Entropy maximization and free energy minimization of multiphase mixtures using particle swarm optimization

Many natural and industrial processes involve multiphase mixtures. Simulations of these processes require accurate and efficient methods to perform phase equilibria computations. We present our results on using the particle swarm optimization method to determine the phase equilibria of multiphase mixtures involving the energetic materials RDX, TNT, and HMX. We have applied this method to two different problems: entropy maximization and Gibbs energy minimization. The former is used to determine the equilibrium state of mixtures where the total internal energy and total volume are specified, while the latter corresponds to the equilibrium state of mixtures where the pressure and temperature are specified. We have found that particle swarm optimization works well for Gibbs energy minimization, and it shows good promise for the more difficult problem of entropy maximization.