Du Jiayu, Li Yanzhi, Wang Xiong, Min Qi
Key Laboratory of Advanced Reactor Engineering and Safety of Ministry of Education, Collaborative Innovation Center of Advanced Nuclear Energy Technology, Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084, China.
Department of Mechanical Engineering, City University of Hong Kong, Hong Kong 999077, China.
ACS Appl Mater Interfaces. 2023 Aug 30;15(34):41121-41129. doi: 10.1021/acsami.3c08009. Epub 2023 Aug 16.
Inhibiting the Leidenfrost effect has drawn extensive attention due to its detrimental impact on heat dissipation in high-temperature industrial applications. Although hierarchical structures have improved the Leidenfrost point to over 1000 °C, the current performance of single-scale structures remains inadequate. Herein, we present a facile high-temperature treatment method to fabricate superhydrophilic nickel foams that demonstrate ultrafast droplet permeation within tens of milliseconds, elevating the Leidenfrost point above 500 °C. Theoretical analysis based on the pressure balance suggests that these remarkable features arise from the superhydrophilic property, high porosity, and large pore diameter of nickel foams that promote capillary wicking and vapor evacuation. Compared to solid nickel surfaces with a Leidenfrost temperature of approximately 235 °C, nickel foams nucleate boiling at high superheat, triggering an order of magnitude higher heat flux. The effects of the pore diameter and surface temperature on droplet permeation behaviors and heat transfer characteristics are also elucidated. The results indicate that droplet permeation is dominated by inertial and capillary forces at low and high superheat, respectively, and moderate pore diameters are more conducive to facilitating droplet permeation. Furthermore, our heat transfer model reveals that pore diameter plays a negligible role in the heat flux at high surface temperatures due to the trade-off between effective thermal conductivity and specific surface area. This work provides a new strategy to address the Leidenfrost effect by metal foams, which may promise great potential in steel forging and nuclear reactor safety.
由于莱顿弗罗斯特效应会对高温工业应用中的散热产生不利影响，抑制该效应已引起广泛关注。尽管分级结构已将莱顿弗罗斯特温度提高到1000℃以上，但单尺度结构的当前性能仍然不足。在此，我们提出一种简便的高温处理方法来制备超亲水性泡沫镍，其在几十毫秒内就能实现超快的液滴渗透，将莱顿弗罗斯特温度提高到500℃以上。基于压力平衡的理论分析表明，这些显著特性源于泡沫镍的超亲水性、高孔隙率和大孔径，它们促进了毛细芯吸作用和蒸汽排出。与莱顿弗罗斯特温度约为235℃的固态镍表面相比，泡沫镍在高过热度下发生核态沸腾，引发的热流高出一个数量级。还阐明了孔径和表面温度对液滴渗透行为和传热特性的影响。结果表明，在低过热度和高过热度下，液滴渗透分别由惯性力和毛细力主导，中等孔径更有利于促进液滴渗透。此外，我们的传热模型表明，由于有效热导率和比表面积之间的权衡，在高表面温度下孔径对热流的影响可忽略不计。这项工作为通过金属泡沫解决莱顿弗罗斯特效应提供了一种新策略，这在钢锻造和核反应堆安全方面可能具有巨大潜力。
