viscosity水的黏度-英文释义

Kinematicviscosityisapropertyofliquidsandgasesthatrepresentshoweasilyagivensubstancecanflow.Inpracticalterms,itiscloselyrelatedtohowthickthesubstanceis.Bothabsoluteandkinematicviscositychangeaccordingtotemperature.Toobtainkinematicviscosity,theabsoluteviscosityofasubstanceisdividedbyitsdensity.KinematicviscosityisrepresentedbytheGreekletternu,whichresemblesa"v;"absoluteviscosityisrepresentedbymu,whichresemblesa"u;"anddensityisrepresentedbyrho,whichresemblesa"p."Theequation,therefore,isv=u/p、Absoluteviscosity,alsocalleddynamicviscosity,measuresasubstanee'sresistancetoflow.Itisdeterminedexperimentallybysandwichingaliquidorgasbetweentwoplatesandapplyingaknownamountofpressuretomovethetopplate—thedynamicviscositydependsonthepressure,theamountoftimeitwasapplied,andthedistancetheplatemovedinthattime.DynamicorabsoluteviscosityisbasedontheInternationalSystemofUnits(SI)unitsofpascal-seconds(Pa*s),whichmeansthatifapressureof1Paisappliedfor1second,theplatewillmovethesamedistanceasthedistancebetweenthetwoplates.Centipoise(cP)isalsoacommonunitfordynamicviscosity—1cPistheviscosityofwateraroundroomtemperature.Theimperialunits,pound-secondspersquarefoot(lb*s/ftA2),areveryseldomusedWhatisthediffirencebetweenkinematicviscosityanddynamicviscosity?Theviscosityofaliquidisanimportantphysicalpropertythataffectsthebehavioroftheliquidasitflows.Highlyviscousliquidsaremoreresistanttodeformationbystressandflowlesseasily,whilelessviscousliquidsflowmoreeasilyandarelessstress-resistant.Thetwomainwaystomeasureviscosityareintermsofdynamicandkinematicviscosity.Thesemeasuresareinterrelated,buthavedifferentapplications.Dynamicviscosity,alsocalledabsoluteviscosity,isthemorecommonlyusedmeasurement.Itmeasurestheresistanceofafluidtoflow—inotherwords,theinternalfrictionofthefluid,orhoweasilyitcandeformundermechanicalstressatagiventemperatureandpressure.Thetechnicaldefinitionofdynamicviscosityistheratioofshearstresstovelocitygradient.Whenforceisappliedperpendiculartothesurfaceofaliquid,itdeformssideways,orshears.Theeaseordifficultyofthisdeformationisthedynamicviscosity,sometimesreferredtosimplyasviscosity.Kinematicviscosity,bycontrast,measurestheresistanceoftheliquidtoflowinthepresenceofgravity.Thismeasureisobtainedbytakingtheliquid'sdynamicviscosityanddividingitbytheliquid'sdensity.Thehighertheviscostyoftheliquid,thelesseasilyitwillflowundertheforceofgravityandthehigheritskinematicviscositywillbe.Dynamicandkinematicviscosityareexpressedindifferentunitsofmeasurement.TheInternationalSystemofUnits(SI)measurementunitsfordynamicviscosityarepascal-seconds.Pascalsareameasurementofpressure—inthiscase,theshearstressappliedtotheliquid—whilesecondsmeasurethetimeittakestodeform.Dynamicviscositycanalsobemeasuredwithaunitcalledthepoise,anothermeasurerelatingpressureversustime.Thecommonunitusedtomeasurekinematicviscosityisthestokes,orsquarecentimeterspersecond,althoughsometimestheSIunitofsquaremeterspersecondisused.Theuseofdynamicandkinematicviscositymeasurementsisessentialforvariousreal-worldapplications.Forexample,itisimportanttoformulatepaintwithacertaindynamicviscositytoensurethatitcanbemixedandappliedinthecorrectthickness.Themeasurementofkinematicviscosityisusedmoreoftenincaseswhereafluidmustflowthroughapipeorlubricatemachinery,asinacarengine.Productssuchasmotoroilthataresubjectedtovaryingphysicalconditionsmusthaveaspecificdynamicandkinematicviscositytobehavecorrectly.Theviscosityoffluidschangesbasedontemperatureandpressure.Forexample,incoldweatheroilthickensandbecomesdenser,causingittoflowlesseasily.Itisimportanttoknowboththedynamicandkinematicviscosityratiosinthissituationtopredicthowtheoilwillbehaveatdifferenttemperatures.