Numerical investigation of conductance of porous media in high vacuum systems

Abstract

In high vacuum systems or materials that have fine capillaries, the molecular transport can be characterized as being free-molecular flow regime. In this flow regime intermolecular interactions can be ignored and flow is determined entirely by molecule–surface collisions. The transport of gases and volatile compounds through porous media and filters with variety of geometries is of great interest in various industrial applications. Although the effect of porosity on gas flow in the most of the flow regimes has been explored, but there are a few investigations on gas transport in porous media and filers at free-molecular regime. In this investigation gas transport in porous media with various porosities and geometries is explored. Test Particle Monte-Carlo (TPMC) method is employed. The walls are assumed to be diffusive. The skeletal portion of the porous media (frame) is modelled by solid spheres. The developed numerical scheme is validated with non porous cases. The effect of porosity, sphere sizes of frame, porous geometry, gas type and temperature on the conductance is examined. The simulations are performed for a porous pipe and porous nozzle. Results demonstrate that porosity and filtration highly affects the conductance of pipe and nozzle and causes great pressure drop in high vacuum systems. The increase of sphere sizes at constant porosity causes conductance to grow. The gas type and temperature of gas affects the conductance of pipe and nozzle too.