Effects of roughness on rarefied gas flow in long microtubes

In this paper, we propose a model that describes the behavior of rarefied gas flow in long microtubes. The inner surface is modeled as an annulus porous film pressed on an impermeable surface. The appropriate slip-flow boundary conditions (the high-order slip-flow model; Weng C-I et al 1999 Nanotechnology 10 373) and the proper porous flow model (the Brinkman-extended Darcy model; Li W-L and H Wang C-C 1999 J. Phys. D: Appl. Phys. 32 1421) are utilized in the core gas region and annulus porous region, respectively. Moreover, utilizing the matched conditions (velocity slip and stress continuity) at the gas/porous interface, we derive the governing equation of pressure distribution in long microtubes. We discuss the effects of pressure drop (P_in - P_out), roughness and gas rarefaction on the pressure distribution and velocity distributions of long microtubes. Moreover, the analytical solution of the pressure distribution for the first-order slip-flow model is obtained. The present results are valuable for the design and analysis of fluid flow in microelectromechanical systems.