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外文翻译--一种新型风动式选粉机对极细粉末分级的研究 英文版.pdf

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外文翻译--一种新型风动式选粉机对极细粉末分级的研究 英文版.pdf

ClassificationofultrafinepowderbyanewpneumatictypeclassifierHiroshiMorimoto,ToshihikoShakouchiGraduateSchoolofEngineering,MieUniversity,Kamihamacho1515,Tsu,Mie5148507,JapanReceived23March2002receivedinrevisedform1September2002accepted14November2002AbstractRecently,therearegreatrequirementsforultrafinepowderinfieldsthatuseadvancedmaterials,forexample,electricpartsinInformationTechnologyITindustry.Especially,therequestforthediametercontrolofultrafinepowderisincreasing.Pneumatictypeultrafinepowderseparator,classifier,isoneoftheequipmentwhichmeetthisrequest.Butthereisnoclarifiedstudyontheflowconditionthatrealizeshighperformance.Inthisstudy,anewpneumatictypeultrafineclassifierisproposedandtherelationbetweentheperformanceandtheflowconditionisinvestigatedbyflowvisualizationwiththetuftgridandoildotmethodsandthemeasurementofgasvelocity.Basedontheresults,itwasknownthatthenewclassifierhasalargeswirlingflowvelocitywhichisabletoclassifyultrafineparticlesaccurately.KeywordsGas–solidflowPneumaticpowderclassifierUltrafinepowderFlowvisualizationVelocitydistribution1.IntroductionAdvancedindustrialmaterials,suchasfineceramics,ultraconductormaterial,magneticfines,tonerusedforprinters,etc.,areusuallyintheformoffinepowder.Recently,duetotherapidprogressoftheInformationTechnologyITindustry,therequirementtocontroltheparticlediameter,suchastomakefinepowderpulverizationuniformlytoarrangefinepowderedparticlesclassificationofinorganicandorganicdrymaterials,haschangeddrasticallyfromtheparticlesizeofAmordertosubAmorderhereafter,itiscalledultrafinepowder,1Amorless.Now,manytypesofpowderclassifiersarecommerciallyavailable.Forexample,therearecyclonetypeseparators1,crossflowairtypeclassifiers2andimpellerwheeltypeclassifiers3,whichareusedwidelyinthemanufacturingprocessofpowderedmaterials,althoughtheclassifiercanclassifyultrafinepowderindryconditionsaccuratelyandthereisnosuchclassifierinindustrialfields.Inthisstudy,anewpneumatictypeofultrafinepowderclassifierhereafter,itiscalledthenewclassifierisintroduced.Thenewclassifierusesanewtypeofswirlingflowandsatisfiestheabovementionedrequirements.Itwasintendedtorealizeanidealflowfieldtogivealargecentrifugalforceforallsuppliedfinepowderthatcanbeclassifiedaccuratelyinultrafinepowder.Theflowconditionwasconfirmedbyflowvisualizationandobservation,themeasurementofgasvelocitydistributionandtheexperimentofclassification.Itisimportanttounderstandtheflowconditionquantitativelywhenrealizingaclassifierwithhighperformance.Inaddition,theclassificationperformancewasconfirmedbyatestthatusessomefineparticles,suchascalciumcarbonateandtungstendioxide.Asaresult,itwasknownthatthenewpneumatictypeclassifiercanclassifyanultrafinepowderofsubAm.2.Conceptofultrafinepowderclassification,experimentalsetupandprocedure2.1.ConceptandexperimentalsetupInordertoclassifyanultrafineparticle,itisveryimportanttoexertalargecentrifugalforceoneachparticle.Thenewclassifierhasaconicalshapedclassificationzoneandthenthemostofswirlingflowpassesthroughthelouver,whichflowsupward,andthenthetangentialvelocityacceleratesrapidlybecausetheswirlingradiusbecomessmaller.Everyparticlecanbegivenalargecentrifugalforcebyalargetangentialvelocity.Thenewclassifierhasnotonlyaveryhighclassificationperformancebutalsoalargefeedrateofmaterial.TheconventionalfinepowderclassiCorrespondingauthor.Tel.81592319384fax81592319663.Emailaddressanglerict.ne.jpH.Morimoto.PowderTechnology131200371–79fierhasahighclassificationperformancebutthefeedrateisverysmallingeneral.Fig.1showsthepneumatictypeclassifier.Theclassifierusesonlyaswirlingflowanddoesnothaveanymovingpartsinsideit.Theclassifierconsistsofadispersionzonei,classificationzoneofconicalshapeiiandguidevanezoneiii.Powderedmaterialissuppliedintothedispersionzoneandtheairisintroducedfromtheoutsideintotheclassifierpassingthroughtheguidevanehereafter,itiscalledthelouver,whichis20mminheightand77mminlengthandgeneratesaswirlingflow.Thedispersionzonehasamainnozzletosupplymaterialof12mmindiameter,thedispersionnozzleanddispersioncone.Theclassificationzonehasalowersurfaceofangleb20jintheclassificationzoneandtheuppersurfaceofanglea60jalsointheclassificationzone.Moreover,thediameteroftheexitpipeD60mmfortheswirlingairflowwithfinepowderexistsatthecenterofthelowersurfaceintheclassificationzoneandtheexhaustslit,5mminwidth,forcoarsepowderexistsattheoutercircumference.Thedispersionconesetatthecenterofthetopintheclassificationzonepreventsthesuppliedmaterialfromflowingtotheexitdirectly.Fig.2showstheschematicdiagramoftheexperimentalsetup.AirflowAirIwithfinepowder,airflowAirIIfordispersionofpowderandairflowAirIIIfromthelouveraresuckedbyblower,andalloftheairflowisexhaustedtotheoutsidethroughbagfilter.Acenteraxisoftheclassifierisassumedtobethexcoordinate,andrcoordinateintheradialseeFig.1.ThepowderladenAirIflowsintotheconicalshapedclassificationzonefromthetopandintheC0xdirection,gravitationaldirection,afterdispersedwellbytheAirII.TheAirIIIflowsintotheclassificationzoneuniformlythroughthepassagebetweenthelouversthataresetatthebottomouterpartevenly.The16piecesoflouveraresetupevenlyinthecircumferentialdirectionA–Asection,andthewidthofthepassagebetweenthelouversischangeableintherangeof1to7mm.Thesettinganglehiofthelouverdependsonthewidthofthepassagebetweenthelouversandcanbesetintherangeof7jto15j.Theswirlingflowisproducedbytheflowthatpassesthroughthepassagebetweenthelouvers.ThevolumetricflowrateratioofAirI,AirIIandAirIIIis7390.Then,theflowcharacteristicsoftheswirlingflowintheclassificationzonedependsontheflowofAirIII.Moreover,theswirlingflowintheclassificationzoneformsathreedimensionalcomplexflowfieldwhereacentrifugalforceisexerted.TheAirIIIflowsintheradialdirectioncenterdirectionoftheconicwhileswirling,andtheflowthatreachestothecenterisexhaustedfromtheexit.Ontheotherhand,therawpowderedmaterialwithafixedquantityandAirIisintroducedintothedispersionzonewithswirlingfromthemainnozzleafterdispersingwellbyAirII.Theswirlingdirectionisthesamedirectionasthatintheclassificationzone.TherawpowderedmaterialFig.1.Ultrafinepowderclassifier.H.Morimoto,T.Shakouchi/PowderTechnology131200371–7972introducedintotheclassificationzonereceivesalargecentrifugalforceintheupperregionoftheconic,andthenthecoarsepowderisseparatedintheradialdirectionandiscollectedfromtheslitatthebottomandoutsideoftheclassificationzonetothehopper.Thedescendingflowwiththeultrafinepowderinthevicinityofthecenteroftheclassificationzoneflowsoutfromtheexitandthebagfiltercollectsthepowder.2.2.MeasurementofvelocitydistributionTheexperimentalsetupusedtomeasurethevelocitydistributioninthisclassifierisshowninFig.3.Ayawmeter4of1.0mmindiameterand300mminlengthwithasingleholeof0.5mmindiameterwasinsertedinrightangleddirectionraxistothecenteraxisxaxisintheclassificationzone.Thevelocitydistributionwasmeasuredinthesectionoftheraxisatx105mm.Theyawmetercanmovealongtheraxisandrotatearounditsownaxis,andcanmeasurethevelocityintherandxdirectionsatanarbitraryradiusposition.Thehorizontaldirectionwasassumedtobeh0j,itwasrotateduptoh120jatevery10j240jintotalvertically,andthepressurewasmeasuredbyusingamercurycolumnmanometerFig.2,.Inthiscase,theamountofallinflowairwasQ6.5m3/minconstant,andthewidthofthepassagebetweenthelouverswaschangedatFig.3.Velocitymeasurementbyyawmeter.Fig.2.Experimentalsetup.H.Morimoto,T.Shakouchi/PowderTechnology131200371–7973wl3,5,and7mm.Theflowdirectionangleinupanddownateachmeasurementpositionwascalculatedfromthepressuredistribution,andthevelocityoftheairflowwascalculatedfromthestaticanddynamicpressures.Everyexperimentforvelocitydistributionwascarriedoutonlyforasinglephase,airflowwhichdidnotwithfinepowder.3.FlowvisualizationsandobservationTounderstandtheflowconditionintheclassificationzonequalitatively,flowvisualizationandobservationbythetuftgridmethodandtheoildotmethodweredone.3.1.TuftgridmethodTheshapeofthetuftgrid5andthetuftusedareshowninFig.4.Theframewasmadebyastainlesssteelstickof/3.0mmandthewireof/0.3mmwasstringedlikethegrid.Thetuftwasmadeofnylonfinefiberwithalength15mmwasbondedatthe73nodesofthewire.Theframewassetattheradiuspositionofasectiononthexaxisintheclassificationzone.Thetuftgridwassetintheclassifiermadebytransparentacrylicresin,andtheexperimentwascarriedoutforonlytheairflow.Theinclinationandfluctuationofthetufteffectedbytheswirlingflowwereobservedfromthehorizontalandperpendiculardirections,andtheywererecordedbyavideocameraFig.2,.3.2.OildotmethodThe35oildotsontheuppersurfaceandthe20pointsonthelowersurfaceintheclassificationzoneatradialtwoplacesevery180jwereusedtofindouttheflowdirectiononthesurfaces.TheamountofallairinflowisQ3.5m3/min,andtheaverageinflowvelocityisVi58m/swl3mmatthelouver,andthetrajectoryoftheoildotaftertheexperimentforonlytheairwasobserved.Theswirlingangleoftheflowonthesurfacewasmeasuredfromthetrajectoryoftheoildot.Themixtureconsistedof77.4liquidparaffininvolume,6.5linseedoil,6.5oleicacidsand9.6titaniawasusedaswhitecoloreddye.4.ApproximatetheoryforcuttingsizeThecuttingsizeoftheclassifierclassificationpointwasapproximatelycalculatedasfollows.Fig.5showsanimitativechartoftheprinciple.Consideringadynamicforcethatexertsontheparticlesuppliedintheclassificationzone,theequationofthemotionofasinglesphericalparticleswirlingonanarbitraryradiuspositionisshownasfollowsp6D3pqpdVrdt¼p6D3pðqpC0qÞrx2C0CDp8D2pqV2rð1ÞTheterminalvelocityoftheparticlecanbedrawnfromEq.1asfollowsdVrdt0Vrt¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi4ðqpC0qÞDprx23qCDsð2ÞMoreover,whentheparticleReynoldsnumberReisintheStokesregion,thedragcoefficientoftheparticleisCD24/ReforRe2,andthenVrt¼ðqpC0qÞD2prx218lð3ÞNow,sincethetangentialvelocityisVtrxVrt¼ðqpC0qÞD2pV2t18lrð4ÞTheflowintheclassificationzoneformsasemifreevortextypeflow.Vtrn¼constð5ÞHowever,thevortexcoefficientnwasabout0.8fromtheexperiment.Therefore,thefollowingrelationcanbeobtainedatthelouverontheradiusR.Vtrn¼ðVicoshiÞRnð6ÞFig.4.Flowvisualizationbytuftgridmethod.H.Morimoto,T.Shakouchi/PowderTechnology131200371–7974

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