Multiphase Flows

In this Chapter we derive the equations of motion of multiphase fluids. In the classical theory of multiphase flow, each phase is associated with its own conservation equations (of mass, momentum, energy and chemical species), assuming that it is at local equilibrium and separated from the other phases by zero-thickness interfaces, with appropriate boundary conditions. Instead, here we describe the so-called diffuse interface, or phase field, model, assuming that interfaces have a non-zero thickness, i.e. they are "diffuse", as it is more fundamental than the classical, sharp interface theory and is therefore more suitable to be coupled to all non-equilibrium thermodynamics results.