Measurements of thermal creep in binary gas mixtures

Thermal creep occurs in all nonisothermal gas-mixture systems. The effect i s more pronounced in rarefied gases and can play a significant role in, for example, microgravity crystal growth experiments, where natural convection is suppressed. Experimental measurements of the thermal creep in gas mixtu res are, however, simply not available. We report experimental measurements of thermal creep in three binary gas mixtures: He:Ar, He:CO2, and Ar:CO2 a t different mole ratios (mixture fractions). A stainless steel two-bulb mea surement system employing seven capillaries to connect the bulbs is used to measure the steady-state pressure differences that develop between the bul bs for each mixture at a selection of total system pressures. Values of the total system pressure that were used range from 0.12 to 10.00 Torr. For al l of the data reported, the two bulbs were held at temperatures of 397 and 297 K for the hot and cold sides, respectively. From the measured pressure differences, experimental values are obtained for a newly identified creep factor from which the thermal creep is extracted. These experimental values agree well with those obtained from some recently reported theoretical exp ressions, provided that suitable values for the accommodation coefficients of the gases are chosen. (C) 1999 American Institute of Physics. [S1070-663 1(99)03506-0].