The effect of thin insulating layer on heat transfer characteristics during quenching of hot metals in saturated water.

Abstract

This paper deals with transient pool-boiling heat transfer to saturated water from hot metals coated with a thin layer of insulating (low thermal conductivity) material. The test specimen selected for the present experiments is a silver cylinder, whose heat transfer surface is coated with a thin refractory paint. The heated cylinder is plunged along its own long axis into the distilled water pool and cooled down to the saturation temperature of water, all under atmospheric pressure. The paint coating produces a great enhancement in heat transfer since the minimum film boiling temperature becomes higher with increasing coating thickness, and since transition from film to transition boiling occurs earlier. The minimum film boiling temperatures measured agree well with the theoretical values predicted by an analytical model, in which direct liquid-solid contacts are assumed to intermittently occur in the film boiling regime.