Analysis of the Determination of Rotational Relaxation Numbers from Thermal Transpiration

New thermal transpiration data are given for He, Ar, N2, and CO in the temperature region between 77 and 300°K. These data are analyzed in terms of the “dusty-gas” flux equation and its differential approximation and in terms of a modified Weber–Schmidt equation. These models produce from the data values of the translational Eucken factor, which is related to the rotational relaxation number in a gas. The analysis indicates that a precise representation of the temperature dependence of the viscosity and independent information about the gas–tube surface interaction must be used to determine unambiguous values for the translational Eucken factor from these measurements.