Phase change calculations for film boiling flows

A new VOF based interface tracking method, termed CISIT, developed by the present authors recently is extended to include heat and mass transfer due to phase change. In this method, the interface is represented by the contour surface of VOF value 0.5. The interface is advanced in a conservative prediction-correction manner to ensure that the distribution of the VOF is a good approximation to the Heaviside function. An important issue related to the mass transfer across the interface is the treatment of the jump condition for the energy equation. The interface is tackled as an internal boundary for temperature field. The heat flux at the boundary is calculated separately in individual phase. However, unlike other studies, the energy equation for the two phases is solved simultaneously in an implicit way. This method is validated through tests on model problems for which theoretical solutions are available. Calculations are then performed to simulate boiling bubble flows emerging from a planar film and a circular film. The latter case also serves to demonstrate that the present methodology is applicable to phase change flows with irregular geometry. Different boiling modes are identified according to the superheated temperatures.