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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.

 

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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.

  We Bring Good Ideas To Life

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.