《轮机英语（二三管轮）》-Lesson 14 Marine Refrigeration

NewWordsandExpressionsrefrigeration[rɪˌfrɪdʒəˈreɪʃn]n.冷藏，制冷isentropic[,aɪsen'trɒpɪk]a.等熵的adiabatic[eɪdaɪə'bætɪk]a.绝热的，隔热的enthalpy['enθ(ə)lpɪ;en'θælpɪ]n.焓，热焓halogenate[hə'lɒdʒɪneɪt]v.卤化hydrocarbon[ˌhaɪdrəˈkɑːbən]n.碳氢化合物，烃bellows[ˈbeləʊz]n.波纹管Veg[vedʒ]n.蔬菜NewWordsandExpressionscompressor[kəmˈpresə(r)]n.压缩机diverter[daɪ'vɜːtə]n.转向器，分流器thermostat[ˈθɜːməstæt]n.温度调节装置defrost[diːˈfrɒst]v.结霜condenser[kənˈdensə(r)]n.冷凝器extract[ˈekstrækt]v.提取equivalent[ɪˈkwɪvələnt]n.等价于onboard[ˈɒnbɔːd]a.船上NewWordsandExpressionssaturation[ˌsætʃəˈreɪʃn]n.饱和restrict[rɪˈstrɪkt]v.限制evacuation[ɪˌvækjuˈeɪʃn]n.撤离，疏散overcharge[ˌəʊvəˈtʃɑːdʒ]v.过充delicate[ˈdelɪkət]a.精致的insulation[ˌɪnsjuˈleɪʃn]n.绝缘lagging['lægɪŋ]a.滞后的expansionvalve

膨胀阀NewWordsandExpressionsbalanceline

平衡管solenoidValve

电磁阀troubleshoot

故障Thebasicvapor-compressionrefrigerationcycleisshowninFig.14-1.Fourmajorthermalprocessestakeplace:evaporation,compression,condensationandexpansion.RefrigerationcycleEvaporation(A-B)isisobaricheatabsorptionintheevaporator.Thegaseousescapeofmoleculesfromthesurfaceofaliquidandisaccomplishedbytheabsorptionofaconsiderablequantityofheatwithoutanychangeintemperature.

Evaporation

CompressionThisistheprocess(B-C)ofisentropiccompressioninthecompressor(frictionlessadiabaticcompressioninidealcycle),usingshaftworkofacompressortoraisethepressureoftherefrigerantvaporobtainedfromtheevaporator(B到C是压缩机中发生的一个等熵压缩过程（理想循环是无摩擦绝热压缩），压缩机的轴功率被用来提高蒸发器出来的制冷蒸汽的压力).Theadditionoftheheatmayplayaroleinraisingthepressure.Increasingthegaspressureraisestheboilingandcondensingtemperatureoftherefrigerant.Thisisaprocess(C-D)ofisobaricheatremovalincondenser.Thehigh-pressuregaseousrefrigerant,whichcarriestheheatenergyabsorbedintheevaporatorandtheworkenergyfromthecompressor,isbroughtintothecondenser,wherethevaporchangesintoaliquidwithextractingheat.Thecondensedrefrigerantliquidisreturnedtothebeginningofthenextcycle.Condensation

ExpansionExpansionprocess(D-A)isconstantenthalpyexpansioninexpansionvalve.thepressureoftherefrigerantliquidisreducedtothelow-pressurelevelandtheboilingtemperatureoftherefrigerantisreducedtobelowthetemperatureofthetemperatureoftheheatsource(D到A是经过热力膨胀阀的等焓膨胀过程。液态制冷剂的压力被减少到低压水平，制冷剂的沸点随之降低到比热源温度还低的水平).Heatenergyequivalentofworkdone=Heatenergyrejected-heatenergyreceived=AreaABCDA+AreaunderADRefrigerationsystemTherefrigeratingsystemsemploytherefrigerantstoremovetheheatfromaspacetotheheatsink.Theiroperatingtemperaturelevelsdependontheapplications.Thecomponentsinvolvedinarefrigerationcyclearethecompressor,condenser/receiver,expansionvalveandevaporatorrespectively.Thepressuredifferencebetweenlowpressureliquidandhighpressurevaporiscreatedbythecompressor.Theworkingfluidemployedastheheatabsorberinanyrefrigeratingprocessiscalledarefrigerant.Itoftenemploysaseawaterregulatingvalvetocontroltheseawaterflowratethroughthecondenser.Theflowofseawaterconvertstheheatoutoftherefrigerantflowattherelativelyhightemperatureinthehighpressurepathofarefrigeratingcycle.Withtheconsiderablereductionofpressureofrefrigerantflow,theevaporatingpointofrefrigerantisaccordinglyreduced.Theliquidrefrigerantabsorbslargeamountoflatentheatandthenvaporizes:ThemostcommonrefrigerantusedonboardisthehalogenatedhydrocarbonsthatareusuallyreferredtoastheFreon.Thesystemshownaboveanddescribedbelowistypicalofthatfittedonmanyshipsotherthanitismorecommontohavetwolowtemperatureroomsratherthanone.CondensationLargersystemshavemultiplecylinderswithanunloadedsystemusingthesuctionpressureasitssignal.Refrigerantiscompressedinthecompressortoapressuredependentuponthetemperatureofthecoolingwatertothecondenser,andtoalesserextentthevolumeofgasinthesystem.Asthetemperatureofthecoolingwaterrisesupsodoestheminimumtemperatureoftherefrigerantliquidrise,andwithitthecorrespondingsaturationpressure.ComponentsOilSeparatorThepurposeoftheoilseparator,situatedonthecompressordischargeline,istoreturnoilentrainedinthegas,backtothecompressorsump(压缩机排出管路上安装油分分离器，其目的是使制冷蒸汽中的滑油分离出来回到压缩机油底壳).Theoilreturnmaybefloatcontrolledasshown,electricsolenoidcontrolledonatimer,oruncontrolledwithasmallborecapillarytubeallowingcontinuousreturn.Withallofthesemethodsashutoffvalveisfittedbetweenseparatorandcompressortoallowformaintenance.Theoilgasmixenterstheseparatorwhereitismadetochangedirection,theheavieroildropletstendtofalltothebottom.Generallyawatercooledtubecooler.Asafetyvalveandventarefitted.Thepurposeoftheventistobleedoffnon-condensablesuchasairwhichcanenterthesystemwhenthesuctionpressureisallowedtofallbelowatmosphericorcanbecontainedwithinthetopupgas.Thepresenceofnon-condensableisgenerallyindicatedbyacompressordischargepressureconsiderablyabovethesaturationpressureoftherefrigerant.Thecoolantflowtothecondenserissometimestemperatureregulatedtopreventtoolowatemperatureinthecondenserwhichcanaffectplantefficiencyduetothereductioninpressure.Belowthecondenser,orsometimesasaseparateunit,isthereservoir.Itspurposeistoallowaccurategaugeofthelevelofrefrigerantinthesystem.Inadditiontothisitalsoallowsaspacefortherefrigerantliquidwhenthesystemis'pumpeddown'(冷凝器下面，有时作为一个独立的部件，是储液器。安装储液器可以矫正系统中制冷剂的液位，除了这一点，还可以用来收集系统抽出的制冷剂).Thisreferstotheevacuationoftherefrigerantgastothecondensertoallowmaintenanceonthefridgesystemwithoutloss.Forsystemnotfittedwithareservoir,asightglassissometimesincorporatedonthesideofthecondenser.CareshouldbegiventoensuringthattheliquidlevelisnottoohighasthisreducesthesurfaceareaofthecoolingpipesavailableforcondensingtheliquidandcanleadtoincreaseddischargepressuresCondenserThermostatandSolenoidValveThesetwoelementsformthemaintemperaturecontrolofthecoldrooms.TheThermostatissettothedesiredtemperatureandgivena3to4degreedifferentialtopreventcycling.Whenthetemperatureintheroomreachesthepre-setlevelthethermostatswitchmakesandtheroomsolenoidisenergizedallowinggastotherefrigerantliquidtotheexpansionvalve.Amanualoverrideswitchisfittedaswellasarelayoperatedisolatingcontactwhichshutthesolenoidwhenthedefrostsystemisinuse.Thepurposeofthisvalveistoefficientlydropthepressureoftherefrigerant.Itachievesthisbypassingtheliquidthroughavariableorificegivingaconstantenthalpypressuredrop.Therefrigerantatlowerpressurehasacorrespondinglowerboilingpoint(saturationtemperature).ThermostatandSolenoidValveUnder-coolinginthecondenserincreasestheefficiencyoftheplantbyallowingmoreheattobeabsorbedduringthevaporizationprocess.Inadditionitalsoreducestheinternalheatabsorptionprocessthatoccursduringtheexpansionstagewhichisduetoasmalldegreeofflashoffaslatentheat(ofvaporization)isabsorbedfromsurroundingliquidtoreducethetemperatureofthebulkliquidtothenewcorrespondingsaturationtemperatureforthereducedpressurebythisprocessofboiling(vaporization)andlatentheatabsorptioni.e.changeofstate,therefrigerantremovesheatfromthecoldrooms.Theexpansionprocessiscontrolledbytheactionofthebellowsandpushpinsactingontheorificevalveplate.Thebellowsiscontrolledbyabulbwhichmeasuresthetemperatureofthegasatoutletfromtheevaporator(波纹管与作用在针阀体上的阀芯的动作控制着制冷剂的膨胀过程，波纹管由一个测量蒸发器出口制冷剂温度的感温包进行控制).Toensurenoliquidpassesthroughtothecompressor,theexpansionvalveissetsothatthegasatoutletfromtheevaporatorhas2to3degreesofsuperheat.ThermostatandSolenoidValveForlargersystemswhereasignificantpressuredropexistsacrosstheevaporatoritisnecessarytofita'Balanceline'.Thisisasmallboretubewhichfeedstheoutletpressurebacktothethermostaticvalve'motor'element.Thereforethemeasuredtemperatureisdirectlyrelatedtothesuperheattemperatureatoutletpressure.Somesystemsaredesignedso5%liquidisavailablethroughtheevaporatortocoattheinternalsurfacesofthetubesincreasingheattransferefficiency.ThermostatandSolenoidValveThisvalveisfittedtothehighertemperaturerooms,vegetableandflour(+5oC)onlyandnottotheMeatandFishrooms(-20oC).Theyservetwomainpurposes.Firstlywhenallsolenoidvalvesareopenedtheyactassystembalancingdiverters,whicharetheyrestricttheliquidflowtotheroomswhichcanbekeptatthehighertemperatureanddeliverthebulktothecolderrooms(第一个作用是当所有电磁阀打开时，蒸发压力调节阀作用到系统的平衡分流器。这会限制流向较高温度的冷藏室的制冷剂液体流量，而大量制冷剂液体流向更低温度的冷冻室).Secondlytheyservetolimitthepressuredropacrosstheexpansionvalvebygivingasetminimumpressureintheevaporatorcoil.Thisinturnlimitsthetemperatureoftherefrigeranttherebypreventingdelicatefoodstuffssuchasvegetablesfrombeingdamagedbyhavingairatverylowtemperaturesblownoverthem.Ultimatelytheymayalsobesettoprovideasafetylimittotheroomtemperaturebyrestrictingthepressuretogiveacorrespondingminimumsaturationtemperatureof0oC.BackpressureregulatorvalveMoisturefreezesontotheevaporatoreventuallycausingarestrictionandreducingtheefficiencyoftheplant.Thismustbeperiodicallyremoved.ForVegandFlourrooms,werenotrestrictedto0oCminimumbythebackpressurevalve,thisiscarriedoutonceperday.FortheMeatandFishroomsthishastobecarriedouttwoormoretimes.Duetothelowtemperatureintheroomsitisnecessarytofitadrainheater.Whenondefrostthesolenoidvalveisshutandthefanisoff.Onsomesystemsatendofdefrostthesolenoidvalveisopenedmomentarilybeforethefanisstarted.Thisallowsmoisturetobesnapfrozenontothesurfaceoftheelement,creatingaroughincreasedsurfaceareaandtherebyincreasingtheheattransferrate(在某些系统中，在融霜结束后，在风机启动前电磁阀顺时开启。这使得制冷剂突然结冻在元件表面，得到了一个增多的粗糙表面积，因此，增加了导热率).DefrostsystemTheeffectsofoverchargeareafullcondenser/receivergaugeglass.SystempressuresarenotaffecteduntilhighlyoverchargedwhenapossibilityofexcessiveHPpressureexists.Underchargecausesfailuretomaintaincoldroomtemperaturesandcompressorcycling.Compressorcyclingiscausedbytherebeinginsufficientgastomaintainthecompressorloadedevenwithallroomsolenoidsopen.Inextremethecompressorwillcutinandout.Underchargeisdetectedbylowlevelsinthecondenser/receivergaugeglass/bubblesinliquidsightglass,compressorcyclingandlowsuctionpressures(在极端情况下，压缩机频繁启停。充剂不足时，冷凝器和储液器液位计中出现低液位、视液镜和压缩机循环中有汽包、吸入压力会降低).EffectsofunderandoverchargeAshiphadrealproblemswiththecontrolofroomtemperatures,oneroominparticular.Attemptsto'balance'thesystemusingthebackpressurevalvesusuallyresultedinroomsstarvedofgasand/orthecompressortrippingonLowPressuretrip.Itturnedoutthatsagononeortwooftheliquidlinepipesallowedoilanddebristobuildupinthissectionandrestrictflow.Onanothershipthelaggingaroundapenetrationpiecehadbeendamagedandwaterhadgotbehinditintotheinsulation.Thisliquidhadfrozenandexertedacrushingforceonthepipesufficienttoseverelyrestricttheflow(在另外一些船上，缠绕在管路上的隔热层损害，水会侵入绝缘层中。水会在管路表面上结冰，因此对管路产生决定性的作用力，足够严重时就会限制管路中制冷剂的流动).Thiswasonlyfoundaftersomesearchingasbeforethelaggingwasremovednothingwrongcouldbeseen.Troubleshoot

Exercises1.Refrigerantenteringthecompressorofarefrigerationsystemshouldbeinwhichofthefollowingconditions?A．Sub-cooledliquid B.Sub-cooledvaporC.Superheatedvapor DLiquid2.Arefrigerantgivesupheatwhenitgoesthrough_____.A.condenser B.evaporatorC.regurgitate D.boilcoilCA

Exercises3.Whenthetemperatureoftherefrigerantflowingoutfromthecondenserisbelowthecondensingtemperature,itissaidtobe_____.A.dry B.super-cooledC.wet D.superheated4.Whichofthestatementslistedconcerningheattransferiscorrect?A.Heatisalwaystransferredataconstantrate.B.Heattransferrateincreasesastemperaturedifferenceincreases.C.Therateofheattransferisnotaffectedbytemperaturedifference.D.Thehightemperatureregionisknownasaheatsink.BB

Exercises5.Thethermalexpansionvalverespondstothe_____.A.amountofsuperheatin