Rotational Collision Number and Eucken Factors from Thermal Transpiration Measurements

Abstract

The formal kinetic theory of Wang Chang and Uhlenbeck as modified by Mason and Monchick provides an explicit expression for the heat conductivity of a polyatomic gas. The rotational collision number is an important parameter in this expression. The maximum differential pressure supported by a thermal transpiration measurement is related to the rotational collision number by the dusty gas model proposed by Mason. Thermal transpiration measurements were made that confirm the dusty gas model relationship and provide rotational collision numbers for nitrogen, oxygen, and carbon dioxide at 366°, 398°, and 444°K. Single values of Zrot were obtained for hydrogen, methane, and tetrafluoromethane. These values of Zrot agree with those obtained by ultrasonic measurements and the kinetic theory equations provide Eucken factors that agree within the experimental error with the factors obtained from direct heat conductivity measurements.