Available mixing rules for vapor viscosity

You can use one of the following mixing rules to calculate the bulk vapor viscosity of a Fluid Type.

SimSci Mixing Rule

where

hm is the vapor viscosity of the mixture

hi is the vapor viscosity of pure component i

yi is the molar composition fraction of component i in the vapor phase

Mi is the molar mass of pure component i

This is the default mixing rule.

Molar Average

Logarithmic Molar Average

Logarithmic Mass Average

Power Molar Average

where

r is an exponent that you specify in the Fluid Editor

Wilke Mixing Rule

Wilke-Brokaw Mixing Rule

where

si is the viscosity collision diameter of component i

sij is the viscosity collision diameter of dissimilar components i and j

TRAPP (transport property prediction)[3,4]

We evaluate the vapor viscosity based on the deviations in a reference fluid, which we assume to be the pure vapor of a reference component, R. We use the following equations to calculate the vapor viscosity of the mixture (hm):

where

hm0 is the vapor viscosity of the mixture at low pressure, which we calculate by using the vapor viscosities from the Lee-Kesler equation of state (EOS) and the Wilke mixing rule

DhENSKOG is a calculated[5] correction factor based on the hard sphere assumption to account for size differences between component molecules

Ei are a set of constant coefficients taken from literature[6]

rc,R is the density of reference component R at its critical temperature and pressure

rc,i is the density of component i at its critical temperature and pressure

MR is the molar mass of reference component R

Pisat is the vapor pressure of component i at the system temperature (T)

PRsat(T0) is the vapor pressure of reference component R at temperature T0

risat is the saturated liquid density of component i at the system temperature (T)

rRsat(T0) is the saturated liquid density of reference component R at T0

wi is the acentric factor of component i

wR is the acentric factor of reference component R

Zc,i is the critical compressibility factor of component i

Zc,R is the critical compressibility factor of reference component R

Because we evaluate the vapor pressure and saturated liquid density of the reference fluid at T0, we must iteratively solve for fi.

Typically, you use this mixing rule for systems of non-polar components at high pressures.

References

1. Wilke, C.R. A Viscosity Equation for Gas Mixtures. J.Chem. Phys. 1950, 18 (4), 517-519

2. Brokaw, R.S. Viscosity of Gas Mixtures; NASA TN D-4496; National Aeronautics and Space Administration, U.S. Government Printing Office: Washington, DC, 1968.

3. Leland, T. W.; Robinson, J. S.; Suther, G.A. Statistical Thermodynamics of Mixtures of Molecules of Different Sizes. Trans. Farad. Soc. 1968, 64, 1447-1460.

4. Ely, J. F.; Hanley, H. J. M. Prediction of Viscosity and Thermal Conductivity in Hydrocarbon Mixtures- Computer Program TRAPP. Proceedings of the 60th Annual Convention of the Gas Processors Association, San Antonio, TX, USA, Mar 23, 1981.

5. Reid, R. C.; Prausnitz, J. M.; Poling, B. E. The Properties of Gases and Liquids, 5th ed.; McGraw-Hill: New York, 1977; pp. 498-502.

6. Reid, R. C.; Prausnitz, J. M.; Poling, B. E. The Properties of Gases and Liquids, 5th ed.; McGraw-Hill: New York, 1977; pp. 493-497.