Improving the critical heat flux (CHF) and avoiding dry out downstream are the keys to enhance the two-phase cooling performance of microchannel heat sinks. In this work, a novel type of bidirectional counter-flow (BCF) microchannels with 600 $\mathrm{\mu }\mathrm{m}$ depth and 300$\mathrm{\mu }\mathrm{m}$ width, giving a hydraulic diameter of 400$\mathrm{\mu }\mathrm{m}$, is fabricated in an oxygen-free copper base. Flow boiling experiments are conducted in bidirectional counter-flow microchannels and conventional unidirectional parallel-flow (UPF) microchannels, with the deionized water being used as the working fluid. Cases under six mass fluxes ranging from 118 kg/m²·s to 370 kg/m²·s and three inlet subcoolings of 30 ℃, 50 ℃, and 70 ℃ are tested. Two-phase flow behaviors in microchannels are simultaneously captured by a high-speed camera. It is found that, unlike conventional UPF microchannels, the location for the onset of nucleate boiling (ONB) in BCF microchannels is moved from downstream to the middle region. The downstream dry-out, which is usually occurred in UPF microchannels, can be well avoided in BCF microchannels due to the substantial feeding of liquid in adjacent microchannels. The CHF in BCF microchannels can be increased by 33.8∼57.2% compared with the conventional UPF microchannels. Under the combined effect of expanded nucleate boiling region and shortened subcooling region, the average heat transfer coefficient (HTC) in BCF microchannels can be increased by 36.6%∼56.7%. More interestingly, the improvement of heat transfer performance is found to be accompanied by a significant reduction in pressure drop for BCF microchannels in all the experiment cases. In addition, two-phase instabilities in terms of wall temperature and pressure drop oscillations can be significantly suppressed by using BCF microchannels instead of the conventional UPF microchannels. This study proposes a more efficient microchannel heat sink design scheme to deal with the microelectronic cooling challenges.

提高临界热通量（CHF）和避免下游干涸是提高微通道散热器两相冷却性能的关键。在这项工作中，一种新型的双向逆流（BCF）微通道具有 600 $\mathrm{\mu }\mathrm{米}$ 深度和300$\mathrm{\mu }\mathrm{米}$ 宽度，水力直径为 400$\mathrm{\mu }\mathrm{米}$, 在无氧铜基中制造。流动沸腾实验在双向逆流微通道和常规单向平行流 (UPF) 微通道中进行，去离子水用作工作流体。^{在 118 kg/m 2} ·s 到 370 kg/m ²的六种质量通量下的情况·s和30℃、50℃、70℃三个入口过冷度进行试验。微通道中的两相流动行为由高速相机同时捕捉。研究发现，与传统的 UPF 微通道不同，BCF 微通道中核沸腾 (ONB) 的开始位置从下游移动到中间区域。由于相邻微通道中大量的液体进料，在 BCF 微通道中可以很好地避免通常发生在 UPF 微通道中的下游干涸。与传统的UPF微通道相比，BCF微通道中的CHF可以增加33.8～57.2%。在扩大的核沸腾区和缩短的过冷区的共同作用下，BCF微通道的平均传热系数（HTC）可提高36.6%～56.7%。更有趣的是，在所有实验案例中，发现传热性能的提高伴随着 BCF 微通道压降的显着降低。此外，通过使用 BCF 微通道代替传统的 UPF 微通道，可以显着抑制壁温和压降振荡方面的两相不稳定性。本研究提出了一种更有效的微通道散热器设计方案来应对微电子冷却挑战。