An Improved Greenspan Acoustic Viscometer

An improved Greenspan acoustic viscometer (double Helmholtz resonator) was used to measure the viscosity of gases at temperatures from 250 to 400 K and at pressures up to 3.4 MPa. The improvements include a vibration damping suspension and the relocation of the fill duct. The fill duct, which is needed to supply gas to the resonator, was connected to the ceInter of the resonator to eliminate acoustic coupling between the resonator and the manifold. In anticipa- tion of handling corrosive gases, all surfaces of the apparatus that are exposed to the test gas are made of metal. The viscometer was tested with argon, helium, xenon, nitrogen, and methane. Isothermal measurements were carried out at 298.15 and 348.15 K and at pressures up to 3.2 MPa. Without calibration, the results differed from published viscosity data by &0.80 to +0.30 (0.470 r.m.s.). These results are significantly better than previous results from Greenspan viscometers. The measurements also yielded the speed of sound, which differed from literature data by +0.160 to +0.200 (0.180 r.m.s.). Adding empirical effective-area and effective-volume corrections to the data analysis decreased the r.m.s. deviations to 0.120 for the viscosity and to 0.0060 for the speed of sound. No unusual phenomena were encouIntered when the viscometer was tested with a helium-xenon mixture between 250 and 375 K.