Thermal transpiration in the slip flow regime.

Abstract

The problem of thermal transpiration in the slip flow regime is studied from both theoretical and experimental aspects. Theoretical results are derived using boundary conditions obtained from kinetic theory considerations. Grad's method of solution of Boltzmann's equation is used to develop the slip velocity at the boundary. Consideration is also given here to surface interaction effects. Experiments have been carried out at Knudsen numbers from about 0.01 to 0.15. The theory is found to agree well with both the experimental data of Arney and Bailey and with the data reported here if sigma, the fraction of molecules reflected diffusely, is assumed to be about 0.8. Theoretical pressure ratio vs. temperature ratio results are plotted in graphs with Knudsen number and sigma as parameters.