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,Mie-University,Kamihama-cho1515,Tsu,Mie514-8507,JapanReceived23March2002；receivedinrevisedform1September2002；accepted14November2002AbstractRecently,therearegreatrequirementsforultrafinepowderinfieldsthatuseadvancedmaterials,forexample,electricpartsinInformationTechnology(IT)industry.Especially,therequestforthediametercontrolofultrafinepowderisincreasing.Pneumatictypeultrafinepowderseparator,classifier,isoneoftheequipmentwhichmeetthisrequest.Butthereisnoclarifiedstudyontheflowconditionthatrealizeshighperformance.Inthisstudy,anewpneumatictypeultrafineclassifierisproposedandtherelationbetweentheperformanceandtheflowconditionisinvestigatedbyflowvisualizationwiththetuftgridandoildotmethodsandthemeasurementofgasvelocity.Basedontheresults,itwasknownthatthenewclassifierhasalargeswirlingflowvelocitywhichisabletoclassifyultrafineparticlesaccurately.Keywords:Gassolidflow；Pneumaticpowderclassifier；Ultrafinepowder；Flowvisualization；Velocitydistribution1.IntroductionAdvancedindustrialmaterials,suchasfineceramics,ultra-conductormaterial,magneticfines,tonerusedforprinters,etc.,areusuallyintheformoffinepowder.Recently,duetotherapidprogressoftheInformationTechnology(IT)industry,therequirementtocontroltheparticlediameter,suchastomakefinepowder(pulveriza-tion)uniformlytoarrangefinepowderedparticles(classi-fication)ofinorganicandorganicdrymaterials,haschangeddrasticallyfromtheparticlesizeofAm-ordertosub-Am-order(hereafter,itiscalledultrafinepowder,1Amorless).Now,manytypesofpowderclassifiersarecom-merciallyavailable.Forexample,therearecyclone-typeseparators1,cross-flowairtypeclassifiers2andimpel-lerwheeltypeclassifiers3,whichareusedwidelyinthemanufacturingprocessofpowderedmaterials,althoughtheclassifiercanclassifyultrafinepowderindryconditionsaccuratelyandthereisnosuchclassifierinindustrialfields.Inthisstudy,anewpneumatictypeofultrafinepowderclassifier(hereafter,itiscalledthenewclassifier)isintro-duced.Thenewclassifierusesanewtypeofswirlingflowandsatisfiestheabove-mentionedrequirements.Itwasintendedtorealizeanidealflowfieldtogivealargecentrifugalforceforallsuppliedfinepowderthatcanbeclassifiedaccuratelyinultrafinepowder.Theflowconditionwasconfirmedbyflowvisualizationandobservation,themeasurementofgasvelocitydistributionandtheexperimentofclassification.Itisimportanttounderstandtheflowconditionquantitativelywhenrealizingaclassifierwithhighperformance.Inaddition,theclassificationperformancewasconfirmedbyatestthatusessomefineparticles,suchascalciumcarbonateandtungstendioxide.Asaresult,itwasknownthatthenewpneumatictypeclassifiercanclassifyanultrafinepowderofsub-Am.2.Conceptofultrafinepowderclassification,experimentalsetupandprocedure2.1.ConceptandexperimentalsetupInordertoclassifyanultrafineparticle,itisveryimportanttoexertalargecentrifugalforceoneachparticle.Thenewclassifierhasaconical-shapedclassificationzoneandthenthemostofswirlingflowpassesthroughthelouver,whichflowsupward,andthenthetangentialvelocityacceleratesrapidlybecausetheswirlingradiusbecomessmaller.Everyparticlecanbegivenalargecentrifugalforcebyalargetangentialvelocity.Thenewclassifierhasnotonlyaveryhighclassificationperformancebutalsoalargefeedrateofmaterial.Theconventionalfinepowderclassi-*Correspondingauthor.Tel.:+81-592319384；fax:+81-592319663.E-mailaddress:anglerict.ne.jp(H.Morimoto).PowderTechnology131(2003)7179fierhasahighclassificationperformancebutthefeedrateisverysmallingeneral.Fig.1showsthepneumatictypeclassifier.Theclassifierusesonlyaswirlingflowanddoesnothaveanymovingpartsinsideit.Theclassifierconsistsofadispersionzonei,classificationzoneofconicalshapeiiandguidevanezoneiii.Powderedmaterialissuppliedintothedispersionzoneandtheairisintroducedfromtheoutsideintotheclassifierpassingthroughtheguidevane(hereafter,itiscalledthelouver),whichis20mminheightand77mminlengthandgeneratesaswirlingflow.Thedispersionzonehasamainnozzletosupplymaterialof12mmindiameter,thedispersionnozzleanddispersioncone.Theclassificationzonehasalowersurfaceofangleb20jintheclassifica-tionzoneandtheuppersurfaceofanglea60jalsointheclassificationzone.Moreover,thediameteroftheexitpipeD=60mmfortheswirlingairflowwithfinepowderexistsatthecenterofthelowersurfaceintheclassificationzoneandtheexhaustslit,5mminwidth,forcoarsepowderexistsattheoutercircumference.Thedispersionconesetatthecenterofthetopintheclassificationzonepreventsthesuppliedmaterialfromflowingtotheexitdirectly.Fig.2showstheschematicdiagramoftheexperimentalsetup.AirflowAirIwithfinepowder,airflowAirIIfordispersionofpowderandairflowAirIIIfromthelouveraresuckedbyblower,andalloftheairflowisexhaustedtotheoutsidethroughbag-filter.Acenteraxisoftheclassifierisassumedtobethexcoordinate,andrcoordinateintheradial(seeFig.1).ThepowderladenAirIflowsintotheconical-shapedclassi-ficationzonefromthetopandintheC0xdirection,gravita-tionaldirection,afterdispersedwellbytheAirII.TheAirIIIflowsintotheclassificationzoneuniformlythroughthepassagebetweenthelouversthataresetatthebottomouterpartevenly.The16piecesoflouveraresetupevenlyinthecircumferentialdirection(AAsection),andthewidthofthepassagebetweenthelouversischangeableintherangeof1to7mm.Thesettinganglehiofthelouverdependsonthewidthofthepassagebetweenthelouversandcanbesetintherangeof7jto15j.Theswirlingflowisproducedbytheflowthatpassesthroughthepassagebetweenthelouvers.ThevolumetricflowrateratioofAirI,AirIIandAirIIIis7:3:90.Then,theflowcharacteristicsoftheswirlingflowintheclassificationzonedependsontheflowofAirIII.Moreover,theswirlingflowintheclassificationzoneformsathree-dimensionalcomplexflowfieldwhereacentrifugalforceisexerted.TheAirIIIflowsintheradialdirection(centerdirection)oftheconicwhileswirling,andtheflowthatreachestothecenterisexhaustedfromtheexit.Ontheotherhand,therawpowderedmaterialwithafixedquantityandAirIisintroducedintothedispersionzonewithswirlingfromthemainnozzleafterdispersingwellbyAirII.Theswirlingdirectionisthesamedirectionasthatintheclassificationzone.TherawpowderedmaterialFig.1.Ultrafinepowderclassifier.H.Morimoto,T.Shakouchi/PowderTechnology131(2003)717972introducedintotheclassificationzonereceivesalargecentrifugalforceintheupperregionoftheconic,andthenthecoarsepowderisseparatedintheradialdirectionandiscollectedfromtheslitatthebottomandoutsideoftheclassificationzonetothehopper.Thedescendingflowwiththeultrafinepowderinthevicinityofthecenteroftheclassificationzoneflowsoutfromtheexitandthebagfiltercollectsthepowder.2.2.MeasurementofvelocitydistributionTheexperimentalsetupusedtomeasurethevelocitydistributioninthisclassifierisshowninFig.3.Ayawmeter4of1.0mmindiameterand300mminlengthwithasingleholeof0.5mmindiameterwasinsertedinright-angleddirection(raxis)tothecenteraxis(xaxis)intheclassificationzone.Thevelocitydistributionwasmeasuredinthesectionoftheraxisatx=105mm.Theyawmetercanmovealongtheraxisandrotatearounditsownaxis,andcanmeasurethevelocityintherandxdirectionsatanarbitraryradiusposition.Thehorizontaldirectionwasassumedtobeh=0j,itwasrotateduptoh=120jatevery10j(240jintotal)vertically,andthepressurewasmeasuredbyusingamercurycolumnmanometer(Fig.2,).Inthiscase,theamountofallinflowairwasQ=6.5m3/min(constant),andthewidthofthepassagebetweenthelouverswaschangedatFig.3.Velocitymeasurementbyyawmeter.Fig.2.Experimentalsetup.H.Morimoto,T.Shakouchi/PowderTechnology131(2003)717973wl=3,5,and7mm.Theflowdirection(angleinupanddown)ateachmeasurementpositionwascalculatedfromthepressuredistribution,andthevelocityoftheairflowwascalculatedfromthestaticanddynamicpressures.Everyexperimentforvelocitydistributionwascarriedoutonlyforasinglephase,airflowwhichdidnotwithfinepowder.3.FlowvisualizationsandobservationTounderstandtheflowconditionintheclassificationzonequalitatively,flowvisualizationandobservationbythetuftgridmethodandtheoildotmethodweredone.3.1.TuftgridmethodTheshapeofthetuftgrid5andthetuftusedareshowninFig.4.Theframewasmadebyastainlesssteelstickof/3.0mmandthewireof/0.3mmwasstringedlikethegrid.Thetuftwasmadeofnylonfinefiberwithalength15mmwasbondedatthe73nodesofthewire.Theframewassetattheradiuspositionofasectiononthexaxisintheclassificationzone.Thetuftgridwassetintheclassifiermadebytransparentacrylicresin,andtheexperimentwascarriedoutforonlytheairflow.Theinclinationandfluctuationofthetufteffectedbytheswirlingflowwereobservedfromthehorizontalandperpendiculardirections,andtheywererecordedbyavideocamera(Fig.2,).3.2.OildotmethodThe35oildotsontheuppersurfaceandthe20pointsonthelowersurfaceintheclassificationzoneatradialtwoplaces(every180j)wereusedtofindouttheflowdirectiononthesurfaces.TheamountofallairinflowisQ=3.5m3/min,andtheaverageinflowvelocityisVi=58m/s(wl=3mm)atthelouver,andthetrajectoryoftheoildotaftertheexperimentforonlytheairwasobserved.Theswirlingangleoftheflowonthesurfacewasmeasuredfromthetrajectoryoftheoildot.Themixtureconsistedof77.4%liquidparaffininvolume,6.5%linseedoil,6.5%oleicacidsand9.6%titania