Correlations for the density and viscosity of fluids for flowmeter calculations part 3 - Viscosity of gases

Part 1 of this series of articles discussed finding the density of gases for flowmeter calculations using real gases as opposed to ideal gases. Part 2 discussed methods of correlating the density of liquids using an Othmer plot of the log of the density of the compound versus the Log of the density of a reference substance both taken at the same critical difference temperature (critical temperature minus temperature). Part 3 discusses the methods of correlating the viscosity of gases, using an Othmer plot of the log of the viscosity of the compound versus the log of the vapor pressure of a reference substance at the same temperature. The viscosity of gases is independent of pressure until it reaches about 10 atm. However the viscosity of gases above this value is correlated by an Othmer plot of the viscosity of the gas versus the log of P-k/rho, where P-k (kinematic pressure) = P + a / V-2, P = pressure, a = Van der Waals' constant, V = molar volume and rho = density of the gas.