A modification of the Benedict–Webb–Rubin equation of state by Professor Kenneth E. Starling of the University of Oklahoma:[3]
,
where is the molar density. The 11 mixture parameters (, , etc.) are calculated using the following relations
where and are indices for the components, and the summations go over all components. , , etc. are the parameters for the pure components for the th component, is the mole fraction of the th component, and is an interaction parameter.
Values of the various parameters for 15 substances can be found in Starling's Fluid Properties for Light Petroleum Systems..[3]
The modified BWR equation (mBWR)
A further modification of the Benedict–Webb–Rubin equation of state by Jacobsen and Stewart:[4][5]
where:
The mBWR equation subsequently evolved into a 32 term version (Younglove and Ely, 1987) with numerical parameters determined by fitting the equation to empirical data for a reference fluid.[6] Other fluids then are described by using reduced variables for temperature and density.[7]
^ abStarling, Kenneth E. (1973), Fluid Properties for Light Petroleum Systems, Gulf Publishing Company, p. 270, ISBN978-0872012936
^Reid, Robert C.; Prausnitz, John M.; Poling, Bruce E. (April 1987), The Properties of Gases & Liquids (4th ed.), New York: McGraw-Hill, p. 741, ISBN978-0070517998
^Younglove, B. A.; Ely, J. F. (1987), "Thermophysical Properties of Fluids II Methane, Ethane, Propane, Isobutane, and Normal Butane", Journal of Physical and Chemical Reference Data, 16 (4): 577, Bibcode:1987JPCRD..16..577Y, doi:10.1063/1.555785, ISSN0047-2689
Benedict, Manson; Webb, George B.; Rubin, Louis C. (1951), "An Empirical Equation for Thermodynamic Properties of Light Hydrocarbons and Their Mixtures. Constants for Twelve Hydrocarbons", Chemical Engineering Progress, 47 (8): 419–422
Benedict, Manson; Webb, George B.; Rubin, Louis C. (1951), "An Empirical Equation for Thermodynamic Properties of Light Hydrocarbons and Their Mixtures Fugacities and Liquid-Vapor Equilibria", Chemical Engineering Progress, 47 (9): 449–454.