James B. Mehl
Dept. of Phys. and Astron., Univ. of Delaware, Newark, DE 19716-2570
Keith A. Gillis
Stephen J. Boyes
Michael R. Moldover
The Natl. Inst. of Stand. and Technol., Thermophys. Div., Gaithersburg, MD 20899
Martin Greenspan and Francis N. Wimenitz [``An Acoustic Viscometer for Gases,'' NBS Rep. 2658 (1953)] proposed the use of double Helmholtz resonators for measurement of the viscous diffusivity of gases. Such resonators, consisting of two cavities coupled by a duct, have a low-frequency mode where the gas oscillates between the cavities. A theoretical model that includes the viscous and thermal losses in the duct, thermal losses in the cavities, duct-end corrections, and fill ducts, have been developed. The resonator dimensions can be chosen so that the damping of the lowest mode is primarily due to viscous losses at the duct walls, and thermal losses at the cavity walls are very small. Several resonators have been constructed, including all-metal and mainly glass designs. Measurements on argon, helium, and propane samples are in very good agreement with the theoretical model.