Experimental Study of Heat Transfer Induced by a Single Vapor Bubble Growth: Influence of Liquid Subcooling

摘要

Heat exchanges during boiling are of high interest for cooling systems. The objective of this work is to investigate heat transfer around a single vapor bubble, the influence of the liquid subcooling and of the heat flux applied on the nucleation surface. Experiments on subcooled pool boiling at atmospheric pressure for a single vapor bubble were conducted and the obtained results are presented. The bubble was created on a downward facing heating element. Generation of the single bubble was achieved on an artificial cavity; the indentation was made on a fluxmeter (Captec Entreprise). FC-72 was used as the test liquid, and its subcooling was maintained to 8 and 14K. Two heating powers were applied on the nucleation surface, and maintained constant during each experiment. Evolutions of bubble size and shape, as a function of wall superheat and liquid subcooling, were followed and studied using a 25 fps video camera. The effect of heating power and subcooling on growth periods were found to be significant. Total heat fluxes during bubble growth were measured using the fluxmeter, for different levels of subcooling and heating powers. Image and data processing has enabled us to show up influence of bubble growth on heat transfer and to determine nucleation periodicity. These preliminary results are discussed.