Computations of flows with phase change by implicit coupling of vof method and boundary conditions based on kinetic theory

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We developed a practical method for the computation of liquid-vapor two-phase flows accompanied by phase change at the interface. In this paper, we propose an intrinsic improvement by introducing a boundary condition at the non-equilibrium interface, which was derived by Sone and Onishi (Journal of the Physical Society of Japan, Vol.44, (1978),pp.1981-1994.) on the basis of the kinetic theory of gases. The boundary condition, which gives the relationship between the phase change rate and the jump in physical properties, was appropriately integrated with a numerical simulation based on continuum mechanics. The interface was captured by the volume-of-fluid (VOF) method with the piecewise linear interface construction (PLIC) scheme to improve the conservation property of volume. This method was applied to simulating film condensation around a horizontal cylinder. Our results showed that heat and fluid phenomena, including condensation to a liquid film, were successfully reproduced. The order of the spatially averaged Nusselt number on the cylinder was in good agreement with the theoretical value. We compared the results of our method with those of a method that obtains the phase change rate without considering the boundary condition on a molecular scale. We found that our method was effective at simulating film condensation.