performance,form17pressurecomparingtheperformanceofadoubleinletcyclonewithPowderTechnology145(2004)operation.However,theincreasingemphasisonenviron-mentprotectionandgassolidseparationisindicatingthatfinerandfinerparticlesmustberemoved.Tomeetthischallenge,theimprovementofcyclonegeometryandper-formanceisrequiredratherthanhavingtoresorttoalterna-tiveunits.Manyresearchershavecontributedtolargevolumeofworkonimprovingthecycloneperformance,byintroducingnewinletdesignandoperationvariables.Theseincludestudiesoftestingacyclonicfractionatorforresearchers,wasdeveloped,andtheexperimentalstudyonaddressingtheeffectofinlettypeoncycloneperformanceswaspresented.2.ExperimentalThreekindsofcycloneseparatorswithvariousinletgeometries,includingconventionaltangentialsingleinlethavebecameoneofmostimportantparticleremovaldevicethatpreferablyisutilizedinbothengineeringandprocesscleanairbyLimetal.6.Inthispaper,thenewinlettype,whichisdifferenttypeofinletfromthatusedbyformersimplicitytofabricate,lowcosttooperate,andwelladapt-abilitytoextremelyharshconditions,cycloneseparatorsKeywords:Cyclone；Symmetricalspiralinlet；Collectionefficiency；Pressuredrop1.IntroductionCycloneseparatorsarewidelyusedinthefieldofairpollutioncontrolandgassolidseparationforaerosolsamplingandindustrialapplications1.Duetorelative2,developingamathematicmodeltopredictthecollectionefficiencyofsmallcylindricalmultiportcyclonebyDeOtte3,testingamultipleinletcyclonesbasedonLappletypegeometrybyMooreandMcfarland4,designingandtestingarespirablemultiinletcyclonesamplerthatminimizetheorientationbiasbyGautamandStreenath5,andparticlesizeandflowrateinthispaper.Experimentalresultindicatedthatthesymmetricalspiralinlet(SSI),especiallyCSSIinletgeometry,haseffectonsignificantlyincreasingcollectionefficiencywithinsignificantlyincreasingpressuredrop.Inaddition,theresultsofcollectionefficiencyandpressuredropcomparisonbetweentheexperimentaldataandthetheoreticalmodelwerealsoinvolved.ShortcommuniDevelopmentofasymmetricalcycloneseparatorBingtaoZhao*,HenggenDepartmentofEnvironmentalEngineering,DonghuaUniversityReceived28October2003；receivedinrevisedAvailableonlineAbstractThreecycloneseparatorswithdifferentinletgeometryweredesigned,directsymmetricalspiralinlet(DSSI),andaconvergingsymmetricalperformancecharacteristics,includingthecollectionefficiencyandsamplingthatusedmultipleinletvanesbyWeddingetal.*Correspondingauthor.Tel.:+86-21-62373718；fax:+86-21-62373482.E-mailaddress:(B.Zhao).Shen,YanmingKangNo.1882,YananRd.,Shanghai,Shanghai200051,China24February2004；accepted3June2004July2004whichincludeaconventionaltangentialsingleinlet(CTSI),aspiralinlet(CSSI).Theeffectsofinlettypeoncyclonedrop,wereinvestigatedandcomparedasafunctionofcationspiralinlettoimprove4750(CTSI),directsymmetricalspiralinlet(DSSI),andconverg-ingsymmetricalspiralinlet(CSSI),weremanufacturedandstudied.ThegeometriesanddimensionsthesecyclonesarepresentedinFig.1andTable1.Toexaminetheeffectsofinlettype,allotherdimensionsweredesignedtoremainthesamebutonlytheinletgeometry.Thepressuredropsweremeasuredbetweentwopressuretapsonthecycloneinletandoutlettubebyuseofadigitalby0.151.15%and0.402.40%inthetestedvelocityrange.Fig.4(a)(d)comparesthegradecollectionefficiencyofthecycloneswithvariousinlettypesattheflowrateof3Fig.2.Schematicdiagramofexperimentalsystemsetup.B.Zhaoetal./PowderTechnology145(2004)475048micromanometer(SINAP,DP1000-IIIC).Thecollectionefficiencywascalculatedbytheparticlesizedistribution,byuseofmicroparticlesizeanalyzer(SPSI,LKY-2).DuetohavingthesamesymmetricalinletinModelBorC,theflowrateofeachinletofmultiplecyclonewasequaltoanotherandcontrolledbyvalve；twonozzle-typescrewfeederswereusedinsameoperatingconditionstodispersetheparticleswithaconcentrationof5.0g/m3ininlettube.Thesolidparticlesusedweretalcumpowderobeyedbylog-normalsizedistributionwithskeletaldensityof2700kg/m3,massmeandiameterof5.97Am,andgeometricdeviationof2.08.Themeanatmosphericpressure,ambienttemperature,andrelativehumidityduringthetestswere99.93kPa,293K,andlessthan75%,respectively.3.ResultsanddiscussionTheexperimentalsystemsetupisshowninFig.2.Fig.1.Schematicdiagramofcyclonesgeometries:(a)conventionaltangentialsingleinlet,ModelA；(b)directsymmetricalspiralinlet,ModelB；(c)convergingsymmetricalspiralinlet,ModelC.3.1.CollectionefficiencyFig.3showsthemeasuredoverallefficienciesofthecyclonesasafunctionofflowratesorinletvelocities.Itisusuallyexpectedthatcollectionefficiencyincreasewiththeentrancevelocity.However,theoverallefficiencyofthecyclonewithsymmetricalspiralinletbothModelsBandCwasalwayshigherthantheefficiencyofthecyclonewithconventionalsingleinletModelAatthesamevelocity；andespecially,thecyclonewithCSSI,ModelChasahighestoverallefficiency.TheseeffectsofimprovedinletgeometrycontributetotheincreaseinoverallefficiencyofthecycloneTable1Dimensionsofcyclonesstudied(unit:mm)DDehHBSab3001504501200112515015060388.34,519.80,653.67,and772.62m/h,withtheinletvelocitiesof11.99,16.04,20.18,and23.85m/s,respectively.Asexpected,thefrictionalefficienciesofallthecyclonesareseentoincreasewithincreaseinparticlesize.Theshapesofthegradecollectionefficiencycurvesofallmodelshaveaso-calledSshape.ThefrictionefficienciesoftheDSSI(ModelB)andCSSIcyclones(ModelC)aregreaterby210%and520%thanthatfortheCTSIcyclone(ModelA),respectively.Thisindicatesthattheinlettypeorgeometrytothecycloneplaysanimportantroleinthecollectionefficiency.Itwasexpectedthatparticlesintroducedtothecyclonewithsymmetricalspiralinlet(ModelsBandC)wouldeasilybecollectedonthecyclonewallbecausetheyonlyhavetomoveashortdistance,andespecially,theCSSI(ModelC)changestheparticleconcentrationdistributionandmakestheparticlepreseparatedfromthegasbeforeenteringthemainbodyofcyclone.Fig.5comparestheexperimentaldataataflowrateof653.67m3/h(inletvelocityof20.18m/s)withexistingclassicaltheories711.Apparently,theefficiencycurvesbasedonMothesandLofflermodelandIoziaandLeithsmethodmatchtheexperimentalcurvesmuchcloserthanothertheoriesdo.ThisresultcorrespondswiththestudycarriedoutbyDirgoandLeith12andXiangetal.13.Fig.3.Overallefficiencyofthecyclonesatdifferentinletvelocities.velocityB.Zhaoetal./PowderTechnology145(2004)475049Fig.4.Gradeefficiencyofthecyclonesatdifferentinletvelocities.(a)Inlet(d)Inletvelocity=23.85m/s.Thecomparisonshowthatsomemodelcanpredictatheoreticalresultthatclosedtheexperimentaldata,butthechangesofflowpatternandparticleconcentrationdistribu-tioninducedbysymmetricalspiralinlethavingeffectsoncycloneperformancewerenottakenintoaccountadequatelyindevelopedtheories.Toexaminetheeffectsofthesymmetricalspiralinletoncycloneperformancemoreclearly,Fig.6wasprepared,depictingthe50%cutsizeforallmodelswithvaryingtheflowrateorinletvelocity.The50%cutsizeofModelsCandBarelowerthanthatofModelAatthesameinletFig.5.Comparisonofexperimentalgradeefficiencywiththeories.=11.99m/s.(b)Inletvelocity=16.04m/s.(c)Inletvelocity=20.18m/s.velocity.Astheinletvelocityisdecreased,the50%cutsizeisapproximatelydecreasedlinearly.Withinletvelocity20.18m/s,forexample,thedecreaserateof50%cutsizeisupto9.88%forModelBand24.62%forModelC.Thisindicatedthatthenewinlettypecanhelptoenhancethecyclonecollectionefficiency.3.2.PressuredropThepressuredropacrosscycloneiscommonlyexpressedasanumbergasinletvelocityheadsDHnamedthepressureFig.6.The50%cutsizeofthecyclones.inletvelocityarepresentedinTable2.Obviously,higherpressuredropisassociatedwithhigherBarth5.18B.Zhaoetal./PowderTechnology145(2004)475050flowrateforagivencyclone.However,specifyingaflowrateorinletvelocity,thedifferenceofpressuredropcoef-ficientbetweenModelsB,C,andAislesssignificant,andvariedbetween5.21and5.76,withanaveragevalue5.63,forModelB,5.225.76,withanaveragevalue5.67,forModelC,and5.165.70,withanaveragevalue5.55,forModelA,calculatedbyregressionanalysis.Thisisanimportantpointbecauseitispossibletoincreasethecyclonecollectionefficiencywithoutincreasingthepressuredropsignificantly.Theexperimentaldataofpressuredropwerealsocomparedwithcurrenttheories1420,andresultsarepresentedinTable3.TheresultsshowthatthemodelofAlexanderandBarthprovidedthebetterfittotheexperimentaldata,althoughforsomecyclonesthemodelsofShepherdandLappleandDirgopredictedequallywell.4.ConclusionsAnewkindofcyclonewithsymmetricalspiralinletdropcoefficient,whichisthedivisionofthepressuredropbyinletkineticpressureqgmi2/2.Thepressuredropcoeffi-cientvaluesforthethreecyclonescorrespondingtodifferentTable2PressuredropcoefficientofthecyclonesCycloneInletvelocity(m/s)model11.9916.04A5.165.18B5.215.27C5.225.35Table3ComparisonofpressuredropcoefficientwiththeoriesTheoryShepherdAlexanderFirstStairmandValue6.405.626.185.01(SSI)includingDSSIandCSSIwasdeveloped,andtheeffectsoftheseinlettypesoncycloneperformanceweretestedandcompared.ExperimentalresultsshowtheoverallefficiencytheDSSIcycloneandCSSIisgreaterby0.151.15%and0.402.40%thanthatforCTSIcyclone,andthegradeefficiencyisgreaterby210%and520%.Inaddition,thepressuredropcoefficientis5.63forDSSIcyclone,5.67forCSSI,and5.55forCTSIcyclone.Despitethatthemultipleinletincreasesthecomplicityandthecostofthecycloneseparators,thecycloneswithSSI,especiallyCSSI,canyieldabettercollectionefficiency,obviouslywithaminorincreaseinpressuredrop.Thispresentsthepossi-bilityofobtainingabetterperformancecyclonebymeansofimprovingitsinletgeometrydesign.References1Y.F.Zhu,K.W.Lee,Experimentalstudyonsmallcyclonesoperatingathighflowrates,AerosolSci.Technol.30(10)(1999)13031315.2J.B.Wedding,M.A.Weigand,T.A.Carney,A10Amcutpointinletforthedichotomoussampler,Environ.Sci.Technol.16(1982)602606.3R.E.DeOtte,Amodelforthepredictionofthecollectionefficiencycharacteristicsofasmall,cylindricalaerosolsamplingcyclone,Aero-solSci.Technol.12(1990)10551066.4M.E.Moore,A.R.Mcfarland,Designmethodologyformultipleinletcyclones,Environ.Sci.Technol.30(1996)271276.5M.Gautam,A.Streenath,Performanceofarespirablemulti-inletcyclonesampler,J.AerosolSci.28(7)(1997)12651281.6K.S.Lim,S.B.Kwon,K.W.Lee,Characteristicsofthecollectionefficiencyforadoubleinletcyclonewithcleanair,J.AerosolSci.34(2003)10851095.7D.Leith,W.Licht,Thecollectionefficiencyofcyclonetypeparticlecollectors:anewtheoreticalapproach,AIChESymp.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