Numerical investigation of film boiling on a horizontal wavy wall

Abstract

Liquid-vapour interface dynamics and instability characteristics together with heat transfer over a wavy wall are studied numerically in the context of saturated natural convection horizontal film boiling. Film boiling computations have been performed using a numerical framework developed for phase change problems on unstructured grids that incorporates a coupled level set and volume of fluid interface capturing algorithm. The film boiling behaviour as influenced by geometric features of the sinusoidal wavy heater is ascertained and discussed in detail. The heater wavelength is varied in a wide range encompassing the disturbance spectrum primarily governing bubble release in horizontal film boiling, for several different amplitude values. A link between geometrical and hydrodynamic aspects is established by showing that the individual peaks of the wavy surface affect interface evolution only for heater wavelengths larger than the critical Rayleigh–Taylor wavelength. Additionally, the effect of wall superheat corresponding to different wavy wall geometries is also discussed. It is observed that the interface dynamics and heat transfer result from a coupled effect of the geometrical features of the heater surface, in addition to an interplay with the wall superheat. While a propensity towards transition in the mode of instability is observed at enhanced wall superheats affecting the interfacial dynamics, the wavy heater topology is observed to avert such a hydrodynamic transition under certain cases. Simultaneously, the effect of wavy geometry on film boiling heat transfer is highlighted to be non-analogous to single phase flows.