Energy exchange between inert gas atoms and a solid surface

Abstract

1. Introduction . — If gas atoms, having energy corresponding to a temperature T 2 , are incident on a solid surface at a temperature T 1 , then the reflected atoms will have a mean energy corresponding to some new temperature T 2 ', which is a function of T 1 and T 2 . For simplicity it is convenient to define Knudsen’s thermal accommodation coefficient as α = lim T 1 → T 2 → T T' 2 - T 2 / T 1 - T 2 . The accommodation coefficient depends on the nature of the gas atom, the nature of the solid surface, and the temperature T. Accommodation coefficients have been measured by various workers, and the present paper is an attempt to give a theoretical explanation of the results of Roberts, who has measured the accommodation coefficient for helium on tungsten at various temperatures, taking particular precautions to obtain a clean surface.