离心泵毕业论文中英文资料对照外文翻译文献.docx

离心泵毕业论文中英文资料对照外文翻译文献.docx

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离心泵毕业论文中英文资料对照外文翻译文献

离心泵

中英文资料对照外文翻译文献

文献名称（外文）CENTRIFUGALPUMPSINTHECHEMICALINDUSTRY

Abstract:

Acentrifugalpumpconvertstheinputpowertokineticenergyintheliquidbyacceleratingtheliquidbyarevolvingdevice-animpeller.Themostcommontypeisthevolutepump.Fluidentersthepumpthroughtheeyeoftheimpellerwhichrotatesathighspeed.Thefluidisacceleratedradiallyoutwardfromthepumpchasing.Avacuumiscreatedattheimpellerseyethatcontinuouslydrawsmorefluidintothepump.Thisarticlestressesonaseriesofcentrifugalpumps，Fromabriefintroductiontotheprinciples.

Keywords:

centrifugalpump,Introduction,Workingprinciple,Cavitation，MechanismofCavitation，SolutionandRemedies

1.Introduction

Pump,deviceusedtoraise,transfer,orcompressliquidsandgases.Fourgeneralclassesofpumpsforliquidsaredescribedbelow.Inallofthem,stepsaretakentopreventcavitation（theformationofavacuum）,whichwouldreducetheflowanddamagethestructureofthepump.Pumpsusedforgasesandvaporsareusuallyknownascompressors.Thestudyoffluidsinmotioniscalledfluiddynamics.

Waterpump,deviceformovingwaterfromonelocationtoanother,usingtubesorothermachinery.Waterpumpsoperateunderpressuresrangingfromafractionofapoundtomorethan10,000poundspersquareinch.Everydayexamplesofwaterpumpsrangefromsmallelectricpumpsthatcirculateandaeratewaterinaquariumsandfountainstosumppumpsthatremovewaterfrombeneaththefoundationsofhomes.

Onetypeofmodernpumpsusedtomovewateristhecentrifugalpump.Earlyversionofthecentrifugalpump,thescrewpump,consistsofacorkscrew-shapedmechanisminapipethat,whenrotated,pullswaterupward.Screwpumpsareoftenusedinwaste-watertreatmentplantsbecausetheycanmovelargeamountsofwaterwithoutbecomingcloggedwithdebris.IntheancientMiddleEasttheneedforirrigationoffarmlandwasastronginducementtodevelopawaterpump.Earlypumpsinthisregionweresimpledevicesforliftingbucketsofwaterfromasourcetoacontaineroratrench.GreekmathematicianandinventorArchimedesisthoughttohavedevisedthefirstscrewpumpinthethirdcenturyBC.LaterGreekinventorCtesibiusdevelopthefirstliftpump.Duringthelate17thandearly18thCenturiesAD,BritishengineerThomasSavery,FrenchphysicistDenisPapin,AndBritishblacksmithandinventorThomasNewcomencontributedtothedevelopmentofawaterpumpthatusedsteamtopowerthepump’piston.Thesteam-poweredwaterpump’sfirstwideusewasinpumpingwateroutofmines.Modern-dayexamplesofcentrifugalpumpsarethoseusedattheGrandCouleeDamontheColumbiaRiver.Thispumpsystemhasthepotentialtoirrigateoveronemillionacresofland.

Alsoknownasrotarypumps,centrifugalpumpshavearotatingimpeller,alsoknownasablade,thatisimmersedintheliquid.Liquidentersthepumpneartheaxisoftheimpeller,andtherotatingimpellersweepstheliquidouttowardtheendsoftheimpellerbladesathighpressure.Theimpelleralsogivestheliquidarelativelyhighvelocitythatcanbeconvertedintopressureinastationarypartofthepump,knownasthediffuser.Inhigh-pressurepumps,anumberofimpellermaybeusedinseries,andthediffusersfollowingeachimpellermaycontainguidevanestograduallyreducetheliquidvelocity.Forlower-pressurepumps,thediffuserisgenerallyaspiralpassage,knownasavolute,withitscross-sectionalareaincreasinggraduallytoreducethevelocityefficiently.Theimpellermustbeprimedbeforeitcanbeginoperation,thatis,theimpellermustbesurroundedbyliquidwhenthepumpisstarted.Thiscanbedonebyplacingacheckvalveinthesuctionline,whichholdstheliquidinthepumpwhentheimpellerisnotrotating.Ifthisvalveleaks,thepumpmayneedtobeprimedbytheintroductionofliquidfromanoutsidesourcesuchasthedischargereservoir.Acentrifugalpumpgenerallyhasavalveinthedischargelinetocontroltheflowandpressure.Forlowflowsandhighpressures,theactionoftheimpellerislargelyradial.Forhigherflowsandlowerdischargepressure,thedirectionoftheflowwithinthepumpismorenearlyparalleltotheaxisoftheshaft,andthepumpissaidtohaveanaxialflow.Theimpellerinthiscaseactsasapropeller.Thetransitionfromonesetoffloeconditionstotheotherisgradual,andforintermediatecondition,thedeviceiscalledamixed-flowpump.

2.TheCentrifugalPump

Thecentrifugalpumpisbyfarthemostwidelyusedtypeinthechemicalandpetroleumindustries.Itwillpumpliquidswithverywiderangingpropertiesandsuspensionswithahighsolidscontentincluding,forexample,cementslurries,andmaybeconstructedfromaverywiderangofcorrosionresistantmaterials.Thewholepumpcasingmaybeconstructedfromplasticsuchaspolypropyleneoritmaybefittedwithacorrosion-resistantlining.Becauseitoperatesathighspeed,itmaybedirectlycoupledtoanelectricmotoranditwillgiveahighflowrateforitssize.

Inthistypeofpump,thefluidisfedtothecentreofarotatingimpellerandisthrownoutwardbycentrifugalaction.Asaresultofthehighspeedofrotationtheliquidacquiresahighkineticenergyandthepressuredifferencebetweenthesuctionanddeliverysidesarisesfromtheconversionofkineticenergyintopressureenergy.

Theimpellerconsistsofaseriesofcurvedvanessoshapedthattheflowwithinthepumpisassmoothaspossible.Thegreaterthenumberofvanesontheimpeller,thegreateristhecontroloverthedirectionoftheliquidandhencethesmallerarethelossesduetoturbulenceandcirculationbetweenthevanes.Intheopenimpeller,thevanesarefixedtoacentralhub,whereasintheclosedtypethevanesareheldbetweentwosupportingplatesandleakageacrosstheimpellerisreduced.Aswillbeseenlater,theangleofthetipsofthebladesverylargelydeterminestheoperatingcharacteristicsofthepump.

Theliquidentersthecasingofthepump，normallyinanaxialdirection，andispickedupbythevanesoftheimpeller．Inthesimpletypeofcentrifugalpump，theliquiddischargesintoavolute，achamberofgraduallyincreasingcross—sectionwithatangentialoutlet．AvolutetypeofpumpisshowninFig.（a）．Intheturbinepump[-Fig．（b）]theliquidflowsfromthemovingvanesoftheimpellerthroughaseriesoffixedvanesformingadiffusionring．

Thisgivesamoregradualchangeindirectiontothefluidandmoreefficientconversionofkineticenergyintopressureenergythanisobtainedwiththevolutetype．Theangleoftheleadingedgeofthefixedvanesshouldbesuchthatthefluidisreceivedwithoutshock．Theliquidsflowsalongthesurfaceoftheimpellervanewithacertainvelocitywhilstthetipofthevaneismovingrelativetothecasingofthepump．Thedirectionofmotionoftheliquidrelativetothepumpcasing--andtherequiredangleofthefixedvanes—isfoundbycompoundingthesetwovelocities．InFig．c，

c.

isthevelocityoftheliquidrelativetothevaneand

isthetangentialvelocityofthetipofthevane；compoundingthesetwovelocitiesgivestheresultantvelocity

oftheliquid．Itisapparent，therefore，thattherequiredvaneangleinthediffuserisdependentonthethroughput，thespeedofrotation，andtheangleoftheimpellerblades．Thepumpwillthereforeoperateatmaximumefficiencyonlyoveranarrowrangeofconditions．

Virtualheadofacentrifugalpump

Themaximumpressureisdevelopedwhenthewholeoftheexcesskineticenergyofthefluidisconvertedintopressureenergy.Asindicatedbelow．theheadisproportionaltothesquareoftheradiusandtothespeed，andisoftheorderof60mforasingle—stagecentrifugalpump；forhigherpressures，multistagepumpsmustbeused．Considertheliquidwhichisrotatingatadistanceofbetweenrandr+drfromthecentreofthepump（Fig．d）．

d

Themassofthiselementoffluiddmisgivenby2πrdrdρ，whereρisthedensityofthefluidand6isthewidthoftheelementoffluid。

Ifthefluidistravelingwithavelocityuandatanangleθtothetangentialdirection．Theangularmomentumofthismassoffluid

=dM（urcosθ）

Thetorqueactingonthefluiddτisequaltotherateofchangeofangularmomentumwithtime，asitgoesthroughthepump

Dτ=dMα/αt（urcosθ）=2πrbρdrα/αt（urcosθ）

Thevolumetricrateofflowofliquidthroughthepump：

Q=2πrbα/αt

Dr=Qρd（urcosθ）

Thetotaltorqueactingontheliquidinthepumpisthereforeobtainedintegratingdτbetweenthelimitsdenotedbysuffix1andsuffix2，wheresuffix1referstotheconditionsattheinlettothepumpandsuffix2referstotheconditionatthedischarge．

Thus，τ=Qρ（

cos

-

cos

）

Theadvantagesanddisadvantagesofthecentrifugalpump

Themainadvantagesare：

（1）Itissimpleinconstructionandcan，therefore，bemadeinawiderangeofmaterials

（2）Thereisacompleteabsenceofvalves．

（3）Itoperatesathighspeed（upto100Hz）and，therefore，canbecoupleddirectlyto

anelectricmotor.Ingeneral，thehigherthespeedthesmallerthepumpandmotorforagivenduty．

（4）Itgivesasteadydelivery．

（5）Maintenancecostsarelowerthanforanyothertypeofpump．

（6）Nodamageisdonetothepumpifthedeliverylinebecomesblocked，provideditisnotruninthisconditionforaprolongedperiod．

（7）Itismuchsmallerthanotherpumpsofequalcapacity．Itcan，therefore，bemadeintoasealedunitwiththedrivingmotorandimmersedinthesuctiontank．

（8）Liquidscontaininghighproportionsofsuspendedsolidsarereadilyhandled．

Themaindisadvantagesare：

（1）Thesingle—stagepumpwillnotdevelopahighpressu