

1. Baha T. Chiad, Naseer K. Kasim, Falah A-H. Mutlak and Aed E. Owaid, "Parabolic Trough Solar Collector – Design, Construction and Testing ", 1st Scientific Conference – College of Science for Women – Baghdad University (2011). 2. Baha T. Chiad, Naseer K. Kasim, Falah A-H. Mutlak and Aed E. Owaid,"Investigation the Effect of the Rim Angle's Changes on the Geometry of Parabolic Trough Solar Collector" Thermal Science Indian Journals, accepted and to be published in 2011.

بغداد جامعة آلية العلوم ءقسم الفيزيا

فالح عبدالحسن مطلك حواس :االسمتصميم وتصنيع مجمع شمسي حوضي ذو القطع المكافئ لتطبيقات الطاقة " :عنوان االطروحة

"الحرارية نصير آريم قاسم . د : المشرفبهاء طعمة جياد . د.ا : المشرف

الخالصة

د صنع المرآز وتصنيع،الدراسة تمثل تصميم ههذ افئ وق واختبار لمجمع شمسي حوضي ذو القطع المكة بلغ ال ا بعرض m2 5.04 تشمسي بمساحة آلي م ترتيب قطع المراي د ت داخلي 5cm وق سطح ال ى ال عل

عة ا ساعدة االش ؤرة بم رت الب عاع واختب اآس لالش سطح ع تخدمت آ ث اس ز حي ةليلللمرآ م . زري تاء االشعاع الشمسي تطوير جهاز التوجيه الشمسي من العناصر الكهربائية وااللكترونية بمحورين في اقتفل الحرارة . المباشر ى نق ة عل ه من قابلي از ب ا يمت ل للحرارة لم استخدم زيت المكائن الصناعي آوسط ناق

لخزن لتر 50ان زيت ذو سعة زودت المنظومة بخزان ووضع داخل الخز. وتحمله لدرجات حرارة عاليةين االول ة آالطاقة الحرارية والحصول على حمل اخ شمسي واالخر للتدفئ واع من . طب ة ان م اجراء ثالث ت

رار الء ح دون ط دني ب ستلم مع تخدام م ى باس ة االول راري للمنظوم يم االداء الح ة لتقي ارب العملي ي التجواء والثانية باستخدام طالء حراري واالخير باستخدام مس رغ من اله م . تلم زجاجي مف ة ن التجارب العملي

ا تحت الظروف المناخ دادانجازه ة للعاصمة بغ الل(33.3o, 44.4o) ي ة خ هر ثالث شرين(اش ، االول تم حساب االداء الحراري للمجمع الشمسي في الجو الخارجي من خالل . )تشرين الثاني وآانون االول ت

ة (الطاقة المستلمة ، لمرآزمن ا ) المفيدة(حساب الطاقة المكتسبة ائع داخل الخزان و ا ) المخزون اءة للم لكفرغ المعلماتصى القيم لهذه قمن خالل الحسابات وجد ا . لحظيةلالحرارية ا باستخدام المستلم الزجاجي المف

ستلم ذا الم زداد من . نظرا لقلة الفقد الحراري له ساعة 30oC درجة حرارة الزيت داخل الخزان ت د ال عندما 135oC صباحا الى عة والنصف التاس عند الساعة الواحدة والنصف بعد الظهر بدون حمل حراري عن

ستلم ة 150oCتبلغ اقصى درجة حرارة للزيت الخارج من الم انون االول النموذجي ام شهر آ من . في ايرغ اجي المف ستلم الزج راري للم د الح ل الفق د ان معام سي وج ع الشم ذا المجم ة له ارب العملي خالل التج

اوز راري ، W/m2C 7.5اليتج د الح امالت الفق ا مع W/m2C 18.3 و ٢٠٫٦ W/m2C ًًبينمة للمجمع . على التوالي لعدم وجود وبوجود الطالء باستخدام المستلم المعدني وبلغ متوسط الكفاءة الحراري

درجات % ٦١ د ال دني عن ستلم المع ة للم اءة الحراري تقريبا باستخدام المستلم المفرغ وتتناقص متوسط الكفنظرا لزيادة الفقد الحراري ، بتوفر الطالء وعدم توفره على التوالي % ٤٠و % ٥١الحرارة العالية بمعدل ار ان منحني االداء للمجمع . ة العالية عند الدرجات الحرار ذا االختب ا لقد اوضحت النتائج العملية له مرتفع

ة المنخفضة د الحراري ى الفواق ذي يعزو ال ارتفاعا ملحوظا عن منحني اداء المجمع النموذجي المماثل واله ة في التوجي ة العالي ذللك للدق ا فكف . نسبيا نظرا لوجود الغالف الزجاجي المفرغ وآ اءة المجمع في عموم

ا ذا المجمع محلي ل ه صنيع مث ى لت ة االول ذه هي المحاول ار ان ه ة . المتوسط مقبولة باعتب وآحصيلة نهائية ة نظيف ا آطاق لنتائج هذا البحث حصلت القناعة العلمية بامكانية االستفادة من هذه التقنية المستخدمة عالمي

ع ظ تالئم م ا يتناسب وي د وبم دى البعي ى الم صة عل ن ورخي ا يمك ن خالله ي م ة والت د المناخي روف البلتنتاجه في ال ه واس م مالحظت ا ت ذا م ة وه سية هائل ة شم ة حراري ى طاق ا بالحصول عل ات المسجلة يومي يان

. درجة١٥٠والتي لها مجال واسع للتطبيقات التي تصل درجة الحرارة فيها الى

الخالصة

واختبار لمجمع شمسي حوضي ذو القطع المكافئ وقد صنع وتصنيع، الدراسة تمثل تصميم ههذ

ا بعرض m2 5.04 تشمسي بمساحة آلية بلغالالمرآز ى 5cm وقد تم ترتيب قطع المراي علساعدة ؤرة بم رت الب عاع واختب اآس لالش سطح ع تخدمت آ ث اس ز حي داخلي للمرآ سطح ال ال

عة ا ةلاالش م تطوير. ليزري ة ت ة وااللكتروني ر الكهربائي ن العناص سي م ه الشم از التوجي جهر سي المباش عاع الشم اء االش ي اقتف ورين ف ل . بمح صناعي آوسط ناق ائن ال ت المك تخدم زي اس

ة رارة عالي درجات ح ه ل رارة وتحمل ل الح ى نق ة عل ن قابلي ه م از ب ا يمت رارة لم زودت . للحلخزن الطاقة الحرارية والحصول لتر 50يت ذو سعة المنظومة بخزان ووضع داخل الخزان ز

ين االول ى حمل ة آعل اخ شمسي واالخر للتدفئ ة . طب واع من التجارب العملي ة ان م اجراء ثالث ترار الء ح دون ط دني ب ستلم مع تخدام م ى باس ة االول راري للمنظوم يم االداء الح ة لتقي ي والثاني

واء باستخدام طالء حراري واالخير باستخدام مستلم م . زجاجي مفرغ من اله ة ن التجارب العمليداد انجازها تحت الظروف المناخ ة خالل (33.3o, 44.4o) ية للعاصمة بغ شرين (اشهر ثالث ت

انون االول ، االول اني وآ شرين الث و . )ت ي الج سي ف ع الشم راري للمجم ساب االداء الح م ح تدة (الخارجي من خالل حساب الطاقة المكتسبة ستلمة ، زمن المرآ ) المفي ة الم ة (الطاق ) المخزون

ائع داخل الخزان و ا اءةللم ة الكف ة ل الحراري ذه ق من خالل الحسابات وجد ا . لحظي يم له صى القات ستلم المعلم ذا الم راري له د الح ة الفق را لقل رغ نظ اجي المف ستلم الزج تخدام الم ة . باس درج

ن زداد م زان ت ل الخ ت داخ رارة الزي ساعة 30oC ح د ال عة و عن صف التاس ى الن باحا ال ص135oC غ اقصى درجة عند الساعة الواحدة والنصف بعد الظهر بدون حمل حراري عندما تبل

ستلم ة 150oCحرارة للزيت الخارج من الم انون االول النموذجي ام شهر آ من خالل . في ايرغ ستلم الزجاجي المف د الحراري للم التجارب العملية لهذا المجمع الشمسي وجد ان معامل الفق

د الحراري ، W/m2C 7.5اليتجاوز امالت الفق ا مع 18.3 و ٢٠٫٦ W/m2C ًًبينمW/m2C دني ستلم المع تخدام الم ود الطالءباس ود وبوج دم وج واليلع ى الت غ متوسط . عل وبل

ع ة للمجم اءة الحراري اءة % ٦١الكف ط الكف اقص متوس رغ وتتن ستلم المف تخدام الم ا باس تقريبدل ة بمع درجات الحرارة العالي د ال دني عن وفر الطالء % ٤٠و % ٥١الحرارية للمستلم المع بت

والي ى الت وفره عل دم ت رار ، وع درجات الح د ال راري عن د الح ادة الفق را لزي ةنظ د . ة العالي لقع ي االداء للمجم ار ان منحن ذا االختب ة له ائج العملي ن اوضحت النت ا ع ا ملحوظ ا ارتفاع مرتفع

سبيا نظرا ة المنخفضة ن د الحراري منحني اداء المجمع النموذجي المماثل والذي يعزو الى الفواقه ة في التوجي ة العالي ذللك للدق رغ وآ ا فكف . لوجود الغالف الزجاجي المف ي عموم ع ف اءة المجم

ا وآحصيلة . المتوسط مقبولة باعتبار ان هذه هي المحاولة االولى لتصنيع مثل هذا المجمع محلية المستخدمة ذه التقني تفادة من ه ة االس ة بامكاني ذا البحث حصلت القناعة العلمي ائج ه ة لنت نهائي

تالئم مع ظ ة عالميا آطاقة نظيفة ورخيصة على المدى البعيد وبما يتناسب وي د المناخي روف البله م مالحظت ا ت ذا م ة وه سية هائل ة شم ة حراري ى طاق صول عل ن الح ا يمك ن خالله ي م والت

يانات المسجلة يوميا والتي لها مجال واسع للتطبيقات التي تصل درجة الحرارة بواستنتاجه في ال . درجة١٥٠فيها الى

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جمهورية العراق

وزارة التعليم العالي و البحث العلمي

جامعة بغداد

العلومآلية

قطع ال ذو مجمع شمسي حوضيتصميم وتصنيع

الحراريةالطاقة لتطبيقاتمكافئ ال

رسالة مقدمة إلىجامعة بغداد / العلومآلية وهي الفيزياءفي الفلسفةالدآتوراهدرجة نيل جزء من متطلبات

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