designs and fabrication of solar parabolic collector

7/26/2019 Designs and Fabrication of Solar Parabolic Collector

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DESIGN AND FABRICATION OF

SOLAR PARABOLIC COLLECTOR

PROJECT REPORT

Submittedin partial fulfillment of the requirements for the award of the degree

of

Bachelor of Technology in Mechanical EngineeringTo

The University of Kerala

By

SUBIN THOMAS

SUJITH S

VAISAKHAN V.S

VINEETH C.S

Department Of Mechanical Engineering

College of Engineering, Thiruvananthapuram16

May, 2011


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DEPARTMENT OF MECHANICAL ENGINEERING

COLLEGE OF ENGINEERING

THIRUVANANTHAPURAM 16

CERTIFICATE

This is to certify that the report entitled DESIGN AND FABRICATION OF SOLAR PARABOLIC

COLLECTOR, submitted by Subin Thomas, Sujith S, Vaisakhan V.S, Vineeth C.Sto the University

of Kerala in partial fulfillment of the requirements for the award of the Degree of Bachelor of Technology

in Mechanical Engineering (stream) is a bonafide record of work carried out by them under our guidance

and supervision.

Dr. G Venugopal

Dept. of Mechanical Engineering,

College of Engineering

Trivandrum

Prof. E Abdul Rasheed

Head of the Department

Dept. of Mechanical Engineering

College of Engineering , Trivandrum


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ACKNOWLEDGEMENT

We express our sincere gratitude to our guide Dr. G.Venugopal , College of Engineering,

Trivandrum for the expert guidance and advice in the project work.

We express our sincere thanks to Sri K K Nanu, Sri Ajith R.R, Lecturer, Staff adviser,

Z.A.Samitha, Professor, senior staff adviser, Prof. E Abdul Rasheed, Head of the Department,

Department of Mechanical Engineering, College of Engineering Trivandrum, for their kind

co-operation during the course of this work.

We would also wish express our sincere gratitude to the staff of the department library and

technical library that helped us in our search for the relevant data and books. Similarly the staff of the

central computer facility of our college did render their valuable help in the task.

We would also wish to record our gratefulness to all my friends and classmates for their help

and their support in carrying out this work successfully. And finally to the Almighty for His providence.

SUBIN THOMAS

SUJITH S

VAISAKHAN V S

VINEETH C S


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ABSTRACT

The energy requirement of the world is expected to increase exponentially in the near future. The

superpowers of tomorrow will be those countries which are self sufficient in their energy needs. It is

estimated that in about 50 years almost all the non-renewable sources of energy will be depleted.

Furthermore, these non-renewable sources have to be phased out due to environmental hazards. This

makes the cleaner renewable fuels as the viable option for future energy requirements and

contemporary researches are aiming in this direction.

No energy is as abundant as solar energy, which is deemed to be the source of all energy on earth.

India being close to the equator and this natural gift make solar energy as a feasible renewable energy

source to power both the inaccessible and rural regions.

The main objective of the proposed project is to design, fabricate and evaluate the performance

parameters of an economically viable solar parabolic trough for the efficient harvesting of solar energy.

Further, the extracted solar energy is converted to mechanical work with the aid of a cost effective

system. The generated mechanical work can be utilized to drive common household machinery and,

thereby, reduces the electricity consumption and promotes the use of ecofriendly solar energy for future

needs.


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CONTENTS

Page No.

1. INTRODUCTION

1.1 GENERAL BACKGROUND

1.1.1 HISTORY 1

1.1.2 SOLAR COLLECTOR 1

1.2 OBJECTIVE 2

1.3 SCOPE 2

1.4 SCHEME 3

2. LITERATURE REVIEW 4

3. STUDY OF COLLECTORS

3.1 STUDY OF DIFFERENT COLLECTORS

3.1.1. SOLAR COLLECTORS WITHOUT CONCENTRATION 6

3.1.2. SOLAR COLLECTORS WITH CONCENTRATION 10

3.2 STUDY OF DIFFERENT WASTE HEAT UTILIZING DEVICES

3.2.1 STIRLING ENGINE 12

3.2.2 MICRO TURBINE 12

3.2.3 ADSORPTION REFRIGERATION SYSTEM 14

3.3 IMPORTANT CONSIDERATIONS FOR DESIGNING A PARABOLIC TROUGH

3.3.1 COLLECTOR APERTURE 15

3.3.2 RIM ANGLE 15

3.3.3 RECEIVER DIAMETER 16

3.3.4 DESIGN ANALYSIS

3.3.4.1 OPTICAL EFFICIENCY 16

3.3.4.2 THERMAL ANALYSIS 17

3.3.5 MIRROR MATERIALS 18

3.3.6 REFLECTOR SUPPORT STRUCTURES

3.3.6.1 STRUCTURAL DESIGN REQUIREMENTS 20

3.3.6.2 WIND LOAD ON REFLECTOR SUPPORT STRUCTURE 20

3.3.7 ORIENTATION AND TRACKING 21

4. STUDY OF ADSORPTION

4.1 THEORY OF ADSORPTION 23

4.2 THEORY OF ADSORPTION REFRIGERATION SYSTEM 23

4.2.1 BASIC PROCESSES

4.2.1.1 HEATING AND PRESSURISATION 24

4.2.1.2 HEATING DESORPTION AND CONDENSATION 24

4.2.1.3 COOLING AND DEPRESSURISATION 24

4.2.1.4 COOLING ADSORPTION AND EVAPORATION 24


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4.3 ADSORBENTS

4.3.1 SILICA GEL 25

4.3.2 ZEOLITES 26

4.3.3 ACTIVATED CARBON 26

4.4 REFERIGERANTS

4.4.1 ETHANOL 27

4.4.2 METHANOL 28

4.4.3 AMMONIA 29

4.3 WORKING OF THE SYSTEM 30

5.CALCULATIONS

5.1 QUALITATIVE ESTIMATION AND BASIC DESIGN OF ADSORPTION SYSTEM

5.1.1 REQUIRED AMOUNT OF ADSORBENT AND REFRIGERANT 32

5.1.2 ADSORBERS 335.2 THERMAL PERFORMANCE OF ADSORBERS

5.2.1 AVAILABLE HEAT 34

5.2.2 HEAT TRANSFER IN ADSORBERS 34

5.3 DESIGN OF SOLAR COLLECTORS 36

5.3.1 SYSTEM DESIGN

5.3.1.1 CIRCULATION PUMP ANALYSIS 36

5.3.2 PARABOLIC REFLECTOR 37

5.3.2.1

FOCAL POINT FIXING 37

5.3.3RECEIVER

5.3.3.1COPPER TUBE 38

5.3.3.2 FLUID FLOWING 39

5.3.3.3 GLASS TUBE 39

5.4 STRUCTURAL ANALYSIS 40

5.4.1 BEARING LOAD 41

5.5MATERIAL STUDY 43

5.CONCLUSIONS

6.1 CONCLUSIONS

6.1.1

ADVANTAGES 47

6.1.2 DISADVANTAGES 47

6.2 RECOMMENDATIONS 48

6.3 SCOPE FOR FUTURE WORK 48

REFERENCES 48


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LIST OF FIGURES/GRAPHS

Index Page No

1. DESCRIPTION OF OPTICAL ERROR 17

2. TRACKING SYSTEMS 22


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1. INTRODUCTION

1.1 GENERAL BACKGROUND

1.1.1 HISTORY

People have harnessed solar energy for centuries. As early as the 7th century B.C., people

used simple magnifying glasses to concentrate the light of the sun into beams so hot they would

cause wood to catch fire. More than 100 years ago in France, a scientist used heat from a solar

collector to make steam to drive a steam engine. In the beginning of this century, scientists and

engineers began researching ways to use solar energy in earnest. One important development

was a remarkably efficient solar boiler invented by Charles Greeley Abbott, an American

astrophysicist, in 1936.The solar water heater gained popularity at this time in Florida,

California, and the Southwest. The industry started in the early 1920s and was in full swing just

before World War II. This growth lasted until the mid-1950s when low-cost natural gas became

the primary fuel for heating American homes. The public and world governments remained

largely indifferent to the possibilities of solar energy until the oil shortages of the

1970s.However there was a revived interest in solar energy due to the rocketing oil prices and

environmental concerns which emphasized on clean energy and environmental conservation.

1.1.2 SOLAR COLLECTOR

A solar thermal collector is a solar collector designed to collect heat by absorbing

sunlight. The term is applied to solar hot water panels, but may also be used to denote more

complex installations such as solar parabolic, solar trough and solar towers or simpler

installations such as solar air heat. The more complex collectors are generally used in solar

power plants where solar heat is used to generate electricity by heating water to produce steam

which drives a turbine connected to an electrical generator. The simpler collectors are typically


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used for supplemental space heating in residential and commercial buildings. A collector is a

device for converting the energy in solar radiation into a more usable or storable form. The

energy in sunlight is in the form of electromagnetic radiation from the infrared (long) to the

ultraviolet (short) wavelengths. The solar energy striking the Earth's surface depends on weather

conditions, as well as location and orientation of the surface, but overall, it averages about 1,000

watts per square meter under clear skies with the surface directly perpendicular to the sun's rays.

1.2 OBJECTIVE

Solar energy is gaining much attention as a result of the increasing natural gas and oil

prices and environmental concerns. And majority of the non renewable resources are at the vergeof depletion and the prices are soaring, the petroleum prices have increased from $ 18.5 in 2000

to $132 per barrel in 2008, and the environmental concerns caused by the burning of these fuels

is greater. So our objective is to harness the solar energy efficiently and effectively and use this

waste energy to produce useful energy and thus reducing the dependence on non renewable solar

energy. We are developing this solar collector and analysis of the adsorption system as a

pioneering works in solar research in our college. This solar collector can be used for further

research by the future batches.

1.3 SCOPE

The effective utilization of eco-friendly solar energy for power generation would results

in reduced dependence on non renewable fuels and consequently pollutant emission levels can be

brought down to a great extend.The effective utilization of eco-friendly solar energy for power

generation would results in reduced dependence on non renewable fuels and consequently

pollutant emission levels can be brought down to a great extend.The geographical data of India


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indicates that solar resources and waste land areas are widely available. These factors together

make India an ideal country for the implementation of solar energy based technologies.

1.4 SCHEME

The first consideration of any power producing system is to decide the capacity of the

system. So we decided to produce enough power to provide cooling for an ordinary room with 4

occupants and the accessories in its cooling load estimate was calculated and the amount of work

to be given was estimated. As a result of literature survey conducted for the various solar

collector systems-parabolic trough collectors was selected-and adsorption system was selected as

the option for producing the cooling effect. This was followed by the analysis of the solarparabolic collector. Detailed designing procedures were carried out for the collector, receiver,

supports and the tracking mechanism. Detailed design drawings and ProE models are made for

each component. The materials and machining processes are selected to suit the requirements

and the components are fabricated accordingly.


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2.LITERATURE SURVEY

Headley.et.al(1994) used a compound parabolic concentrating solar collector of

concentration ratio 3.9 and aperture area 2m2 to power an intermittent solid adsorption

refrigerator and ice maker using activated charcoal (carbon) as the solid adsorption refrigerator

and ice makerusing activated charcoal (carbon) as the adsorbing medium and methanol as thw

orking fluid.Up to 1 kg of ice at an evaporator temperature of -6C was produced, with the net

solar coefficient of performance being of the order 0.02. Maximum receiver/adsorbent

temperature recorder was 154C on a day when the insolation was 26.8 MJ/m2 . The

temperatures in excess of 150C are undesirable since they favour the conversion of methanol to

dimethyl ether, a noncondensable gas inhibits both condensation and adsorption.The major

advantage of this system is its ability to produce ice even on overcast days(insolation

10MJ/m2).There was excessive heating capacity in the system,and only 2% of the incident solar

radiation was converted to the refrigeration effect.The system as it stands is therefore not

economically viable.However,the cost of heating using CPC is about half as expensive as the

cost of heating using electrical power. The CPC is therefore a natural candidate for industrial

process heat generation in temperature region 80C to 200C.

Saha.et.al(2001) experimentally investigated a double stage, four bed,non-regenrative

adsorption chiller powered by solar/waste heat sources between 50C and 70C.The prototype

studied produced cold water at 10C and hada cooling power of 3.2kW with a COP of 0.36,when

the heating source and sink had a temperature of 55C and 30C,respectively.

Flat plate collectors could easily produce hot water to regenerate the adsorbent of the

chiller at this level of temperature.


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Xia.et.al(2004) applied for a patent of a silican gel-water adsorption chiller driven by a

low temperature heat source that wasused to cool a grain depot in th Jiangsu Province,China.This

chiller has two identical chambers and a second stage evaporator with methanol as working fluid.

Experiments performed when hot water at 85C was used to drive the chiller,resulted in a cooling

power close to 4.96 kW,with the corresponding COP around 0.32.

A solar powered compound system used for heating and cooling was developed and

successfully implemented in a golf course in Taiwan.An integrated two bed,closed type

adsorption chiller working on silica gel/water system was developed for the same by Industrial

Technology Research Institute in Taiwan.The solar powered system used to provide hot water at50C to the dormitories and to provide chilled water to the restraunt.It had a cooling power of

9kW and a COP of 0.37.It also had a specific cooling power of about 72W/kg. However in the

field tests performed from july to October,the average cooling power was found to be 7.79kW

and average COP of 0.403,this was investigated.W.S Chang et.al (2008)

Yong Kim et.al(2005) investigated numerically and experimentally, the thermal

performance of a glass evacuated tube solar collector . The solar collector considered consisted

of a two-layered glass tube and an absorber tube. Air is used as the working fluid. The length and

diameter of this glass tube are 1200 and 37 mm, respectively. Four different shapes of absorber

tubes are considered, and the performances of the solar collectors are studied to find the best

shape of the absorber tube for the solar collector. Beam irradiation, diffuse irradiation, and shade

due to adjacent tubes are taken into account for a collector model to obtain a realistic estimation.


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3. STUDY OF COLLECTORS.

3.1 STUDY OF DIFFERENT COLLECTORS

3.1.1.SOLAR COLLECTORS WITHOUT CONCENTRATION

These types of collectors are characterized by not having methodic concentration of solar

energy, so that the relationship between the collector and the surface is almost the absorption

unit.

3.1.1.1 Flat plate solar collector:

Flat plate collectors, developed by Hottel and Whillier in the 1950s, are the most common

type. They consist of

1) A dark flat-plate absorber of solar energy,

2) A transparent cover that allows solar energy to pass through but reduces heat losses,

3) A heat-transport fluid to remove heat from the absorber,

4) A heat insulating backing.

The absorber consists of a thin absorber sheet (of thermally stable polymers, aluminum,

steel or copper, to which a matte black or selective coating is applied) often backed by a grid or

coil of fluid tubing placed in an insulated casing with a glass or polycarbonate cover. In water

heat panels, fluid is usually circulated through tubing to transfer heat from the absorber to an

insulated water tank. This may be achieved directly or through a heat exchanger. Most air heat

fabricates and some water heat manufacturers have a completely flooded absorber consisting of

two sheets of metal which the fluid passes between. Because the heat exchange area is greater

they may be marginally more efficient than traditional absorbers.


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There is a number of absorber piping configurations:

Sharp - traditional design with bottom pipe risers and top collection pipe, used in low

pressure thermosyphon and pumped systems

Serpentine - one continuous S that maximizes temperature but not total energy yield in

variable flow systems, used in compact solar domestic hot water only systems (no space

heating role)

Completely flooded absorber consisting of two sheets of metal stamped to produce a

circulation zone. Because the heat exchange area is greater they may be marginally more

efficient than traditional absorbers.

Thus a flat-plate collector acts as a receptor that gathers energy from the sun and heat up a

metallic plate. The energy stored in the plate is transferred to the fluid. Usually, these collectors

have a transparent cover glass or plastic taking advantage of the greenhouse effect, consisting of

a series of copper tubes, which exposed to the sun absorb solar radiation and it is transmitted to

the fluid passing through its interior. Its application is the production of hot water, air

conditioning and heating of swimming pools.

Air Collectors:

Solar Air Heat collectors heat air directly, almost always for space heating. They are also

used for pre-heating make-up air in commercial and industrial HVAC systems. They fall into

two categories: Glazed and Unglazed.

Glazed systems have a transparent top sheet as well as insulated side and back panels to

minimize heat loss to ambient air. The absorber plates in modern panels can have an absorptivity


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of more than 93%. Air typically passes along the front or back of the absorber plate while

scrubbing heat directly from it. Heated air can then be distributed directly for applications such

as space heating and drying or may be stored for later use.

Unglazed systems, or transpired air systems, consist of an absorber plate which air passes across

or through as it scrubs heat from the absorber. These systems are typically used for pre-heating

make-up air in commercial buildings.

Vacuum Collectors:

These have a double deck envelope, sealed, insulated inside and outside The vacuum that

surrounds the outside of the tube greatly reduces convection and conduction heat loss to the

outside, therefore achieving greater efficiency than flat-plate collectors, especially in colder

conditions. This advantage is largely lost in warmer climates, except in those cases where very

hot water is desirable. The high temperatures that can occur may require special system design to

avoid or mitigate overheating conditions.. They are more expensive, in addition to losing the

effect of vacuum with the passage of time. Its main application is the production of sanitary

water, heating pools, in some commercial applications and air conditioning. here are several

types of evacuated tubes (sometimes also referred to as Solar Tubes).

Type 1 (Glass-Glass) tubes: It consists of two glass tubes which are fused together at one end.

The inner tube is coated with a selective surface that absorbs solar energy well but inhibits

radiative heat loss. The air is withdrawn to evacuate the space between the two glass tubes to

form a vacuum, which eliminates conductive and convective heat loss. These tubes perform very

well in overcast conditions as well as low temperatures. Because the tube is 100% glass, the


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problem with loss of vacuum due to a broken seal is greatly minimized. Glass-glass solar tubes

may be used in a number of different ways, including direct flow, heat pipe, or U pipe

configuration.

Type 2 (Glass-Metal) tubes:It consists of a single glass tube. Inside the tube is a flat or curved

aluminum plate which is attached to a copper heat pipe or water flow pipe. The aluminum plate

is generally coated with Tinox, or similar selective coating. These types of tubes are very

efficient but can have problems relating to loss of vacuum. This is primarily due to the fact that

their seal is glass to metal. The heat expansion rates of these two materials. Glass-glass tubes

although not quite as efficient glass-metal tubes are generally more reliable and much cheaper.

Type 3 (Glass-glass - water flow path) tubes: It incorporates a water flow path into the tube

itself. The problem with these tubes is that if a tube is ever damaged water will pour from the

collector onto the roof and the collector must be "shut-down" until the tube is replaced.

Conical or Spherical Collectors:

Its main feature is that the unit simultaneously captures and storages. Its receiving area is

conical or spherical with a cover glass in the same geometry. With these geometries it ensures

that the surface gets illuminated throughout the day, in the absence of shade, is constant. The

installation is very simple, but there are problems with the stratification of water and the

receiving surface is small. Its main application is the production of hot water through solar

energy.


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3.1.2. Solar Collectors with concentration:

These use special systems in order to increase the intensity of radiation on the absorbing

surface and thus achieve high temperatures in the heat carrier fluid. The main complication is the

need for a monitoring system to ensure that the collector is permanently oriented towards the

Sun.

Parabolic dish

It is the most powerful type of collector which concentrates sunlight at a single, focal point,

via one or more parabolic dishesarranged in a similar fashion to a reflecting telescope focuses

starlight, or a dish antenna focuses radio waves and they're usually programmed to adjust

themselves so that they follow the course of the sun throughout the day

There are two key phenomena to understand in order to comprehend the design of a parabolic

dish.

- The shape of a parabola is defined such that incoming rays which are parallel to the dish's axis

will be reflected toward the focus, no matter where on the dish they arrive.

- The light rays from the sun arriving at the Earth's surface are almost completely parallel. So if

dish can be aligned with its axis pointing at the sun, almost all of the incoming radiation will be

reflected towards the focal point of the dishmost losses are due to imperfections in the

parabolic shape and imperfect reflection.

The losses due to atmosphere between the dish and its focal point are minimal, as the dish is

generally designed specifically to be small enough that this factor is insignificant on a clear,

sunny day.


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Parabolic trough

A parabolic trough is a type of solar thermal energy collector. It is constructed as a long

parabolic mirror (usually coated silver or polished aluminum) with a Dewar tube running its

length at the focal point. Sunlight is reflected by the mirror and concentrated on the Dewar tube.

The trough is usually aligned on a north-south axis, and rotated to track the sun as it moves

across the sky each day.

Alternatively the trough can be aligned on an east-west axis; this reduces the overall

efficiency of the collector, due to cosine loss, but only requires the trough to be aligned with the

change in seasons, avoiding the need for tracking motors. This tracking method works correctly

at the spring and fall equinoxes with errors in the focusing of the light at other times during the

year (the magnitude of this error varies throughout the day, taking a minimum value at solar

noon). There is also an error introduced due to the daily motion of the sun across the sky, this

error also reaches a minimum at solar noon. Due to these sources of error, seasonally adjusted

parabolic troughs are generally designed with a lower solar concentration ratio. In order to

increase the level of alignment, some measuring devices have also been invented.

Heat transfer fluid (usually oil) runs through the tube to absorb the concentrated sunlight.

This increases the temperature of the fluid to some 400C. The heat transfer fluid is then used to

heat steam in a standard turbine generator. The process is economical and, for heating the pipe,

thermal efficiency ranges from 60-80%. The overall efficiency from collector to grid is about

15%, similar to Photovoltaic Cells but less than Stirling dish concentrators.


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3.2 STUDY OF DIFFERENT WASTE HEAT UTILIZING DEVICES

3.2.1 STIRLING ENGINE:

A Stirling engine is a heat engine operating by cyclic compression and expansion of air

or other gas, the working fluid, at different temperature levels such that there is a net conversion

of heat energy to mechanical work.

The Stirling engine is an external combustion engine, as all heat transfers to and from the

working fluid take place through the engine wall. This contrasts with an internal combustion

engine where heat input is by combustion of a fuel within the body of the working fluid. The

Stirling engine encloses a fixed quantity of permanently gaseous fluid such as air as its working

fluid

Typical of heat engines, the general cycle consists of compressing cool gas, heating the

gas, expanding the hot gas, and finally cooling the gas before repeating the cycle. The efficiency

of the process is approaching the efficiency of the Carnot cycle, which depends on the

temperature difference between the hot and cold reservoir, For Stirling engine the higher

temperature for the fluid can be obtained from the output of the solar parabolic collector and the

low temperature region can be the ambient temperature itself. And using this temperature

difference the Stirling engine can work and produce enough mechanical work to drive a

compressor or any other device which can be use to substitute the electrical work.

3.2.2 MICRO TURBINE:

Micro turbines are small combustion turbines with outputs of 25 kW to 500 kW. They

evolved from automotive and truck turbochargers, auxiliary power units (APUs) for airplanes,

and small jet engines. Most micro turbines are comprised of a compressor, combustor, turbine,


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alternator, recuperator (a device that captures waste heat to improve the efficiency of the

compressor stage), and generator. The hot gases from the outlet of parabolic collector-receiver

can be used to drive a micro turbine and which is coupled with shaft of a generator which can be

used to provide electrical output and in addition to it the heat in the working fluid remaining after

running the turbine can be used to heat water to produce hot water for supplementing the various

needs of the household.

Micro turbines offer several potential advantages compared to other technologies for

small-scale power generation, including: a small number of moving parts, compact size,

lightweight, greater efficiency, lower emissions, lower electricity costs, and opportunities to

utilize waste fuels. Waste heat recovery can also be used with these systems to achieve

efficiencies greater than 80%.

Because of their small size, relatively low capital costs, expected low operations and

maintenance costs, and automatic electronic control, micro turbines are expected to capture a

significant share of the distributed generation market. In addition, micro turbines offer an

efficient and clean solution to direct mechanical drive markets such as compression and air-

conditioning.

Micro turbines can be used for stand-by power, power quality and reliability, peak

shaving, and cogeneration applications. In addition, because micro turbines are being developed

to utilize a variety of fuels, they are being used for resource recovery and landfill gas

applications. Micro turbines are well suited for small commercial building establishments such

as: restaurants, hotels/motels, small offices, retail stores, and many others.


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3.2.3 ADSORPTION REFRIGERATION SYSTEM

An adsorption system is a sorption system driven by a heat source. There are two main

processes inside the system: refrigeration and regeneration, the refrigerant is vapourized in the

generator and adsorbed by a solid substance with a very high microscopic porosity. In the

regeneration process, the adsorbent is heated until the refrigerant desorbs and goes back to the

evaporator, which now acts as a condenser. There are several pairs of refrigerant/adsorbent such

as water/zeolite, methanol/activated carbon. The system is not as popular as the absorption

system. However this application can be integrated with solar collectors and the exhaust of the

automobiles.

Solid vapour adsorption is similar to liquid-vapour adsorption system, except the

refrigerant is adsorbed onto a solid desiccant rather than into a liquid.

The various processes in a simple vapour adsorption are

1. At state 1, the adsorber contains adsorbent saturated with a large fraction of refrigerant at

slightly below Pevap.The cool adsorber is heated and desorbs refrigerant vapour

isosterically thereby pressurizing to stage 2.Slightly above Pcond. At this point ,vapour

starts being forced out of the hot adsorber through a one way check valve to the

condenser

2. Isobaric heating desorbs more refrigerant, forcing it into the condenser until state 3 is

attained, where the adsorber is nearly devoid of refrigerant.

3. The hot adsorber is then cooled isosterically,causing adsorption and depressurization,

until the pressure drops below Pevapopening another check valve to allow vapour to enter

the adsorber from the evaporator


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4. Isobaric cooling to state 1 saturates adsorbent, completing the cycle.

SolidVapour heat pumps require low quality heat sources at around 150-200oC.An SCP of

220W/kg adsorbent has been demonstrated and SCP=590 W/kg adsorbent has been predicted.

Three adsorbent-refrigerant pairs have received the most attention to date: zeolite/water,

activated carbon/ammonia and silica gel/methanol.

3.3 IMPORTANT CONSIDERATIONS FOR DESIGNING A PARABOLIC TROUGH

3.3.1 COLLECTOR APERTURE

The collector aperture affects both the optical efficiency and the concentration ratio. With

respect to optical efficiency, the collector aperture affects the collector aperture area loss

(geometric factor) due to abnormal incidence effects. The smaller the collector aperture, the

smaller will be the geometric factor which leads to higher optical efficiency. On the other hand,

for a fixed receiver diameter, the concentration ratio is reduced as the aperture decreases, which

results in higher thermal losses. So the objective is to have a small geometric factor with a large

concentration ratio.

3.3.2 RIM ANGLE

The rim angle is the angle from the rim of the collector to the line normal to the collector

surface passing through the focus, for the same aperture, various rim angles are possible. For

different rim angles, the focus-to-aperture ratio which defines the curvature of the parabola is

changing. It can be demonstrated that, with a 90 rim angle, the mean focus to reflector distance

and hence the reflected beam spread is minimized, so that the slope and tracking errors are less

pronounced. The collector's surface area decreases as the rim angle is decreased. There is thus a

temptation to use smaller rim angles because there is only a small sacrifice in optical efficiency.


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However, it has been proved ~ that the cost of the reduction in the performance with the small

decrease in optical efficiency is greater than the saving in material area. The intercept factor is a

function of rim angle. A rim angle that maximizes the intercept factor should be chosen and is so

close to its maximum over a broad range of values for rim angle that the choice of rim angle

within this range can be determined by other considerations such as mechanical strength and ease

of manufacture.

3.3.3 RECEIVER DIAMETER

The receiver diameter determines the intercept factor and consequently the optical

efficiency. The intercept factor is the ratio of the energy intercepted by the receiver to the totalenergy reflected by the focusing device. Its value depends on the size of the receiver, the surface

angle errors of the parabolic mirror, and the solar beam spread.

3.3.4 DESIGN ANALYSIS

The instantaneous efficiency of a PTC can be calculated from an energy balance on the

receiver tube. The instantaneous efficiency is defined as the rate at which useful energy is

delivered to the working fluid per unit of aperture area divided by the beam solar flux at the

collector aperture plane.

3.3.4.1 Optical Efficiency

The optical efficiency r/o can be expressed as:

o= [K ()] [()n ]

where, ()n= effective transmittance-absorptance factor at normal incidence

= intercept factor at normal incidence,

This definition of the optical efficiency allows a clear distinction between the factors

contributing to it. The first bracketed term is the incidence angle effect. The second bracketed

term representsthe material properties and the last term, the intercept factor, contains the effects

of all optical errors.


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The potential errors (or imperfections) that may be encountered in a PTC are illustrated in Fig. .

They are

Nonspecularity (diffusivity) of the reflector material,

Profile and slope errors of the reflector support structure,

Tracking errors

Misalignment of the receiver with respect to the focal plane of the PTC

3.3.4.2 THERMAL ANALYSIS

The primary function of the receiver subsystem of a PTC is to absorb and transfer the

concentrated energy to the fluid flowing through it. In this process, the absorbing surface of the

receiver will be heated, and its temperature will become considerably higher than that of the

surroundings. For example, depending on the temperature requirements of the application,

operating temperatures, as high as 300C can be attained at the absorbing surface of the receiver

during operation. Subsequently, the temperature difference between the absorbing surface and


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the surroundings will cause some of the collected energy to be transferred back to the

surroundings.

The knowledge of heat loss from the receiver is important for predicting the performance

and, hence, designing PTCs. Proper qualification of the heat loss from the receiver is important

for predicting the performance, and hence, designing PTCs.

There are, three different heat exchanges exist between the components of the receiver. These are

(1) Heat transfer from the absorber tube to the working fluid

(2) Heat exchange between the absorber tube and the glass jacket (glassing)

(3) Heat exchange between the glass jacket and the surroundings.The total heat loss from the collector module can be calculated by:

Qo-L =UIoss(x){Tglass(x)- Ta}dx

Uloss(x) = the heat transfer coefficient for combined convection and radiation heat losses from the

outer surface of the glass jacket

3.3.5 MIRROR MATERIALS

The optical efficiency of PTC modules is largely dictated by the reflectivity of the

materials used. In solar energy applications, back silvered glass plates, anodized aluminum

sheets and aluminized plastic films serve as reflectors. Of the various commercially available

reflector materials Corning 0317glass 1.5 mm thick, having evaporated silver coating, is the best

reflector, since its reflectivity is high at all acceptance angles. The composite glass mirror

manufactured by M/s.Glaverbel, Belgium, having reflectivity of the order of 92% in the solar

spectrum, has been used in several industrial process heat systems.


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3.3.6 REFLECTOR SUPPORT STRUCTURES

The reflector support structure is the primary member of a PTC which provides the

correct optical shape for the reflector surface, maintains the same to within acceptable tolerances

during operation and offers protection during operating and non-operating periods from extreme

weather conditions. Commercially available PTCs have a sandwich structure, a monocoque

structure or a stiffened rib structure.

The choice of materials of these categories is considered on the basis of environmental

stability, durability, mechanical and physical properties, suitability of the construction method,

fitness for high production rates, low total weight and resulting cost.The sandwich structure is a good design, but high precision moulds are required in order to

successfully fabricate high quality PTC. In commercial PTCs, either aluminium or stainless-steel

honeycomb are used as sandwich materials. These are expensive. Alternatively, paper

honeycomb with stainless steel or aluminium skin can be used. In addition to light weight, it is

also cost effective. Although the monocoque structure is quite stiff, its weight per unit area is

somewhat high. Also, it is difficult to achieve the required surface accuracies unless careful

quality control is exercised at every stage of its fabrication. The stiffened rib design is superior to

the above three designs, since it yields high surface accuracy and these can be assembled in situ.

The performance requirements for the PTC structure are:

(1) To provide and maintain the correct optical shape to the reflective surfaces

(2) To maintain the shape within the specified tolerances during operations

(3) To protect the reflective surfaces under extreme weather conditions and

(4) To withstand long term exposure to the environment.


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In engineering terms, these requirements mean that the stresses and the deflections

experienced by the trough and the reflector must remain below specified levels under gravity,

wind and thermal loads, and at the same time, the physical properties of the structure, such as the

size and weight, must be compatible with the overall design objectives.

In addition to these other factors like light weight and low fabrication cost must also be

taken into consideration.

3.3.6.1 STRUCTURAL DESIGN REQUIREMENTS

In addition to geometric parameters, a significant design consideration can be the loadsthat act on the PTC structure:

The weight of the mirror

The weight of the mirror supporting members and

The wind loads.

Of these, the wind load is very important, since it decides the rigidity and integrity of a PTC

structure as well as its foundation requirements.

The Sandia Laboratory of the U.S.A. has specified the following design requirements for a PTC

structure [54]:

survive 120 km/h wind in any position

operate in 40 km/h average wind and

drive to stow in a wind increasing at a rate of 7.5 km/h.

3.3.6.2 WIND LOAD ON REFLECTOR SUPPORT STRUCTURE

In developing solar collectors, wind loading is one of the major structural design

considerations.The shape of the collector, its height above the ground, the collector pitch angle,


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the number and arrangement of collectors in an array and the direction of the wind are several

parameters which can modify the loads applied to the collector. Besides having to safely sustain

maximum expected loads, a tracking collector must also be able to maintain its desired

orientation within a certain accuracy band in typical environments and at minimum cost. In

addition, wind load information in terms of forces and moments is needed from the standpoint of

foundation and other structural design considerations, while the pressure distribution is a

valuable tool to be used in the detailed design of a PTC itself.

3.3.7 ORIENTATION AND TRACKING

PTC modules can be provided with two axis, polar axis, horizontal east-west orhorizontal north-south mountings.. The two axis system is ideal and will give maximum thermal

efficiency. The change in efficiency of polar axis mounting will vary from 0 to 9% over a year.

But, for large systems, the horizontal east-west or horizontal north-south mount is highly

suitable. The analysisfor low latitudes, horizontal north-south orientation is much more suitable

than the horizontal east-west.

To track, a large array of PTC systems for thermal applications, three types of trackers are

commercially available. They are computer tracker, shadow band tracker and flux line tracker.

The computer tracker

A computer tracker uses a clock to compute the sun's position and initiate the collector

rotation to the computer anvil. Shaft encoders mounted on the driving unit provide accurate

accounting of the angular position.

The shadow band sun tracking system.

A shadow based sensor is mounted on the collector and rotated along with it. Two

sensors are separated by a shadowing strip which shades one of the sensors if the tracker is not


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pointed directly at the sun. The sensors produce an error signal when they are not illuminated

equally. This error signal is used to drive the PTC in a proper direction to reduce the signal to

zero.

Flux line tracker.

The flux line tracker has two sensors, which are sensitive to concentrated flux, located

near the receiver. As with shadow band trackers, if the collector is off-pointed, an error signal is

nulled. Flux line trackers are the only tracker versions that orient the collector based on where

the focal line actually is, rather than where it should be.

Sandia Laboratories have developed an efficient computer/flux line tracking system, thetracking angle is calculated with a microprocessor, and the collector is positioned in this

direction. A fine tuning of the tracking angle is accomplished with the flux line tracker. A pair of

resistance wires, helically wrapped around the receiver, provides an error signal. The resistance

wire spans the full length of the receiver and integrates the receiver's entire flux distribution to

find the best tracking angle for the collector as a whole.


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4.STUDY OF ADSORPTION

4.1 THEORY OF ADSORPTION:

Adsorption is caused by London Dispersion forces, a type of Vanderwaals Force which

exists between molecules. The force acts in similar way to gravitational forces between the

planets in adsorption processes atoms, molecules or ions in a gas or liquid phase diffuse to the

surface of an adsorbent and bind to the surface as a result of London Vander Waals forces. The

latter interactions are a result of polarization or non- reflected interactions.

London Dispersion Forces are extremely short ranged and therefore sensitive to the

distance between the carbon surface and the adsorbate molecules. They are also additive,

meaning the adsorption force is the sum of all interactions between all atoms. The short range

and additive nature of these forces results in activated charcoal having the strongest physical

adsorption forces of any material known to mankind.

4.2 THEORY OF ADSORPTION REFRIGERATION SYSTEM

An adsorption cycle for refrigeration does not use any mechanical energy, but only heat

energy. Moreover, this type of cycle basically is a four temperature discontinuous cycle. An

adsorption unit consists of one or several adsorber plus a condenser plus an evaporator,

connected to heat sources .The adsorber or system consisting of the adsorbers exchanges heat

with heating systems at high temperatures and a cooling system at intermediate temperature,

while the system consisting of the condenser plus evaporator exchanges heat with another heat

sink at intermediate temperature and a heat source at low temperature. Vapour is transported

between the adsorber and both the condenser and evaporator. The adsorption refrigeration cycle

consists of four basic processes, which is similar to a conventional vapour compression

refrigeration cycle. The major difference between the two systems is that in adsorption


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refrigeration system we replace the mechanical compressor by a chemical compressor. The

chemical compressor is the adsorption chamber which contains the adsorbent activated charcoal.

The activated charcoal adsorbs the refrigerant-methanol vapour and desorbs it at higher

temperatures and thus produces compression effect. The four basic processes involved in cycles

are:

4.2.1 BASIC PROCESSES

4.2.1.1 HEATING AND PRESSURISATION

During this period, the adsorber receives heat while being closed. The adsorbent

temperature increases, which induces a pressure increases, from the evaporation pressure up tothe condensation pressure. This period is equivalent to the compression in cycles.

4.2.1.2 HEATING DESORPTION AND CONDENSATION

During this period, the adsorber continues receiving heat while being connected to the

condenser, which now superimposes its pressure. The adsorbent temperature continues to

increase which induces desorption of vapour. This desorbed vapour is liquefied in the condenser.

The condensation heat is released to the second heat sink at intermediate temperature. It is

equivalent to the condensation in compression cycles.

4.2.1.3 COOLING AND DEPRESSURISATION

During this period, the adsorber releases heat while being closed. The adsorbent

temperature decreases, which induces the pressure decrease from condensation pressure down to

the evaporation pressure. This period is equivalent to the expansion in compression cycles.

4.2.1.4 COOLING ADSORPTION AND EVAPORATION

During this period the adsorber continues releasing heat while being connected to the

evaporator, which now superimposes its pressure. The adsorbent temperature continues


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decreasing, which induces adsorption of vapour.This adsorbed vapour is vapourized in the

evaporator. The evaporation heat is supplied by the heat source at low temperature. This period

is equivalent to the evaporation in compression cycles.

4.3 ADSORBENTS

Adsorbents are used usually in the form of spherical pellets, rods, moldings, or monoliths

with hydrodynamic diameters between 0.5 and 10 mm. They must have high abrasion resistance,

high thermal stability and small pore diameters, which results in higher exposed surface area and

hence high surface capacity for adsorption. The adsorbents must also have a distinct pore

structure which enables fast transport of the gaseous vapors.

Most industrial adsorbents fall into one of three classes:

Oxygen-containing compounds Are typically hydrophilic and polar, including materials

such as silica gel and zeolites.

Carbon-based compounds Are typically hydrophobic and non-polar, including materials

such as activated carbon and graphite.

Polymer-based compounds - Are polar or non-polar functional groups in a porous polymer

matrix.

4.3.1 SILICA GEL

Silica gel is a chemically inert, nontoxic, polar and dimensionally stable (< 400 C or 750

F) amorphous form of SiO2. It is prepared by the reaction between sodium silicate and acetic

acid, which is followed by a series of after-treatment processes such as aging, pickling, etc.

These after treatment methods results in various pore size distributions.


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Silica is used for drying of process air (e.g. oxygen, natural gas) and adsorption of heavy (polar)

hydrocarbons from natural gas.

4.3.2 ZEOLITES

Zeolites are natural or synthetic crystalline aluminosilicates which have a repeating pore

network and release water at high temperature. Zeolites are polar in nature.

They are manufactured by hydrothermal synthesis of sodium aluminosilicate or another silica

source in an autoclave followed by ion exchange with certain cations (Na+, Li+, Ca2+, K+, NH4+).

The channel diameter of zeolite cages usually ranges from 2 to 9 (200 to 900 pm). The ion

exchange process is followed by drying of the crystals, which can be pelletized with a binder to

form macroporous pellets.

Zeolites are applied in drying of process air, CO2 removal from natural gas, CO removal from

reforming gas, air separation, catalytic cracking, and catalytic synthesis and reforming.

Non-polar (siliceous) zeolites are synthesized from aluminum-free silica sources or by

dealumination of aluminum-containing zeolites. The dealumination process is done by treating

the zeolite with steam at elevated temperatures, typically greater than 500 C (930 F). This high

temperature heat treatment breaks the aluminum-oxygen bonds and the aluminum atom is

expelled from the zeolite framework.

4.3.3 ACTIVATED CARBON

Activated carbon is a highly porous, amorphous solid consisting of microcrystallites with

a graphite lattice, usually prepared in small pellets or a powder. It is non-polar and cheap. One of

its main drawbacks is that it is reacts with oxygen at moderate temperatures (over 300 C).


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Activated carbon can be manufactured from carbonaceous material, including coal, peat,

wood, or nutshells .The manufacturing process consists of two phases, carbonization and

activation. The carbonization process includes drying and then heating to separate by-products,

including tars and other hydrocarbons from the raw material, as well as to drive off any gases

generated. The process is completed by heating the material over 400 C in an oxygen-free

atmosphere that cannot support combustion. The carbonized particles are then "activated" by

exposing them to an oxidizing agent, usually steam or carbon dioxide at high temperature. This

agent burns off the pore blocking structures created during the carbonization phase and so, they

develop a porous, three-dimensional graphite lattice structure. The size of the pores developedduring activation is a function of the time that they spend in this stage. Longer exposure times

result in larger pore sizes. The most popular aqueous phase carbons are bituminous based

because of their hardness, abrasion resistance, pore size distribution, and low cost, but their

effectiveness needs to be tested in each application to determine the optimal product.

Activated carbon is used for adsorption of organic substances and non-polar adsorbates

and it is also usually used for waste gas and waste water treatment. It is the most widely used

adsorbent since most of its chemical and physical properties (e.g. pore size distribution and

surface area) can be tuned according to what is needed. Its usefulness also derives from its large

micropore volume and the resulting high surface area.

4.4 REFERIGERANTS

4.4.1 ETHANOL

Ethanol is known as ethyl alcohol or grain alcohol it is flammable colourless chemical

compound. It is a versatile solvent. It is miscible with water and most of the organic solvents

including the nonpolar liquids such as aliphatic hydrocarbons. Organic solids of low molecular


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weights are usually soluble in ethanol. Among the ionic compounds many mono valent salts are

atleast somewhat ethanol, with salts of large, polarizable ions being more soluble than salts of

smaller ions. Most salts of polyvalent ions are practically insoluble in ethanol.

Ethanols hydroxyl group is able to participate in hydrogen bonding. At the molecular level,

liquid ethanol consists of hydrogen bonded pairs of ethanol molecules; this phenomenon renders

ethanol more viscous and less volatile than less polar organic compounds of similar weight. In

the vapor phase, there is little hydrogen bonding, ethanol vapor consists of individual ethanol

molecules.

Molecular formula C2H6O

Molar mass 46.07 g mol1

Density 0.789 g cm3

Melting point 114C

Boiling point78 C

Vapor pressure 5.95 kPa (at 20 C)

4.4.2 METHANOL

Methanol, also known as methyl alcohol or wood alcohol, is a compound with chemical

formula CH3OH.It is the simplest alcohol, and is light and volatile. Methanol is a colourless

liquid at room temperature and has a slight fruity odour. The boiling point of methanol is

64.5oC.it is miscible with water in all proportions and is lighter than water. Methanol is a neutral

solution and shows negative result for all acid tests. It is poisonous if ingested can cause


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blindness. Methanol is very flammable and burns with a pale blue flame and forms carbon

dioxide and water on complete oxidation or combustion

Molecular formula CH4O

Molar mass 32.04 g mol1

Density 0.7918 g cm-3

Melting point 98to 97 C

Boiling point 65 C

Vapor pressure 13.02 kPa (at 20 C)

Viscosity 5.9 10-4Pa s (at 20 C)

4.4.3 AMMONIA:

Ammonia is a covalently-bonded compound of nitrogen and hydrogen with the formula

NH3. It is a colourless gas with a characteristic pungent odour. It is toxic and corrosive to some

materials, and has a characteristic pungent smell. It is lighter than air and its density is

approximately 60% that of air. It is easily liquefied and liquid boils at -33.7C and solidifies at -

75C to a mass of white crystals. Liquid ammonia has a very high standard enthalpy change of

vapourization and can therefore be used in laboratories in non insulated vessels at room

temperature, even though it is well above its boiling point.

It is miscible with water. All the ammonia contained in an aqueous solution of the gas

may be expelled by boiling. The aqueous solution of ammonia is basic. The maximum

concentration of ammonia in water has a density of 0.880 g/cm3.It does not sustain combustion

and burn readily unless mixed with oxygen, when it burns with a pale yellowish-green flame.


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Molecular formula NH3

Molar mass 17.031 g/mol

Appearance Colourless gas with strong pungent odour

Density 0.86 kg/m3(1.013 bar at boiling point)

Melting point 77.73C

Boiling point 33.34C

4.3 WORKING OF THE SYSTEM

The three adsorbers are operated in 10 minutes cycle. In each 10 mins the adsorber is

heated for 200s and cooled for next 400s.The hot water is passed through the first adsorber by

opening the valve from hot side. The temperature of the adsorber rises slowly. The heating is

continued for 200s. As heating is continued methanol gets desorbed and the pressure inside the

chamber begins to rise. When the gauge indicates 1 bar the outlet valve for methanol is opened

and methanol gas at 1 bar goes to the condenser. The valve is opened very slowly and when the

pressure falls well beyond 1 bar the valve is closed.

After heating for 200s the cooling phase begins .The hot water outlet to adsorber 1 is

closed and the cold water is opened. Mean time the hot water is routed to adsorber 2 for the

heating phase. When the cold water cools the adsorber the temperature falls and more and more

methanol gets adsorbed. As a result the pressure inside the chamber falls. When the pressure

inside reaches 0.1 bar the methanol inlet valve which connects the adsorber and the evaporator

coil is opened and more methanol is allowed to flow in a controlled rate. As more and more

methanol, comes the more it gets adsorbed to a saturated stage. At this juncture the adsorption


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stops and the pressure inside the chamber stops and the pressure begins to build .The inlet valve

is closed stopping the flow of methanol. The adsorbed methanol is released during the heating

phase. After 400s the water inlet from the heater is opened for heating cycle.

The methanol from the adsorber condenses in the condenser. The methanol condenses at

65oC at 1 bar and the highest foreseen ambient temperature is 50oC.The condensed methanol is

then expanded through an expansion device and evaporated in the evaporator coil at 0.1 bar. At

0.1 bar methanol evaporated at 5oC producing cooling effect.


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5. CALCULATIONS

5.1 QUALITATIVE ESTIMATION AND BASIC DESIGN OF ADSORPTION SYSTEM

5.1.1 REQUIRED AMOUNT OF ADSORBENT AND REFRIGERANT

Three adsorbers are used instead so that one of it cn be used for heating the adsorber

rapidly and permitting the other two to be cooled slowly at half the heating rate. A cooling rate

that is half the heating rate incurs half the THTFso that the adsorbent can be cooled closer to

ambient and adsorb more methanol. At any instant, one adsorber is heated while two are cooled

cycle duration is set at 10 min and is divided into thirds. Each adsorber is heated for one third of

the cycle that is 200s and is cooled for the remaining 400s. Their phases are set at evenly spaced

angles of 0,120 and 240, so, at any given instant one adsorber is being heated and the other two

are being cooled. The amount of methanol to be expelled from each adsorber during the heating

phase is

Mr=ool

ha=

= 0.206 kg

The activated carbon at 25 oC can be saturated with upto 55 % methanol. Adding CaCl2

coating boosts adsorptivity to 85% methanol. The dynamic adsorption capacity can be boosted to

49 % at 95oC with CaCl2.Therefore in each adsorber the amount of activated carbon Mads

required to hold

Mr =0.206 kg

Mads =

=

=1.03 kg


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5.1.2 ADSORBERS

Each adsorber is made of thin walled stainless steel of diameters 3 inches. It contains

copper tubes of inches diameter. Steel wool is loosely packed between the tubes to create

copper steel contact. After subtracting the volume of tubes the volume left in the adsorber shell

to accommodate 1.03 kg of activated carbon

Volume of adsorber shell= r2h

= 0.03812 0.3=1.36 10-3

Volume of tubes = 10 r2x h

=10 0.00635

2

0.3=3.80 10-4m3

Net volume available = 1.36 10-33.80 10-4 m3

=1 litre

Each adsorber has Vads=1 l of space to accommodate Mads=1.5 kg of activated carbon as

determined. Activated graphite is porous and must not be firmly compacted to maintain

permeability. The total porosity within the individual particles and between particles in the

aggregate is

Porosity =

=

=51.5%

ads=2.21 kg/ltr

Vads=0.99 litre

Mads=1.06 kg


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5.2 THERMAL PERFORMANCE OF ADSORBERS

5.2.1 AVAILABLE HEAT

The heat provided from the solar collector at ideal conditions is approximately

3.5kW.And the water is cooled from Twaterin=90oC to Twaterout=70

oC,and temperature of the dead

state to be taken as 25oC .Assuming a constant Cp, The available heat is

Qavail=

= 1555W

5.2.2 HEAT TRANSFER IN ADSORBERS

I. REFRIGERANT FLOW RATE

For the adsorber being heated, the methanol flow rate is

Mr=

=

= 0.00382 kg/s

For each of the two adsorbers being cooled, the flow rate is halved:

Mr=0.00191 kg/s

II. THERMAL MASSES

The mass fraction of adsorbed methanol ranges from MFmax=32% at 95oC to MFmin=0%

200oC, for an average of MF=16% at Tads=147oC.This corresponds to 0.378 kg of adsorbed

methanol with a thermal mass of 585.9J/K at Cp=1550 J/kgK.Thus the total sensible thermal

mass of each adsorber is the sum of the thermal masses of the solids: metal, adsorbent, and

average amount of solidified refrigerant

Csolid=MsteelCpsteel+McopperCpcopper+MadsCpads+0.5(MFmax+MFmin) MadsCpads

=3.27519+1.55399+1.51033+0.5 (0.49-0.29) 2.361550

=4230.88 J/K


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III. SENSIBLE AND LATENT HEAT RATES

The total sensible heat rate for each adsorber during the heating phase is

Qsens heating =

=

=1410.29 W

The heat of adsorption is Hads=1151 kJ/kg.The latent (adsorption) heat rate per adsorber

during the heating phase is

Qadsheating =

=

=4066.8 W

Therefore the total heat rate into the heated adsorber during the heating phase is

Qheating =Qsens heating + Qads heating

=1410.29+4066.8

=5476.8 W

IV HTF (HEAT TRANSFER FLUID) FLOW RATE

The mean HTF flowrate through the heated adsorber is

Mhtf =

=

=0.139 kg/s


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5.3 DESIGN OF SOLAR COLLECTORS

Power output

Required output = 5 KW

Discharge = 0.0238 lit/s

5.3.1 SYSTEM DESIGN

The system is designed to provide a temperature of 80o, raising the temperature of the

fluid from the ambient temperature i.e. 30o. Mass flow rate for the required temperature rise and

the velocity of flow is calculated as below.

For 5 KW:Mass flow rate ( =

= 0.0239 kg/s

Velocity of flow; V=

=

Time required for one pass of the fluid =

=

= 39.37 sec

Power input (Solar energy)

Irradiation, = 500 W/

Intensity of radiation on the collector= = 5003.6=1800 W/

For an optical efficiency of 60%,

Intensity of radiation on receiver; =0.6 1800 = 1080 W/

For an incident intensity of 1080 W/and mass flow rate of 0.0239 kg /s, the temperature rise

for a single pass can be found out as follows:

=

=

= 10.8111

5.3.1.1 CIRCULATION PUMP ANALYSIS

Required head; h =18 m = 59.05 ft


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Power of pump; P =1 HP

=

Where

- Power in HP;

h- Head in feet

=

=

= 0.949 lb/s =0.430 kg/s

The mass flow rate required for the receiver is well within the mass flow rate of pump.

5.3.2 PARABOLIC REFLECTOR

Dimensions

Width = 1.2 m

Length = 5 m

Projected area (= 3.6

Defining equation - (A- focal distance)

5.3.2.1 FOCAL POINT FIXING

1. Rim angle () = 30

Focal distance a = 1.601 m or 160.1 cm



3.

Rim angle () = 60



Focal distance a = 0.3 m or 30 cm


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5. Rim angle () = 120


6. Rim angle () = 135

Focal distance a = 0.694 m or 69.4 cmFor optimum focal distance and curve length, a rim angle of 90 is selected for the model.

Selected rim angle = 90

Focal distance = 0.3 m or 30 cm

5.3.3 RECEIVER

Copper tube20mm inner diameter

30 mm outer diameterArea of receiver =DL

Area of receiver exposed to rays (=

=

= 0.1413

Inner cross-sectional area ( ) =

=

= 3.14

Outer cross-sectional area ( ) =

=

= 7.06

Concentration ratio(CR)

CR =

=

25.477

Receiver section

Materialcopper tube

Specification- Inside diameter-20mm

Outside diameter- 30mm

Fluidwater

5.3.3.1 COPPER TUBE

Volume of tube for 3 m length= DtL

Where, D- Mean diameter; t- Thickness; LLength


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= 0.025 0.005 3

= 1.178

Density of copper =8940 kg /

Mass of tube = Volume Density

= 1.178 8940

= 10.53 kg

5.3.3.2 Fluid flowing

Volume of fluid flowing for 3 m length =

L

where( inner diameter ; L- length)

=

() 3

= 1.472

Mass of fluid flowing =Volume Density

= 1.472 1000

= 1.472 kg

5.3.3.3 Glass tube

Volume of fluid flowing for 3 m length = L

= (95)(10)3

= 8.95

Mass of glass tube = Volume density

= 8.95 2230

= 19.958 kg


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5.4 STRUCTURAL ANALYSIS

Deflections of the copper tube under static load

Assuming the tube as a cantilever beam

E= 117GPa

Moment of inertia, I =

(

=

(

= 31906.80

1) Supports at 1 m interval

Deflection, y =

(W- udl value ; Llength; Emodulus of elasticity )

=

= 0.1196 mm

2) Supports at 1.5 m interval

Deflection, y =

=

= 0.692 mm

3) Supports at 3m interval

Deflection, y =

=

= 11.074 mm


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5.4.1 BEARING LOAD

1) WIND LOAD

Max expected wind speed = 60 km/hr = 16.67 m/s

Density of air (at 25oc) = 1.1839 kg/m3

Wind pressure = 0.5 V2

= 0.5 1.1839 16.672

Max Projected Area = 3.6 m2

Max Wind Load = 592.2 N

2)

WEIGHT OF RIBS

Length of L section (25253) = 28 m

Area of L section = 1.41 10-4m2

Density of Mild Steel = 7860 kg/m3

Volume of Steel used = 3.192 10-3m3

Expected Weight = 304.4 N

3)

WEIGHT OF ACRYLIC GLASS

Area = 1.4 3 m2

= 4.2 m2

Thickness = 3 mm

Density of glass = 1180 kg/m3

Volume of glass = 0.0126 m3

Expected Weight =145.9 N

4) WEIGHT OF RECIEVER SECTION

Weight of Copper Tube = 103.3N


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Weight of Water = 14.44N

Weight of Glass Tube = 195.79N

Weight of Receiver Support = 50 N

Total Weight of Receiver = 363.53N

5) MISCELLANEOUS WEIGHTS

Weight of Gear = 30N

Weight of Solid support Pipe:

Expected Length = 2 m

Diameter = 45mmDensity = 7860kg/m3

Weight = 245N

Total Misc Weight = 275N

DESIGN OF BEARING

Static Radial Load on Bearing = 1681. 03 N

=1700 N (approx.)

Dynamic Load can be neglected as there is just one rotation in a day.

Inner Race Diameter= 45mm

Single Row Deep Groove Ball Bearing with ISI No. 10BC02having Static Load Rating of (Co)

of 2160N and Dynamic Load Rating (C) of 3925N is selected.


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5.8 MATERIAL STUDY:

Based on the extensive studies for suitable materials for the various parts of the solar

collector based on their thermal, mechanical and chemical properties.

Various properties are desirable for the various parts of the parabolic collector.

The property of the material that is to be used for coating should be such that it should be

able to withstand high temperatures, have good reflectivity, should be resistive to corrosion and

also should have low transitivity and absorptivity. For this purpose silver seems to be an ideal

candidate but due to the high cost and requirement of heat treated bend glass plate and high cost

of silvering and difficulty in maintaining the silver coating and requirement of extreme carewhile handling the same, makes it not an economically viable solution for the reflective surface.

It was decided that acrylate glass with low cost reflective material coated on the same as a

substitute for the silver for the reflective surface. Another advantage of using the low cost

reflective surface is it can be replaced at a very low cost, once there is a reduction in the

reflectivity of the coating. And the cost of acrylate glass is very low, and has properties

comparable with glass and a good temperature resistance characteristic.

The material used for the structure should be resistive to compression than in tension

should have high strength and capable of taking fatigue loading and also should have good

resistance to corrosion. The structure is to be preferably made of mild steel.

The material used for making the pipe section should be a good conductor of heat, should

be able to maintain its properties for sufficiently high temperature, it should have good

absorptivity , good conductance and preferably low emissivity to avoid radiation loses from the

pipe section and also should be able to resist corrosion as it has to face corrosive environments

both inside and outside due to the usage of ordinary water as heat transfer fluid inside and outer


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surface being exposed to the atmosphere. It is preferred to use copper tubes of diameter 30mm

considering the required mass flow rates and good heat transfer properties.

A summary of the various materials to be used is summarized as follows

MATERIAL SELECTION SUMMARY

USAGE MATERIALS

BACK PLATE ACRYLIC GLASS

RECEIVER COPPER

REINFORCEMENT BAR ALUMINIUM

STRUCTURE MILD STEEL

REFLECTING SURFACE SILVER COATED PAPER

The properties of the various materials used are summarized as follows

ALUMINIUM

Values of conductivity of aluminium:

Temperature Value of k(in W/cm K)

300 2.37

323.2 2.39

350 2.40

Thermal expansion coefficient of Al = 22x10-6W/m K

Overall heat transfer coefficient of Al = 25 W/m2 K

Emissive coefficient, = 0.09 (for commercial sheet).

Lower the Youngsmodulus, higher the specific heat.


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COPPER

Temperature Value of kin W/m/K

300 401

350 396

400 393

500 386

600 379

STEEL

k = 10.55 W/mK.

Overall heat transfer coefficient = 25 W/m2K

SILVER

k = 418 W/mC.

Specific heat = 230 J/kgC.

Fluid Transmission Surface Fluid Value of h

Water Cu Air / gas 13.1 W/m K

Water Cu Water 340.4 W/m K

Steam Cu Air 17 W/m K

Steam Cu Water 1160 W/m K

Water M.S Air / gas 11.3 W/m K

Water M.S Water 340 W/m K


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Air M.S Air 7.9 W/m K

Steam M.S Water 1050 W/m K

Steam Stainless steel Water 680 W/m K

Poly Acrylic Sheeting

Made from thermoplastic composites.

Flexibility and shatter resistance than other glasses.

UV resistance.

High heat resistance.

Fair chemical resistance.

Moderate to high price.

PC & organic glass have equal weight.

Tensile modulus = 5.8G Pa.

Density = 1.43 g/ cm3

.

Water absorption 0.28%

Coefficient of thermal expansion = 30 x 10-6/K

Specific heat = 1.08 J/kg K

k = 0.26 W/m K

Upper working temperature = 140C

Solid PC optical transmission coefficient = 91%

Details and the materials used for the adsorption system were explained earlier.


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4.CONCLUSIONS

4.1CONCLUSIONS

The solar powered adsorption system for cooling has great relevance in the current scenario

of rising fuel prices and global concerns about the environment. A vapour adsorption air

conditioning system that can be powered by solar heat which is available almost free of cost.

And being a stationary system the chance of methanol poisoning, which may occur due to the

high vacuum being maintained can be avoided.

4.1.1. Advantages

1. The system requires nearly no input, it runs on the waste heat which can lead to better

utilization of resources

2. The system works in phase with the cooling requirements, the refrigeration load

increases during the summer time when the solar insolation is maximum. Hence solar

air conditioning can be used with greater efficiency.

3. It has a sound pressure level less than 50 db, bit mechanical sound pressure level is

greater than 80 db. Hence solar air conditioning systems have a very silent operation.

4. Solar refrigeration systems are less sensitive to shocks.

4.1.2. Disadvantages

1. The system needs a warm up time.

2. The refrigerant methanol which is highly flammable and toxic and hence there arises

the question of safety hazards

3. The system works in high vacuum and there is a possibility of poisoning by air.

4. The COP of the air conditioning system is very low compared to the conventional

mechanical systems.


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4.2 RECOMMENDATIONS

1. The adsorbent cam be doped with additives like calcium chloride to, which can

significantly increase the adsorption capacity of activated carbon hence more performance

and the system will get much more compact.

2. The copper pipes in the adsorber and receiver can be internally threaded to increase the

surface area for more effective heat transfer.

3. All hand shut valves used in the system can be replaced by solenoid valves and hence the

system can be automated using a micro controller which responds to signals from the

pressure and temperature sensors.4. An alternate refrigeration system can be developed based on the Peltier effect

4.3 SCOPE FOR FUTURE WORK

1. Research can be done on new adsorption pairs.

2. Experiments can be done on the receiver sections.

3. Research can be done on emerging solar technologies using the solar collector developed.

4. Theoretical results can be experimentally verified.

5. Experimentations can be done with photovoltaic effect as an alternate method to produce

electricity.


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REFERENCES

1. M.A Lambert and B.J Jones,Automotive Adsorption Air Conditioners Powered by Exhaust

Heat Part 1&2,2006

2. R Z Wang,Adsorption Refrigeration Research in Shanghai Jiao Tang University,Renewable

and Sustainable Energy Reviews,2001

3. Wang RZ,Oliveria R.G,Adsorption Refrigeration-An efficient way to make good use of waste

heat and solar energy.Progress in Energy and Combustion Science,2006

4. Lansing FL, Clarke V, Reynold R.,A high performance porous flat-plate solar collector.

Energy 1979

5. S. Kalogirou, Y. Tripanagnostopoulo, M. Souliotis, Performance of solar systems employing

collectors with colored absorber,2004

6. W.S Chang, C.C Wang, C.C Shieh, Experimental study of a solid adsorption cooling system

using flat tube heat exchangers as adsorption bed,Applied Thermal Engineering2007

7. A Boubkari, Perfomance of an adsorptive solar ice maker operating with a single double

function heat exchanger (evaporator/condenser).Renewable Energy(31),2006

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9. Headley, et.al. (1994),Charcoal-Methanol adsorption refrigerator powered by compound

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