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1、Experimenta1eva1uationofacascaderefrigerationsystemprototypewithCO2andNH3forfreezingprocessapp1icationsABSTRACT:AprototypeofacascaderefrigerationsystemusingNH3andCO2asrefrigerantshasbeendesignedandbui1t.Theprototypeisusedtosupp1ya9RWrefrigerationcapacityhorizonta1p1atefreezeratanevaporatingtemperatu
2、reof50aCasdesignconditions.Theprototypeinc1udesaspecificcontro1systemandadataacquisitionsystem.Theexperimenta1eva1uationstartedwiththerea1conditionswithinthedesignoperatingparameters.Subsequent1y,severa1testswereperformedfixingfourCO2evaporatingtemperatures(-50aC,-45aC,-40aCand-35aC).Ateachoneofthee
3、vaporatingtemperatureseva1uated,theCO2condensingtemperaturewasvariedfrom-17.5aCto-7.5aCandanexperimenta1optimumva1ueofCO2condensingtemperaturewasdetermined.Thediscussionsontheexperimenta1resu1tsinc1udetheinf1uenceoftheoperatingparametersonthecascadesystem,sperformance.Inaddition,theexperimenta1resu1
4、tsarecomparedwithtwocommondoub1estagerefrigerationsystemsusingNH3asrefrigerant.Keywords：RefrigerationsystemCascadesystemCarbondioxideAmmonia-deve1opmentPrototype-experimentIntroductionCurrent1ytherefrigerationindustryiswitnessingimportantchangesowingtothefactthatthesyntheticrefrigerants,whichhaveane
5、gativeimpactontheozone1ayerorconsideredresponsib1eforg1oba1warming,havebeenbannedorareintheprocessofbeingout1awedorrestrictedinthenearfuture.Asbetter1ong-terma1ternativesrep1acethem,1orentzen(1994)suggestedtheuseofnatura1substancessuchasammonia,carbondioxideandthehydrocarbonsasrefrigerants,thuscausi
6、ngarenewedinterestinthisarea.Atthebeginningofthe1astcenturyanothernatura1substance,C02,wasusedasrefrigerant.Thiswasrep1acedinthemidd1eofthe1900sbyartificia1refrigerantspresent1ybanned(Kimeta1.,2004).Recent1ypub1ishedresearchesby1orentzen(1994)andPearson(2005)pointoutthattorecommencetheemp1oymentofCO
7、2asarefrigerantoffershighpotentia1whenusedinIowtemperaturerefrigerationSystemsJnc1udedwithintheadvantagesofCO2isthatitisenvironmenta11yfriend1y,non-toxic,non-exp1osive,easi1yavai1ab1eandcanbeusedinrefrigerationprocesseswithinawiderangeoftemperatures(from50C).Inaddition,itiscompatib1ewiththeoi1scommo
8、n1yusedinactua1refrigerationsystems(Bao1ianandYufeng,2007).Itoffers1owpressureratiosandIowspecificvo1umeva1ues,whichwhencoup1edwithhighpressure1eve1sa11owsforreductioninsizeofrefrigerationcomponents(Cabe11oeta1.,2008).ThemaindisadvantagesofCO2asarefrigerantarethehighworkpressures(7.2MPaat30C).1orent
9、zen(1994)1aidspecia1emphasisonthehighpotentia1ofreinitiatingtheuseofCO2asarefrigerantintranscritica1cyc1esandincascaderefrigerationsystems.Withre1ationtothefirstcase,experimenta1resu1tsobtainedfromrefrigerationsystemprototypesdeve1opedbytheautomotiveindustry(Browneta1.,2002;1iueta1.,2005),andinheatp
10、umpsandrefrigerationsystemsfordomesticapp1ications(Neksa,2002;HwangandRadermacher,1999;Hrnjaketa1.,2000),showedsimi1arCOPva1uescomparedtotheCOPobtainedfromsystemsthatuseactua1refrigerants.Gro11andKim(2007)carriedoutanextensivecompi1ationofresu1tsobtainedfromresearchesdeve1opedoverthe1astsevera1years
11、,re1atedtotheuseofCO2intranscritica1systems.RegardingtheuseofCO2incascaderefrigerationsystems,thepairofCO2eNH3hasbeenthecentreofattentionofmuchresearchdeve1opedinrecentyears,generatinghighexpectations.EggenandAf1ekt(1998),PearsonandCab1e(2003),andVanRiessen(2004)showedpractica1examp1esoftheuseofcasc
12、aderefrigerationsystemsforcoo1inginsupermarkets.EggenandAf1ekt(1998)focusedtheirattentiononthedeve1opmentofarefrigerationsystemprototypeforamediumsizedsupermarketinNorway.PearsonandCab1e(2003)pub1ishedco11ecteddatafromarefrigerationsysteminsta11edina1oca11ineofScottishsupermarkets(ASDA).VanRiessen(2
13、004)performedtheeconomica1andtechnica1feasibi1ityofacoo1ingsystemtobeintroducedintoaDutchsupermarket.Themainscopeofthisresearchwasthedesign,constructionandexperimenta1eva1uationofacascaderefrigerationsystemprototypeusingNH3andCO2asrefrigerants,tosupp1yahorizonta1p1atefreezerwith9kWofrefrigerationcap
14、acityat50Cofevaporatingtemperature.Theexperimenta1faci1ityisequippedwithasystemcontro1tomaintaintheoperatingconditionsconstant.Theprototypedesigninc1udesadataacquisitionsystembasedona16-bitsdataacquisitioncardandaPCwhicha11owsrea1timereadingandstorageofthenecessaryvariab1estoca1cu1ateandana1yzetheop
15、eratingparametersthatout1inetheperformanceoftheprototypeandit,smaincomponents.Thediscussionsontheexperimenta1resu1tsobtainedinc1udetheinf1uenceoftheoperatingparametersonthecascadesystemsperformance.Fina11y,theexperimenta1resu1tsobtainedfromtheprototypearecomparedwithtwocommondoub1estagerefrigeration
16、systemsusingNH3asrefrigerant,andwiththesameoperatingconditions.Experimenta1prototypeThecascaderefrigerationsystemismadeoftwosing1estagesystemsconnectedbyaheatexchanger(cascadeheatexchanger).CO2isusedasrefrigerantinthe1owtemperaturesystemandNH3istherefrigerantforthehightemperaturesystem.Inthe1owtemperaturesystemCO2isevaporatedinastain1essstee1horizonta1p1atefreezer.Thep1atefreezerisoverfedwithCO21iquidusinganejector,whicha1soactsasanexpansiondevice,anda11owsthe1iquidcoming
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