Redlich-Kwong fluids, application

Many modifications of the original Redlich/Kwohg equation that appear in the literature are intended for special-purpose applications. The SRJt equation, developed for vapor/liquid equilibrium calculations, is designed specifically to yield reasonable vapor pressures for pure fluids. Thus, there is no assurance that molar volumes calculated by the SRK equation are more accurate than values given by the original Redlich/Kwong equation. 

Equations of state have a much wider application. In this chapter we first present a general treatment of the calculation of thermodynamic properties of fluids and fluid mixtures from equations of state. Then the use of an equation of state for VLE calculations is described. For this, the fugacity of each species in both liquid and vapor phases must be determined. These calculations are illustrated with the Redlich/Kwong equation. Provided that the equation of state is suitable, such calculations can extend to high pressures. 

The simplest form of the pressure explicit equation of state (with independent variables of density and temperature) are those based on a cubic expression of the fluid volume such as the Peng-Robinson and Soave-Redlich-Kwong and these equations are discussed in Chapter 4. When temperature and pressure inputs are available, the cubic equation can be solved non-iteratively for density. Thus, the calculation speed of cubic equations of state is rapid when compared to other methods explained that are provided below, and the use of these equations is quite popular in many industrial applications. Unfortunately, the advantage of speed of calculation is offset by the disadvantage of higher uncertainties. 

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