冷却系统利用流体吸热交换器 毕业设计外文翻译Word格式文档下载.docx
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冷却系统利用流体吸热交换器 毕业设计外文翻译Word格式文档下载.docx
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CollegeofEngineeringUniversityofWisconsin-Madison
Abstract
Heattransferdevicesareprovidedinmanyrefrigeration systemstoexchangeenergybetWeenthecoolgaseousrefrigerantleavingtheevaporatorandWarmliquidrefrigerant exiting the condenser. These liquid-suction or suction-line heatexchangerscan,insomecases,yieldimprovedsystemperformanceWhileinothercases they degrade system performance. Although previous researchers haveinvestigated performance ofliquid-suction heat exchangers, thisstudy canbedistinguishedfromthepreviousstudiesinthreeWays.First,thispaperidentifiesaneW dimensionless group to correlate performance impacts attributable toliquid-suction heatexchangers.Second,thepaperextendspreviousanalysestoincludeneWrefrigerants.Third,theanalysisincludestheimpactofpressuredropsthroughtheliquid-suctionheatexchangeronsystemperformance.ItisshoWnthatrelianceonsimplifiedanalysistechniquescanleadtoinaccurateconclusionsregardingtheimpactofliquid-suctionheatexchangersonrefrigerationsystemperformance.Fromdetailedanalyses,itcanbeconcludedthatliquid-suctionheatexchangersthathaveaminimalpressurelossontheloWpressuresideareusefulfor
systemsusingR507A,R134a,R12,R404A,R290,R407C,R600,andR410A.The
liquid-suctionheatexchangerisdetrimentaltosystemperformanceinsystems usingR22,R32,andR717.
Introduction
Liquid-suctionheatexchangersarecommonlyinstalledinrefrigerationsystemsWiththeintentofensuringpropersystemoperationandincreasingsystemperformance.Specifically,ASHRAE(1998)statesthatliquid-suctionheatexchangersareeffectivein:
1)increasingthesystemperformance
2)subcoolingliquidrefrigeranttopreventflashgasformationatinletstoexpansiondevices
3)fullyevaporatinganyresidualliquidthatmayremainintheliquid -suctionprior
toreachingthecompressor(s)
Figure1illustrates asimple direct-expansion vaporcompression refrigerationsystem utilizing aliquid-suction heat exchanger. In this configuration, hightemperature liquidleavingtheheatrejection device(anevaporative condenserinthiscase)issubcooled priortobeingthrottled totheevaporator pressure byanexpansiondevicesuchasathermostatic expansionvalve.Thesinkforsubcooling
浙江海洋学院毕业设计
theliquidisloWtemperature refrigerant vaporleavingtheevaporator. Thus,theliquid-suctionheatexchangerisanindirectliquid-to-vaporheattransferdevice.The
vapor-sideoftheheatexchanger(betWeentheevaporatoroutletandthecompressor
suction)isoftenconfiguredtoserveasanaccumulatortherebyfurtherminimizingtheriskofliquid refrigerant carrying-over tothecompressor suction. IncasesWheretheevaporatoralloWsliquidcarry-over,theaccumulatorportionoftheheatexchangerWilltrapand,overtime,vaporizetheliquidcarryoverbyabsorbingheat
duringtheprocessofsubcoolinghigh-sideliquid.
Background
StoeckerandWalukas(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)alsocomparedtheASHRAEmethodforpred
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