Development of a multilayer vapor-liquid phase change model for the VOF method and simulation of vapor condensation process¹1The authors greatly acknowledge the financial supports from the National Natural Science Foundation of China (No. U2241254 and No. 22478314).

Current vapor-liquid phase change models often rely on empirical parameters or exhibit inconsistencies when coupled with the Volume of Fluid (VOF) method. To address these limitations, a novel phase change model is proposed. Virtual phases are constructed based on volume fraction, and multi-layer virtual interfaces are established using mesh faces. Mass and energy source terms are derived from energy conservation within computational cells. Simulation results for a one-dimensional and two-dimensional vapor condensation problem show excellent agreement with analytical solutions, thereby validating the accuracy of the proposed model. To gain deeper insights into the condensation mechanisms of vapor bubbles, numerical simulations are conducted for bubble condensation in both enclosed tanks and open channels. The results demonstrate that both sharp-interface and dispersed-interface modeling approaches can yield equivalent predictions. The suction flow induced by bubble condensation significantly influences bubble dynamics. Specifically, variations in tank dimensions lead to a 37% deviation in bubble lifetime. In cases involving multiple simultaneously condensing bubbles, this suction flow is intensified, resulting in accelerated condensation of bubbles located near the tank outlet. Furthermore, an increase in inlet velocity by 0.05 m s⁻¹ during bubble condensation in an open channel reduces the bubble lifetime by 31%. Notably, the initial thermal boundary layer surrounding the bubble imposes a significant effect on the bubble lifetime. Specifically, a thermal boundary layer thickness of 200 μm is capable of prolonging the bubble lifetime by a factor of 50. Owing to the scarcity of measured experimental data regarding the thermal boundary layer, observations of bubble morphology and lifetime acquired via experiments cannot serve as strict quantitative validation benchmarks for phase change numerical models.