The transport properties of helium–xenon mixtures from acoustic measurements

Abstract

Helium–xenon and helium–argon mixtures have been proposed as good choices for working fluids in thermoacoustic refrigerators, because the Prandtl number of the mixture is lower than that of a pure noble gas. Accurate measurements of the viscosity and the Prandtl number, obtained with acoustic resonance techniques, will be presented for three mixtures: He(25%)/Xe(75%), He(50%)/Xe(50%), and He(75%)/Xe(25%). The measurements span temperatures from −20 to 30 °C and pressures up to 2 MPa. The viscosity measurements are performed in a calibrated Greenspan acoustic viscometer [K. A. Gillis, J. B. Mehl, and M. R. Moldover, Rev. Sci. Instrum. 67, 1850–1857 (1996)]. The Prandtl number measurements are performed in a cylindrical resonator that was modified to have a large surface area near the center [K. A. Gillis and M. R. Moldover, J. Acoust. Soc. Am. 97, 3376(A) (1995)]. In this modified cylindrical resonator, damping of the odd-numbered longitudinal modes is primarily due to viscous boundary effects, whereas the even-numbered modes are damped primarily by thermal boundary effects. With the interaction parameters deduced from these measurements, the transport properties of any helium–xenon mixture may be determined. [Work supported by the Office of Naval Research.]