制冷外文期刊.docx

制冷外文期刊.docx

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制冷外文期刊

制冷-外文期刊

JonrnalofAppliedSciences（8）:

788-794,2008

ISSN1812-5654

2008AsianNetworkforScientificInformation

DesigningofColdStoresandChoosingofSystemElements

S.Akdemir

Air-ConditionandRefrigerationProgramme,VocationalSchool,

NamikKemalUniversity,59030Tekirdag,Turkey

Abstract:

Inthisstudy,calculationofcoolingloadandchoosingofthecoolingsystemelementssuchascompressor,condenserandevaporatorwereexplainedfordesigningofthecoldstorage.Transmissionheat（q1）,infiltrationheat（q2）,productheat（q3）,heatofothersources（q4）andunknownandunexpectedheat（q5）whichiscomponentsofthecoolingloadwerecalculated.Inaddition,amountofthecoolingfluidwascalculatedandchoosingofthecompressor,thecondenserandtheevaporatorwereexplained.

Keywords:

Coldstorage,coolingload,compressor,condenser,evaporator

INTRODUCTION

Coolingcanbedefinedasthedecreaseoftemperatureofasubstanceormediumbelowtemperatureofitsenvironment（Anonymous,2001）.Refrigerationisaprocessofloweringthetemperatureandmaintainingitinagivenspaceforthepurposeofchillingfoods,preservingcertainsubstances,orprovidinganatmosphereconductivetobodilycomfort.Storingperishablefoods,pharmaceuticals,orotheritemsunderrefrigerationiscommonlyknownascoldstorage.Suchrefrigerationchecksbothbacterialgrowthandadversechemicalreactionsthatoccurinthenormal

1999）.Taner（1987）andAybers（1992）statedthatthechoiceoftheidealcoolingsystemrequiresgoodcalculationloadandallsourcesofcoolingloadmustbetakeintoconsideration.AccordingtoErol（1993）,determinationofallinputsofcoolingloadwouldnotbepossible,forthisreasontheremaybesomedeviationsinthecoolingloadandthefocuspointmustbeminimizingthedeviation.

Itisexplainedthattheambienttemperatureofcoldstorage,thesituationofstoredproductbeforeenteringtothecoldstore,thedailyworkinghoursandthedeterminationofwhichproductwillbestoredareimportantforcalculationofthecoolingload（Anonymous,1994）.

Thecapacityofthecompressormustbeenoughtosuckandtopumpthecoolinggastothecompressor（Savas,1987）.

Preparingofaninvestmentplanandfeasibilityanalysesforthecoldstoragemustbefirsttodesignacoldstore.Thelocationofthecoldstorage,thedistanceofthestoragetothestoredproduct,transportation,distancetomarket,thedecisionaboutproductstobestoredandaimofthecoldstoragemustbedetermined.Theobjectivesofconstructingacoldstoragemustbetodesignitnotonlyforaspecificproductbutalsofordifferentkindofproducts.Thedesignofsomesmallcoldroomsinsteadofabigcoldstorageaduetotheimpossibilityofcoldstorageofmorethanoneproductminimizestheenergycostandunforeseen.

Forthecalculationofthecoolingloadoftheenvironment,detailedconstructiondesigninformationusedascoldstoreandmeteorologicalconditionsarerequired.Thestepsgivenbelowmustbefollowed（Anonymous,1998c）.

Datacollection:

Buildingcharacteristics（constructionmaterials,buildingsize,colouroftheoutsideofthebuildingandshape）,locationofbuilding（obtainedfromtheconstructionplan）,outsideenvironmentconditions,meteorologicaldata,approvedoutsideenvironmentconditionsfortheproject）,interiorenvironmentalprojectconditions（dryandwetthermometertemperatures,amountoftheventilation）,managementstrategy,operatingdateandtimemustbeselected.

J.AppliedSci.,8（5）:

788-794,2008

Datausage:

Aftercollectingtherelateddata,thecoolingloadmaybecalculatedaccordingtothedeterminedenvironmentalconditions.

Inthisstudy,thewayofcalculationofthecoolingloadforthedesignofcoldstorageandtheselectionofthecoolingsystemelementsaretriedtobeexplained.Howtodesignacoldstorageisexplainedbytheuseofdifferentliteratures.

CALCULATIONOFCOOLINGLOAD

Whiledeterminingtheoutsidetemperatureforcalculationofcoolingload,theaveragetemperatureofthehottestmonthintheyearistakenintoaccount.

Inordertocalculatetheheatloadincoldstorage,theheatamountoftheproducedheatbyallsourcesshouldbedeterminedandsummed.

Theloadoftheheatconsistsofthetransmissionheat（q.）,infiltrationheat（~）,productsheat（q.）,otherheatsources（q4）andunknownandunexpectedheat（q5）forthecalculationofthecoolingload（Ozkol,1999）.Calculationswererealizedaccordingtotheabovegivenexplanations.

Transmissionheat（ql）:

Thecalculationofthetransmissionheatcreatedbywalls,floorandceilingrequiresinformationonthicknessandtypeofisolationmaterialusedinconstructionofcoldroom,constructionofbuilding,physicalspecificationsofthecoldstoragevolume,insideandoutsideenvironmenttemperaturesandtheeffectofsunshine.Followingequationswereusedtocalculatetransmissionheat（Taner,2005;Anonymous,1996b,2001）.

Where:

=Heattransmissionatflatsurface（W）

K=Totalheattransmissioncoefficient（

）

A=Areaofheattransmission（

）

=Temperatureofoutsideorneighbourvolume（K）

=Insidevolumetemperature（K）

（2）

Where:

=Coefficientofheattransmissionofoutsidesurface（

）

=Coefficientofheattransmissionofinsidesurface（

）

=Materialthickness（rn）

=Thermalconductivity（

）

HeattransmissioncoefficientscanbeselectedfromdifferentliteraturessuchasOzkol（1999）andAnonymous（2001）.

Followingequationisusedforpracticalcalculations（Taner,2005）.

（3）

Maineffectivefactoronoverallheattransmissioncoefficient（K）isthermalconductivity（

）andmaterialthickness.Theeffectofotherfactorscanbegenerallyneglected.Thicknessesofisolationmaterialsdetermineduetoinvestmentandmanagementcosts.Koverallheattransmissioncoefficientcanbetakenbetween0.25and0.06

.

Thecalculationof

"outsidetemperature"isdeterminedaccordingtothehottestmonthoftheyear.However,asmallervalueoftheoutsidetemperaturemaytakeintoaccountbecauseofeconomicalreasons.Throughbenefitingfromtheinformationoflong-termtemperaturedata,calculatedoutsidetemperatures,wetanddrytemperaturedataarealsogivenbyOzkol（1999）.

Infiltrationheat（

）:

Theinfiltrationheatloadisdefinedasthevalueobtainedthroughtheentranceoftheairwithahigherenthalpytothecoldstoeage.

Somestructuraldeformationssuchaswindows,doorsandwalls,whichcausetoairleakagemayoccur.Airleakagecreateadditionalheatloadduringthecoldstorage.Thisheatloadcanbecalculatedbyusingfollowingequation（Erol,1993;Anonymous,1998c）.

（4）

Where:

=Heatproducedbyairchangingandleakageair（

）

=Specificheatofhumidair（1300

）（Erol,1993）

=Dailynumberofairexchanging（Erol,1993;Anonymous,2001）

=Volumeofcoldstorage（

）

=Storagetemperature（K）

Productheat（

）:

Themostimportantfactorforthedeterminationoftheinsidetemperatureisthepurpose

ofthecoldstorageuse.Insidetemperaturerequiredforcoolingisdefinedasstoragetemperature（Erol,

1993）.

Thefactthatsomestoredproductscontainwaterintheirstructure,causetosomechangessuchasthedecreaseofthetemperatureduringstorage,thecondensationofwatervapour,waterandliquidfreezing,heatoutcomeifanychemicalreactiontakesplace.

J.AppliedSci.,8（5）:

788-794,2008

Storedproductwhichcontainwaterintheirstructurecreateheatloadbylosingtheirlatentheatwhilecondensationorfreezing.

Itisknownthatstoredproductsespeciallyfruits,vegetablescontinuetheirvitalityafterharvestingandtheydiffuseheatasaresultofsomechemicalreactionstotheirenvironmentduringthisperiod（Erol,1993;Anonymous,1998b;Cemerogluetal.,2001）.

Ifcoldstoredmaterialsareplacedintoplasticorwoodenboxes,heatloadoftheseboxesmustbetakenintoconsideration.

Equation5calculatesheatloadcreatedbycoldstoredproduct（Cemerogluetal.,2001）.

（5）

Where:

=Heatproducedbycoolingabovefreezingpoints（W）

=Heatmustbetakenduringfreezing（W）

=Deepcoolingafterfreezingofcoldstoredproduct（W）

=Maturationheat（W）

Coolingmaybeclassifiedasshort-termcoldstorageandlong-termcoldstorage

Calculationofheatloadpre-coolingabovefreezingpoint（

）:

Precoolinglengthenstoragetimeaftermakingtheproductwaitfor24hinacoldroom.

Theamountofheat,whichmustbetakenfromstoredproducttodecreaseitstemperaturetocoldroom'stemperatureandheatusedtodecreasetemperatureofstoredproductfromt1tot2,canbecalculatedwiththefollowingequation.

Where:

q31Heatproducedbycoldstoredproduct（W）

GAmountofthestoredproduct（kg）

CISpecificheatuptoproductfreezing（kJkg-IK）

（Anonymous,1998b,2001）

TcutOutsidetemperature（K）

T,Insidetemperature（K）

M,Coolingtime（h）

LFLoadingfactor

Productsmaybeplacedintopre-coolingroomsbeforebeingplacedintostorages.Thegreatdifferencesbetweenthetemperatureoftheproductandthestoragecausetoexcessiveworkofevaporators.Thisistakenintoconsiderationasloadingfactorduringthecalculationofcoolingload.TheloadingFactorisonlyrequiredforcoldstoreswhichhasapre-coolingroom.

Weightofthedailyboxesenteredtocoldstoreiscalculatedasfollows:

（7）

Where:

=Totalnumberofboxesforacoldstore

=Weighofabox（kg）

Heatproducedwhilefreezing（q32）

Where:

Heatproducedwhilefreezing（W）

Freezingheatofstoredproduct（Jkg-I）

Freezingtime（h）（Anonymous,1998a）

Deepcoolingafterfreezing（q33）

Where:

q3JDeepfr