Abstract: To further expand the application range of microchannel boiling heat transfer in the field of high heat flux electronic equipment cooling, an experimental study is conducted on the dynamic characteristics of boiling generation and development, as well as the overall heat transfer characteristics of microchannel heat exchangers with parallel multiple channels. The results indicate that in microchannel heat exchangers with parallel multiple channels, there are significant differences in the initiation positions of boiling bubbles among the parallel microchannels. The deviation in the non-uniformity of the boiling inception position is relatively small under the influence of mass flow rate and decreases initially and then increases with the increase of heat flux density. Both subcooled boiling and saturated boiling heat transfer mechanisms occur simultaneously within the microchannels. Bubbly flow can happen in both boiling mechanisms, while slug flow and annular flow regimes only occur in the saturated boiling region. The heat flux density has a significant impact on the heat transfer mechanism within the channel, the wall temperature along the flow path, and its variation pattern. Within the heat flux density range of 63~80 kW/m2, the sudden expansion effect at the outlet plenum chamber cause the wall temperature at the heat exchanger's outlet reduce first, then increase, and then reduce again. As the heat flux density increases to 104~252 kW/m2, the wall temperature fluctuations in the microchannels are smaller, and temperature uniformity is enhanced. The overall boiling heat transfer characteristics of the heat exchanger show a turning point when the outlet refrigerant dryness at the microchannel exit is 0.02. The overall heat transfer coefficient of the heat exchanger increases with the increase of both mass flow rate and heat flux density, with the mass flow rate having a higher sensitivity to the average heat transfer coefficient.

Key words: microchannels, parallel channels, boiling heat transfer, non-uniformity

摘要： 为进一步拓展微通道沸腾传热在高热流密度电子设备冷却领域的应用范围，实验研究了具有并联多流道的微通道换热器中沸腾产生发展的动态特性以及换热器的整体传热特性。结果表明，在并联多流道的微通道换热器中，各并联微通道间沸腾气泡的起始位置存在显著差异，沸腾起点位置的不均匀度标准偏差受质量流率的影响较小，随热流密度增加先降低后增加；在微通道内同时发生过冷沸腾和饱和沸腾两种传热机制，两种沸腾机制中均能发生泡状流流型，弹状流流型和环状流流型仅发生在饱和沸腾区域；热流密度对通道内换热机制、沿程壁面温度及其变化规律具有显著影响，在热流密度为63~80 kW/m2的范围内，出口均流室突扩效应导致换热器出口壁面温度先降低后增加再降低；热流密度增至104~252 kW/m2时，微通道中壁面温度波动较小，温度均匀性增强；换热器整体沸腾传热特性在微通道出口处出口制冷剂工质干度为0.02时出现转折，换热器整体换热系数随质量流率和热流密度增加而增加，质量流率对平均换热系数的影响敏感度更高。

关键词: 微通道, 并联通道, 沸腾传热, 不均匀度