PREDICTABLE MODELING OF HEAT-TRANSFER COEFFICIENT BETWEEN SPRAYING WATER AND A HOT SURFACE ABOVE THE LEIDENFROST TEMPERATURE

In order to evaluate the cooling intensity of water spray impacting on a hot metallic surface above the Leidenfrost temperature, the formula tion of heat transfer coefficient in the forced convection boiling reg ion has been made as a function of the droplet size, the impinging vel ocity and the number density of droplets whose parameters are independ ent of each other. So far, many works on the mist/spray cooling proces s have been made, in particular, from an experimental point of view. H owever, the general procedure capable of evaluating heat transfer rate between a hot metallic surface and water spray has not been establish ed yet, because there are a large number of parameters affecting the s pray cooling process. Then, we have experimentally derived a new formu la consisting of the above three parameters to be dominant for heat tr ansfer rate in the spray cooling process. The stainless steel surface heated to about 900 degrees C has been cooled by water spray of simila r to 20 degrees C and the time history of the surface temperature has been measured. We have selected some kinds of full cone nozzles whose characteristics such as the average droplet diameter, the velocity and the distribution of water flux have been different from each other, a nd performed the cooling tests using them. Finally, the formula capabl e of giving best-fit to the experimental results has been proposed. Th e effect of the spraying characteristics on the heat transfer rate has been discussed from an experimental point of view.