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.PowderTechnology112200079–86StudiesontheeffectofswirlnumbersonstronglyswirlingturbulentgasparticleflowsusingaphaseDopplerparticleanemometerL.X.Zhou,Y.Li,T.Chen,Y.XuDepartmentofEngineeringMechanics,TsinghuaUni˝ersity,Beijing100084,PeoplesRepublicofChinaAbstractTheeffectofswirlnumbersontheflowbehaviorofstronglyswirlingturbulentgasparticleflowswithswirlnumbersofss0.47,1.0,.1.5and2.1insuddenexpansionandcyclonechambersisstudiedusinga2Danda3DphaseDopplerparticleanemometersPDPA..TheaxialandtangentialtimeaveragedandtherootmeansquareRMSfluctuationvelocitiesofgasandparticlephasesandparticleconcentrationaremeasured.Theresultshowsthattheswirlnumberhasanobviouseffectontheaxialvelocityprofiles,theRankinevortexstructureoftangentialvelocityprofiles,therelationshipbetweentwophasevelocities,theturbulenceintensitylevelandtheanisotropyofturbulence.KeywordsGasparticleflowsStronglyswirlingflowsPDPAmeasurement1.IntroductionSwirlinggasparticleflowsareencounteredincycloneseparators,cyclonecombustors,hydrocyclonesandswirlwxburnerrcombustors1,2.However,mostofthepresentwxstudiesarelimitedtoasinglegasphaseflowfield3–5.wxYuuetal.3studiedthegasflowfieldinacycloneseparatorusingprobeandhotwiresystems,andtheresultsshowareductionofgasaxialandtangentialvelocitiesinthepresenceofparticles.TheprobemeasurementsmadewxbySilvaandNebra4givesimilarresults.ThestudiesbywxOgawaetal.5demonstratedthattherewasnodistinctdifferencebetweenthedustladengasflowandthepureairflowinacyclonechamber.Obviously,probemeasurementscannotgivegasparticletwophaseflowfield.StudiesusingconventionalandmodifiedLaserDopplerVe.wxlocimeterLDV2,6showsimilarbehaviorofgasandparticleflowfieldse.g.,Rankinevortexstructuresof.tangentialvelocityprofilesandslipvelocitybetweengasandparticlephasesinswirlingflows.However,eventhemodifiedLDVmeasurementscannotgivereliableresults,becauseitisunabletoidentifyparticlesizesandtheeffectofparticlesizeisincludedintheparticleturbulentfluctuation.ThephaseDopplerparticleanemometerCorrespondingauthor.Tel.q861062782231faxq861062785569..Emailaddresszhoulxmail.tsinghua.edu.cnL.X.Zhou..PDPAmeasurementsallowobtainingthedetailedinformationofparticlevelocity,sizeandconcentration.ThePDPAwasfirstusedtostudysuddenexpansionswirlinggasparticleflowwithswirlingnumberss0.47bySomwxmerfeldandQiu7.Theirresultsdemonstratethedifferentbehaviorofparticlesofdifferentsizesinswirlingflows.However,noPDPAmeasurementsofstronglyswirlinggasparticleflowsarereported.Inthispaper,thePDPAsystemisusedtostudystronglyswirlinggasparticleflowsinsuddenexpansionandcyclonechamberswithtangentialinlets.Theswirlnumberswerevariedfrom1.0to1.5and2.1.Theresultsarecomparedwiththoseforthecaseofss0.47andanalyzed.Thepurposeofthisstudyistoclarifytheeffectofswirlnumbersonthebehaviorofswirlinggasparticleflows.2.ExperimentalsetupandmeasurementmethodsTheexperimentalsetupisshowninFig.1aandb.Itconsistsofatestsection,afeedingsystemandaPDPA.system.ThetestsectionisaplexiglasschamberFig.1b.withoneaxialinletf60mmplustwosymmetric.rectangulartangentialinlets6832mm.Thechamberisatubeof812mmlengthandaninnerdiameterof120mm.Ononeside,aslotisopenedandapieceofopticalglassismounted.Theexittubeisacylinderof1500mmL.X.Zhouetal.rPowderTechnology112200079–8680.Fig.1.a1Dataprocessor2signalprocessor3converter4transformer5powersupply6waterpurifier7laser8lasercontroller9splittinggroup10emitterunit11receiver12testsection13flowstabilizer14cycloneseparator15powderfeeder16flow.meter17valve18and19compressor.bExperimentalsetup.lengthand96mmdiameter,towhichalargersuddenexpansionchamberisconnectedforprotectingthetestsectionfromthedisturbanceofdownstreamflows.Acycloneseparatorisusedtocollecttheparticles.Twoblowerswithvariableflowratessupplytheaxialandtangentialflowsviathevalves,wherebytheflowratemaybeadjusted.Theflowratesweremeasuredbythreeseparateflowmeters.Sphericalglassbeadsofsizesrangingfrom0to150mmwereusedinmeasurements.TheparticlesizedistributionisshowninFig.2.Particlesbelow10mmweretakenasthegastracer.Thisavoidedmismatchedrefractiveindicesbetweenseedinganddispersedphaseparticlesandalsoeliminatedinterferencebetweenparticles.ThewidesizedistributionallowsobtainingthedifferentbehaviorofparFig.2.Particlesizedistribution.Fig.3.PDPAinstrumentation1,laser2,splitter3and4,lens5,measuringvolume6,receiver7,filter8,detector.ticleswithdifferentsizes.Particlesareintroducedfromtheaxialinletusingascrewfeeder.A3DPDPA,madebyDantecInc.,anda2DPDPAmadebyAerometrics,wereusedtomeasuresuddenexpansiongasparticleflows.Asforthemeasurementtechnique,the3DPDPAwithabackwardscatteringarrangementisshowninFig.3.Itisawellknownandwidelyusedtechnique.TheparticlevelocityismeasuredbasedontheDopplerfrequencyshift.TheparticlesizeandconcentrationaremeasuredbasedonthephasedifferencecausedbyMiescatteringandthenumberofparticlespassingthemeasuringvolumeduringacertaintimeinterval.TheparametersoftheopticalsystemareshowninTables1and2.Themeasurementswereperformedatfivecrosssectionsinthechamber,andforeachsection,thereareabout25–35measuringlocationsalongthediameter.Inthesinglephaseflowmeasurement,morethan1000samplesweretakenateachmeasuringlocation,while2000–5000samplesweretakenfortwophaseflowmeasurement.TheinletflowconditionsaregiveninTables3–5.TheswirlnumberisdefinedasD3r222rwurdrH0Ss,D3r22DrurdrH40whereDistheinletdiameterandDisthechamber34diameter.Duringtheexperiments,thetangentialinletflowvelocitywasconstant,andtheaxialinletflowvelocitywasTable1TransmittingopticsUUUxyz.Wavelengthofthelasermm514488476.FrequencyshiftMHz404040.Beamseparationmm747474.Diameterofmeasuringvolumemm1.351.351.35.Focallengthofthelasermm500500500.Fringeseparationmm3.53.313.23Fringenumber363636L.X.Zhouetal.rPowderTechnology112200079–8681Table2ReceivingopticsThemaximumdetecteddiameter260.24mm53Themaximumdetectedconcentration210rcmOffaxialangle1478Focallengthofreceivinglength600mmThevaluablesignlevely6dBThemaximumphaseerror258Themaximumsphericalerror15..increasedfrom0case1to12mrscase3,andinturn,decreasedtheswirlnumberfrom2.1downto1.0.3.ExperimentalresultsanddiscussionFigs.4–12showthemeasurementresultsforcyclonic.gasparticleflowswithss2.1case1.ThecomparisonbetweentheparticleladengasandthepuregasflowfieldisgiveninFigs.4–7.Figs.4and5showthegeneralbehaviorofcyclonictwophaseflowfieldwshapedaxialvelocityprofileswithanannularreverseflowzoneandRankinevortextangentialvelocityprofilesoftwophases.Itcanbeseenthatthepresenceofparticlesreducesthegastangentialvelocityeverywhere.Thegasaxialvelocitydecreasesinthenearwallzone,butincreasesinthenearaxiszone..ThemeasuredfluctuationvelocitiesFigs.6and7showthecentralpeakandtheincreasedvaluenearthewall,becauseofthelargevelocitygradientinthesolidbodyrotationregionandtheregionnearthewall.Thecomparisonbetweenthesetwofiguresshowsthattheaxialfluctuationvelocitiesaremuchsmallerthanthetangentialones,demonstratingthehighanisotropyofturbulentfluctuations.Moreover,thesefiguresindicatethatthepresence.ofparticlesreducesgasrootmeansquareRMStangentialfluctuationvelocityalmosteverywhereandaxialfluctuationvelocityinmostregionsbutincreasesthelatteroneinreverseflowzones.Forparticleconcentration,alargeamountofparticles.almostconcentratesinthenearwallregionFig.12duetothestrongcentrifugalforce.Figs.8–11givethecomparisonbetweenthetwophasetangential,axialvelocitiestogetherwiththeRMSfluctua.tionvelocitiesfortwoparticlesizes60and100mm.Table3.Inletflowconditioncase1Axialinletvelocity0mrsTangentialinletvelocity10mrsSwirlnumber2.1Particlemeandiameter76.3mm3Particlematerialdensity2400kgrmParticlemassloading0.01kgsolidrkggasTable4.Inletflowconditioncase2Axialinletvelocity5mrsTangentialinletvelocity10mrsSwirlnumber1.5Particlemassloading0.01kgsolidrkggasFigs.8and9showthattheparticletangentialvelocitylagsbehindthegastangentialvelocityalmosteverywherewiththelargerparticleshavinglowervelocitiesduetotheirhigherinertia.Theparticleaxialvelocitylagsbehindthegasaxialvelocityonlyinthenearwallregion.ItcanbeseenfromFigs.10and11thattheparticleturbulentfluctuationislowerthanthegasfluctuationinmostregionsbothinaxialandtangentialdirections,andthelargertheparticlesize,thesmallertheparticlefluctuation.Figs.13,15–18givethemeasurementresultsforthe.suddenexpansionflowswithss1.5case2.AscanbeseenfromFig.13,inthiscasetheaxialvelocitiesoftwophaseshavenowshapeddistributionsasthatforthecases..ofss2.1Fig.4and0.47Fig.14,butarehigherneartheaxisandlowerwithasmallpeaknearthewall.Theparticleaxialvelocitylagsbehindthegasoneinmostregions,andthevelocityslipbetweentwophasesincreaseswiththeincreaseinparticlesize,buttherelativeslipisnotverylarge.Inthenearwallregion,theparticleaxialvelocityisslightlylargerthanthegasvelocity.Theparticletangentialvelocitylagsbehindthegastangentialveloc.ityFig.15,andthelargertheparticlesize,themorethelag.Inthefirstandsecondsections,thestructureofrigidbodyrotationintangentialvelocityprofilesisnotobviousbecauseoftheinjectionofaxialnonswirlingflows.Inthesubsequentsections,duetotheincreasingeffectofcentrifugalforce,thetangentialvelocitydistributionoftwophasesshowsanobviousRankinevortexstructurewiththegraduallyvanishingeffectofinletconditions.Fig.16givestheparticleandthegasaxialfluctuationvelocitieswithhighervaluesnearthewallandlowervaluesneartheaxis.Unlikethatincase1,thereisnopeakvalueneartheaxisinthiscase.Theparticleaxialfluctuationvelocityissmallerthanthatofthegasphase,anddecreaseswiththeincreaseofparticlesize.Theseresultsaresimilartothoseforcase1.Fig.17indicatesthattheparticletangentialfluctuationvelocityissmallerthanthatofthegasphaseinmostregions.Thisissimilartothatforcase1andthosewxreportedpreviously2,6,7bothforweaklyandstronglyswirlinggasparticleflows.Table5.Inletflowconditioncase3Axialinletvelocity12mrsTangentialinletvelocity10mrsSwirlnumber1.0Particlemassloading0.01kgsolidrkggasL.X.Zhouetal.rPowderTechnology112200079–8682..Fig.4.Gastangentialmeanvelocitiesmrscase1...Fig.5.Gasaxialmeanvelocitiesmrscase1...Fig.6.Gastangentialfluctuationvelocitiesmrscase1...Fig.7.Gasaxialfluctuationvelocitiesmrscase1...Fig.8.Twophasetangentialtimeaveragedvelocitiesmrscase1...Fig.9.Twophaseaxialtimeaveragedvelocitiesmrscase1.Fig.10.Twophasetangentialfluctuationvelocities...Fig.11.Twophaseaxialfluctuationvelocitiesmrscase1.
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