Local heat-transfer coefficient in spray cooling of hot surface.

The local heat transfer in spray cooling is theoretically and experimentally studied. The theoretical expression of the heat-transfer coefficient is presented. The distribution characteristics of spray, i.e., the number flux and the size and velocity distributions of the droplets at a given location are combined with the single droplet characteristics upon impingement onto hot surface, i.e., the droplet heat-transfer coefficient, he bottom radius changing with time and the retention time of the drop at the surface. On the basis of expression, the local heat-transfer coefficient is evaluated at various locations in a full-cone spray, the distribution characteristics of which are known. Experiments on the spray-cooling rate of hot surface of a small metal specimen indicate both the fundamental validity and the limitation of the theory.