液压与气压传动英汉双语 教学课件 作者 陈淑梅第2章Chapter_2.ppt

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1、Chapter2FundamentalHydraulicFluidMechanics2.1PerformancesoftheHydraulicOil2.2Hydrostatics2.3Hydrodynamics2.4CharacteristicsofFluidFlowinPipeline2.5FlowRateandPressureFeaturesofOrifice2.6HydraulicShockandCavitation2.1.1Themainperformances2.1.2Therequestsandchoiceofhydraulicoil2.1Performan

2、cesoftheHydraulicOil1.Density(Kg/m3)2.Compressibility2.1.1Themainperformancesthecoefficientofcompressibility,Kisthebulkmodulusofelasticity（2-2）（2-1）Kisdefinedastheratioofthechangeinpressure()torelativechangeinvolume()whilethetemperatureremainsconstant.3.ViscosityTheexperimentshaveprovedth

3、atfrictionforcebetweenthetwofluidmoleculescanbedescribedasWhereisviscositycoefficient,alsodynamicviscosity.Fig.2-1ThesketchofviscosityThesketchofviscosityisillustratedbyFig.2-1.（2-3）Cohesionbetweentwomolecules……Therearethreemethodstodescribetheviscosity:absoluteviscosity,Kinematicviscosit

4、yandrelativeviscosity.(1)Dynamicviscosityorabsoluteviscosity(Pa•s)or(N•s/m2)μ(2)Kinematicviscosity(mm2/s)ν（2-4）(3)Relativeviscosity(conditionalviscosity)Therelativeviscosity0EwhichusedinChinaistestedbythe0Eviscometer,suchasFig.2-2.Fig.2-2Principleof0EviscometerFig.2-2illustratesthe0Evisco

5、meterprinciple.Takethenote0Etdescribestheviscosity:Theconversionformulabetweenthe0Eandkinematicviscosityis:(m2/s)(4)Viscosity-temperature:Fortheviscositylessthan150Eandthetemperature300C～1500C,theviscosity-temperatureformulaisdescribeasfollowing:WealsocanlookupfromFig.2-3.（2-5）（2-6）（2-7）(

6、5)Viscosity-pressure（2-8）(6)Othersperformances:physicalandchemical,suchasanti-inflammability,anti-oxygenation,anti-concreting,anti-foamandanti-corrosionetcFig.2-3Theviscosity-temperatureofhomemadeoilsRequestTheoilplaystworolesoftransmissionenergyandlubricationonthesurfacesofworkinginterac

7、tion.Therequestsforthehydraulicfluidsare:appropriateviscosity,thegoodinpropertyoffavorableviscosity－temperature,agoodlubricity,chemicallyandenvironmentallystabilities,compatiblewithothersystemmaterialsandsoon.2.1.2Therequestsandchoiceofhydraulicoil2.ChoiceThehydraul