雷諾數(shù)計(jì)算公式

雷諾數(shù)計(jì)算其中D為物體的幾何限度（如直徑）對(duì)于幾何形狀相似的管道，無(wú)論其ρ、v、D、η如何不同，只要比值Re相同，其流動(dòng)情況就相同泊肅葉公式管的半徑 R管的長(zhǎng)度 l兩端壓強(qiáng)流體的粘度/薩瑟蘭公式Viscosityingasesarisesprincipallyfromthemoleculardiffusion

thattransportsmomentumbetweenlayersofflow.Thekinetictheoryof

gasesallowsaccuratepredictionofthebehaviorofgaseousviscosity.Withintheregimewherethetheoryisapplicable:ViscosityisindependentofpressureandViscosityincreasesastemperatureincreases.JamesClerkMaxwell

publishedafamouspaperin1866usingthekinetictheoryofgasesto

studygaseousviscosity.(Reference:J.C.Maxwell,"Ontheviscosityor

internalfrictionofairandothergases",PhilosophicalTransactions

oftheRoyalSocietyofLondon,vol.156(1866),pp.249-268.)EffectoftemperatureontheviscosityofagasSutherland'sformula

canbeusedtoderivethedynamicviscosityofanidealgasasafunctionofthetemperature:where:η

=viscosityin(Pa·s)atinputtemperature

Tη0

=referenceviscosityin(Pa·s)atreferencetemperature

T0T

=inputtemperatureinkelvinT0

=referencetemperatureinkelvinC

=Sutherland'sconstantforthegaseousmaterialinquestionValidfortemperaturesbetween0<

T

<555Kwithanerrorduetopressurelessthan10%below3.45MPaSutherland'sconstantandreferencetemperatureforsomegasesGasC[K]T0[K]η0[10-6

Pa

s]air120291.1518.27nitrogen111300.5517.81oxygen127292.2520.18carbondioxide240293.1514.8carbonmonoxide118288.1517.2hydrogen72293.858.76ammonia370293.159.82sulfurdioxide416293.6512.54helium79.427319ViscosityofadilutegasThe

Chapman-Enskogequation

maybeusedtoestimateviscosityforadilutegas.Thisequationis

basedonsemi-theorethicalassumptionbyChapmanandEnskoq.The

equationrequiresthreeempiricallydeterminedparameters:the

collisiondiameter(σ),themaximumenergyofattractiondividedbythe

Boltzmannconstant(?/к)andthecollisionintegral(ω(T*)).T*=κT/εReducedtemperature(dimensionless)η0

=viscosityfordilutegas(uP)M

=molecularmass(g/mol)T

=temperature(K)σ

=thecollisiondiameter