ONSET OF DRY-WALL HEAT TRANSFER IN LOW-MASS-FLUX SPRAY COOLING

Abstract

Abstract An experimental investigation was performed to study a low-mass-flux, spray nucleate boiling phenomenon termed dry wall during which all the impinging liquid is immediately vaporized upon contact with the heated surface. Measurements of wall heat flux and spray coolant mass flux were performed together with a characterisation of spray parameters (such as local droplet size and velocity), using a laser-based diagnostic technique. Two different atomizing nozzles were used and the effect of liquid subcooling on the transition was also studied. The transition to the dry-wail heat transfer regime was found to correlate well with the average global concentration of the spray obtained by the ratio of the spray mass flux to the average spray velocity. The experimental results showed that above a concentration of approximately 0.20 kg/m3, no evidence was seen of transition to dry wall. This concentration corresponding to transition was found to be independent of the two different nozzle types used in the study.