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1、Readingmaterial20BasicStirredTankDesignThedimensionsoftheliquidcontentofavesselandthedimensionsandarrangementofimpellers,bafflesandotherinternalsarefactorsthatinfluencetheamountoftheenergyrequiredforachievinganeededamountofagitationorqualityofmixing.Theinternalarrangementsdependontheobje
2、ctivesoftheoperation:whetheritistomaintainhomogeneityofareactingmixtureortokeepasolidsuspendedoragasdispersedortoenhanceheatormasstransfer.Abasicrangeofdesignfactors,however,canbedefinedtocoverthemajorityofthecases,forexampleasinFig.4.4(a).TheVesselAdishedbottomrequireslesspowerthanaflat
3、one.Whenasingleimpelleristobeused,aliquidlevelequaltothediameterisoptimum,withtheimpellerlocatedatthecenterforanall-liquidsystem.Economicandmanufacturingconsiderations,however,oftendictatehigherratiosofdepthtodiameter.BafflesExceptatveryhighReynoldsnumbers,bafflesareneededtopreventvortex
4、ingandrotationoftheliquidmassasawhole.Whensolidsarepresentorwhenaheattransferjacketisused,thebafflesareoffsetfromthewalladistanceequaltoone-sixththebafflewidthwhichisaboutone-twelfththetankdiameter.Fourradialbafflesatequalspacingarestandard;sixareonlyslightlymoreeffective,andthreeappreci
5、ablylessso.Whenthemixerneeded,particularlyatlowviscosity.DraftTubesAdrafttubeisacylindricalhousingaroundandslightlylargerindiameterthantheimpeller.Itsheightmaybelittlemorethanthediameteroftheimpelleroritmayextendthefulldepthoftheliquid,dependingontheflowpatternthatisrequired.Usuallydraft
6、tubesareusedwithaxialimpellerstodirectsuctionanddischargestreams.Animpeller-drafttubesystembehavesasanaxialflowpumpofsomewhatlowefficiency.Itstoptobottomcirculationbehaviorisofparticularvalveindeeptanksforsuspensionofsolidsandfordispersionofgases.ImpellerSizeThisdependsonthekindofimpelle
7、randoperatingconditionsdescribedbytheRoynolds,Froude,andPowernumbersaswellasindividualcharacteristicswhoseeffectshavebeencorrelated.Forthepopularturbineimpeller,theratioofdiametersofimpellerandvesselfallsintherange,d/,thelowervaluesathighrpm,ingasdispersion,forexample.Imp
