Softness expansion of gaseous transport properites. II. Moderately dense gases

摘要

The first density corrections to gaseous transport properties for the inverse power potential f = f0(s/r)nare evaluated according to the theory of Curtiss, Snider, and cohyphen;workers. A linear softness expansion predicts that the first density corrections are positive for largenbut negative for smalln, and that the changes of sign occur atn= 32.75 andn= 8.42 for the viscosity and thermal conductivity, respectively. Direct numerical integration yieldsn= 29.60 andn= 7.07, respectively. These results explain the opposite signs of density corrections to the two transport properties seen in high temperature experimental data, where, effectively,n= 12. Predictions of the modified Enskog theory are compared and contrasted with the above results. It is shown that some of the Sniderndash;Curtiss (collisional transfer) collision integrals may be simplified, one of them being the usual dilute gas omega integral with Smithrsquo;s collision lifetime included in the integrand.