Polyatomic thermal creep flows through long microchannels at large temperature ratios

Abstract

Rarefied polyatomic gas flows through long microchannels of circular cross section due to small temperature and pressure gradients have been studied on the basis of the Rykov model in a wide range of the gas rarefaction and for various values of the reference flow temperature. Results are presented for N2, CO2, CH4, and SF6 representing linear and nonlinear polyatomic gas molecules. The present numerical results for N2 and CO2 are in good agreement with the corresponding results of previous studies. In addition, a simple method of calculation of the thermal creep under large temperature differences, which has been proposed in previous studies for monatomic gases, is extended in the present work in the case of polyatomic gases. The results based on the polyatomic modeling differ significantly from the corresponding monatomic ones and the differences depend on the gas rarefaction, the working gas, and the flow temperature. Special attention is also given to the computation of the thermomolecular pressure effect in the case of polyatomic gases under large temperature ratios. Furthermore, the dependence of both the thermal creep and the thermomolecular pressure effect on the viscosity variation with temperature along the microchannel is pointed out. Finally, the numerical data are provided as supplementary material for modeling any polyatomic gas flow in a wide range of the gas rarefaction and flow temperatures.