Development of a Phase-Field Method for Phase Change Simulations Using a Conservative Allen-Cahn Equation

Two-phase flows including a phase change such as liquid-vapor flows play an important role in many industrial applications. A deeper understanding of the phase change phenomena is required to improve the performance and safety of nuclear power plants. For this purpose, we developed a phase change simulation method based on the phase-field method (PFM). The low computational efficiency of the conventional PFM based on the Cahn-Hilliard equation is an obstacle in practical simulations. To resolve this problem, we presented a new PFM based on the conservative Allen-Cahn equation including a phase change model. The wettability also needs to be considered in the phase change simulation. When we apply the conventional wetting boundary condition to the conservative Allen-Cahn equation, there is a problem that the mass of each phase is not conserved on the boundary. To resolve this issue, we developed the mass correction method which enables mass conservation in the wetting boundary. The proposed PFM was validated in benchmark problems. The results agreed well with the theoretical solution and other simulation results, and we confirmed that this PFM is applicable to the two-phase flow simulation including the phase change. We also investigated the computational efficiency of the PFM. In a comparison with the conventional PFM, we found that our proposed PFM was more than 100 times faster. Since computational efficiency is an important factor in practical simulations, the proposed PFM will be preferable in many industrial simulations.