Refrigeration and Air conditioning - Rajagiri School of ...

1 Introduction to Refrigeration and Air conditioning Refrigerationisaprocessofachievingandmai ntainingalowtemperaturebelowthatofsurrou ndingsWhich of the following can be called as a Refrigeration process??a)Coolingofhotingotfrom10000 Ctoroomtempb)Coolingofapotofwaterbymixin gitwithalargeblockoficec)Coolingofhumanb eingsusingaceilingfand)Coolingofhotwater bymixingitwithtapwatere)Coolingofwaterby creatingvacuumoveritf)Coolingofahotcupof coffeebyleavingitonatableSYLLUBUSMODULE 1 Introduction , Airrefrigerationsystems-ReversedJoulecyc le,Aircraftrefrigerationsystems, 2 Vortextuberefrigeration-Verylowtemperatu rerefrigerationsystems(conceptonly).Adia baticdemagnetizationofparamagneticsalts. methodsofimprovingCOPofsimplecycle-super heating,undercooling,Liquidsuctionheatex changer, 3 Refrigerantsandtheirproperties-Eco-frien dlyRefrigerants,mixedrefrigerants,select ionofrefrigerantsfordifferentapplication s. Vapourabsorptionsystems-Ammonia 4 ,quick-freezing. Refrigerationsystemcomponents-Compressor s,condensers,expansiondevices, chargingofrefrigerant 5 Airconditioning-meaningandutility, ,dry,wetanddewpointtemperature humidity,specifichumidity,absolutehumidi ty, ,Psychrometricchart-Psychometricprocesse s-adiabaticmixing-sensibleheatingandcool ing-humidifyinganddehumidifying, ,stateandmassrateofdehumidifiedairquanti ty-Freshairsupplied-airrefrigeration.

2 6 , Airdistributionsystems-ductsystemanddesi gn-Airconditioningofrestaurants,hospital s,retailoutlets,computercenter,cinemathe atre, BOOKST/RBOOK TITLE/AUTHORS/PUBLICATION ,RefrigerationandAir- conditioning ,McGraw -Hill, ,RefrigerationandAir- conditioning ,Dhanpa tRai, ,RefrigerationandAir- conditioning ,Khanna Publishers,NewDelhi,2014T4 ManoharPrasad,RefrigerationandAir-Condit ioning,NewAgeInternational, ,RefrigerationandAir- conditioning ,McGraw -HillPublishingCompany, ,PrinciplesofRefrigeration,PearsonEducat ionIndia, ,BasicRefrigerationandAir- conditioning , , TheJews,theGreeks,RomansandtheEgyptiansd idnotuseiceandsnowtopreservefood,butprim arilyasameanstocoolbeverages. 500BC TheYakhchal(meaning"icepit"inPersian)isa nancientPersiantypeofrefrigerator. Thestructurewasbuiltofawaterresistantmor tarcalledSAROOJ,thatisresistanttoheattra nsfer,intheshapeofadomeabovetheground. Itwasoftenusedtostoreice,butsometimeswas usedtostorefoodaswell. Icehousesarebuildingsusedtostoreicepacke dwithinsulation,oftenstraworsawdust.

3 IceHousewouldbenearariverorstream,anddee pinthegroundtomaximizerefrigeration. Theicetrade,alsoknownasthefrozenwatertra de,wasa19th-centuryindustry,centeringont heeastcoastoftheUnitedStatesandNorway,in volvingthelarge-scaleharvesting,transpor tandsaleofnaturalicefordomesticconsumpti onandcommercialpurposes. In1806,FredericTudor,(latercalledasthe IceKing )begunthetradeinicebycuttingitfromHudson Riverandexportsit. MostIceBoxesweremadeofwoodwithaninterior linedwithtin, ,longer. Becausetheicewouldeventuallymelt, Icewasmadebykeepingathinlayerofwaterinas hallowearthentray,andthenexposingthetray tothenightsky. ThewaterloosesheatbyradiationtotheStrato sphere,whichisataround-550 Candbyearlymorninghoursthewaterfreezesto ice. coolingArtificialRefrigeration ScottishprofessorWilliamCullendesignedas mallrefrigeratingmachinein1755. Cullenusedapumptocreateapartialvacuumove racontainerofdiethylether,whichthenboile d,absorbingheatfromthewaterwhichisinther malcontact. Vaporpressure&LatentheatJacobPerkins(9 July1766 30 July1849)wasanAmericaninventor, , Perkinsiscreditedwiththefirstpatentforth evapor-compressionrefrigerationcycle,ass ignedonAugust14,1835andtitled,"Apparatus andmeansforproducingice,andincoolingflui ds.

4 TheideahadcomefromanotherAmericaninvento r,OliverEvans,whoconceivedoftheideain180 5butneverbuiltarefrigerator. prototypewasn JohnGorrie(October3,1802 June29,1855)wasaphysician,scientist,inve ntor,andhumanitarian HereceivedhismedicaleducationattheColleg eofPhysiciansandSurgeonsoftheWesternDist rictofNewYorkinFairfield. After1845, ,1851, Electric Refrigerator WhiletheuseoftheIceBoxlastedintothe20 s& 30 s, CYCLE Refrigeration SYSTEMSASSUMTIONS Theworkingfluidisafixedmassofairthatbeha vesasanidealgas. Thecycleisassumedtobeaclosedloopcycle. Alltheprocesseswithinthecyclearereversib le. Carnot cycle Ideal reverse Brayton cycle(Joule or Bell-Coleman cycle) Process1-2:Reversible,adiabaticcompressi oninacompressor Process2-3:Reversible,isobaricheatreject ioninaheatexchanger Process3-4:Reversible,adiabaticexpansion inaturbine Process4-1:Reversible,isobaricheatabsorp tioninaheatexchanger Forfixedheatrejectiontemperature(T3)andf ixedrefrigerationtemperature(T1), reverse Brayton cycle TheactualreverseBraytoncyclediffersfromt heidealcycledueto:a)Non-isentropiccompre ssionandexpansionprocessesb)Pressuredrop sincoldandhotheatexchangers Thenetworkinputincreasesduetoincreaseinc ompressorworkinputandreductioninturbinew orkoutput.

5 Therefrigerationeffectalsoreducesduetoth eirreversibilities. Asaresult,theCOPofactualreverseBraytoncy cleswillbeconsiderablylowerthantheidealc ycles. TYPESO pensystems Coldairattheexitoftheturbineflowsintoaro omorcabinandcoldHXdoesn texist. Willtakefreshairfornextcycle. Insuchacase, Thesamegas(air)flowsthroughthecycle. Lowsidepressurecanbeaboveatmospheric. Thesesystemsareknownasdenseairsystems. Gasesotherthanair( ) cooling systemsWhycoolingsystemsinAircraft??? Largeinternalheatgenerationduetooccupant s,equipmentetc. Heatgenerationduetoskinfrictioncausedbyt hefastmovingaircraft Rameffect Airischeap,safe, Coldaircandirectlybeusedforcoolingthusel iminatingthelowtemperatureheatexchanger( opensystems)leadingtolowerweight. Maincompressoroftheaircraftitselfcanbeus edforcompression. Types aircraft Refrigeration cycle Theoutsidelowpressureandlowtemperatureai r(state1)iscompressedduetorameffecttoram pressure(state2). Thepoweroutputoftheturbineisusedtodrivet hefan,whichmaintainstherequiredairflowov ertheaircooler.

6 Duetoirreversibilities,theactualpressure attheendoframmingwillbelessthanthepressu reresultingfromisentropiccompression. Theratioofactualpressurerisetotheisentro picpressureriseiscalledas:Ramefficiency, Ram= Thissimplesystemisgoodforgroundcooling(w hentheaircraftisnotmoving) system Thissystemconsistsoftwoheatexchangers(ai rcoolerandaftercooler). Italsoincorporatesasecondarycompressor,w hichisdrivenbytheturbineofthecoolingsyst em. Thissystemissuitableforhighspeedaircraft ,whereinthevelocityoftheaircraftprovides thenecessaryairflowfortheheatexchangers. Aseparatefanisnotrequired, Ambient System Usedinveryhighspeedaircraftapplication. Atveryhighspeedtheramairtemperatureistoo hightoworkasagoodHXcoolant. Soitexpandsinthefirstcoolingturbinebefor eitusedinHXascoolant. Cooling System Alsousedinhighflightspeedsie,supersonica irplanes. Partofthecooledairtothecabinfromthecooli ngturbineisusedtocooltheairintheregenera tiveHXafterramaircooling. ForhigherandhigherspeedBootstrapEvaporat ivetypeisalsoused.

7 Evaporative Ty