Heat transfer and crisis phenomena with intense boiling in the falling wave liquid films

Abstract

Experimental data on heat transfer with intense evaporation in the falling films of liquid nitrogen were analysed. According to data generalization, heat transfer at evaporation becomes more intense under the precrisis modes at high heat fluxes for two studied boundary conditions on the heat-releasing surface: Tw ≈ const and qw ≈ const. The relative contributions of conductive and convective components of heat transfer for different heat fluxes were estimated due to statistical treatment of the wave characteristics carried out by the capacitance probes for measurement of the local liquid film thickness. It was found out that heat transfer intensification is mainly caused by a drastic decrease in thermal resistance of the local zones with intensely evaporating residual layer between large waves. At that, the convective component of heat transfer related to wave perturbations on a free surface of a liquid film decreases significantly with a rise of heat fluxes. New data on pulsations of the local temperature of the heat-releasing surface were obtained at different points along the flow with the modes of “dry spot” formation.