壅塞流(临界流、阻塞流、窒息流、Choked Flow)简介英文版.ppt

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1、Restriction&ChokedFlowRestrictionandChokedFlowRestrictionRestrictionismainlyusedtoachievecontrolledorrestrictedflowofprocessmedium.Suchasorifice,venturitube,controlvalve,etc.ChokedflowAflowingfluidcanreachalimitingconditionwhenpassingthrougharestriction,thatthema

2、ssflowwillnotincreasewithafurtherdecreaseinthedownstreampressurewhileatagivenupstreampressureandtemperature.ThisiscalledChokedFlow.RestrictionandChokedflowinChemicalEngineeringPositiveapplicationOneapplicationofchokedflowisincrackingreactors.Maintainingequalflowt

3、hroughparallelreactortubesisessentialtoensureevenresidencetimeinthecrackingreactor.Installingarestrictionorificeatthe entranceofeachreactortubeachieveschokedflow.Providedthatchokedflowismaintained,flowratesarenotaffectedbyanyvariationinreactortubepressuredrop.Neg

4、ativeeffectItisusuallydesirabletoavoidchokingconditionsinaliquidsystem,becauseitoftenaccompaniescavitation,two-phaseflowwhichcandamageequipment.2ChokedFlowChokedFlowinGasesCriticalPressureRatioMassFlowRateChokedFlowinLiquidsValveMaxAllowablePressureDropCavitation

5、andflashing3ChokedFlowinGasesChokedflowisalimitingconditionthatwhengaspassingtherestrictioninpipetheflowwillnotincreasewithafurtherdecreaseinthedownstreampressurewhileupstreamconditionisfixed.ChokedflowoccurswhengasvelocitiesacrossarestrictionintheflowpathbecomeS

6、ONICi.e.ataMachnumberof1.Chokedflowisindependentofrestrictiondownstreamconditions.Anyfurtherdropinthedownstreampressurewillnotresultinanincreaseingasflow.4ChokedFlowinGases--CriticalPressureRatioThepressureratio(DownstreamPressure/UpstreamPressure)atwhichchokedfl

7、owoccursisknownastheCriticalPressureRatio.Assumingisentropicflow,itcanbecalculatedusingthefollowingequation:Kistheratioofspecificheatsatconstantpressuretoconstantvolume,Cp/Cv,alsocalledtheadiabaticindex.Asaruleofthumb,theKis1.4formostdi-atomicgases.WhenKis1.4,the

8、CriticalPressureRatiois0.53,applicabletoawiderangeofcommongasesapproximately.GasK=CP/CVPD/PUDryair1.4000.53Nitrogen1.4040.53Oxygen1.4000.53Hydrogen1.4100.53Car