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ACOMPARATIVEEXPERIMENTALSTUDYOFTHERMALPERFORMANCEOFTHREESOLARAIRHEATERSHAVINGDIFFERENTABSORBERAREA

VIKASKUMAR¹,BALIRAMKUMAR²,HARIKUMARSINGH3

1,2,3DepartmentofMechanicalEngineering,CentreofExcellence,RenewableandSustainableEnergyStudies,SureshGyanViharUniversity,Jaipur,India‐302025

ABSTRACT

Thismainaimofthisexperimentwascomparethreesolarairheatershavingdifferentabsorberarea,simplesinglepasssolarairheater(SAHs)(TypeI),singlepassSAHshavingaluminumwiremesh(TypeII)andsinglepassSAHshavingaluminumfins(Type III). In type IIusedaluminumwiremeshwere insertonabsorberplate, inorder todeliver improvedheat transfersurface.A5mmdoubleglassplateusedtocoveringthecollector,todecreaseconvectiveheatlossestotheambiance.Thesethree types of experimental setup were analyzed for various air flow rates (4.20 m/s and Natural Convection) andtemperature condition versus time. The collector incline was adjusted to 26° and south faced, which is seemly for thegeographicalpositionofJaipur(26.9260°N,75.8235°E).InthisexperimentontheSAHswereworkinginthesunshinydaysofMay‐June2015.Themaximumthermalefficiency46.02%wasachievedintypeIIIatairflowrate4.20m/s.

Keywords: SolarAirHeater,AluminumWiremesh,aluminium fins,ThermalEfficiency,Heat losses, SolarFluxw/m2andabsorber plate, Double glass cover, Pressure losses, convective heat transfer coefficient.

1. INTRODUCTION

Solarairheater isauniquetypeofheat interchangethatabsorbs and converts solar radiant energy to heat. Solarairheaterareusedlowtomoderatetemperaturesuchasspace heating, timber seasoning, crop drying, paintspraying operations and other industrial or agriculturepurpose.Thebasicconstructionofsolarairheatersimpleand easy. The system was thermally shielded from theback and from the side. The two transparent windowglass of 5mm thickness was using for cover plate. Thistypeofdevicehas fewer corrosionand fewer amountofescape difficulty as related by liquid flat plate collector.The main drawback of solar air heater is that thecoefficientofheat transferby theabsorberplateandairstreamislow,thentheoutcomeislowthermalefficiencyof solar air heater. In solar air heater manyimplementationhavebeendeveloptobetterheattransfercoefficient between the absorber plate and air streampassingthrough.Themodifyfactorsofthesolarairheaterefficiency are collector depth, wind velocity, absorberplate material, collector length, falling solar flux, etc.Insertingaluminiumwiremeshandaluminiumfinstotheabsorberplatebecauseitwasincreaseheattransfertothepassing air and also itwas increase itspressuredrop inthecollector.

The main reason of various implement was to improvethe efficiency of solar air heaters by applying severalmethods. The system was using various shapes andseveraldimensionofair flowpassage inplate typesolarair collector. In theoretical models ranges perform as atechnique to improve the disadvantages of solar airheater. In this system the improvement of heat transferarea single flow solar air heater have been identify, theresults was improve its thermal performance. The gooddistribution of flow was depend on collector obstacles.Theimprovementofconventionalairheaterperformanceusingfinnedandv‐corrugatedairheaters.

Inthisprojecttherepresentationofthermalefficiencyinthree typessuchasTypeI,Type IIandTypeIIIsolarairheaterrespectively.ThethermalefficiencyoftheseTypeswas analysis in three modes. The comparison amongperformance of designed simple single pass air heater(TypeI),singlepasssolarairheaterwithaluminiumwireMesh (Type II), and single pass solar air heater withaluminium fins (Type III). The construction of solar airheater cum dryer experimentally set‐up (details in nextsection) was done on roof of ISBM, Suresh Gyan ViharUniversity Jaipur. Its latitude angle was 26.92600 N,longitude75.82350E,altitude431mabovethesealevel),Rajasthan,India.Theefficiencycalculationofnewlysolarairheatercumdryertotheexperimentalmeasurements.In this experiment, themeasurement of various air flowrates (4.20 m/s, natural convection), these values wasdetermine the thermal efficiency of solar air heater andtheconditionsofairtemperatureversustime.

2. EXPERIMENTALSET‐UP

Solarairheatergenerallyconsistsofplywoodstrongbox,absorber plate (aluminium), transparent cover (glass orplastic), material for insulating, passage of air and fan.SAHsaresystematicallyshownin figure1.1andpicturesofTypeI,TypeIIandTypeIIIareshowninfigure1.2,1.3and1.4respectively.

In thisexperiment solarairheaterwasworking in threevarious Types such as Type I, Type II and Type IIIcorrespondingly. The strong box was making by 12mmthicknessplywood.Theinnermeasurementofstrongboxwas1476mm×726mm×174mm.The24mmthicknessofthermoColewasusingforinsulationonsidesandbottomofstrongbox.The22gaugethicknessofaluminiumsheetwas using for absorber plate. This aluminium sheetwaspaintedbyblackdarkrubbercoatedpainttoabsorbmoreand more heat. The two transparent window glass of5mm thickness was using for cover plate. All the threeTypes was using double glass cover. The two fans 12v

VIKAS KUMAR et al. Volume 3 Issue 4: 2015

Citation: 10.2348/ijset07151107 Impact Factor- 3.25

ISSN (O): 2348-4098 ISSN (P): 2395-4752

International Journal of Science, Engineering and Technology- www.ijset.in 1107

each were using to force the air through the collector.These fans was connected on voltage divider in seriesconnectionforsupplyandmaintainthespeedofair.ThedeviceLM‐35temperaturesensorwasusedtomeasuringthetemperatureatanypointinSAHssuchasinlet,outlet,absorber plate, within the glass plate, below the glasscover and absorber correspondingly. The device alcoholthermometer was using for measuring the environmenttemperature.Thesolarfluxwasmeasuredbysolarpowermeterinw/m2onbothhorizontalpositionalongwith260angle.TheairvelocityofSAHstogetherwithsurroundingair velocity at outlet was measured by the Digitalanemometer (METRAVI AVM‐05) device. The gapping

between cover glassplateand containerboxwaspastedbyputty.TheenragestickwasusedtomakecertainnoairgapintheSAHs.Theabsorberplatewassituatedincentreof the plywood strong box at 127mmdepth from top ofthebox.

The interior of strong plywood boxwas coated by darkblack paint. In Type I absorber plate was completelysituated in the centre of collector strong box. In Type IIaluminium wire mesh were inserting on absorber plateandeachaluminiumwirewascoatedinblack.InTypeIIIaluminium finswere attached in the absorber plate andeachfinswascoatedbydarkblackpaint.

Fig‐1.1:Outlookrepresentationofsolarairheater

Fig.‐1.2:SimplesinglepassSAHs(TypeI)

Fig.‐1.3:SinglepassSAHshavingaluminiumwiremesh(TypeII)

Fig.‐1.4:SinglepassSAHshavingaluminiumfins(TypeIII)

3. MEASUREMENTPROCEDUREAfter putting in roof of ISBM Gyan viahr university,Jaipur; the three different Types of SAHs were goneworking some days below weather conditions. Thedevice LM‐35 temperature sensor cables point wassituated at different point of solar air heater. The solarair heater was bend 260 angle and south faced. TheexperimentationofSAHswasoperatedinthecleardaysof May‐June 2015. The experiment was performedbetween10AMto3:30PM.Thereadingwasnotedownattheperiodof30minutes.Inthisexperimentthewindspeed, air velocity at outlet, solar radiation (vertically260angleandhorizontally),inletandoutlettemperatureof heater, Ambient temperature, above glasstemperature, absorber plate temperature and innertemperature were obtained or respectiveexperimentation during the steady state stage byinterval of 30minutes. Thedevice LM‐35 temperaturesensor was used to measuring the temperature at anypoint in SAHs. The solar flux was measured by solarpowermeterinw/m2onbothhorizontalpositionalongwith 260 angle. The air velocity of SAHs together withsurroundingair velocityat outletwasmeasuredby theDigital anemometer (METRAVI AVM‐05) device. Thedevicealcoholthermometerwasusingformeasuringtheenvironment temperature. The bend angle of solar airheaterwasmeasuredbyMagneticbase.



ISSN (O): 2348-4098 ISSN (P): 2395-4752


4. NOMENCLATURE

SAH Solarairheater

Qu Collectorusefulenergygain(W)

I Solarradiation(W/m2)

Ac Surfaceareaofthecollector(m2)

ṁ Massflowrate(kg/s)

Cp Specificheatofairatconstantpressure(kJ/kgK)

Ta,out Temperatureofairatoutlet

Ta,in Temperatureofairatinlet

Ρ Densityofair(kg/m3)

A Crosssectionareaofpipeatexit(m2)

V Velocityofairatexit(m/s)

P Pressure(N/m2)

Ν Specificvolume(m3/kg)

R Specificgasconstant(J/kgK)

ha Convectiveheatlossforair

Qtotal Totalheatlosses

λ Darcy‐ Weisbachfrictioncoefficient

Ʃξ minorlosscoefficient

Dp pressureloss(pa,N/m2)

5. THERMALPERFORMANCEANALYSIS

Thermal efficiency (η)of the solar airheater isdefinedas the ratio of the useful energy gain to the solarradiationincomingtothesolarairheater:

η=Qu/IAc (1)

WhereQuisthecollectorusefulenergygain(W),Iisthesolar radiation (W/m2) on the heater surface, Ac is thesurfaceareaofthecollector(m2).Theusefulenergygain(Qu)canbecalculatedbyfollowingequation:

Qu=ṁCp(Ta,out–Ta,in) (2)

Whereṁ is themass flowrate (kg/s),Cp is the specificheat of air at constant pressure (kJ/kg.K), Ta, out is thetemperatureofairatoutlet,Ta, in is thetemperatureofairatinlet.

PuttingQufromequation(2)inequation(1),weget:

η=ṁCp(Ta,out–Ta,in)/IAc (3)

EquationforMassflowrate(ṁ)is:

ṁ=ρAV (4)

Where ρ is the density of air (kg/m3), A is the crosssectionareaofpipeatexit(m2)andV is thevelocityofairatexit(m/s).

Density of air (ρ) can be calculated by followingequation:

Pν=RT (5)

WherePisthepressure(N/m2),νisthespecificvolume(m3/kg),Risthespecificgasconstant(287J/kg.K)andTisthetemperature.

νcanbewrittenas:

ν=1/ρ (6)

So,equationforρis:

ρ=P/RT (7)



ISSN (O): 2348-4098 ISSN (P): 2395-4752


Energylosses:

1/U=1/ha+dx1/k1+dx2/k2

Where,

dx1=ThicknessofthermoCole

dx2=thicknessofplywood

k1=thermalconductivityofthermoCole

k2=thermalconductivityofplywood

Convectiveheattransfercoefficient(ha),

ha=2.5(∆T)0.25w/m2(standardvalueforha)

Qsides=UAc(Ta,out–Ta,in)

Qbottom=UAc(Ta,out–Ta,in)

Qtop=UAg(Ta,out–Ta,in)

Where,

Ac=Areaofcollectorasm2

Ag=Areaofglassasm2

Qtotal=Qsides+Qbottom+Qtop

Qtotal=98.88Wattor99Joule/second

Q=UA∆T

Pressurelossescanbecalculatedas:

dp=λ(l/dh)(ρrv2/2)+Ʃξ1/2ρrv2

Where

dp=pressureloss(pa,N/m2)

λ=Darcy‐Weisbachfrictioncoefficient

l=lengthofcontainer

dh=diameter(m)

Ʃξ=minorlosscoefficient

Airflowcanbecalculatedas

Q=πr2/4×exitairvelocity(m/s)

ForWiremesh

AreaofWiremesh=6a2(for1hole)

ForFins

Lengthoffin=102mm

Widthoffin=51mm

Areaof1fin=½l×b

6. RESULTANDDISCUSSIONS

Fig.‐2.1:TemperaturevariationwithtimeforTypeIcollectorwithairflowrate4.20m/sonMay30,2015

Figure.‐2.2:variationofThermalefficiency(%)withtimeforairheaterTypeIat4.20m/sairflowrateon

May30,2015

Figure‐2.1 represents the 30 minutes intervaltemperature deviations and the velocity of exit airwas4.20m/s in the testing. The secondary axis representsthesolarflux(w/m2).Themaximumsolarfluxobtainedin everyday was 965 w/m2. While assumed it wasincreaseinthemorningtoagreatestvalue998W/m2atnoonanddecreasebeginning inafternoon.Theaveragetemperature at everyday on inlet/ surrounding, outlet,absorber plate, inside glass surface, among glass andabsorber,wasmeasuredwhile42.46,71.40,81.30,78.80correspondingly. Every day average solar flux wasobtainedas800.76w/m2.Theaveragethermalefficiencywasdetermined42.02as4.20m/s.ThevariancebytheaverageoutletandinlettemperatureofTypeIatexitairvelocity 4.20 m/s, throughout the experiment inrepresentsinfigure2.2.

Figure4.1:averagethermalefficiency(%)versustimeofTypeIandTypeIIandTypeIIIat4.20m/s.



ISSN (O): 2348-4098 ISSN (P): 2395-4752


7. CONCLUSIONS

Adetailedexperimentalstudywasconductedtoevaluatetheenergyefficienciesofthreetypes,TypeI,TypeIIandTypeIIIsolarairheaters.Accordingtothetotheresultof the experiments, the single flow solar air heaterhaving aluminum wire mesh and single flow solar airheater having aluminium fins introduced for increasingthe heat‐transfer area at exit air velocity 4.20 m/s,leading to improved thermal efficiency. The maximumthermal efficiency is measured by 46.12% in type IIISAHs.

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ISSN (O): 2348-4098 ISSN (P): 2395-4752


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