Investigation of heat transfer in rarefied gases over a wide range of Knudsen numbers

Heat exchange between W, Pt, Ta, and Ni filaments and He, Ne, Ar, Kr, Xe, D2, N2, CO2, and air at 300 K is measured experimentally using a transient hot-wire technique with an RC oscillator (Semionov et al., 1979) and a capacitance micromanometer. The results are presented in tables and graphs and shown to be in good agreement with the predictions of BGK theory as solved variationally. The energy-accommodation coefficients are determined and found to vary monotonically with the well depth of the intermolecular interaction potential and to be significantly depressed by surface impurities, which are effectively removed by annealing in vacuum or rarefied H2 (as demonstrated in thermal-flash tests). X-ray structural analysis reveals little filament recrystallization during the 20 sec or less of thermal refining.