Greenspan acoustic viscometer for gases

Double Helmholtz acoustic resonators, first proposed by Greenspan for measuring the viscosity of gases, were tested with helium, argon, and propane. Two different resonators were tested extensively with all three gases. For each of these instruments, the results for the viscosities of the three gases were consistent within +/-0.5% at pressures spanning the range 25-1000 kPa. Without calibration, the viscosities deduced from one viscometer were systematically 1% larger than data from the literature; the viscosities from the second viscometer were systematically 3% larger than data from the literature. Ii the systematic differences were removed for each viscometer by calibration with a single gas at a single temperature and pressure, then nearly all the results for both instruments would have fallen within +/-0.5% of the data from the literature. In these viscometers, the test gases are in contact with robust metal parts only; thus, these instruments are applicable to a very wide variety of gases over a very wide range of temperatures.