Abstract: In order to explore the boiling flow and heat transfer characteristics in the rectangular periodic expansion-constriction microchannel, rectangular periodic expansion-constriction microchannels of different sizes are established, and deionized water is used as the working fluid to carry out numerical simulation under the conditions of inlet velocity of 0.2 m/s and heat flux of 50 W/cm2. The results show that there are enlarged and contracted cross-sectional structures in the rectangular periodic expansion-constriction on microchannels. The enlarged part of the microchannel provides a nucleation site, which is conducive to bubble nucleation and increases the heat exchange area. With the increase of the periodic frequency of the expansion-constriction structure, the more intense the coupled heat transfer between cavitation and boiling in the microchannel, there are still more small bubbles in the middle and downstream regions of the channel. The number of small bubbles along the channel increases, the gas content increases, and the heat transfer performance continues to improve. In addition, the maximum temperature of the wall along the microchannel gradually decreases, and the temperature distribution along the channel become more uniform. The rectangular periodic expansion-constriction microchannel reduces the contact area between the bubble and the wall, and reduces the frictional pressure drop between the two phases. But the expansion-constriction of the microchannel increases the resistance to flow in the channel. The pressure drop in the expansion-constriction microchannel increases with the increase of the γ of the structural parameters. At the same time, the comprehensive performance of flow heat transfer in the microchannel increases first and then decreases with the increase of the frequency of the expansion-constriction channel. When the structural parameter of γ is 0.2, the comprehensive performance of the rectangular periodic expansion-constriction microchannel is the best, which is 34% higher than that of the rectangular straight microchannel.

Key words: rectangular periodic expansion-contraction, microchannel, cavitation boiling coupling, numerical simulation, heat transfer enhancement

摘要： 为了探究矩形周期性扩缩微通道内沸腾流动与传热特性，建立了不同尺寸的矩形周期性扩缩微通道，使用去离子水作为工作流体，在入口速度为0.2 m/s，热流密度为50 W/cm2的条件下进行数值模拟。结果表明，矩形周期性扩缩微通道中存在扩大和缩小的截面结构，微通道中的扩大部分提供了成核位点，有利于气泡成核且增大换热面积。随着扩缩结构的周期性频率增加，微通道中空化和沸腾耦合传热越剧烈，通道的中下游区域仍存在着较多小气泡，通道沿程小气泡数量增多，含气率增加，传热性能不断提高，并且微通道沿程壁面最高温度逐渐降低，通道沿程温度分布更加均匀。矩形周期性扩缩微通道减少了气泡与壁面的接触面积，减少了两相摩擦压降，但是微通道中扩大和收缩部分增加了通道中的流动阻力，周期性扩缩微通道中的压降随着结构参数γ增大呈增大趋势。同时微通道中流动传热的综合性能随扩缩通道变化频率增加呈现先增大后减小的趋势，当结构参数γ=0.2时，矩形周期性扩缩微通道的综合性能最好，比矩形直微通道提升了34%。

关键词: 矩形周期性扩缩, 微通道, 空化沸腾耦合, 数值模拟, 强化换热