Calculations of thermodynamic equilibrium in systems subject to gravitational fields

The objective of this work is to present a procedure for the calculation of chemical and phase equilibrium (CPE) in multicomponent mixtures subject to the effect of gravitational fields. The specifications are the total volum e, initial number of moles of each species and temperature. The problem is formulated as the minimization of a modified form of the Helmholtz function that contains a term to account for the potential energy. To solve this pr oblem, the system is divided into layers. It is assumed that each of these layers is a homogeneous part of the system, and that each phase occupies a specified number of layers. Layers in the same phase are assumed to have th e same size whereas those in different phases typically have different size s. In the minimization of the modified Helmholtz function, the independent variables are the volume fraction of each phase (thereby defining the locat ion of the interfaces) and the number of moles of each species in each laye r, taking into account the possibility of chemical reactions. The procedure is used to calculate density and pressure profiles with height for pure fl uids close the critical point and composition profiles for reactive and non -reactive mixtures. (C) 2000 Elsevier Science Ltd. All rights reserved.