Investigation of the Crisis of Heat Transfer under Conditions of Boiling on an Inclined Surface Facing Downward

Abstract

An experimental investigation is performed of the crisis of heat transfer under conditions of boiling on an inclined extended (1 to 2 m) surface facing downward and immersed in a large pool of water. The effect of water subcooling on the value of critical heat flux (CHF) is investigated for the plate slopes of 8, 12, and 16° at a pressure close to atmospheric. The experimental results indicate that the critical heat flux increases with the surface slope. An anomaly in the dependence of the CHF on subcooling Δt is revealed, namely, the existence of a minimum of the CHF under conditions of water subcooling of 20(±10)°С. Such a nonmonotonic dependence of the CHF on subcooling was previously observed under conditions of subcooled water boiling in pipes at relatively high values of the circulation rate. No such effect was previously described in the literature for the conditions of pool boiling of liquid. Based on the hypothesis on the effect of water subcooling on the velocity of the steam-liquid layer formed at the surface being heated and intensifying the precritical boiling of the liquid, an explanation is suggested of such a nonmonotonic pattern of the dependence of the CHF on subcooling. A theoretical model which makes it possible to include the effect of the orientation of the heat-transfer surface, of subcooling, and of pressure is used to derive the correlation for the CHF which generalizes the experimental data.