大学课件-化工原理-第2章流动小结

FluidcharactersForceexertedonthefluidmassforcesurfaceforceTypesofFluids(1)Incompressibleandcompressiblefluid(2)Newtonianandnon-Newtonianfluid(3)IdealandrealfluiddyduAFForanincompressiblefluid222111uAuA21GG2211uAuA21VVContinuity(Massconservation)TheFluidinMotion21mmqq21VVqq（1）Staticfluid–staticfluidequ.2211pgzpgz222221112121upgzupgz（2）Idealfluid-Bernoulic’sequ.(3)Realfluid-MomentumequationRupgzWupgze222221112121MomentumChangesinaFluidRupgzWupgze222221112121kgJ/fehuggpzHuggpz222221112121mNJ/MomentumequationfepupgzWupgz222222111112121PamJ3/gHQQWPeePPe/2000eR4000eR40002000eRFluidflowinpipeStreamlineTurbulentflowTransitionalflowdGduReTheNatureofFluidFlowlaminarsub-layerBoundarylayer99%u∞Boundarylayer(chapter11)separationofboundarylayer（1）viscosity（2）pressuregradientisnegative（3）kineticenergyexhaustduringflowFlowinaPipeDevelopingflowFullydevelopedflowτuRe≤2000uumaxd层流时流体在圆管中的速度分布)1(422221rsrlppuVelocityDistribution,StreamlineFlowmax221218urlppuav2Thekineticenergyperunitmass:2/2uVelocityDistribution,TurbulentFlowRe≥4000umaxururRd湍流时流体在圆管中的速度分布82.0maxuuav1Thekineticenergyperunitmass:2/2uFrictionloss22udlPf242'28222udlfPudlfPudlPffffhgRPfMoodyfrictionfactorFanningfrictionfactorDarcyfrictionfactorLaminarmotion2000Re(Re)fFrictionfactorHagen-Poiseuilleequation232dlupfRe8(Re)f282udlPfuP4000Re20004000Re)(Re,dTurbulentmotionTransitionalregion75.1uPFullyturbulentflow)(Re,d2uP)(dMiscellaneousFrictionLossesThefrictionlossoccurringasaresultof•Suddenenlargement•Suddencontraction•Variouspipefittings--elbow,union,valves(gate,globe,needle)22udlRe22uRgudlgudllhgudlfgudllfhgudlfgudllfhgudlgudllhefefefef2)(22)4(242)'(2'2)8(2822222222PressureMeasuringDevices(a)Thesimplemanometer(b)U-tube(c)Thewell-typemanometer(d)Theinclinedmanometer(e)TheinvertedmanometerMeasurementofFluidFlowThePitottubeTheOrificeMeterTheVenturiMeterRotameterRupgzWupgze222221112121kgJ/fehuggpzHuggpz222221112121mNJ/MomentumequationfepupgzWupgz222222111112121PamJ3/PumpingEquipmentForLiquidsThepositivedisplacementtypeCentrifugalpumps•Reciprocatingpump(往复泵）Thepistonpump(活塞泵）Theplungerorrampump（柱塞泵）Thediaphragmpump（隔膜泵）Themeteringpump（计量泵）•Positivedisplacementrotarypump（转动泵）Thegearpump（齿轮泵）Thescrewpump（螺杆泵）ThepositivedisplacementtypeTheCentrifugalPumpTheprincipleandstructureAirbind（气缚）VirtualheadHemQnstructurefgWHee),,(VolumeticrateQNshaftworkpowerNeeffectivepowergQHGWNeee%100NNe%100NgQHeEfficiencymQnstructurefgWHee),,(Hydraulicefficiency,Volumetricefficiency,Mechanicalefficiency0481216202428321024222018161412263020100807060504004268NkWHemη%Qm3/h4B20n=2900rpm020406080100120图2-124--20型离心泵的特性曲线ηHeNOperatingcharacteristicsFactorsonperformanceofthepumpPhysicalpropertiesofliquidtobedeliveredRotationspeedImpellerdiameterCavitation（气蚀）sKppNPSH(netpositivesuctionhead)(净正吸上高度或汽蚀余量）gpgugphguNPSHsfkk2221121(a)NPSHr(必需汽蚀余量)(b)NPSHa(装置汽蚀余量)gphzgpNPSHsfa100SNPSHNPSHraTheheightinstallationofthepump(安装高度）UprightnessheightbetweeninletofthepumpandtheleveloftheliquiddeliveredThemaximumheightinstallationZmaxrfsoNPSHhgpgpzo1maxAllowableheightinstallationSZZmaxZZSystemcharacteristics2BQALpipelinegivenafor：gpzAgddlB42)(82BQAL2bQkHeeHLHLQQHeQba流量QHe图2-18管路的特性曲线Factorsaffectingsystemcharacteristics1）A(1)Δz(2)ρQDHeqVAC，0pbyaffectednotisA，0pA,2）BslopeB,slopeB,HighresistanceLowresistanceQDHeQ图2-20节流调节时工作点的变化HeAHeDQACDBAE'E1)Toadjustthevalve，，，)(HLQvalveClosesystemcharacteristicsvarypumpcharacteristicsbefixedResistanceonvalveAdjustmentofflowrateBDHHHQM'HeQQMEHeMHeMnn'MM'Q~HeQ'~He'3)(nnNNNotbeusedfrequently.nnQQ2)(nnHHee)(22DDQQ222)(DDHHee322)(DDNN2)TochangepumpcharacteristicsPumpoperatesinParallelHe并HeABdbCQ1Q并图2-22离心泵的并联操作gleparallelHHsingleparallelQQsin2Dutypoint,2spsQQQspHHPumpoperatesinSeriesgleseriesQQsingleseriesHHsin2DutypointgleHHHseriesglesin2singleseriesQQsinHe串HeABdbQ串图2-22离心泵的串联操作cc'VΔ(z+p/ρg）0HeHeQ图2-24组合方式的选择ab2'211'Lowresistancepipeline---inparallelhighresistancepipeline---inseriesPumpingEquipmentforGasesAccordingtotheoutletpressureandthecompressionratiorr=outletpressure/inletpressure(absolute)•Fans(通风机)：P1.471104Pa(g)，r1.15•Blowers(鼓风机)：1.471104–2.942105Pa(g)，r4•Compressors(压缩机)：P2.942105Pa(g)，r4