关键词: 数值模拟, 单气泡, 三维, 核态沸腾, 微柱表面, 微结构导流

Abstract:

Compared with the smooth surface, micro-pillar structured surfaces can enhance nucleate boiling significantly. The enhancement mechanism mainly includes increasing heat transfer area, increasing nucleation site density, reducing bubble departure diameter, etc. Few in-depth studies have been done on the diversion effect of microstructure gaps. In this paper, the three-dimensional multiphase fluid integral model is used to define the important geometric and time dimensionless parameters of single-bubble boiling on the microstructure surface. Through the analysis of velocity field and pressure field, the interaction of bubbles, micro-columns and surrounding liquid during the boiling process is discussed. The results show that the gap of the microstructure promotes the liquid backflow. Furthermore, the diversion effect in the channels established between the liquid-vapor interface at the bubble bottom and the substrate is the most obvious, which leads to an increased liquid flow rate, an accelerated bubble departure and the heat transfer enchancement of the single bubble-boiling. At the same time, the diversion effect of the microstructure promotes the formation of a high pressure thin film at the bottom and the sidewall of micropillar structures, in which the thin liquid film at the bottom has a capillary drainage capability and can maintain the liquid heat transfer area at the micropillar root in the bubble. The thin liquid film on the sidewall of the micropillars replaces the original dryout region, the heat transfer area is correspongdingly increased and the heat transfer efficiency is improved significantly.

Key words: numerical simulation, single bubble, three-dimensional, nucleate boiling, micro-pillars structured surface, microstructure diversion