The exchange of energy between gas atoms and solid surfaces

Abstract

If gas molecules with average energy corresponding to a given temperature strike the surface of a solid at a different temperature, the average energy of the gas molecules leaving the surface does not in general correspond to the temperature of the solid but depends also on their average energy before staking it. In order to exclude complications due to the transfer of rotational energy we shall consider only monatomic gases. Let the average translational energy of the molecules before striking the surface at temperature T 2 correspond to a temperature T 1 , and let the average translational energy of the molecules after leaving the surface correspond to a temperature T 2 ' (see fig. 1). Modifying slightly a suggestion made by Maxwell* in a different connection, Smoluchowski assumed that the change in the temperature of the gas molecules brought about by striking the surface is proportional to the difference between the temperature of the surface and that of the gas molecules before striking it ; that is, that T 2 - T 1 = a , (T 2 - T 1 ). (1) The constant of proportionality a was later called the accommodation coefficient by Knudsen. Smoluchowski applied this idea to explain the so-called temperature jump at the surface of a solid.