Improved initial density dependence of the viscosity and a corresponding states function for high pressures

The initial density correction to gaseous viscosity using accurate realistic potentials of the noble gases is evaluated using the Rainwater-Friend theory. It is shown that this theory works satisfactorily for densities up to about 2 mol dm(-3). Due to the superimposability of the noble gas potential functions, a universal function of the reduced second viscosity virial coefficient is obtained over the entire reduced temperature range. At densities beyond the range of the theory, a variant of the excess viscosity is developed, by which the viscosity of the different gases can be easily calculated above the critical temperature for pressures up to 900 MPa. The accuracy of this method is within the experimental uncertainties. (C) 1998 Elsevier Science B.V. All rights reserved.