雷诺数计算P vDRe 二n其中 D 为物体的几何限度（如直径）对于几何形状相似的管道，无论其p、v、D、n如何不同，只要比值Re相同，其流动情 况就相同泊肃叶公式 管的半径 R 管的长度 l 两端压强 p , pdvdr流体的粘度 n 1(p - p )兀 r2 + n 2 兀 rl12q 8 n ip - p =匚12兀 R 4萨瑟兰公式Viscosity in gases arises principally from the molecular diffusion that transports momentum between layers of flow. The kinetic theory of gases allows accurate prediction of the behavior of gaseous viscosity.Within the regime where the theory is applicable:Viscosity is independent of pressure andViscosity increases as temperature increases.James Clerk Maxwellpublished a famous paper in 1866 using the kinetic theory of gases to study gaseous viscosity. (Reference: J.C. Maxwell, On the viscosity orinternal friction of air and other gases, Philosophical Transactionsof the Royal Society of London, vol. 156 (1866), pp. 249-268.)Effect of temperature on the viscosity of a gasSutherlands formula can be used to derivethe dynamic viscosityof an ideal gas asa functionof the temperature:where:n = viscosity in (Pas) at input temperature Tn0 = reference viscosity in (Pas) at reference temperature T0T = input temperature in kelvinT0 = reference temperature in kelvinC = Sutherlands constant for the gaseous material in questionValid for temperatures between 0 T 555 K with an error due to pressure less than 10% below 3.45 MPaSutherlands constant and reference temperature for some gasesC T0nKK10-6 Pa s291.1518.27300.5517.81292.2520.18293.1514.8288.1517.2293.858.76293.159.82293.6512.54air 120 nitrogen 111 oxygen 127 carbon dioxide 240 carbon monoxide118 hydrogen 72 ammonia 370 sulfur dioxide 416 helium 79.4 273 19Viscosity of a dilute gasThe Chapman-Enskog equationmay be used to estimate viscosity for a dilute gas. This equation is based on semi-theorethical assumption by Chapman and Enskoq. The equation requires three empirically determined parameters: the collision diamete r (o), the maximum ene rgy of att raction di vided by the Boltzmann constant (e/k) and the collision integ ral (w(T*).T* = kT/ Reduced tempe rature (dimensionless) n0 = viscosity for dilute gas (uP)M = molecular mass (g/mol)T = temperature (K)o = the collision diamete r (A)e / k = the maximum ene rgy of att raction divided by the Boltzmann constant (K) 3口 = the collision integ ral