The BP, SR, and SC methods described above expend a large percentage of their computational effort during each iteration in the calculation of K values, enthalpies, and derivatives thereof. An algorithm designed to significantly reduce that effort was developed by Boston and Sullivan [Can. J. Chem. Engr., 52, 52 (1974)]. The MESH equations are solved in an inner loop using simple, approximate equations for K values and enthalpies. The empirical constants in these equations are determined and infrequently updated from the more rigorous, but complex, K value and enthalpy correlations in an outer loop, using calculated compositions and temperatures from the inner loop. Thus, the method is referred to as the inside-out method. The iteration variables for the outer loop are the constants in the approximate thermodynamic-property equations in the inner loop. The iteration variables for the inner loop are related to stage j
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