Saturated film boiling over a circular cylinder subjected to horizontal cross-flow in the mixed regime

Abstract

Film boiling over a circular cylinder in a horizontal cross-flow of saturated liquid is studied in the mixed regime that is characterized by a combined influence of buoyancy and flow inertia at low magnitudes of the Froude number (Fr). Liquid-vapor interface evolution and the ensuing vapor wake dynamics together with heat transfer have been determined through a computational framework developed for phase change problems on two-dimensional unstructured grids using a coupled level set and volume of fluid interface capturing method. While the quasisteady nature of ebullition cycle is gradually lost as Fr increases, the effect of cross-flow orientation with respect to gravity is shown to be nontrivial in the mixed regime. A direct consequence of the orthogonal gravity and flow fields is an anomalous impairment of heat transfer with an increase in cross-flow velocity under certain conditions, which is discussed in detail. Simultaneously, the film boiling behavior as influenced by several other hydrodynamic and thermal parameters is also ascertained. The interplay between buoyancy and inertia is further highlighted while discussing the interdependent liquid and vapor wake characteristics in the mixed regime with horizontal cross-flow. The liquid wake behavior is shown to result not only from the bluff body geometry but also the instantaneous vapor wake profiles, with the wall superheat affecting the time scale of wake interaction. Finally, a reduction factor (ξ) is proposed and determined as a function of the Froude number, which is used in conjunction with a correlation for upward cross-flow film boiling to predict the heat transfer.