Study of Slug Flow Inside Vertical Capillaries With Phase Change

Numerical simulations of a slug flow in a vertical capillary tube undergoing phase change are conducted to obtain detailed information on flow and thermal fields of such flows. The VOF (Volume of Fluid) method is adapted to handle two-phase flow. The PLIC (Piecewise Linear Interface Calculation) scheme is used for the advection of the gas-liquid surface, while the CSF (Continuum Surface Force) model is employed for the calculation of surface tension. The growth of a single vapor bubble is numerically predicted under evaporation or condensation conditions. A qualitative comparison of the numerical results with the preliminary experiment is also carried out. Results of the numerical prediction agree fairly well with experimental counterparts. It is found that the evaporation or condensation process of a bubble can be classified depending on if the bubble has a spherical shape or a shell shape. Phase change is enhanced when a bubble has a shell shape reflecting the thin liquid part formed near the solid wall.