Boiling heat transfer enhancement by “bubble train”

With the great demand of computing power, data centers are experiencing a substantial expansion in scale, and the associated high energy consumption has emerged as a critical concern. Two-phase immersion cooling holds great promise in solving the energy consumption issues of data centers owing to its remarkable heat transfer capabilities. Improving the boiling performance is of utmost importance for immersion cooling technique. In this study, a novel heat transfer enhancement approach is proposed, which utilizes piezoelectric ceramics to induce the vibration of a flexible heater. Experimental results demonstrate that the surface boiling heat transfer coefficient of the flexible heater exhibits a 55.67% increase compared to that of a fixed surface, and the critical heat flux is enhanced by 25.99%. A unique “bubble train” phenomenon is observed at a vibration frequency of 200 Hz, and the bubble departure frequency is increased by a maximum of 362.10%. The conditions of velocity and heater displacement for bubble coalescence are determined. Through the coupling of the vibration characteristics of the heater and those of bubble growth, the optimal frequency range for bubble train is derived, along with its corresponding formula. This research provides a theoretical foundation for the development of boiling-enhanced surfaces based on flexible materials and benefits the bubble manipulation.

伴随算力需求的持续攀升，数据中心正迎来规模的大幅扩容，伴随产生的高能耗问题已成为行业亟需应对的核心关切。两相沉浸式冷却（two-phase immersion cooling）凭借其卓越的传热性能，在破解数据中心能耗难题方面展现出巨大应用潜力。提升沸腾换热性能对于沉浸式冷却技术而言至关重要。本研究提出一种新型强化传热方案：利用压电陶瓷（piezoelectric ceramics）驱动柔性加热器（flexible heater）产生振动。实验结果显示，相较于固定表面，柔性加热器的表面沸腾换热系数提升了55.67%，临界热通量（critical heat flux）提升了25.99%。在振动频率为200Hz时，观测到独特的“气泡串（bubble train）”现象，且气泡脱离频率（bubble departure frequency）最高提升了362.10%。研究明确了气泡合并（bubble coalescence）所需的流速与加热器位移条件。通过耦合加热器振动特性与气泡生长特性，推导得到气泡串形成的最优频率范围及其对应计算公式。本研究为基于柔性材料的强化沸腾表面开发提供了理论支撑，同时可为气泡操控技术提供有益参考。