Thermal conductivity of two binary mixtures of gases of equal molecular weight

Abstract

The paper reports new measurements of the thermal conductivity of two binary mixtures at a nominal temperature of 27.5°C but over a pressure range. The two systems, N 2-CO (three compositions up to 12MPa) and N 2O-CO 2 (four mixtures up to 4.2 MPa) have been chosen because they consist of molecules of similar structure and equal molecular weight (28.01 and 44.01, respectively). Moreover, the zero-density viscosity is identical within each mixture. The results have been extrapolated and fitted to equations in the usual way. The zero-density thermal conductivity in each system varies systematically with composition and differs by about 4% for the pure components in each case. This is a measure of the effect of the internal degrees of freedom on thermal conductivity. In the absence of a reliable theory, it is shown that the equations of kinetic theory can be used to represent the composition-dependence of zero-density thermal conductivity with a judicious choice of two quantities which cannot be calculated independently. In both systems, both the excess thermal conductivity λ( T, ϱ) - λ( T, 0) and the ratio λ( T, ϱ)⧸ λ( T, 0) are sole functions of density with a remarkable degree of precision. The variation of the thermal conductivity with density could be predicted quit accurately with the aid of the theory due to Mason.