雷诺数计算公式.doc

雷诺数计算其中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、v、D、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两端压强流体的粘度/萨瑟兰公式Viscosity in gases arises principally from the molecular diffusionthat transports momentum between layers of flow. The kinetic theory ofgases allows accurate prediction of the behavior of gaseous viscosity.Within the regime where the theory is applicable: Viscosity is independent of pressure and Viscosity increases as temperature increases.James Clerk Maxwellpublished a famous paper in 1866 using the kinetic theory of gases tostudy 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 formulacan be used to derive the dynamic viscosity of an ideal gas as a function of the temperature:where: = viscosity in (Pas) at input temperatureT 0= reference viscosity in (Pas) at reference temperatureT0 T= input temperature in kelvin T0= reference temperature in kelvin C= 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 gasesGasCKT0K010-6Pasair120291.1518.27nitrogen111300.5517.81oxygen127292.2520.18carbon dioxide240293.1514.8carbon monoxide118288.1517.2hydrogen72293.858.76ammonia370293.159.82sulfur dioxide416293.6512.54helium79.427319Viscosity of a dilute gasTheChapman-Enskog equationmay be used to estimate viscosity for a dilute gas. This equation isbased on semi-theorethical assumption by Chapman and Enskoq. Theequation requires three empirically determined parameters: thecollision diameter (), the maximum energy of attraction divided by theBoltzmann constant (/) and the collision integral (T*). T*=T/ Reduced temperature (dimensionless) 0= viscosity for dilute gas (uP) M= molecular mass (g/mol) T= temperature (K) = the collision diameter () / = the maximum energy of attraction divided by the Boltzmann constant (K) = the collision integral