Thermal Diffusion in a Lorentz Gas

Regarding an isotropic Lorentz gas, thermal transport properties are discussed at the most elementary level. Lorentz’s original equations for heat and matter flows are reformulated in terms of kinetic quantities of dilute gases to clarify the nature of transport coefficients from the viewpoint of linear nonequilibrium thermodynamics including the Onsager reciprocal theorem. Especially referring to thermal diffusion properties of the Lorentz gas, Lorentz’s transport equations are studied by using the transported internal energy E^** and the internal energy of transport E^* which are connected with E^**{=}E^*{+}{\bar{E}}, where \bar{E} is the partial molecular internal energy. In this case, E^*{=}kT/2 and \bar{E}{=}(3/2)kT, and hence E^**{=}2 kT, using the Boltzmann constant k and the temperature T. A special case, E^* being a constant activation energy of usual diffusion, is briefly discussed.