experimental and graphical evaluation of solar power with … dr anil... · 2018-12-15 ·...

etInternational Journal on Emerging Technologies 4(1): 88-98(2013) ISSN No. (Print): 0975-8364

ISSN No. (Online): 2249-3255

Experimental and Graphical Evaluation of Solar Power with Respectof Different Solar Panel Matrices and Material

Jitendra Kumar Diwakar* and Anil Kothari**

*Department of Mechanical Engineering, Rajiv Gandhi Proudyogiki Vishwavidyalaya, Bhopal, (MP)**Department of Training and Placement, Rajiv Gandhi Proudyogiki Vishwavidyalaya Bhopal, (MP)

(Received 10 February, 2013 Accepted 20March, 2013)

ABSTRACT: Energy is the capacity of doing work. It is most important and primary input for development.All living organism needs energy for their operations .which they derived from the environment. Man hasrequired and used the energy ever since he came on the earth. Primitive man gets energy in the form of byeating plants and animals. Later on he discovered fire and with the advancement he discovered variousenergy. Which he used for his domestic, industrial, transportation, agricultural, and other needs Energy isavailable in number of forms such as mechanical, thermal, electrical, chemical, biological energy and energyin matter. Energy is also a fundamental quantity, which in joules (J) and can be defined the work done.When a force of one Newton moves through one meter.

I. INTRODUCTION

APPLICATION OF SOLAR ENERGYSolar Collector: It can be used as sub-systems in manysystems meant for the urination of solar energy Possibleapplication of solar air heaters are drying or curing ofagricultural products, space heating for comfort,regulation of dehumidification agents, seasoning oftimber, curing of industrial products such as plastics. Ingeneral solar air heaters are quite suitable for low andmoderate temperature applications as their design arerelatively simple .

Types of solar collectorGlazed flat – plate solar collectors

Glazed flat-plate collectors are very common and areavailable as liquid- based and air –based collectorsThese collectors are better suited for moderatetemperature application where the demand temperatureis 30-70.c and ./ or for application that require heatduring the winter months the liquid based collectors are

most commonly used for the heating of domestic andcommercial hot water buildings and indoor swimmingpools The air based collectors are used for the heatingof building ventilation air and crop-drying

Concentrating solar collectorsBy using reflectors to concentrated sun-light on theabsorber of the solar collectors. the size of absorber canbe dramatically reduced Which reduced heat losses andincrease efficiency at high temperature. Anotheradvantage is that reflector can cost substantially less perunit area then collectors.This class of collector is used for high temperatureapplications such as stream production for thegeneration of electricity and thermal detoxification.There are four basic type of concentrating collectors

1. Parabolic trough2. Parabolic dish3. Power tower4. Stationary Concentrating collector

Fig.1. Various types of concentrating collectors.

Air based solar collectorThe energy collected from air based solar collectorscan be used for ventilation air heating. Space heatingand crop drying. The most common application inCanada is for ventilation air heating.

Types of solar collectors for heato Flat plate collectorso Evacuated tube collectorso Comparisons of flat plate and

evacuated tube collectorso Air

Diwakar and Kothari 89

Types of solar collectors for electricity generationo Parabolic trougho Parabolic disho Power towero Solar pyramids

Solar air heaterSolar air heater use solar panels to warm air which isthen conveyed into a room. The basic components ofa solar air heater include solar collector panels, a ductsystem and diffusers. Systems can operate with orwithout a fan. Without a fan the air is distributed bythe action of natural ventilation system.

Effect of Parameters on Thermal Performance ofSolar air heater

The performance of solar air heater is acomplex function of various parameters which can beclassified as:

(i) System parameters(ii) Operation parameters(iii) Meteorological parameters

Improvement of Performance of solar air heaterIn order to utilize solar energy usable economicallyone of the important requirements is its efficientcollection. A solar collector is a special type of heatexchanger that convert isolation (I/A) in to thermalenergy.Various factors useful for expressing the performanceof flat plate solar collectors:The average plate temperature, depends upon the-

• Temperature of incoming fluid• Geometrical details of collector• Fluid flow rate• Intensity of solar radiation

The performance of flat plate collector has beenfound to depend strongly on the losses from theabsorber surface, the rate of incident solar radiationand the rate of heat transfer form the absorber p[lateto the air.It is therefore found that the performance of solar airheater can be improved using anyone or combinationof the following technique

1. Enhancement of intensity of solarradiation incident upon the solarcollector.

2. Reduction of thermal losses.3. Improvement of heat transfer from

absorber plate to the air.

Enhancement of Intensity of Solar RadiationReflecting surface can be used to increase the energyyield of the flat plate solar collectors. Also theperformance of flat plate collector can be

significantly enhanced by radiations of reflectors,which increase the total collection area.Concentration ratio up to 4and temperature up to 180o

can be achieved in booster system with a flat platesolar air heater.

Reduction of Thermal LossesThermal losses from the collector can be reduced inthe following ways:

Use of multiple glass cover: When collectoroperates at moderately high temperature, use of twoor more glass covers is a normal practice. This helpin reducing the convective as well as radiative heatloss from the collector.

Use of alternative medium or vacuum in space:Convective heat losses can be minimized byoptimizing the gap spacing and the use of alternativemedium in the space between two covers. The use ofmany gases can reduce the heat losses by 34 %alternatively partially evacuated space by 10 %reduction in presence can reduce losses by 85 %. Acombination of moderate vacuum and a selectivesurface (a=0.9, b=0.15) can be increase the dailyenergy collection by as much as 278 % and efficiencyof more then 40 %.

Selective coating on absorber plate: For operatingthe collector at high efficiency it is desirable to havea surface of high absorptance for solar radiations andlow emittance for long wave radiations. This type ofsurface is possible since 98 % of the energy inincoming solar radiation is contained within thewavelength of 0.3 micron whereas the emitted longwave radiations even from a black body at400K liesin the wave length range of more then 3 microns.This will reduce the irradiations from the absorbersurface.

Use of two pass system: These losses can be stillfurther lowered significantly by making air flow intwo passes, firstly through the space between twoglass covers and then through the absorber plate duct.It has been shown that two pass made of operation issuperior to single pass mode of operation; the glasscover is cooled by the air thereby reducing the toplosses. It has been reported that outer glass covertemperature were lower by 2.5-5oC over the day andwas much nearer to the atmospheric temperaturescompared to those when collector was operated in aconventional single pass made. Consequently 10 – 15% higher efficiencies were obtained. Also a two passsystem does not cost anything extra and secondly;ordinary glass can be used for covers as energyabsorbed in the covers is returned to the air.


Use of honeycomb structures: Honeycomb structurecan be used in the space between the absorber plateand the glass cover to suppress free convection heattransfer across the air gap and reduce the radiation lossfrom the collector .An array of rectangular cells fromthe honeycomb structure. The honeycomb cells areproperly shaped and coated with thin, highly reflectingbut infrared absorbing walls to limit convection andradiation losses to the glass cover.

II. EXPERIMENTAL PROCEDURE

The experimental setup used in the presentinvestigation, as shown in figure was designed,fabricated , installed and used for data collection onheat transfer and fluid flow characteristics of solar airheaters with packed bed and without packed bed. Itconsist of a test section having two identical ducts, onesmooth duct (like that in a solar air heater in commonuse)and the other one is similar but provided with apacked bed using wire screen matrices.

1. Both the duct had an identical length of 1.6 mwidth of 0.62m, and depth of 025m. (havingDh =0.048) and were made of softwood, bothinclined at an angle of 200 to the horizontal.

2. The smooth (or conventional) duct(figure)had an absorber plate of 2 mm GI sheet .Itwas blackened with black board paint on theside facing solar radiation. It had a 3 mmthick glass sheet cover fixed 20 mm abovethe absorber plate. The side and bottom ofthe duct were insulated with thermocol sheet(Thermocol is a commercial insulation offoamed polystyrene having thermalconductivity 0.037 W/mK ). The reason forusing two duct in the present set up was tocompare the performance at the sameoperating condition such as mass flow rate,insulation and inlet fluid temperature.

3. The packed bed duct( Figure) had 2 mm GIsheet having several layer of wire meshscreen arranged one above the other on the onthe upper side of the GI sheet while below itthere was a 50 mm of thermocol and 12 mmplywood. The sides were made of softwood25mm thick. A glass cover was provided onthe upper side which rested on batons fittedadjacent to the side wall at a height of 25mm.Another glass cover was fixed at a height of20mm above the first one and supported onthe frame, leaving a stagnant air gap of 20mmbetween the two glass cover.

4. A wooden exit section provided at the outletof the test duct which was followed by amixing device, namely baffles for mixing theair. The exit section was reduced the effect of

sudden change on the rest section. Themixing device enabled measure of the bulkmean temperature at the outlet of the testsection. The cross section area matched withthat of the test duct. Three equally spacedbaffle plates at the exit section were providedfor the purpose of mixing the hot air comingout of the solar collector to obtain a uniformtemperature of the air at outlet.

5. The mixing section was connected to theMILD STEEL pipe fitting through atransition piece and flexible pipes.

6. A 2.2 kW (3.0 h.p.) centrifugal blower wasused for drawing air through the duct.

7. Calibrated orifice plates, one in each wereused to measure the air flow rates in bothducts. The orifice plate arrangement wasdesigned for the flow measurement in thepipe. The orifice plate was fitted between theflanges, so align that it remained concentricwith the pipe. The length of the pipe straightmild steel provided was based on pipediameter d1,which is minimum of 10d1on theupstream side and 5d1 on the downstreamside of the orifice plate.

8. Fig. shows the dimensions of the packed bed,location of the pressure tap and layout of thethermocouple.

9. The temperature distribution in the bed of thetest section was measured by means of pre-calibrated copper-constantan thermocouplesand temperature of the air at the inlet andoutlet were measured by digital thermometer.

10. Digital micro-voltmeter was used to indicatethe output of the thermocouple in 0C.thetemperature measurement system wascalibrated to yield temperature values(t+0.1)0C.

11. The pressure drop across the test section wasmeasured by using calibrated micro-manometers.

Experimental setup procedureThe experimental data has been collected by followingthe procedure described in ASHRAE StandardHandbook (1977) for testing the solar air collectoroperating in open loop flow mode. Data pertaining to agiven mass flow rate between 10 a.m. and 2 p.m. at aninterval of 45 minute were taken on a clear sky day.Before starting the experiment, all the joints of duct,inlet section, mixing device and pipe fittings wereexamined for leakage and leakage was sealed by usingglass putty. While recording the temperature, the ice-bath and lead wire for micro-voltmeter were protectedfrom direct solar radiation.


The blower was run for an hour and thereafter, thethermocouple readings for wire mesh temperatures atvarious locations and inlet and outlet air temperatures,pyranometer readings for intensity of solar radiationand manometer readings for pressure drop across theduct were recorded for a particular day. Experimentaldata were collected for flow rates ranging from 0.027to 0.033 kg/s for four set of matrices (as described inTable). It may be recalled that the parameters thatstrongly influence the heat transfer coefficient andfriction factor include porosity, P which is determinedby the geometry i.e. diameter and pitch of individualwires in the mesh and number of layers that have beenfilled into a given space; and the flow rate of airthrough the bed. Earlier studies have shown that the

systems and flow parameters that are consideredimportant to influence the heat transfer and frictioncharacteristics are given below:(i) Transverse pitch to diameter ratio of wire, pt/dw

(ii) Number of layer and porosity product, 1/nP(iii) Packed bed Reynolds number, Rep

Table shows the list of geometrical parameters to beused for the study of heat transfer and friction factor inthe present case.It is well known that in order to investigate the effectof a given parameter; other parameters must be heldconstant while collecting data on the variation ofdependent parameters as a function of independentparameters.

Fig.2. Layout of experiment set-up.

Fig.3. Duct.Instruments requiredAs per the figure of experimental set-up, we requirefollowing instruments:

1) Digital Thermometer2) Selector switch3) Digital micro Voltmeter4) Manometer5) Electric wires for connection6) Ice box etc.

The following instrumentation is sued and attachedwith the experimental set up for measurement.

ORFICE METERFor the measurement of rate of air flow through

the test ducts orifice plates have been orifice plate isfixed between two flanges fixed with straights M.S.pipe e.g. 80 mm inner diameter. The length of theM.S. pipe upstream of the orifice meter was 800 mmand towards the downstream of the orifice plate was400 mm. Specification of the orifice plate and itslocation in the pipe line has been shown in figure.


MANOMETERAn inclined tube manometer is connected to the

pressure taps for the measurement of pressure drop,(pΔp)0 across each orifice plate. Mass flow rae canbe calculated using the following expression:

M=Cd ×Ao×[2× ρair×∆Po/(1-ß4)]

Fig. 4. Selector switch and Mili-Voltmeter.Where,Cd is the coefficient of discharge, B0 is the ratio oforifice diameter to pipe diameter, A2 is theorifice area, P is the density of air.Both the orifice plates were calibrated using astandard pitor tube. The pitot tube measured the localvelocity across the diameter of the pipe having orificeplates. The experimental values of local velocitieswere used to calculate the average velocity of the airin the pipe. With the knowledge of this averagevelocity, density of air and corss sectional area of the

pipe, mass flow rate of the air were obtained. Thesevalues of mass flow rate and reading of manometeryielded the value of the coefficient of discharge

PYRANOMETERA Pyranometer, model No 0052 supplied by M/s

National Instruments Ltd. Calcutta, India wasused to measure the intensity of solar radiation. ThePyranometer was kept at an inclination of 250C withthe horizontal which is also the slope of solarcollectors. This way the solar insolation falling on theinclined collector was measured directly from thepyranometer.

THERMOMETERDigital thermometer of range 00 to 1000 C

was ued to measure temperatures at the inlet andoutlet of air.

Fig.5. Photograph of micro manometer. Fig.6. Photograph of square wire mesh.

Fig.7. Photograph of hexagonal wire mesh Fig.. Photograph of rectangular wire mesh.


III. EXPERIMENTAL DATA,

The experimental data was used to determine thedesired parameter as given below. All the propertiesof air, viz., density, viscosity specific heat, Pandtlnumber used in the calculation, were evaluated at thearithmetic mean of the inlet and outlet temperature ofair.

Average flow Temperature (Tf ):The average air temperature is calculated

as the arithmetic mean of the inlet and outlettemperature of air.

Tf = (Ti+To)/2Average Plate Temperature (Tpm):

This is the average plate temperature of themeasurement made along the length and depth of thepacked bed.

Tpm= (T1+T2+T3+T4+T5+T6)/6Where,

T1, T2, T3, T4, T5, T6 are the temperaturereadings along the depth and length of the packedbed.

Pressure Drop (∆P o):

This is the pressure drop occurring along theinclined manometer and calculated as

∆Po=∆h×9.81×ρm×1/5Where

∆h=Mercury difference in inclinedmanometer,(m)

ρm= density of fluid used ininclined manometer,(kg/m3)

Mass Flow Rate (m):This is the mass of air flowing through the solar

air duct per second and calculated as:M=Cd ×Ao×[2× ρair×∆Po/(1-ß4)]

WhereCd=Coefficient of discharge of orifice=0.62Ao=Area of the orifice plate, m2(πdo2/4)=5.515×10-4

m2

Do =Dia of orifice plate ρair=Density of air flowingthrough the duct,(1.15 kg/m3)ß =Ratio of Diameters(do/dp) i.e.(26.5/53) = 0.5Porosity of bed (P):Porosity of bed is calculated as:

Frontal Area (Af):Af = W×D

Where, W=width of duct (0.62m)D= depth or height of duct (0.025m)

Heat Transfer Area (A):\

Hydraulic Radius (rh):

Relative Mass Flow Rate (Go):Go (kg/s-m2) the mass flow rate per unit area of theduct and calculated as:

Reynolds Number (Rep)

Friction Factor (fp):

Where, ∆p = Pressure drop across the duct (N/m2)U=velocity of air through the duct (Go/ρair)L=Length of duct, mHeat Transfer Rate(Q):The heat transfer rate Q to the air can be determined

as

Heat Transfer Co-efficient (h):

Exergy(E)E = m.CpΔT – m. CpTe.In.(To/Ti) – m.R.Te.In(Po/Pi)

+ I.A (1- Te/Ts)Dimensionless Exergy(Ed)


Table (a) Observation Table for Smooth Duct.

Table (b) Experimental data for Square void matricesPorosity=0.962, dw =0.48mm, pt= 2.3mm, no of layer (n) = 6

Table (C) Experimental data Square void matricesP=0.974, dw = 0.48mm, pt =2.3mm, no of layer (n) = 4

MassFlow

Rate(kg/s)

Insolation(W/m2)

InletTemp.

(Ti)In 0C

OutletTemp.(To)

In 0C

AveragePlate

Temp.(Tpm)In 0C

Averageflow

Temp.(Tf)In 0C

Efficiency(η) %

0.0261 900 43.9 50.8 68.6 47.35 25.63

0.0276 885 41.8 48.8 66.9 45.3 26.44

0.0294 830 40.8 47.8 64.8 44.3 28.1

0.0312 850 39.6 46.9 61.9 43.2 28.320.033 840 36.4 44.1 60.8 40.25 30.65

Mass FlowRate(kg/s)

m

HydraulicRadius

rh(m)

ReynoldsNo.(Re)

Heattransfer

coefficienth(W/m2/k)

NusseltNo.(Nu)

FrictionFactor

(f)p

Efficiency(η) %

0.0261 0.00321 1161 9.05 2.02 0.0251 46.46

0.0276 0.00321 1228 9.46 2.13 0.0232 49.67

0.0294 0.00321 1308 9.86 2.22 0.0219 55.19

0.0312 0.00321 1388 10.25 2.32 0.0203 62.12

0.033 0.00321 1469 10.71 2.43 0.0188 66.16

Mass FlowRate(kg/s)m

HydraulicRadius hm

ReynoldsNo.(Re)

Heattransfercoefficienth(W/m2/k)

NusseltNo.(Nu)

FrictionFactor(f)p

Efficiency(η) %

0.0261 0.00449 1603 6.35 2.01 0.0241 38.3

0.0276 0.00449 1695 6.61 2.10 0.0228 39.3

0.0294 0.00449 1806 6.91 2.19 0.0212 40.72

0.0312 0.00449 1916 7.21 2.29 0.0196 42.51

0.033 0.00449 2027 7.56 2.41 0.0179 44.97


Table (D) Experimental data for Rectangular void matricesP=0.974, dw = 0.34mm, pt= 2.9mm, no of layer (n) = 6

Table (E). Experimental data for Hexagonal void matricesP=0.99, dw = 0.38mm. , pt =17.23 mm, no of layer (n) =6

Validation of Experimental Set-upBefore collecting the data from the experimental

set-up, the system was tested for by validity byexperimentation on a smooth to determine theNusselt number and the friction factor. These valuesof the Nusselt number and the friction factor werecompared with those obtained from the Dittus andBoelter correlation and Blasius equation given inSaini and Saini. The Nusselt numbers have amaximum deviation of 18% while the maximumdeviation of the friction factor is 8.99% from thepredicted values by the (Dittus and Boelter).

The Nusselt number for a smooth reactangularduct is given by the Dittus and boelter is givenbelow:-

The modified Blasius equation was used as givenbelow:-

In this experimental, the aim to increase collectorefficiency and decrease exergy losses using passivemethod in packed bed solar air heater. When a

comparison was made between collectors the dayshaving approximately the same radiation were used.The results obtained from the collectors designed aredepicted in figure the efficiency in each collector isalso given in these figures in term of mass flow rates.Increase mass flow rates so increase efficiency ofcollector. However, the outlet temperature of airsignificantly changes with the geometry of theabsorber. As known, the incident solar radiation isone of the most important parameters in the packedbed solar heater. The temperature of absorbersurfaces increased up to 70 0C depending on theincident solar radiation. In addition, the outlettemperature of air increased 67oC in the lowest massflow rate (0.0261 kg/s), and 60 oC in highest massflow rate (0.033 kg/s). this behavior may beexplained by longer constant times of air with the hotsurfaces inside the collector. As seen from the results,the collector efficiency increased with increasingmass flow rate of air. When the radiation ismaximum, collector efficiency is also maximum.

MassFlow

Rate(kg/s)M

HydraulicRadius

rh(m)

ReynoldsNo.(Re)

Heattransfer

coefficientH(W/m2/k)

NusseltNo.(Nu)

FrictionFactor

(f)p

Efficiency(η) %

0.0261 0.00558 1969 4.89 1.975 0.0232 38.3

0.0276 0.00558 2082 5.11 2.02 0.0216 39.3

0.0294 0.00558 2218 5.5 2.18 0.0201 40.720.0312 0.00558 2353 5.7 2.26 0.0179 42.51

0.033 0.00558 2489 5.94 2.36 0.0161 44.97

Mass FlowRate(kg/s)M

HydraulicRadiusrh(m)

ReynoldsNo.(Re)

HeattransfercoefficientH(W/m2/k)

NusseltNo.(Nu)

FrictionFactor(f)p

Efficiency(η) %

0.0261 0.008541 2994 2.96 1.85 0.0221 33.01

0.0276 0.008541 3166 3.04 1.98 0.0207 32.69

0.0294 0.008541 3373 3.14 2.16 0.0189 30.96

0.0312 0.008541 3576 3.51 2.22 0.0171 29.5

0.033 0.008541 3786 3.71 2.29 0.0154 27.91


The radiation values change in range of 650 W/m2

and 900 W/m2 and it reaches the maximum in themidday.

According to figure maximum efficiency of square6 layer is 65%, 61% in square 4 layer, 55% inrectangular wire mesh, 48% in hexagonal wirematrix, 31% in smooth plate, for maximum massflow rates. Figure Nusselt number increased withincreasing Reynolds number It is depend on porosityof wire matrix, lower porosity with high nusselt no.and lower reynold no. According to figure high

efficiency of lower porosity material i.e square 6layer and lower efficiency of high porosity i.ehexagonal wire matrixAccording to figure dimensionless exergy lossesmore in case of high porosity material i.e. hexagonal,with lower reynold no and lower dimenionless exergylosses in case of lower porosity material i.e. squarematrix with lower reynold no figure shows that Edmore occurs in lower reynold no.It is clear that when the efficiency is maximum, the

exergy loss is minimum.

GRAPHS

Fig. 9(a). Comparison of Experimental and predicted Fig. 9(b). Comparison b/w friction factor and reynold novalues of Nusselt no. vs. Reynolds number

Fig. 9(c). Efficiency Vs Time of square 6 layer. Fig. 9(d). Effect of Reynolds number on Nusselt numberfor different matrices.


Fig. 9(e) Efficiency Vs Time of square 4 layer. Fig. 9(f) Efficiency Vs Time of Rectangular wire matrix

Fig. 9(g) Efficiency Vs Time of Hexagonal wire matrix. Fig. 9(h) Efficiency Vs Time of smooth plate.

Fig. 9(i) Effect of different wire matrix on efficiency.

IV. RESULT AND DISCUSSION Dimensionless exergy losses more in case of

high porosity material i.e. hexagonal, withlower reynold no and lower dimensionlessexergy losses in case of lower porositymaterial i.e. square matrix with lowerreynold no shows that Ed more occurs inlower reynold no.

Maximum efficiency of square 6 layer is65%, 61% in square 4 layer, 55% inrectangular wire mesh, 48% in hexagonalwire matrix, 31% in smooth plate.Maximum efficiency in case of higher massflow rate in any wire mess.

REFERENCES

[1]. ASHRAE Standard 93-77 (1977) Methods oftesting to determine the thermal performance of solarcollectors. ASHRAE, New York.[2]. Ahmad A., Saini J. S. and Varma H. K. (1996)Thermohydraulic performance of packed bed solarair heaters. Energy Conv. Manag 37, 205-214[3]. Irfan Kurtbas , Aydin Durmus (2004) Efficiencyand exergy analysis of a new solar air heater.23119Elazig, Turkey.[4]. Hikmet Esen Experimental energy and exergyanalysis of a double- flow solar air heater havingdifferent obstacles on absorber plates, firat university.


[5]. H.H. Ozturk, A. Bascentincelik, Energy andExergy efficiency of a packed-bed heat storage unitfor greenhouse heating.[6]. J.S Saini Paul B.,. (2004). Optimization of bedparameters for packed bed solar energy collectionsystem. Renewable Energy 29, 1863–1876[7]. M.K.Gupta, S.S. Kaushik,Performanceevaluation of solar air heater for various artificialroughness geometries based on energy, effective andexergy efficiencies.IIT Delhi.

[8]. Chiou J. P., El-Wakil M. M. and Duffie J. A.(1965) A slit and expanded aluminium-foil matrixsolar collector. Solar Energy 9, 73-80.[9]. Collier R. K. (1979). The characterization ofcrushed glass as a transpired air heating solarcollector material. In Proceedings of ISES Silver.

experimental and graphical evaluation of solar power with … dr anil... · 2018-12-15 ·...

Documents