## Z 6 m ln yi ln x 2 qln j Xl

Z 6k^kj

ln yC = 'n f#(!)qi>n * # «i M j r"Z VkRk k qi = z VkiQk

ln yf = Z Qk(ln Tk-ln rki)) k ln Tk = Qk(1 - ln Ek - Fk) ln Tkk) = Qki)(1 - ln Eki)-Fki)) Ek = 6i^ik # 62^2k # 63^3k # ••

XmQm

X XnQn

XXVm

Once again, only pure component and binary data are needed to calculate the parameters. uniquac parameters for over 6000 binary systems have been tabulated in the dechema data series on VLE.

unifac Group Contribution Method

When values of Margules, van Laar, Wilson, NRTL or uniquac parameters are not available in the literature, or when no VLE data for the system of interest have been measured, the unifac (uniquac functional group activity coefficients) method may be used to estimate activity coefficients. The unifac method is a group contribution technique for the estimation of the parameters amn of the excess Gibbs energy model. The method expresses the molar excess Gibbs energy as a sum of a combinatorial part and a residual part and uses the same combinatorial part as the uniquac equation. In terms of the activity coefficient:

Since the group volume parameters Rk and the group area parameters Qk are known, the only unknowns in the unifac equations are the group interaction parameters amn and anm. These have been tabulated for a large number of groups. Moreover, updated parameters are published regularly in the literature. The unifac method has been successfully applied to a wide variety of binary and multicompo-nent systems.

## 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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