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中英文对照外文翻译(文档含英文原文和中文翻译)换热器的优化选型【摘要】板式换热器的优化选型是根据换热器的用途和工艺过程中的参数和NTU=KA/MC=△t/△tm,即传热单元数NTU和温差比(对数平均温差—换热的动力)选择板片形状、板式换热器的类型和结构。【关键词】平均温差NTU板式蒸发器冷凝器1平均温差△tm从公式Q=K△tmA,△tm=1/A∫A(t1-t2)dA中可知,平均温差△tm是传热的驱动力,对于各种流动形式,如能求出平均温差,即板面两侧流体间温差对面积的平均值,就能出换热器的传热量。平均温差是一个较为直观的概念,也是评价板式换热器性能的一项重要指标。1.1对数平均温差的计算当换热器传热量为dQ,温度上升为dt时,则C=dQ/dt,将C定义为热容量,它表示单位时间通过单位面积交换的热量,即dQ=K(th-tc)dA=K△tdA,两种流体产生的温度变化分别为dth=-dQ/Ch,dtc=-dQ/Cc,d△t=d(th-tc)=dQ(1/Cc-1/Ch),则dA=[1/k(1/Cc-1/Ch)]·(d△t/△t),当从A=0积分至A=A0时,A0=[1/k(1/Cc-1/Ch)]·㏑[(tho-tci)/(thi-tco)],由于两种流体间交换的热量相等,即Q=Ch(thi-tho)=Cc(tco-tci),经简化后可知,Q=KA0{[(tho-tci)-(thi-tco)]/㏑[(tho-tci)/(thi-tco)]},若△t1=thi-tco,△t2=tho-tci,则Q=KA0[(△t1-△t2)/㏑(△t1/△t2)]=KA0△tm,式中的△tm=(△t1-△t2)/㏑(△t1/△t2)。顺流△tm=[(thi-tci)-(tho-tco)]/㏑[(thi-tci)/(tho-tci)]逆流△tm=[(thi-tco)-(tho-tci)]/㏑[(thi-tco)/(tho-tci)]对于各种流动型式,在相同的进口、出口温度条件下,逆流的平均温差最大。当板式换热器入口和出口两流体的温差△t1和△t2之间的差不大时,可采用算术平均温差(△t1+△t2)/2,一般△t1/△t2小于1.5时,可采用,若△t/△t2为3时,则误差约为10%。1.2传热单元数法在传热单元数法中引入一个无量纲参数NTU,称为传热单元数,它表示板式换热器的总热导(即换热器传热热阻的倒数)与流体热容量的比值NTU=KA/MC,它表示相对于流体热容流量,该换热器传热能力的大小,即换热器的无量纲“传热能力”。对于板式换热器来说,KA/MC=△t/△tm,式中△t/△tm称为温差比,上式中的右边的工艺过程用NTUp表示,左边的换热设备的条件用NTUE表示。NTUp是流体温度的变化与平均温差的比值,表示的是用1℃△tm的变化引起几度流体温度变化的值,当△tm大时,NTUp则小;当△tm小时,它有变大的倾向。相反,在NTUp变大的过程中,△tm的温度变化较大,NTUp较小时,其△tm的温度变化较小(见表1)。表1△tm,NTUp的关系△tm大△tm小NTUp小NTUp大NTUp大NTUp小△tm的温度变化大△tm的温度变化小板式换热器的优化设计计算,就是在已知温差比NTUE的条件下,合理地确定其型号、流程和传热面积,使NTUp等于NTUE。1.3换热过程和NTU与供热空调相关的换热过程如下如示:⑴用蒸汽加热水⑵水—水换热a.蒸汽133→133℃c.一次水65→60℃水5→65℃(生活热水)二次水45←40℃(采暖)b.蒸汽133→133℃d.一次水14→9℃水55→65℃(采暖)二次水13←7℃(制冷)e.一次水29→24℃二次水26←21℃(制冷机的冷却)以上5例工艺过程的NTUp(见表2)表2供热空调工艺过程的NTUp过程△tmNTUpa133→133℃5→65℃94.86(65-5)/94.86=0.632b133→133℃55→65℃72.88(65-55)/72.88=0.13c65→60℃45←40℃20.00(45-40)/20=0.25d14→9℃13←7℃1.44(13-7)/1.44=4.17e29→24℃26←21℃3.00(26-21)/3=1.671.4板式换热器和NTUENTUE表示板式换热器的能力,换热器的面积是具有一定传热长度的单位传热体的组合,总传热长度是单位长度和流程数的乘积。当NTUE是总数时,若每1流程数为NTUe时,则NTUE=n·NTUe(其中n是流程数)。当NTUe=NTUE=NTUp时,换热器为单程。若NTUe﹤NTUp时,则换热器应为多流程,故设计时应先预定n。由于每种板片单程的NTUe值基本上是定值,如适合表2中e的流量为25m3/h的单程板式换热器的NTUe为17㎡。从NTUe=A·K/MC可知,当NTUe为定值时,A·K成反比,仍以e为例,当K=500kcal/㎡·h·℃时,A=1.67×25000/500=83.5㎡,流程数n=83.5/17≈5。当K=2500kcal/㎡·h·℃时,A=16.7㎡,流程数n=1。每一流程的NTUe如下所示:K=500,NTUe=NTUE/n=0.33,K=2500时,NTUe=1.67。由此可知,根据NTUe即可求出换热器的流程数,传热系数和传热面积。从以上可知,若板式换热器设计不合理,可能使换热面积过大,也可能使板间流速太高,阻力过大。1.5板式换热器制造技术的进步,板片种类的增加,提高了板式换热器对各种工艺过程的适应性。⑴大NTU(∽8),小△tm(∽1~2)的板式换热器满足了区域供冷和热泵机组蒸发器、冷凝器的要求。从以上分析可知,△tm是换热的驱动力,若△tm小,即意味着驱动力小,要实现两种流体之间的换热,必须增大传热系数,增大传热面积,为了使传热面积不至过大,唯一的是增大传热系数K。①浅密波纹板片是北京市京海换热设备制造有限责任公司开发的新型板片,它的传热系数约为7000W/㎡·K,是水平平直波纹板的2倍,是人字形波纹板的1.5倍,在区域供冷中时,检测的△tm约为1.2。在作为冰蓄冷的乙二醇和冷冻水的换热器使用中,△tm约为1.5。②板式蒸发器、板式冷凝器也是北京市京海换热设备制造有限责任公司开发的适应于热泵机组的新型换热器。与管壳式蒸发器、冷凝器相比,它具有如下优点:单位体积内板式蒸发器、板式冷凝器的传热面积约是管壳式换热器的3倍;板式蒸发器的传热系数约为1000~1200W/㎡·K,板式冷凝器的传热系数约为1500~2000W/㎡·K均为管壳式换热器的2~3倍;在板式蒸发器上采用了使制冷剂液体分布均匀的分配器装置,当蒸发器板片数较多时,可能会出现制冷剂液体分配不均的,不能充分利用所有蒸发传热面积,使蒸发温度低于设计计算温度。采用分配器后即能克服上述问题。有关单位检测数据说明,板式蒸发器、板式冷凝器的传热系数在△tm约为2.5~3℃时,在1500~2000W/㎡·K之间,且阻力小,满足了热泵机组的要求。⑵小NTU(∽0.3~2),大△tm(∽40~90℃)的板式换热器满足了热回收工艺和工艺加热、冷却的要求。当工艺过程在大△tm的条件下进行换热时,说明驱动力大,所需的传热面积较小,对传热系数要求也不高,但,这种工艺过程或者工作压力高,或者工作温度高,或者工艺加热、冷却过程的液体中含有纤维或直径较大的颗粒,对板式换热器的承压、耐温能力提出了要求,对换热器的板间距提出了要求。①排(烟)气—水板壳式换热器(省能器),排(烟)气—空气板壳式换热器(空气预热器)是北京市京海换热设备制造有限责任公司和兰石化共同开发出来的新型板式换热器,全焊接板式换热器中介质的换热是通过板管束来实现的,组成板管束的板片由专用模具压制成型,全焊接式板束装在压力壳内。波纹板片具有静搅拌作用,能在很低的雷诺数下形成湍流,且污垢系数低,传热系数是管壳式换热器的2~3倍。为了适应换热量大,流体压降小的要求,板间距大,当量直径约为28㎜。为了满足工艺的要求板束工作压力(反压)P≤4.5Mpa,板束工作压力(正压)同壳体工作压力,不受限制;工作温度t≤550℃。乌鲁木齐石化分公司40万吨/年连续重整采用了进料(冷介质)和出料(热介质)的板壳式换热器,进料流量50t/h,进、出口温渡88℃,470℃。出料流量50t/h,进、出口温度100℃,500℃,对数平均温差约38℃,总传热系数约为380kcal/㎡·h·℃,热负荷达23×106kcal/h,进料压降20Kpa,出料压降50Kpa。②多效蒸发板式加热器(换热器),这种换热器既是工艺加热装置,又是重要的热回收装置。以前由于板式换热器的流道小(板间距1.5~5.0㎜),不适宜于气—气换热和蒸气冷凝;且易堵塞,故不宜用于含悬浮物的流体。为了尽量地发挥板式换热器的长处,克服存在问题,适应工艺的要求,北京市京海换热设备制造有限责任公司开发出了新型的多效蒸发板式换热器,这种板式换热器属宽流道型,其板间距为8.0㎜,适合于蒸气冷凝,适合于含悬浮物的流体,且不易堵塞,最大处理量达1200m3/h。原文NewplateheatexchangeroptimizationSelectionAbstract:TheplateheatexchangerSelectionisbasedontheoptimizationoftheuseofheatexchangersandintheprocessoftheparametersandNTU=KA/MC=△t/△tm,thatis,transferunitsofNTUandthetemperaturedifferencethan(theaveragetemperaturedifference--Heattransferinpower)chooseplateshapes,plateheatexchangerandthetypeofstructure.
Keywords:theaveragetemperaturedifferencebetweenNTUplateevaporatorcondenser1averagetemperaturedifference△tm
Whentheheatexchangertoheat-dQ,whenthetemperaturerosetodt,C=dQ/dt,Cwillbedefinedasheatcapacity,itsaidunitsoftimethroughtheexchangeofheatperunitarea,dQ=K(th-tc)dA=K△tdA,twoofthefluidtemperaturechangesweredth=-dQ/Ch,dtc=-dQ/Cc,d△t=d(th-tc)=dQ(1/Cc-1/Ch),whiledA=[1/k(1/Cc-1/Ch)]•(d△t/△t),whentheA=0pointstoA=A0when,A0=[1/k(1/Cc-1/Ch)]•㏑[(tho-tci)/(thi-tco)],becauseoftwofluidexchangebetweentheheatequivalent,thatis,Q=Ch(thi-tho)=Cc(tco-tci),thesimplifiedKnow,Q=KA0([(tho-tci)-(thi-tco)]/㏑[(tho-tci)/(thi-tco)]),if△t1=thi-tco,△t2=tho-tci,Q=KA0[(△t1-△t2)/㏑(△t1/△t2)]=KA0△tm,in-△tm=(△t1-△t2)/㏑(△t1/△t2).Down△tm=[(thi-tci)-(tho-tco)]/㏑[(thi-tci)/(tho-tci)]Countercurrent△tm=[(thi-tco)-(tho-tci)]/㏑[(thi-tco)/(tho-tci)]Forvariousflowpatternsinthesameimport,exportundertheconditionsoftemperature,theaveragetemperaturedifferencebetweenthelargestcounter-current.Whentheplateheatexchangerimportandexportofthefluidtemperaturedifferencebetweenthetwo△t1andthedifferencebetween△t2notavailablewhenarithmeticaveragetemperature(△t1+△t2)/2,General△t1/△t2lessthan1.5,Maybe,if△t/△t2for3:00,theerrorisabout10percent.1.2thenumberoftransferunitsIntheheattransferunitoftheintroductionofafewdimensionlessparametersNTU,knownasthenumberoftransferunits,itsaidplateheatexchangerofthetotalthermalconductivity(heatexchangerheatresistanceofthecountdown)andtheratiooffluidheatcapacityNTU=KA/MC,itsaidinrelationtoheatfluidflow,heattransfercapacityoftheheatexchangerofthesizeoftheheatexchangerthatis,non-dimensional"heattransfercapability."Theplateheatexchangerfor,KA/MC=△t/△tm,where△t/△tmknownasthetemperaturedifferencethan,ontherightsideoftheprocessusedNTUpthatlefttheconditionsofheattransferequipmentusedNTUEsaid.NTUpisfluidtemperaturechangesintemperatureandtheaverageratiothatisused1℃△tmofseveralchangesinthevalueoffluidtemperaturechanges,when△tmlarge,NTUpissmallwhen△tmhours,ithasbecomebiggerThetendency.Onthecontrary,inNTUplargerintheprocess,△tmofthelargertemperaturechanges,NTUpsmaller,its△tmsmallchangesintemperature(seetable1).Table1△tm,NTUprelations△tmlarge△tmsmallNTUpsmallNTUplargeNTUplargeNTUpsmall△tmlargechangesintemperature△tmsmallchangesintemperaturePlateheatexchanger,theoptimaldesign,isknownNTUEtemperaturedifferencethantheconditions,todetermineareasonablemodel,processesandheattransferarea,equivalenttoNTUpNTUE.1.3heattransferprocessandtheNTUHeatingandair-conditioningrelatedtotheheattransferprocessiftheshowareasfollows:⑴steamheatingwater⑵water-waterheatexchangera.steam133→133℃c.awater65→60℃Water5→65℃(hotwater)Secondarywater45←40℃(heating)b.Steam133→133℃d.awater14→9℃Water55→65℃(heating)secondarywater13←7℃(refrigeration)e.awater29→24℃
Secondarywater26←21℃(refrigeratorcooling)MorethanfivecasesoftheprocessNTUp(seetable2)Table2heatingair-conditioningprocessofNTUpprocess△tmNTUpa133→133℃5→65℃94.86(65-5)/94.86=0.632b133→133℃55→65℃72.88(65-55)/72.88=0.13c65→60℃45←40℃20.00(45-40)/20=0.25d14→9℃13←7℃1.44(13-7)/1.44=4.17e29→24℃26←21℃3.00(26-21)/3=1.671.4plateheatexchangerandNTUENTUEplateheatexchangerthatthecapacityofheatexchangeristhesizeofacertainlengthoftheheatandthecombinationofheattransferunits,thetotallengthofheattransferprocessisthelengthandnumberofunitsoftheproduct.WhenthetotalnumberofNTUEis,ifthenumberofprocessesforevery1NTUe,thenNTUE=n•NTUe(wherenisthenumberofprocesses).WhenNTUe=NTUE=NTUp,theheatexchangerforone-way.IfNTUe<NTUp,theheatexchangerformanyprocesses,itshouldbedesignedtotargetn.Aseachplateofone-wayNTUevalueisessentiallyfixedvalue,suchasineTable2fortheflowof25m3/hoftheone-wayNTUeplateheatexchangerfor17squaremeters.FromNTUe=A•K/MCtellsusthatwhenNTUetobeonduty,A•Kisinverselyproportional,stilleexample,whenK=500kcal/㎡•h•℃time,A=1.67×25000/500=83.5㎡,theprocessofn=83.5/17≈5.WhenK=2500kcal/㎡•h•℃time,A=16.7squaremeters,theflowofn=1.EachprocessNTUeasfollows:K=500,NTUe=NTUE/n=0.33,K=2500when,NTUe=1.67.So,canbeobtainedunderNTUetheflowofheatexchangers,heattransfercoefficientandheattransferarea.Fromtheabovewecanseethatiftheplateheatexchangerdesignunreasonableandlikelytoheattransferareaistoolarge,mayalsobepartitionedsothatflowistoohigh,toomuchresistance.1.5plateheatexchangermanufacturingandtechnologicalprogress,platetypeofincrease,raisingtheplateheatexchangerofthevariousprocessesofadaptation.⑴theNTU(∽8),small△tm(∽1~2)theplateheatexchangertomeetthedistrictcoolingandheatpumpunitsevaporator,condenserrequirements.Fromtheaboveanalysisknow,△tmisthedrivingforceofheattransfer,if△tmsmall,meansthatthedriverofsmall,toachievetheheattransferbetweenthetwofluid,wemustincreaseheattransfercoefficient,increasingheattransferarea,inordertoHeattomakeuptoolarge,istheonlyincreaseheattransfercoefficientK.
①shallowplateofcorrugatedBeijing,Beijingistheheattransferequipmentmanufacturerslimitedliabilitycompanydevelopedanewtypeofplate,theheattransfercoefficientofabout7000W/㎡•K,istheleveloftheflatcorrugatedboardtwotimes,ischevronCorrugatedsheetsof1.5times,intheregionalcooling,thedetectionof△tmisabout1.2.Asinicestorageofethyleneglycolandchilledwateruseintheheatexchanger,△tmisabout1.5.②plateevaporator,condenserplateBeijing,Beijingisalsotheheattransferequipmentmanufacturerslimitedliabilitycompaniesadapttothedevelopmentofanewtypeofheatpumpunitsintheheatexchanger.Andtheshell-and-evaporator,comparedtothecondenser,whichhasthefollowingadvantages:unitvolumeintheevaporatorplate,theplatecondenserisaheattransferareaofshellandtubeheatexchangerofthreetimestheplateevaporatorheattransfercoefficientAbout1000~1200W/㎡•K,thecondenserplateheattransfercoefficientofabout1500~2000W/㎡•KareshellheatexchangertwotothreetimestheplateontheevaporatorusedtoRefrigerantdistributorofliquidevenlydistributeddevices,whentheevaporatorplateafewmore,maybeunevendistributionofliquidrefrigerantandcannottakefulladvantageofalltheheatandevaporationarea,evaporationtemperaturelowerthanthecalculateddesigntemperature.Afteradistributorovercometheseproblems.Detectionofdataontherelevantunits,evaporatorplate,theplatecondenserintheheattransfercoefficient△tmabout2.5~3℃,in1500~2000W/㎡•Kbetweentheresistanceandsmall,satisfyingtheheatpumpunitsRequirements.⑵smallNTU(∽0.3~2),the△tm(∽40~90℃)oftheplateheatexchangertomeettheheatrecoveryprocessandtheprocessheatingandcoolingrequirements.Whentheprocessinthe△tmconductedunderconditionsofheattransfer,thatdrivingforce,theheatandthesmaller,theheattransfercoefficientdemandisnothigh,butthatthisprocessorhigh-pressurework,orworkHightemperature,orprocessheatingandcoolingprocessintheliquidcontainingfiberdiameterorlargerparticles,theplateheatexchanger,thepressure,temperatureandabilitytorequest,theheatexchangertotheplatespacingrequirements.
①Pai(breathing)gas-watershellheatexchanger(Provincecan),Pai(breathing)gas-shell-airheatexchangers(airpreheater)isaheatexchangerinBeijingBeijing-equipmentmanufacturerslimitedliabilityPortlandpetrochemicalcompaniesandco-developedanewtypeofplateheatexchanger,allweldedplateheatexchangerintheheattransferthroughthemediumtoachievethecontrolboard,composedofboardcontrolbytheplateforformingmoldsuppression,all-welded-Beaminstalledinthepressureshell.Corrugatedplatewithstaticmixing,inaverylowReynoldsnumberformedundertheturbulence,andlowcoefficientofdirt,theheattransfercoefficientistheshellandtubeheatexchangerofthetwoorthreetimes.Inordertoadapttotheheattransfer,fluidpressureontherequest,boardspace,equivalentdiameterofabout28mm.Inordertomeetthedemandsofworkpre
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