制冷外文文献.docx

制冷外文文献.docx

《制冷外文文献.docx》由会员分享，可在线阅读，更多相关《制冷外文文献.docx（23页珍藏版）》请在冰豆网上搜索。

制冷外文文献

Keywords:

Steady-statesimulation、Semi-empiricalmodel、Domesticrefrigerators、Experimentalvalidation

1.Introduction

Ahouseholdrefrigeratoriscomposedofathermallyinsulatedcabinetandavapor-compressionrefrigerationloopasshowninFig.1.Theserefrigerationsystems,onthewhole,consumealargeamountofenergysincehundredsofmillionsarecurrentlyinuse,anddozensofmillionsarecomingontothemarketeveryyear.Anunderstandingoftheoperationalcharacteristicsofarefrigerationsystemisvitalforanyenergyoptimizationstudy,notonlytopredictitsperformance,butalsotoaidthedecisionmakingduringthedesignprocess.

Therefrigeratorperformanceisusuallyassessedbyoneofthefollowingapproaches:

（i）simplifiedcalculationsbasedoncomponentcharacteristics;（ii）componentanalyzesthroughcommercialCFDpackages;and（iii）standardizedexperiments.Althoughthefirsttwotechniquesplayimportantrolesincomponentdesign,theydonotprovideenoughinformationoncomponentmatchingandsystembehavior,whichisonlyobtainedbytestingtherefrigerator

inacontrolledenvironmentchamber.Thesetests,however,aretimeconsumingandexpensive.Afasterandlesscostlyalternativeistheuseofcomputermodelstosimulatethethermal-andfluid-dynamicbehaviorofrefrigerationsystems.

Manymathematicalmodelshavebeenproposedinthepastforrefrigeratormodeling.Inoneoftheearlieststudies,DavisandScott[1]developedamathematicalmodeltopredictthesteady-statecomponentbehavioroverarangeofoperatingconditions,consistingofindividualcomponentsub-modelsthatcombinedfirst-principleswithanumberofempiricalparametersobtainedfromtheliterature.Simplisticmodelswereusedforheatexchangersastheevaporatingandcondensingpressureswereassumedtobeknown.Thecompressormodel,ontheotherhand,consideredthein-cylindercompressionandthepressuredropsinthesuctionanddischargevalves.Nomodelhasbeenprovidedfortheexpansion

device.

Afewyearslater,theUnitedStatesDepartmentofEnergy（USDOE）sponsoredthedevelopmentofasteady-statesimulationmodelforhouseholdrefrigerators,whichwasintendedtobeadoptedasareferencetoestablishtheenergytargetsforAmericanhouseholdmanufacturers[2].BasedontheUSDOEmodel,severalincrementalstudieswerethencarriedout.First,Abramsonetal.

[3]incorporatedasub-modelforthecapillarytube-suctionlineheatexchanger,andthemodelwasadaptedtosimulateatwo-door‘Combi’refrigerator.Later,Reevesetal.[4]improvedtheoverallcomputationalperformanceusingthee-NTUmethodforheatexchangermodeling,andpolynomialfitsforthecompressormassflowrateandpowerconsumption.

Morerecently,Kleinetal.[5]proposedafirst-principlesmodelforsimulatingthesteady-statebehaviorofa230-lall-refrigerator,whichcomprisedthefollowingcomponentsub-models:

anaturaldraftwire-and-tubecondenser,aplate-type‘roll-bond’evaporator,acapillarytube-suctionlineheatexchanger,ahermeticreciprocatingcompressor,andaninsulatedcabinet.Themodelwasestablishedbasedonthemass,momentumandenergyconservationlaws,heattransferequations,equationsofstateoftheworkingmediaandempiricalcorrelationsderivedfromexperimentaldata.Thecapillarytube-suctionlineheatexchangersub-modelwasderivedfromamoresophisticatedmodel[6]throughafractionedfactorialdesigntechnique,whilstthecompressorsub-modelwasbasedoncurvefittingsofcalorimetricdata.

Inallofthestudiesmentionedabove,themodelsdependedonreliablecomponent-levelperformancedata,whichrequiredpurpose-builtexperimentalfacilitiesfortestingeachcomponent.Inthepresentstudy,therequiredempiricalinformationwasgathereddirectlybytestingtherefrigeratorinacontrolledtemperatureandhumiditychamber.Inordertodoso,therefrigerationsystemwasproperlyandcarefullyinstrumentedtominimizeanyaffectonitsperformance.Theconservationlawswereemployedtoestablishthegoverningequationsthatdescribethesystembehavior.Eachcomponentwasmodeledusingalumpedapproach,basedonphysicalprinciplesandemployingempiricalparameters（e.g.,heattransfercoefficientsandfrictionfactors）,adjustedtofittheexperimentaldata.Themodelshowedgoodagreementwithexperimentaldataduringthevalidationexercise.

2.Experimentalwork

Thetestswereperformedwitha430-ltop-mountfrost-freerefrigerator,assembledwithahermeticreciprocatingcompressor,anaturaldraftwire-and-tubecondenser,andatube-fin‘no-frost’evaporator.ThesealedsystememployedHFC-134aastheworkingfluid（130g）andsyntheticoilasthelubricant（250ml）.Theairtemperaturesinthefreezerandinthefresh-foodcompartmentswerecontrolledbyathermostatandbyathermostaticdamper,respectively.

Therefrigeratorwasinstrumentedandinstalledinsideanenvironmentchamber.T-typethermocoupleprobeswereimmersedintherefrigerantflowpassageandabsolutepressuretransducerswithameasurementuncertaintyof±0.1%ofthefullscalewereinstalledatsevenpointsalongtherefrigerationloop,asshowninFig.1.ACoriolis-typemassflowmeterwithameasurementuncertaintyof±0.03kg/hwasinstalledatthecompressordischarge.Thesurroundingairtemperaturewasmeasuredbyfivethermocouplesplacedaroundtherefrigerator.Thefreezerandthefresh-foodairtemperaturesweremeasured,respectively,bythreeandsixthermocouplesplacedwithinthesecompartments.AllT-typethermocouplesemployedinthisstudyhaveameasurementuncertaintyof±0.3C.Thecompressorandfanpowerconsumptionweremonitoredusingadigitalpoweranalyzerwithameasurementuncertaintyof±0.1%.A112-channelsystemwasemployedfordataacquisition.Testswereperformedbeforeandaftertheinstrumentationsetuptocheckforanydiscrepanciesinthesystemperformance.

Additionaladjustmentswereintroducedintothesystemtoallowtheobtainmentofthedesiredinformation.Aneedlemeteringvalvewasinstalledasanauxiliaryexpansiondeviceupstreamofthecapillarytube.Theoriginalfixedcapacitycompressorwasreplacedbyavariablecapacitycompressor.Thewallheatloopwasby-passedandthedefrostheaterswereturnedoff.Thethermostatic

mechanismofthedamperwasremovedandtheaperturewaskeptconstantlyopened.Thecompressorandfanpowerconsumptionandspeedwerecontrolledandmeasuredindependently.ThecompressorpowerconsumptionandspeedweremeasuredwithaYokogawaWT230poweranalyzer.Thefanspeedwasmeasuredusinginfraredlight.Intotal,13variableswereexperimentallystudied,sevenweregeometriccharacteristicsofthesystemandtheothersixwereoperationalvariables.

Thegeometriccharacteristicswerevariedindifferentcombinationswhichgeneratedeightdifferentsystemconfigurations,asshowninTable1.Eachconfigurationwastestedcontrollingthefollowingsixoperationalvariables:

（i）ambienttemperature;（ii）compressorspeed;（iii）refrigerantcharge;（iv）auxiliaryexpansiondeviceopening;（v）fanspeed;and（vi）internalheating.Atotalof168testswereperformed,approximately20testsforeachconfiguration.Independentexperimentalsetupswereusedtomeasurethecapillarytubeinnerdiameter,theinternalvolumesofthecomponents,andthecabinetoverallthermalconductance.Therangeoftestedconditionsisshowedinthepressure–enthalpydiagramofFig.2.Itisworthofnotethatthisdatasetcanalsobeusedforcomponentanalysis.

Fig.1.Schematicrepresentationofthevapor-compressionloop.

3.Mathematicalmodel

Formodelingpurposes,therefrigerationsystemwasdividedintofivecomponentsub-models:

（i）compressor,（ii）capillarytube-suctionlineheatexchanger,（iii）condenser,（iv）evaporator,and（v）refrigeratedcabinet.Eachofthecomponentsub-modelsaredescribedbelow.Moredetailedinformationcanbefoundin[7].

3.1.Reciprocatingcompressor

Inmostreciprocatingcompressors,theenteringrefrigerantpassessuccessivelythroughthecompressorshell,thesuctionmufflerandthesuctionvalvetothecompressionchamber,whereitisexpelledthroughthedischargevalvetothedischargemuffler.Thecompressormassflowrateequationwasbasedonthevolumetricefficiency,ƞ

asdefinedby[8]

（1）

wherewandNarethecompressormassflowrate（kgs

）andspeed（s

）,respectively,V

isthecompressionchambervolume（m

）,andv

isthespecificvolumeatthecompressorinlet（m

kg

）.

Thecompressordischargeenthalpy,h

wasobtainedfromanoverallenergybalance

（2）

whereƞ

istheoverallcompressionefficiency.ThecompressionpowerW

wascalculatedasfollows:

（3）

Thecompressorheatreleaseratewascalculatedbyanoverallthermalconductance,UA

relatedtothetemperaturedifferencebetweenthedischargeline,t

andthesurroundingair,t

.

Thecompressorvolumetricandoverallefficiencyvaluesandtheoverallcompressorthermalconductancewereallfittedtotheexperimentaldata,yielding

whereUA

isgivenin（WK

）,p

andp

in（bar）,t

andt

in（

C）,andNin（rpm）.AscanbeseeninFig.3,thissetofequationspredictstheexperimentaldataformassflowrate（Fig.3a）andpowerconsumption（Fig.3b）within±10%errorbands,andthecompressordischargetemperature（Fig.3c）withdeviationsof±5

C.

Fig.3.Validationofthecompressorsub-model:

（a）massflowrate,（b）power

consumptionand（c）compressordischargetemperature

3.2.Heatexchangers:

condenserandevaporator

Thecondenserisanaturaldraftwire-and-tubeheatexchanger,inwhichtheair-sidetemperatureisassumedtobeuniform.Thecondenserwasdiv