冷库制冷技术知识(Cold storage refrigeration technology knowledge)

1、冷库制冷技术知识（Coldstoragerefrigerationtechnologyknowledge）Thecoldstoragerefrigerationtechnologyknowledge.Txt9loveisadropofdew,kissthedrysoil,rainitwithwarmth,withadiamondfirm,lookingforwardtotheflashinglightofthebrokensoilfertility;afreezingpointofloveinlifeisnot,itisaflowingriver,therivermakesourlifebea

2、utifulscene.ColdstoragerefrigerationtechnologyknowledgeColdstoragerefrigerationtechnologyknowledgeRefrigerationreferstotheuseofrefrigerationequipmenttoremoveheatfromalimitedspacetoreducethetemperaturetothedesiredlevel.Thisprocessisdoneby*heattransfer.Somecommonlyusedtermsforrefrigerationarebrieflyde

3、scribedasfollows:1.1temperatureThetemperatureisusedtorepresentthematerialofheatandcold,thedegreeoftemperatureoftheavailablethermometertomeasure,suchastheglassthermometer,theliquidinthepipeaftertheheatexpansion,theliquidlevelrises,thecoolingshrinkage,lowliquidlevel,theliquidlevelofsaidleveltemperatur

4、e.Hereareabriefdescriptionofseveralstandardsfortemperaturevalues.A.Celsiusunderstandardpressure,thefreezingpointofwateras0degrees,theboilingpointas100degrees,in0and100degreesbetweentheequilibriummomentinto100lattice,eachlatticeisldegrees,withthesymbolCsaid.B.Fahrenheitunderstandardpressure,thefreezi

5、ngpointofwateris32degrees,andtheboilingpointisbetween212degreesandtwobalancedcarvedinto180lattice,eachlatticeisldegrees,tosignoF.C.Kelvin(alsocalledKelvin)totheCelsiusscaleasthebasis,tothefreezingpointofwateris273.16degrees,theboilingpointofwateris373.16degrees,thetheoryofmaterialmolecularmovementto

6、stopallpointsas0degrees,withthesymbolKsaid.ThecommonlyusedscaleisCelsius,Fahrenheit,kelvin.Theconversionformulasbetweenthemareasfollows:Fahrenheitcentigrade:ChinasCelsiusconversion:Kelvinsrelationtocelsius:T=T+273.16Type:T:Kelvin,K;t:oCCelsius.1.2caloriesThetemperatureofanobjectindicatesthedegreeoft

7、hermalmotionofthematerialmolecule,andthetemperaturealsoindicatestheenergyleveloftheobject.Thisenergyiscalledheatenergy.Whenthetemperatureoftwodifferentobjectsincontact,thetemperaturegraduallytendstobeuniform,theheattransferfromhightemperaturetolowtemperatureoftheobjectobject,theobjectemitsandabsorbs

8、theheatenergyiscalled.Thecommonlyusedunitsofheatare:A.undernormalatmosphericpressure,lgramsofwaterheatingorcooling,anditstemperatureriseordecreaseldegreescentigrade,theaddedorremovedheatiscalledlcard,expressedinsymboliccal.Theclampingunitistoosmall,theprojectoftenuses1000timestorepresentkcalorkcal.T

9、hesymboliskcal.B.Britishthermalunitsunderstandardpressure,11b(LB)(11b=0.454kg)waterheatingorcooling,thetemperatureisincreasedordecreasedLoFdegreesFahrenheit,addedorremovedfromtheheatiscalledaBritishthermalunit,thesymbolisBtu.C.JouleIntheinternationalsystemofunits,theunitofheatisequaltotheunitofwork,

10、expressedinjoule.Jouleisequivalenttotheactionof1N(Newton)force,themovingpointofacommonmovingpoint,movingL,m(meters)inthedirectionofforce.Therefore,intheinternationalsystemofunits,Jouleistheunitofworkandenergy,theuseofsuchunitstosimplifythecalculation,JoulessymbolisJ.Ourlegalunitofheatisjoule.Theconv

11、ersionbetweenJouleandcardis:1kJ(kJ)=0.239kcaI(kcal)Lkcal(kcal)=4.19kJ(kJ)Othercommonlyusedconversionformulasare:1kcal(kcal)=3.969Btu(Britishthermalunit)LBtu(Britishthermalunit)=252cal(card)1kcal(kcal)=427kg.M(kgm)1kW(kw)=860kca1/h(kcal/time)1,theUnitedStatescoldton=3024kca1/h(kcal/time)1Japancoldton

12、=3320kca1/h(kcal/h)1.3specificheatWhenanysubstanceisaddedtotheheat,itstemperaturewillrise.Butwhenthesamemassofdifferentsubstancesrisesthesametemperature,theamountofheataddedisdifferent.Tocompareeachother,theamountofheatrequiredfortheLkgwatertemperatureriseby1degreesissetat4.19kJ.Asastandard,theratio

13、ofheatrequiredbyothersubstancestotheirspecificheatiscalledspecificheat.IfthetemperatureofLkgwaterincreasesbyLdegreescentigrade,thespecificheatvalueis4.19kJ(kgDEGC),whilethetemperatureofLandkgcopperincreasesbyLDEGC,only0.39kJ,andthespecificheatofcopperis0.39kJ(kg.4.19kJ).Differentmaterialshavetheirsp

14、ecificheatvalue,andthefollowingtableisthespecificheatvalueofseveralmaterials.SpecificheatvalueofseveralmaterialsMaterialname,specificheatkJ(kg*K)materialname,specificheatkJ(kg=K)water,4.19ammonia(liquid),4.609ice,2.095ammonia(gas),2.179glass,0.754air(dry),1.006copper,0.390steel,0.461Knowingthespecif

15、icheatvalueofamaterial,youcancalculatetheamountofheatneededtocoolitdown.Forexample,tocool5kg70DEGCto15DEGC,theheattoberemovedis:Q=mcD,t=5*4.19*(70-15)=l152.25,kJ:M:waterquality,kg;C:specificheatofwaterkJ(kg=K);DT:temperaturedifferenceK.1.4sensibleheatHeatingthematerialofsolid,liquidorgaseous,aslonga

16、sthesameintheformofheat,addafterthetemperatureofthematerialisincreased,thenumberofaddingheatinthetemperaturecanbedisplayed,thatdoesnotchangethephysicalformcausedbythetemperaturechangeofheatiscalledsensibleheat.Iftheliquidwaterisheated,aslongasitremainsliquid,itstemperaturerises;therefore,sensiblehea

17、tonlyaffectsthechangeoftemperature,andthesurfacedoesnotcausethechangeoftheformofmatter.Forexample,thecomputerroomoritscomputerorprogram-controlledswitchhasalargeamountofheat.Itbelongstosensibleheat.1.5latentheatWaterheatingoftheliquid,watertemperature,whenreachedtheboilingpoint,althoughtheheatadded,

18、butthewatertemperaturedoesnotrise,stayintheboilingpoint,theaddedheatonlytoturnwaterintosteamfromaliquidtoagas.Thisheat,whichdoesnotchangethetemperatureofthematerialandcausesthechangeofthestate(alsoknownasthephasechange),iscalledlatentheat.Suchasthecomputerroom,stafffever,andventilationbeltintotheair

19、moisturecontent,theseheatiscalledlatentheat.(totalheatequalsthesumofsensibleheatandlatentheat.)1.6pressureGasesarecomposedofmolecules,andmillionsofmoleculesfrequentlyhittheinnerwallofavesselinirregularmotion.Theforceactingverticallyontheunitsurfaceoftheinnerwalliscalledpressure.Inengineering,thecomm

20、onunitsformeasuringgaspressureare:kg/cm2,ormmHg(mmHg),andthelegalunitinChinaisPa(Pascal).A.atmosphericpressuresurroundstheearthsairlayer,andthepressureontheunitearthssurfaceiscalledatmosphericpressure.UsuallyexpressedinB.UnitsareexpressedinkPaPaorkPakPa.Atmosphericpressurevarieswithaltitude.Alsoduet

21、oseasonalchangesinclimateandheight.Astheatmosphericpressureisdifferent,thephysicalpropertiesoftheairandthephysicalparametersthatreflectthephysicalpropertiesoftheatmospherechange.Therefore,inthedesignandoperationofairconditioning,weshouldconsiderthesizeofthelocalairpressure,otherwiseitwillcausesomeer

22、rors.Therearethreekindsofpressure:thepressuremeasuredbyinstrument(calledworkingpressure,thatistablepressure),localatmosphericpressureandabsolutepressure.Theirrelationship:Absolutepressure=localairpressuretenworkingpressureOnlyabsolutepressureistheparameterofthemoistair.Partialpressureofwatervaporand

23、partialpressureofsaturatedwatervaporinB.Inmoistair,watervaporaloneoccupiesthevolumeofmoistairandhasthesamepressureasthewetair.Thisiscalledthepartialpressureofwatervapor,expressedinPq.Thewetairisamixtureofdryairandwatervapor,sothetotalpressureofthewetairshouldbePgbythedryair,andthepartialpressurePqof

24、thewatervaporwillbesuperposed.P=PgtenPqOrB=PgtenPqInair-conditioningengineering,thewetairconsideredistheatmosphere,sothetotalpressureofwetairPisthelocalatmosphericpressureB.Atagiventemperature,themorehumidtheairis,themorewatervaporitcontains,andthegreaterthewatervaporpressure.Whenthewatervaporconten

25、texceedsacertainlimit,theexcesswaterwillprecipitatewaterintosteam.Thisshowsthatatthispoint,themoisturecontentofthehumidairreachesthemaximum,andthesaturatedairissaturated.Itiscalledsaturatedair.Atthispoint,thepartialpressureofthewatervaporiscalledthepartialpressureofsaturatedwatervapor.Thepressuredep

26、endsonlyonthetemperature,andthehigherthetemperature,thegreaterthepressure.Atthesametime,therelationshipbetweenpressureandboilingpointisalsogreat.Loweringthepressurecanlowertheboilingpointoftheliquidandincreasetheboilingpointbyincreasingthepressure.Thus,eachpressureactingontheliquidhasacorrespondingb

27、oilingpoint.Forexample,under1.0133xl05Pa.Waterboilsat100degrees;ifthepressurerisesto2.41*105Pa,theboilingpointofwateris138degrees;ifthepressuredropsto0.43*105Pa,theboilingpointofwateris84.5degreescentigrade.Intherefrigerationsystem,theevaporationtemperatureiscontrolledbycontrollingtheevaporationpres

28、sure.1.7evaporationandboilingEvaporationreferstotheprocessofgasificationonthefreesurfaceofaliquid.Forexample,theevaporationofwater.Thecooldryingprocessofclothes.Evaporationisduetothehighenergymoleculesonthesurfaceoftheliquidtoovercomethegravitationalpullofliquidmolecules,outoftheliquidsurfaceintospa

29、ce.Inthesameenvironment,thehighertheliquidtemperature,thefastertheevaporation.Inrefrigerationengineering,manyproblemsinvolveevaporationprocess,suchashumidificationanddryingprocessincoolingtowerandairconditioning.Thehumidifierofinfraredhumidifierbelongstosurfaceevaporationprocess.Boilingistheprocesso

30、fseveregasificationinwhichbubblesareformedinsidetheliquid.Forexample,theboilingprocessofwater.Undercertainpressure,theliquidisheatedtoacertaintemperaturebeforeitbeginstoboil.Duringthewholeboilingprocess,theheatabsorbedbytheliquidisallusedforitsvolumeexpansionandphasechange,sothegasliquidtemperaturer

31、emainsthesame.Suchaselectrodes,humidifiersbelongtotheboilingprocess.1.8thermalconductivity(alsocalledthermalconductivity)Thermalconductivityisaphysicalquantitythatindicatestheabilityofamaterialtoconductheat.Ifthesametwothickmaterial,isapieceofcopper,apieceofcorkpieces,puttheminitselfthanhightemperat

32、ureenvironment,canimmediatelyfeelthetemperatureriseofthecopperblock,corkblockinashortperiodoftimedonotfeel.Thisshowsthattheabilityoftwokindsofmaterialsofdifferentheatconduction,theheatconductionabilityofthedifferentmaterialstodigitalrepresentationiscalledthermalconductivity,itsvalueisequalto:whenthe

33、materiallayerthicknessofLM,onbothsidesoftemperaturedifferenceof1degrees,throughtheLMheatconductioninthe2surfaceareaof1hthesymbolLsaid,theunitiskcal/MHC,thenationallegalunitsofW/mKorJ/mhKconversion,therelationshipbetweenthemis:1W/mK=0.860kcal/MHC.Differentmaterialshavedifferentthermalconductivity,whi

34、chisrelatedtothecomposition,densityandmolecularstructureofthematerial.Themainfactorsaffectingthethermalconductivityofthesamematerialaredensityandhumidity.Whenthedensityislarge,thecoefficientofthermalconductivityislarge,andtheheatconductivityislargewhenthehumidityislarge.1.9heatreleasecoefficientWhen

35、freezingasubstance,suchasblowingonthesurface,itfreezesfasterthanitdoeswithoutblowing.Saidheatcapacityintheconditionofdifferentphysicalquantitiesbetweenthedifferentsubstancescalledheatcoefficient,thevalueisequaltotheperhour,persquaremeter,whenthetransferbetweenfluidandsolidwalltemperatureislDEGCwhent

36、heheat.Insymbolica,theunitiskcal/(M2hDEGC),andtheinternationalsystemofunitsisW/(M2K)orJ/(M2hDEGC),andtheconversionrelationshipbetweenthemis:1W/(m,2,K)=0.860kcal/(M,2,H)1.10specificvolumeanddensityThemassofaunitvolumeofmoistairiscalleddensity.Expressedinsymbolicr:Thevolumeoccupiedbytheunitmassofmoist

37、airiscalledspecificvolume,expressedinsymbolicV,i.e.:Medium:M:thequalityofmoistair,kg;V:thevolumeoccupiedbymoistair,inM3.Thetwoarereciprocal,andthereforecanonlybeconsideredasastateparameter.1.11heattransfercoefficientTheheattransfersfromthehightemperaturesidefluidtothelowtemperaturesidefluidthroughth

38、eflatwall.Inadditiontothetemperaturedifferencebetweenthetwosidesandthesizeoftheheattransferarea,theheattransfercapacityisrelatedtothethermalconductivityoftheflatwall,thethicknessoftheflatwallandtheheatreleasecoefficientatbothsidesofthewall.Rankallfactorsintoanequation,thatis:Q=KFDt(kJ/h)Formula:Q:he

39、atdelivered(kJ/h);F:flatwallsurfacearea(M2);DT:temperaturedifferenceDt=T1-T2(DEGC);K:heattransfercoefficientkJ/(M2hDEGC)Kistheheattransfercoefficient,whichisnumericallyequaltotheheatdeliveredbythecoldfluidfromonesideoftheheattotheothersidewhenthetemperaturedifferencebetweenthetwosidesislDEGC,andtheL

40、andHpassthroughtheLM2heattransferarea.TheunitiskJ/(M2hDEGC)orW/(m,2,K).1.12humidityHumidityistheamountofwaterthatindicatestheamountofwatervaporinwetair.Therearethreewaysofexpressingit.A.absolutehumidityLm3thequalityofhydroussteaminmoistair.ThesymbolisZ,andtheunitiskg/m3:Formula:MQ:steamquality,unitk

41、g;V:thevolumeoccupiedbywatervapor,thatis,thevolumeofmoistair,theunitism3.Absolutehumidityisnotconvenienttouse.Itdoesnotdirectlyreflectthedrynessandhumidityofthemoistair.B.moisturecontentTheamountofwatervaporperkilogramofdryairiscalledmoisturecontent.ThesymbolisD,andtheunitiskg/kg(dry):Medium:MQ:weta

42、irwatervaporquality,unitkg;Mg:wetairdryairquality,unitkg.B.relativehumidity,wetair,partialpressureofsteam,andtheratioofpartialpressureofsaturatedwatervaporatthesametemperaturearecalledrelativehumidity.SymbolJmeans:Pq:watervaporpressurePqb;atthesametemperature,saturatedwatervaporpressure,fromtheformu

43、lacanbeseen,Jvalueissmall,indicatingthattheairisdry,onthecontrary,theairishumid.WhenJ=0,fordryair;J=100%,forsaturatedair.ThedrynessandhumidityoftheaircanbedirectlyseenfromthesizeoftheJ.JandDareparametersofairhumidity,themeaningisdifferent,Dsaidthewatervaporcontent,butnotairclosetosaturationdegree;wh

44、ileJcanexpresstheairclosetothesaturationlevel,butnotthatofwatervaporcontent.1.13dewpointtemperatureAtacertainatmosphericpressure,themoistureintheaircondensesintowater(condensation)whenthemoisturecontentisconstant.WhentheDisconstant,theairtemperaturedropsfromaunsaturatedstatetoasaturatedstate,atwhich

45、pointtherelativehumidityoftheairisj=1O0%.Inairconditioningtechnology,theairiscooledtodewpointtemperaturetoachievethepurposeofdehumidifyinganddryingtheair.BasicknowledgeofcoldstorageThefirststep:thechoiceofcoldstorageaddressAccordingtothenatureoftheuse,coldstoragecanbedividedintostoragecoldstorage,re

46、tailcoldstorage,productioncoldstorageofthreecategories.Theproductioncoldstorageisbuiltintheproducingareawherethesupplyofgoodsisrelativelyconcentrated,andthefactorsoftransportationconvenience,marketconnectionandsoonarealsoconsidered.Coldstorageisbestbuiltinacoolplacewherethereisnosunlightorhotair,and

47、smallcoldstorageisbestbuiltindoors.Thereshouldbegooddrainageconditionsaroundthecoldstorage,thegroundwaterlevelshouldbelow,itisbettertohaveabarrieratthebottomofthecoldstorage,andkeeptheventilationwellandkeepdry,whichisveryimportanttothecoldstorage.Inaddition,beforetheconstructionoftherefrigerator,the

48、three-phasepowersupplyshouldbeinstalledaccordingtothepowerofthechiller.Ifthecoldstorageiswater-cooled,thetapwaterpipeshouldbelaidandthecoolingtowershouldbebuilt.Thesecondstep:determinethecapacityofcoldstorageThesizeofthecoldstorageshouldbedesignedaccordingtothemaximumamountofagriculturalproductstobe

49、storedannually.Thiscapacityiscalculatedaccordingtothevolumerequiredtostoretheproductinthecoldstorage,alongwiththeaisles,thespacebetweenthestackandthewall,theceiling,andthespacebetweenthepackages.Determinethecapacityofthecoldstorage,thendeterminethelengthandheightofthecoldstorage.Coldstoragedesignmus

50、talsoconsiderthenecessaryancillarybuildingsandfacilities,suchasworkroom,packaging,sortingroom,toolslibraryandloadingandunloadingdesk.Thethirdstep:theselectionandinstallationofthermalinsulationmaterialsincoldstorageTheselectionofthermalinsulationmaterialsincoldstoragemustbeinaccordancewithlocalcondit

51、ions,notonlywithgoodheatinsulationperformance,butalsoeconomicallyandpractically.Thecoldinsulationmaterialsofseveraltypes,oneisprocessedintoafixedshapeandspecificationsoftheplatelength,widthandthicknessofthebaseplateisfixed,canchoosethecorrespondingspecificationaccordingtotheneedsoflibraryinstallatio

52、n,hightemperature,coldstorageisgenerally10cmthickbaseplate,coldstorageandfreezingcoldlikeusing12cmor15cmthickbaseplate;arefrigeratorcanbeusedspraypolyurethanefoam,thematerialissprayeddirectlyintotherefrigeratortobebuiltofbricksorconcretewarehouse,bothwaterproofandheatsetting.Heatinsulationmaterialsa

53、repolyurethane,polyphenylenegreaseandsoon.Polyurethanedoesnotabsorbwaterandhasbetterheatinsulation,butthecostishigher;thewaterabsorptionofthepolyphenylfatisstrong,andtheheatinsulationispoor,butthecostislow.Thestructureofmoderncoldstorageisdevelopingtowardassemblytypecoldstorage.Itismadeintoacoldstor

54、agecomponentincludingmoisture-prooflayerandheatinsulationlayer.Itcanbeassembledonsite.Theadvantageisthattheconstructionisconvenient,fastandmoving,butthecostisrelativelyhigh.Thefourthstep:theselectionofcoldstoragesystemTheselectionofcoldstoragecoolingsystemismainlytheselectionofcoldstoragecompressorand