RESEARCH ON BUBBLE DYNAMIC CHARACTERISTICS IN THE POWER DEVICE PHASE CHANGE HEAT EXCHANGER

Abstract

Phase change heat exchangers are widely used in power devices because of their high efficiency and compactness. In order to further improve the performance of phase change heat exchangers, a visual power device phase change heat exchanger with a cross-sectional area of 180 mm × 20 mm was experimentally investigated to reveal the link between the dynamic characteristics of bubbles and the boiling heat transfer mechanism. The experiment obtained the dynamic bubble characteristics such as bubble generation, growth, departure, and coalescence under different heat fluxes. The relevant bubble departure diameter and frequency were found according to the measurement obtained from photographs. The experimental results showed that a single bubble grows rapidly at the nucleation site on the heating wall of the heat exchanger under low heat flux. As the heat flux increases, the nucleation site density on the wall increases, the bubble departure frequency increases significantly, and the phenomenon of bubble coalescence begins to appear. Moreover, a modified boiling bubble departure diameter correlation was developed, and the predictions of the bubble departure diameter were validated against different databases. The predictions agreed better with the experimental data and had some adaptability with other data, which provides a useful reference for engineering applications of the power device phase change heat exchanger.