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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
