雷诺数计算公式

1、P vD雷诺数计算Re =n其中D为物体的几何限度（如直径）其流动情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， 况就相同泊肃叶公式 TOC o 1-5 h z 管的半径R管的长度l两端压强p,p流体的粘度n 1(p - p )兀 r2 + n 2 兀 rl = 012dr_= q v 8 n i12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 kinet

2、ic 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 gas

3、es 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 dy

4、namic viscosityof an ideal gas asa functionof the temperature:where:n = viscosity in (Pa-s) at input temperature Tn0 = reference viscosity in (Pa-s) at reference temperature T0T = input temperature in kelvint0 = reference temperature in kelvinC = Sutherlands constant for the gaseous material in ques

5、tionValid 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 gasesGasCKT0K10-6 Pa sair120291.1518.27nitrogen111300.5517.81oxygen127292.2520.18carbon dioxide240293.1514.8carbon monoxide118288.1517.2hydro

6、gen72293.858.76ammonia370293.159.82sulfur dioxide416293.6512.54helium79.427319Viscosity 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

7、determined parameters: the collision diameter (q), the maximum energy of attraction di vided by the Boltzmann constant (c/k) and the collision integral (s(T*).T* = kT/e Reduced temperature (dimensionless)n0 = viscosity for dilute gas (uP) M = molecular mass (g/mol)T = temperature (K)o = the collision diamet