A Novel, Multi-scale Diffuse Interface Method for Macro-scale Multiphase Flows with Micro-scale Modeling of Phase Change*

It is a grand challenge to accurately model phase-change multiphase flows because of the tight coupling between thermodynamics and transport phenomena in 3D. The classical diffuse interface methods implicitly capture the phase interface, and phase change across interface, through solving the coupled equilibrium and non-equilibrium Gibbs energies. The equilibrium energy results in phase separation, while the non-equilibrium energy promotes molecular diffusion across interface. The balance of the two yields a rapid, smooth transitioning interface. However, classical methods capture a physical interfacial transition, whose thickness is extremely smaller than the scale of macro-scale problems below critical conditions. This research proposes a novel diffuse interface method through developing a new non-equilibrium Gibbs energy model, which bridges the micro-scale interfacial phenomena with the macro-scale flows. The new non-equilibrium model proposed here consists of (1) a nucleation potential originated from the phase stability computation, and (2) an averaged gradient term based on the phase equilibrium flash calculation. Our results show accurate predictions of the phase change and evolution in binary mixtures at different temperatures and pressures.