道路吸尘清扫车吸嘴的颗粒去除性能的数值模拟研究大学毕业论文英文文献翻译及原文Word文件下载.docx
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道路吸尘清扫车吸嘴的颗粒去除性能的数值模拟研究
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2017.02.14
附录Ⅱ
Numericalstudyonparticleremovalperformanceofpickupheadforastreetvacuumsweeper
BofuWu*,JinlaiMen,JieChen
SchoolofMechanicalEnglishShanghaiJiaoTongUniversity,Shanghai,200240,China
ABSTRACT
Thepurposeofthispaperistoinvestigatetheparticleremovalperformanceofpickupheadforastreetvacuumsweepernumerically.Anintegrated3Dnumericalmodelwasconstructedbasedonparticlesuctionprocessincomputationalfluiddynamics(CFD)software.Theairflowthroughthepickupheadwastreatedasacontinuum,whileparticlesweremodeledasdispersedphase.TheReynoldsstressmodel(RSM)anddiscreteparticlemodel(DPM)werechoseninordertopredicttheairandparticlesflowaccurately.Thenumericalsimulationresultsshowthatthesweeper-travelingspeedandthepressuredropacrossthepickupheadhavegreateffectsontheparticleremovalperformance.Theremovalefficiencyofparticlesincreaseswiththelowersweeper-travelingspeedorthehigherpressuredrop,andsmallsizeparticleshavehighergradeefficiencythanthatoflargesizeparticlesunderthesameoperatingconditions.Moreover,theremovalmassflowrateofparticlesincreaseswiththehighersweeper-travelingspeed.Therefore,atrade-offshouldbeconsideredamonghighremovalefficiency,lowenergyconsumption,andhighremovalmassflowrate.Throughthenumericalsimulation,theeffectivenessofstreetvacuumsweeperforremovingparticlesfromroadsurfaceisevaluated,andanoptimaloperatingconditionisobtained.Besides,moreinformationisgeneratedtobetterunderstandtheparticlesuctionprocessofthepickuphead.
Keywords:
Pickuphead;
Particleremovalperformance;
CFD;
Sweeper-travelingspeedPressuredrop
1.Introduction
Currently,thereisawidespreadconcernoverthepollutionofparticlematter.Dustandsiltarethemajorsourcesofparticlematterpollution,theremovalofwhichthereforeattractsconsiderableattention[1].Streetsweepingistypicallypracticedtoremovetheaccumulationofdustandsiltfromroadsurfacetoimproveaesthetics,publichealthy,andstormwaterquality,soitisconsideredasaneffectivepollutantcontrolpracticeformanylocalauthorities[2,3].Pickupheadisthekeycomponentofstreetvacuumsweeper,whichisdesignedtopickupparticlesefficientlyfromroadsurfaceandsendthemtodustcollectionhoppersmoothly.Theparticleremovalperformanceofthepickupheadisthemostimportantindexforastreetvacuumsweeper.
Manyresearcheshavebeenperformedonestimatingtheparticleremovalperformanceofstreetsweeping.Forexample,astudybyChangetal.[4]evaluatedtheeffectivenessofstreetsweepingandwashingforcontrollingambienttotalsuspendedparticlesbyexperiments,whichindicatedthatthestreetsweepingandwashingprocesswaseffectiveatremovingdustandsiltfromurbanroads.However,someresearcherssuchasVazeandChiew[5]consideredthatthecontributionofstreetsweepingtoenvironmentalqualitywasnotveryclear,andmayhaveanadverseimpactbecausestreetsweepersdidnotpickupsmallersizeparticleseffectively.KangandStenstorm[6]studiedthestreetsweepingeffectivenessasastormwatermanagementpracticebyusingstatisticalpoweranalysis.Theypointedoutthattheeffectofstreetsweepingshouldnotbeunderestimatedbecausesomepreviousresearcheswerebasedoninsufficientdata.Therefore,newmethodswereneededtoevaluatethestreetsweepingeffectiveness.
Astheparticleremovalperformanceforstreetvacuumsweepervariesbasedonsweepingtechnology,operatingconditions,sweepingfrequency,streetdirtloadingandparticlesizedistribution[7],itisnecessarytodeveloparepeatableandreliablemethodtocalculatetheparticleremovalperformanceofpickupheadforastreetvacuumsweeper.Inordertoevaluatetheparticleremovalperformanceofpickuphead,engineersgenerallyconcentrateontwoparameters,thesweeper-travelingspeedandthepressuredropacrossthepickuphead.Theirinfluencesontheparticleremovalefficiencyandtheparticleremovalmassflowratedirectlyrelatetotheperformanceofthestreetvacuumsweeper.Chenetal.[8]investigatedtheinfluenceofsweeperstructureandsweeper-travelingspeedontheparticleremovalperformancebyexperiments.Theyfoundthatthewingplateofpickupheadandthesweeper-travelingspeedhadgreatinfluenceonthecriticalpickupvelocityofparticles.Meanwhile,theyanalyzedtherelationshipoftheparticlepickupvelocitiesandtheairflowrates.
Withtherapiddevelopmentofthecomputertechnology,thecomputationalfluiddynamics(CFD)hasbeensuccessfullyadoptedtostudyvariousindustrialpneumaticconveyingprocesses[9,10].Althoughmanyworkshavestudiedtheparticleremovalperformancebyexperimentsoverthepastdecades,fewworksconsideredtheparticleremovalperformanceofpickupheadusingCFD.Xuetal.[11]conducteda3Dnumericalsimulationontheflowfieldofpickupheadandgassystemforahighwaymechanicalsweeper.Theyanalyzedtheinteractionbetweenthepickupsystemandthefiltersystem,andoptimizedthecombinedsystembasedonnumericalresults.Zengetal.[12]employedtheCFDtechnologytosimulatetheflowfieldofpickuphead.Thestudyshowedthattheperformanceofstreetsweepingwasimprovedsignificantlybychangingthestructureofpickuphead,andthenumericalsimulationprovedthattheCFDwasaneffectivetooltocalculatetheflowfieldcharacteristicsofpickuphead.However,theseworksdidnotaccountfortheinfluenceofparticlesontheflowfieldduringtheinvestigation,sotheparticleremovalefficiencyandtheparticleremovalmassflowratecannotbeobtained.Moreimportantly,influencesofthesweeper-travelingspeedandthepressuredrop,whicharethemostimportantparameters,shouldnotbeneglectedwhilemodelingtheperformanceofpickuphead.
Gascycloneisthedevicethatutilizescentrifugalforcetoseparateparticlesfromcarriergas,whereaspickupheadforastreetvacuumsweeperisthedevicethatemploysvacuumpressuretosuckupparticlesfromroadsurface.Therefore,theparticleremovalperformanceofpickupheadwillbealsocalculatedbyusingtheCFDapproach,whichhasbeenvalidatedbythesuccessfulinvestigationoftheparticlecollectionperformanceofgascyclones[13,14].
Theaimofthepresentstudyistoinvestigatetheparticleremovalperformanceofpickupheadundervarioussweeper-travelingspeedsandpressuredropusingcommercialCFDprogramFluent6.3.ThenumericalCFDmodelisverifiedbysweepingfieldexperiments.Basedonthenumericalresults,thebalanceamongtheparticleremovalefficiency,thepressuredropacrossthepickupheadandtheremovalmassflowrateisconsidered,andanoptimaloperatingconditionisobtained.
2.Sweepingfieldexperiments
Astreetvacuumsweeperwithanenginepowerof57kwwasusedinthiswork.Itusedanelaboratelydesignedvacuumsystemfordustspickup.Fig.1showedthatthestreetvacuumsweeperwaspickingupsandparticlesfromexperimentalroadsurfacebyusingapickuphead.Asstreetvacuumsweepermovesforward,thecentrifugalfanmountedonthesweeperestablishesavacuuminthedustcollectionhopper.Particleslayatrestontheroadsurfaceinitiatetoroll,slideandbounceascertainairflowvelocityisreached,andthentheyarevacuumedthroughthefournarrowslots(front,rear,leftandright)intothepickuphead.Afterenteringthepickuphead,mostparticlesarepickedupbytheairflowandthensentfromoutletintothedustcollectionhopperthroughavacuumhose,butsomewillescapefromtherearnarrowslottotheoutsideofthepickuphead.TheschematicdiagramofthepickupheadusedinthesweepingfieldexperimentsisshowninFig.2,anditsmaindimensionsaregiveninTable1.
Fig.1.Pickingupsandparticlesfromroadsurfaceinthefieldexperiments.
Fig.2.Schematicdiagramofthepickuphead.
Inthefieldexperiments,thesafetyfactorwasvitalimportantbecauseitwouldbedangerousifmeasurementsstoppedtraffic.Therefore,aroadwithouttrafficwaschosen,asshowninFig.1.Ontheroadsurface,a2.0m×
1.8msamplingsurfacewasselectedandpaintedwhite.Sandswerespreaduniformlyonthesamplingsurfaceastestparticleswiththedensityof2500kg/m3,andthemassloadingwassetas0.1kg/m2.ThesandparticlesizedistributionYdbymasscanbedefinedbyusingRosin–Rammlerdistribution
wheredpistheparticlediameter,d̅istheparticlemeandiameterandnisthespreadparameter.
Calculatedfromthesanddata,theparticlemeandiameterandthespreadparameterare81μmand5.95,respectively.ThecumulativesizedistributionofsandparticlesisplottedinFig.3.
Fig.3.Thecumulativesizedistributionofsandparticles.
Thesweepingfieldexperimentswerecarriedoutatthesweepertravelingspeedof6,7,8,9,10,11,12,13,and14km/h,andtheparticleremovalefficiencywasobtainedbymeasuringthemassofthecollectedsandsfromthesamplingsurfacebeforeandaftersweeping.Theairflowvelocityandpressuredropmeasurementswereperformedusinghot-wireanemometryandmanometer,respectively.
3.Physicalmodelandgridgeneration
Inordertosimulatetheparticlesuctionprocessdescribedabove,severalassumptionsweremadeinthisstudy,asillustratedinFig.4.
1)Thepickupheadmovedforwardataconstanttravelingspeedduringstreetsweeping.
2)Aroundthefournarrowslots,therewasanexter