DESIGN AND DEVELOPMENT OF SOLAR WATER HEATING SYSTEM USING PHASE CHANGE MATERIAL
Abstract - Solar energy is readily available almost all year long and can be used to generate electricity and heat. Over time, interest of public and government in solar energy has skyrocketed. However, it has the drawback of not producing as intended during off-seasons. A useful method of storing thermal energy that offers the benefit of high energy storage density and isothermal storage is by the usage of a latent heat storage system with PCM. Energy is stored using PCM, which is then used to heat water for domestic usage at night. This makes sure that hot water is accessible all day long. This system consists of solar water heating setup along with a PCM based tube in shell heat exchanger is designed in this work which will be integrated with solar water heating system.
Key Words: Phase Change Material (PCM), Solar Water Heater, Thermal Energy Storage System, Heat Transfer Fluid
1.INTRODUCTION
The main driving cause behind efforts to more effectively utilizedifferentrenewableenergysourcesarethecontinual riseingreenhousegasemissionsandtheriseinfuelprices. Direct solar radiation is regarded as one of the most promising energy sources in many parts of the world. Researchers are looking for novel, sustainable energy sources all across the world [1, 2]. A current difficulty for technologists is the storage of energy in acceptable forms thatcanbetraditionallyconvertedintotheneededform[3]. Energy storage plays a significant role in energy conservationbyloweringtheimbalancebetweensupplyand demand as well as enhancing the efficiency and dependability of energy systems [4] A useful method of storingthermalenergythatoffersthebenefitsofhighenergy storage density and isothermal storage is the usage of a latent heat storage system that uses PCMs. Fully refined paraffinwaxisusedinthesystem[5].PCMsarefrequently used in latent heat thermal storage system for solar engineering, spacecraft thermal control applications and heat pumps. PCM applications for building heating and coolinghavebeenstudiedwithinthelasttenyears.PCMsare appealing in a variety of applications due to they are abundant and can melt and solidify at a wide range of temperatures[6]
1.1 OBJECTIVES
To design a cheap and easy to integrate energy storagesystemforsolarwaterheatingsystem.
TostudyandselectoptimumPCMforthesystem.
ToFabricateascalemodelofthesolarwaterheating setupwithPCM.
1.2 SCOPE
Thisworkincludes,designanddevelopmentofasmallheat exchanger, in order to establish the effectiveness of using paraffinwaxasasuitablePCMinsolarwaterheatingsystem. The paraffin wax is incorporated in the heat exchanger, whichactsasthermalenergystoragedevice.
2. SELECTION CRITERIA FOR PCM
The selection of PCM is crucial for solar thermal energy storage. There are different ways to classify PCMs such as phasechangetemperature,materialpropertiesetc.Common factorsduringtheselectionofPCMsinclude:thermodynamic properties, kinetic properties, chemical properties and economicproperties.ThenormalparaffinsoftypeCnH2n+2 is a family of saturated hydrocarbons with very similar properties.ParaffinsbetweenC5andC15areliquids,andthe rest are waxy solids. Paraffin wax is used widely in commercialorganicheatstoragePCM.Itcontainsofstraight chainhydrocarbonswhichhavemeltingtemperaturefrom 23°to67°C.Paraffinwaxischosenduetoitsnotendencyto segregate, stable properties after 1500 cycles and affordability. The effects of super-cooling during the crystallization can be dealt with by means of adding a nucleatingagent.
Asinthermalenergystoragethewatertemperaturevariesin between40to60°Candthemeltingtemperatureofparaffin waxis54°Citisthemostsuitable.
3 WORKING
Duringsunshineperiod,asmentionedinFig-1,valve1iskept open and valve 2 is kept closed. The cold water from the storagetankgoesthroughthesolarcollector,absorbingheat energyfromthesolarradiations.Itthenpassescompletely throughthePCMheatexchanger,whereitlosesitsheatand transfersittothePCM.Itthengoesbacktothestoragetank. In this way, the PCM gains heat energy which will be then usedtoheatwaterduringnon-sunshineperiod.Duringnonsunshineperiod, valve 1iskept closedand valve 2iskept open.Thenormalwaterfromthestoragetankflowsthrough thePCMheatexchanger,absorbingheatenergyfromtheheat storedinthePCM.Itthengoesbacktothestoragetank.By thiswaythewaterisheatedbyabsorbingtheheatstoredin thePCM.
Amountofhotwatertobestored
Anaveragehomeneedsaboutthreebucketsofwatereach day when it is not sunny. Using a 20 litres bucket as an example,thetotalvolumeneededis60litres.However,we areconsideringdevelopingaheatexchangertoheat10kgof waterforourexperimentalpurposes.Ahigher-requirement systemmightbedesignedusingthesamemethod.
Amountofheatenergytobestored
athinginthewinter.So, 20to foracomfortablebath.
Initialtemperatureofwater
Ti
Final(desired)temperatureofwater Tf Tf –Ti
Heatcapacityofwater, Cv =4.187kJ/kg
Hence, amount of heat required to carry out the abovetransition(Q) =mwater x(Tf –Ti)xCv =10x25x4.187 =1046.75kJ
Hence,amountofenergyneedstobestored=1046.7kJ
EstimatingRequiredamountofPCM
Amountofenergytobestored(Q1) =1046.75kJ
HencemassofPCMtobeincorporated,mpcm =Q1/(Latentheat) =1046.45/206 =5.0816kg.
Henceapproximately5.1kgofPCMneedstobeincorporated intheheatexchanger.
Selectionofheatexchangerforenergystorageunit
Thesimplestsortofheatexchangerisatubeinshelldesign. ThiskindofexchangermakesitsimpletoincorporatePCMs. Theheattransferfluid(HTF),inthiscasewater,flowsfrom theinnertubeoftheheatexchanger,whichcontainsthePCM
DimensionsofEnergystorageunit
Assumenoofenergystoragepipestobeused (n)=7
MassofPCMineachunit =mpcm /n =5.0813/7 =0.7259kg
VolumeofPCMtobeused(Vpcm) =Mpcm/unitxῥpcm =0.7259x789 =0.00092002m3
a) Design of Energy storage unit
Cross sectional area of outer portion of heat exchanger(A2) =Vpcm/l =0.00092002/0.5 =0.00184005m2
MaterialofInnerPiper Copperbeingbestsuitedforheattransferwithheat transferrateof isselected
ConsideringstandarddiameterofInnerPipe(d1) =0.019m
Standardouterdiameterofcopperinnerpipe(d2) =0.022m
Crosssectionalareaoftheinnerpipe(A1) =1.5393x10-5m2
MaterialofouterPipe
ConsideringthepurposeofinsulationPVCisselected asitpreventsthemeltedwaxtosolidifyaftercharging.
theinternaldiameterofouterpipe(D1)
⁄ x((A1+A2)/π) ½ =0.05m
OuterdiameterforPVCouterpipe(D2) =0.053m
Placement of heat exchanger in energy storage device
Clearancebetweentwoheatexchangingunits(C) Fromstandardchartminimumclearance =0.25xD2 =0.013m
Asthisisminimu j 6 ” AD
Pitch =D2+C =0.053+0.013 =0.066m
b) Area Estimation of Collector
TotalAreaofCollector(Ac) =[(quantityofwaterxCv)+Gt]/100 =[(10x4.187)+5.8]/100 =0.48m2
5. MANUFACTURING AND ASSEMBLY OF MODEL
To assess the effectiveness of a solar water heater, it is necessary to compute its thermal efficiency, which represents the proportion of the energy input from solar radiationtothepoweroutputintermsoftheresultingwater temperature This calculation is crucial for evaluating the performance of the solar water heater. By measuring the inletwatertemperature25.3°Candformerlyimplementing thetemperaturereadingsinthecalculation,theefficiencyis calculatedas:
AsampleefficiencycalculationofDay1at9.00am:
EnergyInputwithPCMat(Qin) =Ac×Gt =0.48x5.71 =2.7408kW
EnergyOutputwithPCM(Qout) ( × ×Δ )/ =(10x4.2x8.2)/1000 =0.3444kW
E P M(η) =Qout /Qin =0.3444/2.7408 =0.1257 =12.57%
6. RESULTS AND DISCUSSION
The results of the experimental work, provide a comprehensivecomparison ofasolarwaterheatingsetup withoutPCMandwithPCM
Table-2: Resultsofexperimentalwork
Parameters Without PCM With PCM
TemperatureofInput
WaterinMorning (9.00Hours) C C
TemperatureofOutput
WaterinEvening (21.00Hours) C C
Temperature
DifferenceAfter12 Hours C C
Avg. Efficiency 12.26 % 25.97 %
The comparison as done in Table-2 is based on various temperature and efficiency measurements over a specific period of time. To simplify the experimentation and calculationprocess,theprototypemodelwasusedtocollect dataforashorterperiod.However,theresultsobtainedcan beusedasabasisforactualsolarwaterheatingsystems,as theproportionofresults mightbesimilar.Itcanbefound thatincreasingthequantityofPCMandthecapacityofthe plant tends to increase the efficiency and temperature difference.
TheChart-1demonstratesthatthesetupwithPCMisbetter at preserving the temperature for a longer duration and reducingheatloss,incomparisontothesolarwaterheating setupwithoutPCM
7. CONCLUSIONS
IntegratingPCMinsolarwaterheatingsystemsisofgreat benefit. With appropriate parameter selection and integrationofaPCMintheheatexchangerofasolarwater heating system, hot water can be maintained with a consistenttemperaturenearthemeltingtemperatureofthe PCM foran extended period of time.Itwas foundthatthe PCMbasedsolarwaterheatingsetuphavehighpotentialto replacesolarwaterheatingsetupwithoutPCMtoenhance thethermalefficiencyofsolarwaterheatingsetup
Based on the experimental work carried out, following conclusionsaredrawn:
Fullyrefinedparaffinwaxhasasuitabletransition temperature range of 45 to 55°C and a relatively highlatentheatof206kJ/kg.Inaddition,itdoesnot exhibit any sub-cooling. Utilization of PCM with lowermeltingtemperatureisbeneficialtoenhance energy performance of the solar water heating setup
The cost to incorporate the system is economical withamoderateinstallationcostoftheunitanda verylowmaintainingcostmadethiskindofsolar waterheatingsoefficient.
A functional prototype model was created that effectively retained the temperature of heated water for a longer duration compared to a solar waterheatingsetupwithoutPCM.
Theprototypemodelofasolarwaterheatingsetup wasabletoachievea10%increaseinefficiencyby integratingaPCMsetup.
A collector-storage water heating system is extremely endorsedforlow/mediumtemperatureapplicationsasthey can store solar energy in the form of latent heat during daytimeandcanprovideheatatnighttimeorunavailability ofsunradiationtoproducehotwater.
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