We determined the viscosity of seven gases (Ar, CH4, C3H8, N2, SF6, CF4, C2F6) by interpreting frequency-response data from a Greenspan acoustic viscometer with a detailed model developed by Gillis, Mehl, and Moldover. The model contains a parameter er that characterizes the viscous dissipation at the ends of the viscometer s duct. It was difficult to determine er accurately from dimensional measurements; therefore, we adjusted er to fit the viscosity of helium on the isotherm 298 K (0.6 MPa < p < 3.4 MPa). This calibration was tested by additional viscosity measurements using four, well-studied, polyatomic gases (CH4, C2H6, N2, and SF6) near 300 K and by measurements using argon in the range 293 K < T < 373 K. For these gases, nearly all of the present results agree with reference values to within 0.5 % ( 0.4 % in the limit of zero density). We also measured the viscosities of CF4 and C2F6, between 210 K and 375 K and up to 3.3 MPa with average uncertainties of 0.42 % and 0.55 %, respectively. At the highest density studied in CF4 (2746 mol m 3), the uncertainty increased to 1.9 %; of this 1.9 %, 0.63 % resulted from the uncertainty of the thermal conductivity of CF4, which other researchers estimated to be 2 % of its value at zero-density. As an unexpected bonus, the present Greenspan viscometer yielded values of the speed of sound that agree, within 0.04 %, with reference values.
Citation: International Journal of Thermophysics
Pub Type: Journals
acoustic viscometer, argon, carbon tetrafluoride, hexafluoroethane, methane, nitrogen, propane, sulfur hexafluroride, viscosity