亲/疏水表面微结构和周期性脉动流及其协同作用强化沸腾换热机理研究

Boiling heat transfer always shows severe deterioration at high heat flux/in microgravity, and the primary reason lies in the fact that the large bubble is difficult to depart from heater surface and prevents the fresh liquid from accessing the heater surface for evaporation. In order to solve this problem, new hydrophilic/hydrophobic structures by alternate arrangement of hydrophobic micro-pin-finned surface and hydrophilic surface are proposed based on self-developed high-efficiency micro-pin-finned structures. Meanwhile, periodic pulsatile flow is employed with the new microstructured surfaces, which can promote the bubble departure due to destabilization and accelerate bubble detachment by bubble slipping from hydrophobic surface to hydrophilic surface, and thus enough fresh liquid can be supplied to the heater surface for further enhancing heat transfer. Mechanism of boiling heat transfer enhancement by using hydrophilic/hydrophobic surface microstructure and periodic pulsating flow with synergistic effect will be studied. From the perspective of micro and mesoscopic flow on heater surface, which is the key factor influencing boiling heat transfer performance, evolutional rule of vapor-liquid interface movement on microstructured surface can be obtained by using infrared camera to measure wall temperature distribution. Visual observation of bubble dynamics can be observed by using high speed CCD camera. Multi-scale modeling including micro, meso and macro scales of boiling heat transfer over microstructured surface will be constructed. Based on analysis of experimental and simulation results, we aim at revealing the mechanism and internal relation among micro/mesoscopic flow, boiling heat transfer characteristics and bubble dynamics over microstructured surfaces. Moreover, the designed principle and technology of high efficient boiling heat transfer enhancement will be proposed. The research will further improve the theories of boiling heat transfer enhancement, and provide technical support for efficient cooling of high-power thermal devices.

高热流密度/微重力下沸腾换热性能往往严重恶化，其根本原因在于加热面大汽泡难以脱离而阻碍液体供应和蒸发。针对这一难题，在已开发的高效换热柱状微结构基础上，提出疏水柱状微结构和亲水面相结合的新型亲/疏水表面微结构，并利用周期性脉动流促进加热面汽泡失稳脱离和促使汽泡从疏水结构滑移至亲水面而加速脱离，保障液体顺利供应而进一步强化换热。研究亲/疏水表面微结构和周期性脉动流及其协同作用强化沸腾换热机理。从加热面微细观流动这一影响沸腾性能的关键因素入手，利用红外热像技术测量加热面温度分布获得汽液相界面运动演化规律，通过高速CCD分析汽泡动力学行为，从微观、介观和宏观三个尺度组合构建微结构表面沸腾换热模型；实验和数值分析结合揭示微结构表面微细观流动特征、汽泡动力学行为及其与沸腾换热之间的内在联系规律，提出高效强化沸腾换热技术。研究可进一步补充和完善现有强化沸腾换热理论，为大功率热设备冷却提供技术支撑。

针对高热流密度/微重力下沸腾换热性能严重恶化的难题，本项目开展了强化沸腾换热实验、理论与技术以及数值计算研究。在实验方面，开发了多种亲/疏水微结构表面，并通过高频往复脉动流实现流动沸腾换热效果的显著强化。高频往复脉动流与微结构表面结合使对流换热系数提高3.8倍，临界热流密度提升2.6倍。在理论与技术方面，通过对沸腾换热汽泡动力学以及汽泡与其相界面所诱发的微观液体流动的研究，建立了气泡动力学模型和临界热流密度预测模型，揭示微结构表面微细观流动与换热特征、汽泡动力学行为及沸腾换热性能之间的内在联系及其强化换热机理。在被动换热技术方面，基于气泡合并过程中的表面能向动能转换的思想，提出了通过耦合柱状微结构的钉扎效应和非均匀纳米墙的团簇式成核效应促进气泡脱离进而实现沸腾传热强化的新策略；在主动换热技术方面，揭示了往复脉动流动通过破坏热边界层强化对流换热，并通过限制气泡生长时间、促进气泡脱离并改善液体补给提升临界热流密度的作用机理。在数值计算方面，开展不同尺度沸腾强化换热过程的模拟研究。提出了微观汽泡成核机制的探究思想—“PK”准则，揭示了不同影响因素下的微汽泡成核机制。提出了可提高LB热伪势模型求解两相问题出口边界稳定性的处理方法以及基于非结构化网格、适体结构化网格和非结构化自适应网格VOSET方法，构建了对应的相变模型。构建了三维细微通道内流动沸腾传热精细化数值模拟方法，揭示了流动沸腾流型、传热主导机制和临界热流密度触发机制。共发表期刊论文80篇，申请中国发明专利21项(授权16项)、国际专利2项(授权1项)，培养博士6名、硕士8名。本项目完成了预期目标和指标，研究成果有效解决了高热流密度和微重力下沸腾性能严重恶化导致散热能力低下的问题，进一步补充和完善现有强化沸腾换热理论和技术，为大功率电子器件高效冷却和空间高效两相热管理系统提供理论和技术支撑。