A low Mach number diffuse-interface model for multicomponent two-phase flows with phase change

This study introduces a four-equation, two-phase diffuse interface model designed to simulate two-phase, low-Mach flows with phase change. The model is extended to multicomponent gas by incorporating an additional equation for the vapor mass fraction transport. The methodology accounts for interfacial mass transfer driven by differences in the chemical potentials of the phases. A distinctive feature of our model is its ability to discretely conserve the mass of each phase, total momentum, and enthalpy, while maintaining a steady interface thickness, which is critical for the numerical stability and accuracy of two-phase flow simulations. Furthermore, the model effectively handles high density and viscosity ratios, making it robust across a wide range of applications. In addition to the general model suited for weakly compressible components, we also present a reduced model for fully incompressible components. The numerical methods are verified against several established benchmarks for fully incompressible systems with mass transfer. The low-Mach formulation is validated against sharp-interface simulations of the same problem; the results of a three-dimensional simulation of a sedimenting droplet undergoing evaporation are also illustrated.