Study of the Dynamics of Flow and Heat Transfer in Draining Intensely Evaporated Wave Films of Liquid

Abstract

The dynamics of flow and heat transfer in gravity flow of wave films of cryogenic liquid over vertical heated surfaces under the conditions of evaporation and boiling have been studied experimentally. The studies have been conducted on heated surfaces with the length along the flow of 12, 20, 42, and 64 mm within the variation range of the Reynolds number at the inlet of 10−2000. The work has showed different dynamics in the development of crisis phenomena during film boiling, depending on the length of the heated surface. It has been shown that on short thick-wall heaters the drying of the heat-release surface is related to complete rejection of the developed liquid jets directly at the inlet to the heat-release zone. It is found that on heat-release surfaces, which have greater length along the flow, a variety of the crisis develops that is conditioned by propagation of the temperature perturbation upstream in the heat-transfer wall. Generalization of the obtained experimental data shows that under the conditions of development of the given type of heat-transfer crisis the critical heat flux can be substantially lower than the one calculated by the known hydrodynamic models of its description. At the parameters of the heat-transfer wall implemented in the experiments, an autowave transition develops; this transition is characterized by displacement of the nucleate-boiling zone by the front of drying when a critical size of "dry" spots in the lower part of the heat-release surface has been reached.