文献翻译-换热设备

外文翻译HEAT-EXCHANGEEQUIPMENTHeatenergyistransferredbyavarietyofmethods,includingconductioninelectric-resistanceheaters;conduction-inexchangers,boilers,andcondensers;radiationinfurnacesandradiant-heatdryers;andbyspecialmethodssuchasdielectricheating.Oftentheequipmentoperatesundersteady-stateconditions,butinmanyprocessesitoperatescyclically,asinregenerativefurnacesandagitatedprocessvessels.Thispagedealswithequipmenttypeswhichareofmostinteresttoaprocessengineer,namely,tubularexchangers,condensers,scraped-surfaceexchangers,andagitatedvessels.HeatExchangersHeatexchangersaresoimportantandsowidelyusedintheprocessindustriesthattheirdesignhasbeenhighlydeveloped.Standardsareavailablecoveringindetailmaterials,methodsofconstruction,techniqueofdesign,anddimensionsforexchangers.Mostexchangersareliquid-toliquid,butgasesandnoncondensingvaporscanalsobetreatedinthem.Thissimpledouble-pipeexchangerisinadequateforflowratesthatcannotreadilybehandledinafewtubes.Ifseveraldoublepipesareusedinparallel,theweightofmetalrequiredfortheoutertubebecomessolargethattheshell-and-tubeconstruction,whereoneshellservesformanytubes,ismoreeconomical.Thisexchanger,becauseithasoneshell-sidepassandonetube-sidepass,iscalled1-1exchanger.Intheexchangertheshell-sideandtube-sideheat-satisfactoryoverallcoefficientistobeattained.Thevelocityandturbulenceoftheshell-sideliquidareasimportantasthoseofthetube-sideliquid.Topreventweakeningofthetubesheetstheremustbeaminimumdistancebetweenthetubes,anditisnotpracticabletospacethetubessocloselythattheareaofthepathoutsidethetubesisassmallasthatinsidethetubes.Ifthetwostreamsareofcomparablemagnitude,thevelocityontheshellsideislowincomparisonwiththatonthetubeside.Forthatreason,bafflesareinstalledintheshelltodecreasethecrosssectionoftheshell-sideliquidandtoforcetheliquidtoflowacrossthetubebankratherthanparallelwithit.Theaddedturbulencegeneratedinthistypeofflowfurtherincreasetheshell-sidecoefficient.The1-1exchangerhaslimitations.Highervelocities,shortertubes,andamoresatisfactorysolutiontotheexpansionproblemarerealizedinmultipassconstruction.Multipassconstructiondecreasethecrosssectionofthefluidpathandincreasesthefluidvelocity,withacorrespondingincreaseintheheat-transfercoefficient.Thedisadvantagesarethattheexchangerisslightlymorecomplicatedandthefrictionlossthroughtheequipmentisincreasedbecauseofthelargervelocitiesandthemultiplicationofexitandentrancelosses.Anevennumberoftube-sidepassormultipassexchangers.Theshellsidemaybeeithersingle-passormultipass.Acommonconstructionisthe1-2parallel-counterflowexchanger,inwhichtheshell-sideliquidflowsinonepassandthetube-sideliquidintwoormorepasses.The1-2exchangerhasanimportantlimitation.Becauseoftheparallel-flowpass,theexchangerisunabletobringtheexittemperatureofonefluidveryneartotheentrancetemperatureoftheother.Anotherwayofstatingthesamelimitationisthattheheatrecoveryofa1-2exchangerisinherentlypoor.Abetterrecoveryofheatcanbeobtainedinthe2-4exchanger,whichhastwoshell-sideandfourtube-sidepasses.Thistypeofexchangeralsogiveshighervelocitiesandalargeroverallheat-transfercoefficientthana1-2exchangerhavingtwotube-sidepassesandoperatingwiththesameflowrates.Forheattransferbetweenfluidsatlowormoderatepressures,belowabout20atm,plate-typeexchangersarecompetitivewithshell-and-tubeexchangers,especiallywherecorrosion-resistantmaterialsarerequired.Metalplates,usuallywithcorrugatedfaces,aresupportedinaframe;hotfluidpassesbetweenalternatepairsofplates,exchangingheatwiththecoldfluidintheadjacentspaces.Theplatescanbereadilyseparatedforcleaning;additionalareamaybeprovidedsimplybyaddingmoreplates.Unlikeshell-and-tubeexchangers,plateexchangerscanbeusedformultipleduty;i.e.,severaldifferentfluidscanflowthroughdifferentpartsoftheexchangerandbekeptseparatefromoneanother.Plateexchangersarerelativelyeffectivewithviscousfluids.CondensersSpecialheat-transferdevicesusedtoliquefyvaporsbyremovingtheirlatentheatsarecalledcondensers.Thelatentheatisremovedbyabsorbingitinacoolerliquidcalledthecoolant.Sincethetemperatureofthecoolantobviouslyisincreasedinacondenser,theunitalsoactsasaheater,butfunctionallyitisthecondensingactionthatisimportant,andthenamereflectsthisfact.Condensersfallintotwoclasses.Inthefirst,calledshell-and-tubecondensers,thecondensingvaporandcoolantareseparatedbyatubularheat-transfersurface.Inthesecond,calledcontactcondensers,thecoolantandvaporstreams,bothofwhichareusuallywater,arephysicallymixedandleavethecondenserasasinglestream.Extended-surfaceEquipmentDifficultheat-exchangeproblemsoccurwhenoneoftwofluidstreamshasamuchlowerheat-transfercoefficientthantheother.Atypicalcaseisheatingafixedgas,suchasair,bymeansofcondensingsteam.Theindividualcoefficientforthesteamistypically150timesthatfortheairstream;consequently,theoverallcoefficientisessentiallyequaltotheindividualcoefficientfortheair,thecapacityofaunitareaofheatingsurfacewillbelow,andmanyfeetoftubewillberequiredtoprovidereasonablecapacity.Othervariationsofthesameproblemarefoundinheatingorcoolingviscousliquidsorintreatingastreamoffluidatlowflowrate,becauseofthelowrateofheattransferinlaminarflow.Toconservespaceandtoreducethecostoftheequipmentinthesecases,certaintypesofheat-exchangesurface,calledextendedsurfaces,havebeendevelopedinwhichtheoutsideareaoftubeismultiplied,orextended,byfins,pegs,disks,andotherappendagesandtheoutsideareaincontactwiththefluidtherebymademuchlargerthantheinsidearea.Thefluidstreamhavingthelowercoefficientisbroughtintocontactwiththeextendedsurface,andflowsoutsidethetubes,whiletheotherfluid,havingthehighcoefficient,flowsthroughthetubes.Theoverallheat-transfercoefficientwillbesignificantlyincreasedusingextended-surfaceexchangers.Scraped-surfaceExchangersViscousliquidsandliquid-solidsuspensionsareoftenheatedorcooledinscraped-surfaceexchangers.Typicallythesearedouble-pipeexchangerswithafairlylargecentraltube,4to12in.indiameter,jacketedwithsteamorcoolingliquid.Theinsidesurfaceofthecentraltubeiswipedbyoneormorelongitudinalbladesmountedonarotatingshaft.Theviscousliquidispassedatlowvelocitythroughthecentraltube.Portionsofthisliquidadjacenttotheheat-transfersurfaceareessentiallystagnant,exceptwhendisturbedbythepassageofthescraperblade.Heatistransferredtotheviscousliquidbyunsteady-stateconduction.Ifthetimebetweendisturbancesisshort,asitusuallyis,theheatpenetratesonlyasmalldistanceintothestagnantliquidandtheprocessisexactlyanalogoustounsteady-stateheattransfertoasolid.regenerativeheatexchangerReferredtoasaccumulator.Regenerativeheatexchangerusedinaclassofheattransferequipment.Containingsolidfillerforheatstorage.Withrefractorybricksandothergenerallatticestructurefire(sometimeswithametalbandwaveform,etc.).Heattransferintwophases.Thefirststage,thehotgasthroughthethermallattice,thelatticeheattofireupandstorage.Thesecondphase,thecoldgasthroughthethermallattice,latticeacceptedbythefireandheatsavingsisheated.Thisalternatingtwophases.Usuallyalternateuseoftwostoragedevices,thatis,whenthehotgastoenterwhenacoldgasintoanotherbrowser.Commonlyusedinthemetallurgicalindustry,suchastheregeneratorofopen-hearthsteel.Alsousedforthechemicalindustry,suchasgasfurnaceortheairpreheaterchamber,artificialoilofregenerativeplantcrackingfurnace.serpentinetypeheatexchangerAsaserpentinetypeheatexchangerheattransfercomponents.Itisanoldheatexchanger.Itssimplestructure,manufacture,installation,cleaningandmaintenanceconvenience,lowpricesandisparticularlyapplicabletohigh-pressurefluidcooling,condensation,itisstillwidelyusedinmodern.However,serpentinetypeheatexchangerbulky,heavy;unitmetalconsumptionandmoreheattransferarea,heattransferperformanceofthelow.Coolingtubeinaccordancewiththewaythedifferentfluids,serpentinetypeheatexchangerisdividedintoimmersionandspray-type.spiralheatexchangerBytwoparallelmetalplatesmadeoftwovolumesspiralchannel,coldthermalfluidwoodenpartitionbetweenthespiralheatexchangerforheattransfer.Spiralplateheatexchangerhasremovableandnon-demolitionofthetwotypes.Cannotscrewdownthestructureofheatexchangerisrelativelysimple,spiralchannelweldedatbothendsofall.Detachablespiralplateheatexchangerspiralchannelinadditiontothetwoendsofthesealstructure,theotherwiththesametypecannotberemoved.Inordertoincreasethepressurecapacityofspiralplate,sheetandplateinthedistancebetweenthesupportcolumns.Fluidcylinderontheimportandexportlawtotakeoverandtakeoverthetwotangential.plate-finheatexchangerAsaplateandfinheatexchangerheattransfercomponents.Itismainlybytheplatebeamandconstituteafirst-classletters.Thereareanumberofplate-beamchannel.Ineachchannelbetweentwoflatfinsplacedandsealedonbothsideswithseals.Indifferentwaysaccordingtofluidflow,coldfluidheatchannelspacingwithDiegohomeandthousandsofweldingintoawhole,thatismadeofplate-beam.Two-wayfluidflowcurrentcross-flowandcounter-current,suchaswrong.ABfluidheadbytheentrancetothedistributionsegmentasadeflectorplatebeamintotherespectivechannel,andthenbyanotherparagraphofthedistributionofdeflectorheadleadtotheexportandledtothetwopartitionscountercurrentheattransferfluidwas.Finsarecommonlyusedporousflatandcorrugatedzigzagform.umbrellatypeplateheatexchangerUseoftheumbrellawithcorrugatedheattransferplateasaheatexchangercomponents.HeatexchangerumbrellaofChinaandSwedeninthe20thcentury,theearly60screatedseparateintowebandtwobee-typescrew.Itsstructureisbasicallythesameaswiththeplateheatexchanger,byapairofend-plate(bonnet,floor)andthesuperpositionofmanyumbrellaplateintotheplate-beamstructure,bearingsupportfromtheentireequipment.Coldandhotfluid(A,Bfluid)flowsthroughtheplate-beam,respectively,intheodd-numberedoreven-numberedlayerbetweenlayersandwithspecial-shapedplatebetweenthegasketandnotmixed,notleakage.Fluidflowsbetweentheplatesis:web-stylealongtheflowangleintothesurfaceoftheumbrella;BeeLo-styleafterthesuperimposedplateformedintoahelicalspiralflowchannels.Heatexchangerumbrellaforsmallflow,asmalltemperaturedifference,highviscosityoftheheattransferfluid.换热设备热能以各种方法进行传递，包括电阻加热器中的传导，换热器、沸腾器和冷凝器中的传导和对流，锅炉和辐射干燥器中的辐射，以及如介电加热等特殊方法。通常设备是在稳定状态条件下操作的，但是很多过程中为循环操作，列如在交流换热炉和搅动的容器中，本页将讨论工艺工程师最感兴趣的各种类型的设备，称为管式换热器，冷凝器，刮面换热器和搅拌器。换热器在过程工业中，换热气器是如此的重要并如此广泛被应用，以至于他门的设计已经得到高度的发展。已有的换热器的规格详细地概括了材料、制造方法、设计技术和尺寸。绝大多数换器是液液换热气，但在换热器中也可以处理气体和不冷凝的蒸汽。对于在少量管子中不能稳定地控制的流速的情况，简单的套管式换热器不适合，如果几个套管并行使用，外侧管子所需金属的重量非常大，而壳管式结构中将一个外壳作为许多管子使用，故壳管式结构显得更经济。因为这种换热器有一个壳程和一个管程，所以被称为1-1式换热器。在换热器中壳程和管程的传热系数具有相当的重要性，两者必须都大，才能得到一个满意的总热系数。壳程液体和管程液体的流速和湍动同样重要。为了防止管子固定板的强度减弱，管子之间必须有一个最小距离，而且管子放置过密以致管外侧即壳程的通道面积和管内即管程的通道面积一样小是不可能的。如果两股物流有相当的流量，壳程的流速就会比管程的小。因此，在壳内放置挡板以减少壳程流体流动的截面积，迫使液体垂直地流过而不是平行地流过管束。这种流行产生的附加湍动进一步提高了壳程的传热系数。1-1型换热气有一些局限性，而多程换热器实现了高流速，短管子以及对膨胀问题的更满意的解决方法。多程换热器降低了流体的流通截面积，提高了流速，从而导致热传系数的相应提高。其缺点有：（1）这种换热器稍微复杂些，（2）高速流和重复的出口损失导致通过设备的摩擦损失增加。在多程换热器中采用偶数的管程。而壳程可以是单程的和多程的。常用的设计是1-2型平行逆流换热器，其中壳程液体流过一个壳程而管程液体流过两个或多个管程。1-2型换热器也有一个重要的缺点。由于采用的是平行流行，故这种换热器不能将一路流体的出口温度接近于另一路流行的入口温度。换句话说，1-2型换热器的热回收率必然很差。较好的热回收率可在2-4型换热器中实现。这类换热器有两个壳程和四个管程。相对于只有两个管程的1-2型换热器，在同样的流量下操作，2-4型换热器极比较高的流速和比较大的总传热系数。对于低于大约20大气压的中低压下流体间的换热，板式换热器可以和壳管式换热器相媲美，特别是当需要采用防腐蚀材料时。通常带有波纹面的金属板用框架支撑，热流体通过间隔的板间，与相邻板间的冷流体进行热交换。板可以轻易拆开进行清洗。，通过增加板数可以简单地提供附加的传热面积。和壳管式换热器不同，板式换热器可以用于多股流的换热目的，例如几个不同的流体分别流过换热器的不同部分而且相互之间保持分离。板式换热器对于粘稠的流体相对更有效。冷凝器通过取走潜热用于蒸汽液化的特殊传热设备称为冷凝器。潜热被一个称为冷凝剂的较冷的液体所吸收而除去。由于在冷凝器中冷凝剂的温度被明显地升高了，所以冷凝器的作用也象一个加热器。但是从功能上讲冷凝作用是重要的，它的名字也反映了这个事实。冷凝器分为两种类型，第一种称为壳管式冷凝器，需要冷凝的蒸汽和冷凝剂被一个管式的传热面所分开。第二种称为接触式冷凝器，冷凝剂和蒸汽（两者通常都是水）直接进行混合，然后作为唯一的物流离开冷凝器。扩展表面的换热器当两股物流中一股物流的导热系数比另一股小得多时，就出现了热交换困难的问题。典型的例子是通过新华通讯社凝蒸汽去加热一种不流动的气体，例如空气。单独蒸汽的导热系数通常是空气流的150倍之多，结果总的传达室热系数基本上等于单独空气的传热系数，加热面的单位面积的换热量将很低，所以需要很长的管子来提供适当的容量。同样问题的其它形式也出现于粘稠液体的加热或冷却以及流速很低的物流的处理中，因为在层流中热传递的速率很低。对于上述情况，为了节省窨和降低设备的成本，开发了一些特定的热交换表面，称为扩展的表面，即管子的外表面通过采用翅、钉子、圆片及其它附属物被大量增加或扩展，这样和流体接触的外表面积也比内表面积的大得多。将低导热系数的物流和扩展的表面接触，