BOILING ON FREE-FALLING SPHERES: DRAG AND HEAT TRANSFER COEFFICIENTS

Abstract

Abstract Experiments have been conducted to measure drag (Cg) and heat transfer coefficients (h) and to study the boding nature on heated spheres free-falling in saturated and subcooled water. Simultaneous measurements of the transient sphere velocity and temperature during the fall enabled calculation of cD, heat fluxes and h values. It has been found that the drag decreases with the initial sphere temperature, T0. The measured results, as well as still and motion photography, show that at10⩾ 450° Cfilm boiling pre vaih, with low heat fluxes at the beginning of the transient. In some cases the film collapses, leading to a transition to disturbed-film and micro-bubble regimes, associated with larger heat fluxes and also solid-liquid interactions, with lateral motion of the sphere )“ shoot-off” )