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This paper describes two different theoretical methods of calculating Prandtl numbers for mixtures of noble gases at moderate temperatures and pressures. In order to limit the scope and length of this work, only binary mixtures containing helium and one other noble gas (neon, argon, krypton, or xenon) were considered during this study. However, with relatively slight modifications, the methods described in this work for calculating Prandtl numbers should be applicable to other binary noble gas systems. In addition, theoretical gas mixture viscosities and thermal conductivities were compared with the corresponding experimentally measured values at 20.0 øC in order to provide a better assessment of the quality of the Prandtl number calculations. The results of this study should be useful to researchers and design engineers involved in optimizing the operation of acoustic refrigeration systems.

SynopsisThe permeability coefficient for oxygen diffusing through a sample of Teflon-PFA tubing was determined experimentally. The source of the diffusing oxygen was ambient temperature air surrounding a coiled length of the PFA tubing. High pressure nitrogen was directed through the center of the PFA tubing. Oxygen permeating from the low pressure ambient air source, through the PFA tubing, and into the flowing high pressure nitrogen was observed in the effluent gases as they passed through a trace oxygen analyzer. By this means, oxygen concentrations in the effluent nitrogen were determined as a function of varying nitrogen flow rates, at nitrogen gas pressures of 4.4 and 7.8 atm (absolute), within the tubing bore. All measurements were also carried out at ambient temperatures of 21 1°C. In addition, a theoretically related graphical method of evaluating the experimental data was developed and subsequently employed t o actually determine the oxygen permeability coefficient for this system.

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