文献翻译-换热器的使用和介绍

8.英文文献翻译TheuseandintroductionoftheheatexchangerAheatexchangerisadevicebuiltforefficientheattransferfromonemediumtoanother,whetherthemediaareseparatedbyasolidwallsothattheynevermix,orthemediaareindirectcontact.Theyarewidelyusedinspaceheating,refrigeration,airconditioning,powerplants,chemicalplants,petrochemicalplants,petroleumrefineries,andnaturalgasprocessing.Onecommonexampleofaheatexchangeristheradiatorinacar,inwhichtheheatsource,beingahotengine-coolingfluid,water,transfersheattoairflowingthroughtheradiator.Heatexchangersmaybeclassifiedaccordingtotheirflowarrangement.Inparallel-flowheatexchangers,thetwofluidsentertheexchangeratthesameend,andtravelinparalleltooneanothertotheotherside.Incounter-flowheatexchangersthefluidsentertheexchangerfromoppositeends.Thecountercurrentdesignismostefficient,inthatitcantransferthemostheatfromtheheat(transfer)medium.Seecountercurrentexchange.Inacross-flowheatexchanger,thefluidstravelroughlyperpendiculartooneanotherthroughtheexchanger.Forefficiency,heatexchangersaredesignedtomaximizethesurfaceareaofthewallbetweenthetwofluids,whileminimizingresistancetofluidflowthroughtheexchanger.Theexchangersperformancecanalsobeaffectedbytheadditionoffinsorcorrugationsinoneorbothdirections,whichincreasesurfaceareaandmaychannelfluidfloworinduceturbulence.Thedrivingtemperatureacrosstheheattransfersurfacevarieswithposition,butanappropriatemeantemperaturecanbedefined.Inmostsimplesystemsthisisthelogmeantemperaturedifference(LMTD).SometimesdirectknowledgeoftheLMTDisnotavailableandtheNTUmethodisused.ShellandtubeheatexchangerShellandtubeheatexchangersconsistofaseriesoftubes.Onesetofthesetubescontainsthefluidthatmustbeeitherheatedorcooled.Thesecondfluidrunsoverthetubesthatarebeingheatedorcooledsothatitcaneitherprovidetheheatorabsorbtheheatrequired.Asetoftubesiscalledthetubebundleandcanbemadeupofseveraltypesoftubes:plain,longitudinallyfinned,etc.ShellandTubeheatexchangersaretypicallyusedforhighpressureapplications(withpressuresgreaterthan30barandtemperaturesgreaterthan260C.Thisisbecausetheshellandtubeheatexchangersarerobustduetotheirshape.Thereareseveralthermaldesignfeaturesthataretobetakenintoaccountwhendesigningthetubesintheshellandtubeheatexchangers.Theseinclude:Tubediameter:Usingasmalltubediametermakestheheatexchangerbotheconomicalandcompact.However,itismorelikelyfortheheatexchangertofoulupfasterandthesmallsizemakesmechanicalcleaningofthefoulingdifficult.Toprevailoverthefoulingandcleaningproblems,largertubediameterscanbeused.Thustodeterminethetubediameter,theavailablespace,costandthefoulingnatureofthefluidsmustbeconsidered.Tubethickness:Thethicknessofthewallofthetubesisusuallydeterminedtoensure:oThereisenoughroomforcorrosionoThatflow-inducedvibrationhasresistanceoAxialstrengthoAbilitytoeasilystocksparepartscostSometimesthewallthicknessisdeterminedbythemaximumpressuredifferentialacrossthewall.Tubelength:heatexchangersareusuallycheaperwhentheyhaveasmallershelldiameterandalongtubelength.Thus,typicallythereisanaimtomaketheheatexchangeraslongaspossible.However,therearemanylimitationsforthis,includingthespaceavailableatthesitewhereitisgoingtobeusedandtheneedtoensurethattherearetubesavailableinlengthsthataretwicetherequiredlength(sothatthetubescanbewithdrawnandreplaced).Also,ithastoberememberedthatlong,thintubesaredifficulttotakeoutandreplace.Tubepitch:whendesigningthetubes,itispracticaltoensurethatthetubepitch(i.e.,thecentre-centredistanceofadjoiningtubes)isnotlessthan1.25timesthetubesoutsidediameterTubecorrugation:thistypeoftubes,mainlyusedfortheinnertubes,increasestheturbulenceofthefluidsandtheeffectisveryimportantintheheattransfergivingabetterperformance.PlateheatexchangerAnothertypeofheatexchangeristheplateheatexchanger.Oneiscomposedofmultiple,thin,slightly-separatedplatesthathaveverylargesurfaceareasandfluidflowpassagesforheattransfer.Thisstacked-platearrangementcanbemoreeffective,inagivenspace,thantheshellandtubeheatexchanger.Advancesingasketandbrazingtechnologyhavemadetheplate-typeheatexchangerincreasinglypractical.InHVACapplications,largeheatexchangersofthistypearecalledplate-and-frame;whenusedinopenloops,theseheatexchangersarenormallyofthegasketedtypetoallowperiodicdisassembly,cleaning,andinspection.Therearemanytypesofpermanently-bondedplateheatexchangers,suchasdip-brazedandvacuum-brazedplatevarieties,andtheyareoftenspecifiedforclosed-loopapplicationssuchasrefrigeration.Plateheatexchangersalsodifferinthetypesofplatesthatareused,andintheconfigurationsofthoseplates.Someplatesmaybestampedwithchevronorotherpatterns,whereothersmayhavemachinedfinsand/orgrooves.RegenerativeheatexchangerAthirdtypeofheatexchangeristheregenerativeheatexchanger.Inthis,theheat(heatmedium)fromaprocessisusedtowarmthefluidstobeusedintheprocess,andthesametypeoffluidisusedeithersideoftheheatexchanger(theseheatexchangerscanbeeitherplate-and-frameorshell-and-tubeconstruction).Theseexchangersareusedonlyforgasesandnotforliquids.Themajorfactorforthisistheheatcapacityoftheheattransfermatrix.Alsosee:Countercurrentexchange,Regenerator,EconomizerAdiabaticwheelheatexchangerAfourthtypeofheatexchangerusesanintermediatefluidorsolidstoretoholdheat,whichisthenmovedtotheothersideoftheheatexchangertobereleased.Twoexamplesofthisareadiabaticwheels,whichconsistofalargewheelwithfinethreadsrotatingthroughthehotandcoldfluids,andfluidheatexchangers.Thistypeisusedwhenitisacceptableforasmallamountofmixingtooccurbetweenthetwostreams.Seealso:Airpreheater.PlateFinheatexchangerThistypeheatexchangerusessandwichedpassagescontainingfinstoincreasetheeffectivityoftheunit.Thedesignsincludecrossflowandcounterflowcoupledwithvariousfinconfigurationssuchasstraightfins,offsetfinsandwavyfins.FluidheatexchangersThisisaheatexchangerwithagaspassingupwardsthroughashoweroffluid(oftenwater),andthefluidisthentakenelsewherebeforebeingcooled.Thisiscommonlyusedforcoolinggaseswhilstalsoremovingcertainimpurities,thussolvingtwoproblemsatonce.Itiswidelyusedinespressomachinesasanenergy-savingmethodofcoolingsuper-heatedwatertobeusedintheextractionofespresso.DynamicscrapedsurfaceheatexchangerAnothertypeofheatexchangeriscalleddynamicheatexchangerorscraped-surfaceheatexchanger.Thisismainlyusedforheatingorcoolingwithhigh-viscosityproducts,crystallizationprocesses,evaporationandhigh-foulingapplications.Longrunningtimesareachievedduetothecontinuousscrapingofthesurface,thusavoidingfoulingandachievingasustainableheattransferrateduringtheprocess.TheformulausedforthiswillbeQ=A*U*LMTD,wherebyQ=heattransferrate.Phase-changeheatexchangersInadditiontoheatinguporcoolingdownfluidsinjustasinglephase,heatexchangerscanbeusedeithertoheataliquidtoevaporate(orboil)itorusedascondenserstocoolavaporandcondenseittoaliquid.Inchemicalplantsandrefineries,reboilersusedtoheatincomingfeedfordistillationtowersareoftenheatexchangers.Distillationset-upstypicallyusecondenserstocondensedistillatevaporsbackintoliquid.Powerplantswhichhavesteam-driventurbinescommonlyuseheatexchangerstoboilwaterintosteam.Heatexchangersorsimilarunitsforproducingsteamfromwaterareoftencalledboilersorsteamgenerators.Inthenuclearpowerplantscalledpressurizedwaterreactors,speciallargeheatexchangerswhichpassheatfromtheprimary(reactorplant)systemtothesecondary(steamplant)system,producingsteamfromwaterintheprocess,arecalledsteamgenerators.Allfossil-fueledandnuclearpowerplantsusingsteam-driventurbineshavesurfacecondenserstoconverttheexhauststeamfromtheturbinesintocondensate(water)forre-use.Inordertoconserveenergyandcoolingcapacityinchemicalandotherplants,regenerativeheatexchangerscanbeusedtotransferheatfromonestreamthatneedstobecooledtoanotherstreamthatneedstobeheated,suchasdistillatecoolingandreboilerfeedpre-heating.Thistermcanalsorefertoheatexchangersthatcontainamaterialwithintheirstructurethathasachangeofphase.Thisisusuallyasolidtoliquidphaseduetothesmallvolumedifferencebetweenthesestates.Thischangeofphaseeffectivelyactsasabufferbecauseitoccursataconstanttemperaturebutstillallowsfortheheatexchangertoacceptadditionalheat.Oneexamplewherethishasbeeninvestigatedisforuseinhighpoweraircraftelectronics译文：换热器的使用和介绍换热器是一种热量从一种介质流向另一种介质的高效换热设备，两种介质之间相隔一隔离板，使两者不混合，或两种介质直接接触。换热器产品广泛的应用于空间供暖，制冷，空调，发电厂，化工厂，化工厂，炼油厂以及天然气加工等等。其中换热器的一个非常常见的例子就是汽车散热器，它的热源存在热的发动机，其冷却液为水，它流过散热器从而将热量传递给空气。换热器的分类可以根据其流动方式来。可分为平行流换热器和逆流换热器。平行流换热器：两种流体在同一端进入热交换器，在互相平行的另一边流出。逆流换热器：其中的流体分别从换热器的两端进入。两种换热器中逆流的设计是最有效的，因为它可以从最快地让传热介质转让。在叉流换热器，流体流向大致相互垂直的通过一个交换机。为了提高效率，可以将换热器最大限度地增大两种流体之间的墙的面积，同时最大限度地减少流体流动的阻力。换热器的性能，也可以通过在一个或两个方向影响，增加表面积和可流动或引起动荡。驱动其温度在传热表面不同的位置，但需要一个适当的平均温度来定义。最简单的方法就是对数平均温差（法）。有时的对数平均温差直接的结果是不可用的，需要用NTU法。管壳式换热器管壳式换热器由一系列的管组成。一套包含这些管的流体要么加热或冷却。而第二流体运行在正在加热或冷却的流体周围，以便于它可以提供的热量或吸收的热量所需的管。一套管称为管束，管的几种类型有：平，纵肋等等。管壳式换热器一般用于高压和高温的环境。.这是因为管壳式换热器强大的结构和性能。管壳式换热器有几个突出的设计特点，在设计时应先考虑管壳式换热器。这些措施包括：管直径：使用一个小的管直径使经济和紧凑的换热器。然而，这种热交换器犯规更快和小尺寸使机械清洗污垢困难更可能的是。要战胜污垢和清洁的问题，可用于较大的管径。因此，要确定管的直径，可用空间，成本和结垢流体性质必须考虑。管的厚度：管材的壁的厚度通常是确保其有足够的厚度来用于腐蚀那流致振动性轴向强度：轴向强度是通过在壁的最大压差的确定。管长度：换热器通常是比较便宜的，因为它的较小的外壳直径和长管长度。因此，通常有一个目的使换热器尽可能用更长的时间。然而，这里有许多限制，包括提供的空间，它将使用和需要有长度的两倍所需的长度的管确保使管可以取出和更换。同时，它必须记住，长、薄管难以取出和更换。管间距：当设计管时，这时需保证管间距（即，实际的中心距离相邻管）不小于1.25倍管外径管波纹管型，主要用于内胎，可增加流体的湍流的影响，这是非常重要的影响热传递的性能。板式热交换器这是另一种类型的热交换器。板式换热器是一个由多个薄的分隔板组成，它有非常大的表面积和传热流体通道。，在一个给定的空间，这叠板装置比管壳式换热器更加有效。另外垫片和焊接技术的进步使得板式换热器越来越用于实际之中。在暖通空调的应用中，这类大型换热器又被称为板和框架。当使用开放式回路时，这些热交换器通常需要进行定期拆卸和垫圈式的清洗、检查。而有许多类型的永久粘合板换热器，