Numerical Investigation on Heat Transfer Performance and Bubble Characteristics of Rectangular Channels under Different Low-Pressures

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A numerical model of water evaporator was established based on the problem of insufficient heat sink in onboard electronic equipment of aerospace vehicles, and the heat transfer characteristics and bubble characteristics of water evaporator units in low-pressure environments were studied. This article uses a multiphase flow numerical method based on fluid volume (VOF) and a user-defined function (UDF) to numerically study the pool boiling heat transfer characteristics in low-pressure environments. The focus of the study is on the bubble characteristics and heat transfer characteristics of rectangular unit channels in water evaporators under different pressures (7 kPa, 1.6 kPa, and 0.872 kPa). In addition, the influence of time characteristics on boiling heat transfer was also investigated. The research results indicate that bubbles slide upwards along the wall and do not separate from the wall during the sliding process, but instead merge with adjacent bubbles to form larger bubbles. The attachment of bubbles to the wall surface will deteriorate the heat transfer characteristics, and the bubble wake formed during the sliding process of bubbles has a strengthening effect on heat transfer. The distribution of bubbles along the rectangular height is uneven, and the heat flux near the wall is negatively correlated with the gas content. An increase in vapor content leads to a decrease in the heat flux transferred by the fins. In addition, the influence of different low pressures on pool boiling heat transfer characteristics and bubble dynamics was investigated, and it was found that the heat transfer coefficient and heat flux increase with the increase of pressure. At the same time, the boiling curves of water under different pressure conditions were further derived. The study on the boiling heat transfer performance and bubble behavior of rectangular fins in low-pressure environments provides reference value for the structural design of low-pressure water evaporators and the study of low-pressure pool boiling heat transfer performance.