## P

where ¿kl = 2Bkl — Bkk — Bll. The fugacity coefficient of any component in the vapour phase can thus be calculated if the second virial coefficients of the pure components and the cross second virial coefficients are available. Since the truncated virial equation is only applicable to gases at low to moderate pressures, fugacity coefficients calculated using eqn [30] are generally only employed when eqn [20] is used to calculate VLE.

### Pressure-explicit Cubic Equation of State

Cubic equations of state express the pressure as a cubic function of the molar volume, and their origin stems from the van der Waals equation, which was the first cubic equation of state to represent qualitatively both vapour and liquid phases. Several hundred modification of the van der Waals equation have been reported in the literature. An example of a recent modification that is better able to represent P-V-T-x data for both vapour and liquid mixtures is the equation of state proposed by Patel and Teja in 1982. This equation may be written as:

where B is the second virial coefficient, C the third virial coefficient, and so on. Typically, the two-terms truncated form of the virial equation is used for gases at low pressures:

## Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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