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Bryan Chambers – 16 April 2009
©1911 General Electric Company* 1/3
Vapor Compression Refrigeration CycleAn Introduction for GE Appliance Salesmen
ThepurposeofthispublicationistoeducateGEApplianceSalesmenontheVaporCompression
RefrigerationCycle – thenewlydiscoveredprocessthatmakestheGERefrigeratorpossible.Salesmen
shouldbeabletoexplainthecycletoacustomerandidentifythepartsinvolved.
TheVaporCompressionRefrigerationCycleisaprocessthatcoolsanenclosedspacetoatemperature
lowerthanthesurroundings.Toaccomplishthis,heatmustberemovedfromtheenclosedspaceand
dissipatedintothesurroundings.However,heattendstoflowfromanareaofhightemperaturetothatofa
lowertemperature.Howcanwemakethereversehappen?ThisiswheretheVaporCompression
RefrigerationCyclestepsin.
Duringthecycle,asubstancecalledtherefrigerantcirculatescontinuouslythroughfourstages.Thefirst
stageiscalledEvaporationanditisherethattherefrigerantcoolstheenclosedspacebyabsorbingheat.
Next,duringtheCompression stage,thepressureoftherefrigerantisincreased,whichraisesthe
temperatureabovethatofthesurroundings.Asthishotrefrigerantmovesthroughthenextstage,
Condensation ,thenaturaldirectionofheatflowallowsthereleaseofenergyintothesurroundingair.Finally,duringtheExpansion phase,therefrigeranttemperatureisloweredbywhatiscalledtheauto-
refrigerationeffect.Thiscoldrefrigerantthenbeginsthe Evaporation stageagain,removingmoreheatfrom
theenclosedspace.
Eachofthefourstageswillnowberevisitedindetail,explainingthephysicalchangesthatoccurinthe
refrigerantandthedevicesusedtoaccomplishthesechanges.Avisualrepresentationofthecycleis
displayedbelow.Withtheexplanationofeachstage,apictureofthepartresponsibleisincludedtoaidin
identification.
8/13/2019 Bryan Chambers - Technical Definition & Description
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Bryan Chambers – 16 April 2009
©1911 General Electric Company* 2/3
EvaporationDuringthisstage,therefrigeranttravelsthroughadevicecalledanevaporator
thathasalargesurfaceareaandtypicallyconsistsofacoiledtubesurrounded
byaluminumfins.Thecoldfluidisamixtureofliquidandvaporrefrigerantas
itbeginsthisstage.Whileflowingthroughtheevaporator,alltheliquid
evaporatesandabsorbsheatfromtheenclosedspace.Theenergyabsorbedisusedtochangethestateoftherefrigerantfromliquidtovapor.Thislowers
thetemperatureofthespace,alongwithwhateverfoodorbeveragesare
storedinit.Therefrigerantexitsthisstageasa saturated vapor.
CompressionTheheatthatwasabsorbedintheEvaporationstagemustbereleasedinto
thesurroundings,butthiswillnothappenunlessthetemperatureofthe
refrigerantishigherthantheoutsideair.Thisisthepurposeofthe
Compressionstage.Adevice,predictablycalledacompressor,raisesthe
pressureoftherefrigerantvapor.Duetobasicthermodynamicprinciples,this
causesthetemperatureoftherefrigeranttorise,leavingthestageasa
superheated vapor.Energyisneededtopowerthecompressor,whichiswhy
electricityisrequiredtooperatearefrigerator.
CondensationNowthatwehaveincreasedthetemperatureoftherefrigerantabovethatof
thesurroundings,wecandissipatetheheatnecessarytocontinuethe
process.Thisisaccomplishedwithadeviceverysimilartotheevaporator.It
alsousesacoiledtubewithaluminumfins,butmayhavedifferentdimensionsthantheevaporatortoaccommodatethedifferentstateoftherefrigerant.As
thehotvaporflowsthroughthecondenser,theoutsideairremovesenergy
andtherefrigerantbecomesasaturated liquid.Atthispointtheslightestdrop
inpressurewillinitiateevaporation,whichisthebasisforthefinalstageofthe
process.
ExpansionTobeginanewcycle,allthatmusthappenisaloweringoftherefrigeration
temperaturetobelowthatoftheenclosure.Thisisthekeytotheentirecycle,
becausethiswastheproblemthatwestartedwith.However,inthissituation
wecanutilizewhatiscalledtheauto refrigeration effect.Whenasaturated
liquidexperiencesasuddendropinpressure,asmallamountofliquidis
instantlyvaporizedandthetemperatureofthemixtureisdrasticallyreduced.
Thiscoldliquid-vapormixturecannowbeginanewcycle.Thepressuredrop
isaccomplishedbythesimplest,yetmostimportant,partofthesystem – a
simpleflowrestriction.Thispartiscommonlycalledathrottleorexpansion
valve.
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Bryan Chambers – 16 April 2009
*This is not an official copyright. Neither this document nor its author have any affiliation with GE; logos and slogans are used only to simulate
a hypothetical GE publication for the purpose of a course assignment.
SummaryTheVaporCompressionRefrigerationcycleisasimplefourstageprocessthatcoolsasmallenclosedarea
toatemperaturelowerthanthesurroundings.Duringthecycle,arefrigerantremovesheatfromthe
enclosedspaceanddissipatesittothesurroundingair.TheEvaporatordrawsheatfromthespaceasthe
coldliquid-vaporrefrigerantevaporates.TheCompressorincreasesthepressureofthevapor,which
increasesthetemperatureabovethatofthesurroundingair.TheCondenserthenreleasesheattothe
surroundingsasthehotvaporrefrigerantcondenses.ThissaturatedliquidpassesthroughtheExpansionValve,abruptlyloweringthepressureandinitiatingtheauto-refrigerationeffect.Thisdropsthetemperature
oftherefrigerantandbeginsanewcycle.
Afterreadingthisdocument,youshouldbeabletoanswermostquestionsaskedbycustomers.Ifyouare
interestedinlearningmore,contacttheGEApplianceEngineeringDepartment.
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Glossary
Evaporation Theprocessofchangingthephysicalstateofasubstancefromaliquidtoavapor.Therate
ofevaporationcanbeincreasedbyincreasingtemperature,decreasingpressure,oracombinationofboth.
Energyisabsorbedfromthesurroundingsduringevaporation.Thesteamrisingfromahotcupofcoffeeis
anexampleofevaporationthatyoucansee.
Condensation Theprocessofchangingthephysicalstateofasubstancefromavaportoaliquid.Thiscan
beaccomplishedbydecreasingtemperature,increasingpressure,oracombinationofthetwo.During
condensation,energyisreleasedintothesurroundings.Acommonexampleisthemoisturethatcollectson
theoutsideofaglasscontainingacoldbeverage.
Saturated Vapor Asubstanceisconsideredasaturatedvaporifit’sinthevaporstage,butjustbarely.This
meansthattheslightestincreaseinpressureorremovalofheatwillbegincondensation
Saturated Liquid Similartothesaturatedvaporphase,asaturatedliquidisintheliquidstage,butbarely.
Thismeansthattheslightestdecreaseinpressureoradditionofheatwillbeginevaporation.
Superheated Vapor Afiniteamountofenergymustberemovedfromasuperheatedvaporbeforecondensationbegins.Asaturatedvaporthatisheatedbecomesasuperheatedvapor.
Auto Refrigeration Effect Whenasaturatedliquidexperiencesasuddendropinpressure,asmallportion
ofthatliquidinstantlyvaporizes.Avaporcontainsmoreenergythanitsliquidcounterpartatthesame
temperature,butenergyisnotaddedtothemixture.Therefore,thetemperatureofthemixturedecreases.
Ifyouhaveeverusedanaerosolkeyboardcleanerandwerebaffledbyhowcoldthecangot,youwere
witnessingtheauto-refrigerationeffect.