Noble gas-carbon dioxide thermal diffusion factors: Anomalous behavior for Ar/Co₂

Abstract

Thermal diffusion factors for equimolar mixtures of neon and argon with carbon dioxide have been measured in the temperature range from 250 to 700 K. The data were obtained in a 20-tube trennschaukel, or “swing separator.” The Ne/CO₂ system demonstrated the expected increase α _T with increasing temperature as predicted by the Chapman-Enskog theory using spherically symmetrical interaction potentials and elastic collisions. The thermal diffusion factor for Ar/CO₂, however, demonstrated an inverse temperature effect which is not explained by the simplified kinetic-theory model used for the calculation. While this effect has ben observed by other workers, the present data exhibit a less precipitous decrease with temperature. Using interaction potentials available in the literature, it was possible to calculate theoretically accurate values of α _T for Ne/CO₂ but not for Ar/CO₂. In the latter case the small mass difference produced very small values of α _T, the peculiar behavior of which undoubtedly lies in nonnegligible asymmetric and inelastic effects not taken into account in the calculations.