Study the effects of heated wall profile and superheat on bubble evolution in film boiling using a VOF-CSF phase change model

Abstract

This paper presents a numerical method for two-fluid flows with phase change phenomenon. The motion of interface is captured using volume of fluid (VOF) method along with a geometrical reconstruction method called PLIC. Interfacial source terms for surface tension, heat and mass transfers are modelled and integrated with the governing equations of VOF model available in commercial CFD software, ANSYS- Fluent, using user-defined functions (UDFs). The model is used to simulate a film boiling problem where vapor bubbles are emanating from the film covering a heated wall. The effects of heated wall profile modification and the degree of superheat on transient vapour bubble evolution are analysed in details. It is found that an increase in heated wall surface area or degree of superheat enhances the vapour bubble formation and emission significantly. It is evident from the simulations that the combined effect is possible when these parameters are increased together. These enhancement techniques have proved to reduce the time difference between two consecutive bubble rises from the thin film covered the heated wall surfaces.