The friction factor of a rarefied gas flow in a circular tube

An expression for the estimation of the Poiseuille number for internal rarefied flows is developed. The derived formula is given in terms of dimensionless quantities, which are obtained by the solution of the flow based on kinetic theory. The formulation is applied to the fully developed flow of a gas in a circular tube, and tabulated results of the Poiseuille number are presented in the whole range of the Knudsen number and for various values of the accommodation coefficient. Also, in the slip regime, a closed-form expression for the Poiseuille number is derived and a brief discussion on the proper estimation of the viscous slip coefficient is provided. (c) 2007 American Institute of Physics.