Forced Convection Film Boiling on Spherical and Plane Geometries

Abstract

Forced convection film boiling has been studied experimentally using three different heated specimens and the transient cooling technique. Data are presented for the variations of heat transfer coefficient and film thickness with surface temperature and water subcooling and for the influence of subcooling on the minimum film temperature. The characteristics of the vapour/liquid interface during the transients have been observed and recorded on video. The condition of the surface of the film depended largely on water subcooling and could be described as smooth, rippled or turbulent. Three modes of film collapse were identified: an explosive collapse at high subcoolings, a progressive collapse for low subcoolings, during which a quench front moved upwards over the surface, and an explosive-progressive mode at intermediate subcoolings. With the latter mode, which has not been previously reported, the vapour film reformed briefly following an explosive generation of vapour at first contact between the hot surface and the liquid. A quench front then moved progressively upwards, initiating nucleate boiling on the entire specimen surface.