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RefrigerationSystemPerformanceusingLiquid-SuctionHeatExchangersS.A.Klein,D.T.Reindl,andK.BroWnellCollegeofEngineeringUniversityofWisconsin-MadisonAbstractHeattransferdevicesareprovidedinmanyrefrigerationsystemstoexchangeenergybetWeenthecoolgaseousrefrigerantleavingtheevaporatorandWarmliquidrefrigerantexitingthecondenser.Theseliquid-suctionorsuction-lineheatexchangerscan,insomecases,yieldimprovedsystemperformanceWhileinothercasestheydegradesystemperformance.Althoughpreviousresearchershaveinvestigatedperformanceofliquid-suctionheatexchangers,thisstudycanbedistinguishedfromthepreviousstudiesinthreeWays.First,thispaperidentifiesaneWdimensionlessgrouptocorrelateperformanceimpactsattributabletoliquid-suctionheatexchangers.Second,thepaperextendspreviousanalysestoincludeneWrefrigerants.Third,theanalysisincludestheimpactofpressuredropsthroughtheliquid-suctionheatexchangeronsystemperformance.ItisshoWnthatrelianceonsimplifiedanalysistechniquescanleadtoinaccurateconclusionsregardingtheimpactofliquid-suctionheatexchangersonrefrigerationsystemperformance.Fromdetailedanalyses,itcanbeconcludedthatliquid-suctionheatexchangersthathaveaminimalpressurelossontheloWpressuresideareusefulforsystemsusingR507A,R134a,R12,R404A,R290,R407C,R600,andR410A.Theliquid-suctionheatexchangerisdetrimentaltosystemperformanceinsystemsusingR22,R32,andR717.IntroductionLiquid-suctionheatexchangersarecommonlyinstalledinrefrigerationsystemsWiththeintentofensuringpropersystemoperationandincreasingsystemperformance.Specifically,ASHRAE(1998)statesthatliquid-suctionheatexchangersareeffectivein:1)increasingthesystemperformance2)subcoolingliquidrefrigeranttopreventflashgasformationatinletstoexpansiondevices3)fullyevaporatinganyresidualliquidthatmayremainintheliquid-suctionpriortoreachingthecompressor(s)Figure1illustratesasimpledirect-expansionvaporcompressionrefrigerationsystemutilizingaliquid-suctionheatexchanger.Inthisconfiguration,hightemperatureliquidleavingtheheatrejectiondevice(anevaporativecondenserinthiscase)issubcooledpriortobeingthrottledtotheevaporatorpressurebyanexpansiondevicesuchasathermostaticexpansionvalve.Thesinkforsubcooling浙江海洋学院毕业设计2theliquidisloWtemperaturerefrigerantvaporleavingtheevaporator.Thus,theliquid-suctionheatexchangerisanindirectliquid-to-vaporheattransferdevice.Thevapor-sideoftheheatexchanger(betWeentheevaporatoroutletandthecompressorsuction)isoftenconfiguredtoserveasanaccumulatortherebyfurtherminimizingtheriskofliquidrefrigerantcarrying-overtothecompressorsuction.IncasesWheretheevaporatoralloWsliquidcarry-over,theaccumulatorportionoftheheatexchangerWilltrapand,overtime,vaporizetheliquidcarryoverbyabsorbingheatduringtheprocessofsubcoolinghigh-sideliquid.BackgroundStoeckerandWalukas(1981)focusedontheinfluenceofliquid-suctionheatexchangersinbothsingletemperatureevaporatoranddualtemperatureevaporatorsystemsutilizingrefrigerantmixtures.Theiranalysisindicatedthatliquid-suctionheatexchangersyieldedgreaterperformanceimprovementsWhennonazeotropicmixturesWereusedcomparedWithsystemsutilizingsinglecomponentrefrigerantsorazeoptropicmixtures.McLinden(1990)usedtheprincipleofcorrespondingstatestoevaluatetheanticipatedeffectsofneWrefrigerants.HeshoWedthattheperformanceofasystemusingaliquid-suctionheatexchangerincreasesastheidealgasspecificheat(relatedtothemolecularcomplexityoftherefrigerant)increases.DomanskiandDidion(1993)evaluatedtheperformanceofninealternativestoR22includingtheimpactofliquid-suctionheatexchangers.Domanskietal.(1994)laterextendedtheanalysisbyevaluatingtheinfluenceofliquid-suctionheatexchangersinstalledinvaporcompressionrefrigerationsystemsconsidering29differentrefrigerantsinatheoreticalanalysis.Bivensetal.(1994)evaluatedaproposedmixturetosubstituteforR22inairconditionersandheatpumps.Theiranalysisindicateda6-7%improvementforthealternativerefrigerantsystemWhensystemmodificationsincludedaliquid-suctionheatexchangerandcounterfloWsystemheatexchangers(evaporatorandcondenser).Bittleetal.(1995a)conductedanexperimentalevaluationofaliquid-suctionheatexchangerappliedinadomesticrefrigeratorusingR152a.TheauthorscomparedthesystemperformanceWiththatofatraditionalR12-basedsystem.Bittleetal.(1995b)alsocomparedtheASHRAEmethodforpredictingcapillarytubeperformance(includingtheeffectsofliquid-suctionheatexchangers)Withexperimentaldata.PredictedcapillarytubemassfloWofactualmeasurements.Thispaperanalyzestheliquid-suctionheatexchangertoquantifyitsimpactonsystemcapacityandperformance(expressedintermsofasystemcoefficientofperformance,COP).Theinfluenceofliquid-suctionheatexchangersizeoverarangeofoperatingconditions(evaporatingandcondensing)isillustratedandquantifiedusinganumberofalternativerefrigerants.RefrigerantsincludedinthepresentanalysisareR507A,R404A,R600,R290,浙江海洋学院毕业设计3R134a,R407C,R410A,R12,R22,R32,andR717.ThispaperextendstheresultspresentedinpreviousstudiesinthatitconsidersneWrefrigerants,itspecificallyconsiderstheeffectsofthepressuredrops,anditpresentsgeneralrelationsforestimatingtheeffectofliquid-suctionheatexchangersforanyrefrigerant.Hea