4. Recommendations for estimating the viscosity of dense gases

Several estimation methods have been discussed in this dossier. At atmospheric pressure, gas viscosity is calculated with good accuracy from critical parameters and a corresponding state relation. If we consider the medium-density gas range, which extends from atmospheric pressure to a few tens of MPa, at temperatures above the critical temperature and densities below the critical density, several options are available for calculating viscosity. If experimental values of viscosity along one isotherm are available as a function of pressure, viscosity along another isotherm can be estimated from thermal pressure. However, if the density is known, it is preferable to use the residual viscosity. If no pressure viscosity measurements are available, constants a and β can be estimated from the critical parameters to determine approximate viscosity values by two different methods.

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