Multicomponent Systems

Besides their technological importance in the chemical and petroleum industry, there is a great scientific interest in studying multicomponent systems due to the challenges to overcome when dealing with their dynamics and patterns in non-equilibrium states. Homogeneous non-ideal mixtures may segregate into two or even more phases when the temperature is decreased. The segregation mechanisms have a molecular origin and are due to the attractive forces between the molecules of the same species when these forces are dominant in comparison with diffusion and cross-interactions. The correct understanding of these complex systems requires, thus, a multiphysics approach and this complexity is a major difficulty for numerical simulations based on discrete forms of the macroscopic equations. On the other hand, the knowledge of the macroscopic equations that govern the highly non-linear physical processes when a non-ideal mixture changes from an equilibrium state to another is important for establishing a reference framework that every multiphysics model must satisfy. In this chapter, these macroscopic equations are derived based on the second law of thermodynamics. Particular attention is given to the molecular origin of segregation. Some lattice-Boltzmann simulation results are presented at the end of the chapter.