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1、Readingmaterial20BasicStirredTankDesignThedimensionsoftheliquidcontentofavesselandthedimensionsandarrangementofimpellers,bafflesandotherinternalsarefactorsthatinfluencetheamountoftheenergyrequiredforachievinganeededamountofagitationorqualityofmixing.Theinternalarrangementsdependontheobjectives
2、oftheoperation:whetheritistomaintainhomogeneityofareactingmixtureortokeepasolidsuspendedoragasdispersedortoenhanceheatormasstransfer.Abasicrangeofdesignfactors,however,canbedefinedtocoverthemajorityofthecases,forexampleasinFig.4.4(a).TheVesselAdishedbottomrequireslesspowerthanaflatone.Whenasin
3、gleimpelleristobeused,aliquidlevelequaltothediameterisoptimum,withtheimpellerlocatedatthecenterforanall-liquidsystem.Economicandmanufacturingconsiderations,however,oftendictatehigherratiosofdepthtodiameter.BafflesExceptatveryhighReynoldsnumbers,bafflesareneededtopreventvortexingandrotationofth
4、eliquidmassasawhole.Whensolidsarepresentorwhenaheattransferjacketisused,thebafflesareoffsetfromthewalladistanceequaltoone-sixththebafflewidthwhichisaboutone-twelfththetankdiameter.Fourradialbafflesatequalspacingarestandard;sixareonlyslightlymoreeffective,andthreeappreciablylessso.Whenthemixern
5、eeded,particularlyatlowviscosity.DraftTubesAdrafttubeisacylindricalhousingaroundandslightlylargerindiameterthantheimpeller.Itsheightmaybelittlemorethanthediameteroftheimpelleroritmayextendthefulldepthoftheliquid,dependingontheflowpatternthatisrequired.Usuallydrafttubesareusedwithaxialimpellers
6、todirectsuctionanddischargestreams.Animpeller-drafttubesystembehavesasanaxialflowpumpofsomewhatlowefficiency.Itstoptobottomcirculationbehaviorisofparticularvalveindeeptanksforsuspensionofsolidsandfordispersionofgases.ImpellerSizeThisdependsonthekindofimpellerandoperatingconditionsdescribedbyth
7、eRoynolds,Froude,andPowernumbersaswellasindividualcharacteristicswhoseeffectshavebeencorrelated.Forthepopularturbineimpeller,theratioofdiametersofimpellerandvesselfallsintherange,d/,thelowervaluesathighrpm,ingasdispersion,forexample.Imp
