## C X ZiCi

(2v + b + c) + [4bc + (b + c)2 ]1/2 \ (2v + b + c)-[4bc + (b + c)2]1/2 )

In the above equations, the subscript c denotes a value at the critical point. Note that by setting the parameter c = 0 in eqn , the Patel-Teja equation reduces to the Redlich-Kwong-Soave equation of state; and by setting c = b, it reduces to the Peng-Robinson equation of state. Both the Redlich-Kwong-Soave and the Peng-Robinson equations are widely used in process design calculations. For nonpolar fluids, Cc and m are calculated from the following relationships in terms of the acentric factor w:

ln ' (2v + b + c) - [4bc + (b + c)2]i/2 2(2v + b + c)[4bc + (b + c)2 ]i/2

A knowledge of Pc, Tc and w is therefore sufficient to calculated the parameters of the equation of state. Alternatively, Cc and m may be calculated from experimental values of the vapour pressure and liquid density of the substance. Several other forms of eqn  suitable for complex molecules have been proposed.

The parameters a, b and c for a mixture can be calculated using the following mixing rules:

Eqn  can be used to calculate both the vapour-and liquid-phase fugacity coefficients. In the case of vapour phase, z, = yi and v is the vapour molar volume, whereas for the liquid phase, zl = x, and v is the liquid molar volume. The ratio of the two fugacity coefficients yields the K value under the conditions of interest. ## Solar Panel Basics

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