Thermal Diffusion Factor and Quantum Collision Integrals for the H2–4He System: The Effect of Inelastic Collisions

Abstract

Effective potential study of rotationallyvibrationally inelastic collisions between He and H2We have extended our measurements of the composition dependence of the thermal diffusion factor of the hydrogen-helium system to lower temperatures in search of the inelastic (rotational) collision effect reported by Ghosh et aI. and Mathur and Watson. We measured aT as a function of composition in a seventube trennschaukel at an average temperature of 82°K and failed to find any maxima or minima greater than our average experimental scatter of approximately ±1O%. We have also determined the temperature dependence of the thermal diffusion factor for an equimolar mixture from 30 to 550 0 K which is characterized by a broad maximum at approximately 125°K. A sharp decrease in aT was observed on the low temperature side of the maximum while a gradual, almost linear decrease was obtained on the high temperature side. We have calculated quantum mechanical transport collision integrals for hydrogen-helium assuming an (exp-6) spherical interaction potential and have used them to evaluate [aTJ3, the third order Chapman-Enskog approximation to the thermal diffusion factor. The theoretical calculations are in excellent agreement with the experimental determinations.

Transport and relaxation properties of isotopomeric hydrogen–helium binary mixtures. I. H2–He mixtures

“…Murphey [28], Van Ee [29] and Van de Ree et al [27] all report values of T that depend only weakly on mixture composition (a result also found in [30,31]) and are essentially constant (at least within experimental error) over quite large temperature intervals. Where one of these temperature intervals contains one or more of the temperatures in figure 7, the corresponding value for T has been plotted for comparison both with our calculations and with the more extensive data of [30,31].…”

“…The most accurate and complete measurements appear to be those of Taylor and Weissman [30] and Taylor [31]. Figure 7 provides a comparison between the mole fraction dependence of the thermal diffusion factor T calculated from the Tao PES and the experimental values.…”

“…A number of thermal diffusion experiments have been carried out for hydrogen isotope-rare gas mixtures, amongst which are the measurements of Murphey [28], Van Ee [29], Van de Ree et al [27] and Taylor and coworkers [30,31]. The most accurate and complete measurements appear to be those of Taylor and Weissman [30] and Taylor [31].…”

“…Figure 7 provides a comparison between the mole fraction dependence of the thermal diffusion factor T calculated from the Tao PES and the experimental values. The temperatures at which these comparisons have been made are those for which the measurements of [30,31] have been carried out, namely 82, 215, 273 and 373 K. Calculations were carried out at these four temperatures using codes written to evaluate approximations obtained recently [69] for two different sets of basis functions that give equivalent descriptions of the thermal conductivity coefficient at the first Chapman-Cowling level. As can be seen from figure 7, the two approximations differ only near X A ¼ 0, and then not by much for binary mixtures of H 2 with 4 He.…”

“…Transport and/or relaxation data available for H 2 -helium binary mixtures include, specifically: diffusion [20][21][22][23][24][25][26], thermal diffusion [27][28][29][30][31], and rotational relaxation [12] data for both 3 He-H 2 and 4 He-H 2 mixtures, and viscosity [32][33][34], thermal conductivity [35][36][37][38], thermal diffusion fieldeffect [39] and flow birefringence data [40] for H 2 -4 He mixtures.…”