Jiao Yunlong, Wang Jiaxiang, Guo Yuhang, Du Yu, Zhu Yongqing, Ji Jiawei, Liu Xiaojun, Liu Kun
Institute of Tribology, Hefei University of Technology, Hefei 230009, China.
School of Electrical Engineering and Automation, Anhui University, Hefei 230601, China.
Langmuir. 2024 Oct 1;40(39):20773-20782. doi: 10.1021/acs.langmuir.4c02942. Epub 2024 Sep 18.
This study explores the kinetic behavior of droplets impacting microtextured surfaces under a Leidenfrost temperature, employing high-speed photography and picosecond laser micromachining techniques. The investigation focuses on two types of microtextured surfaces with totally different surface peak-valley features: a negatively skewed surface with micropit arrays ( < 0) and a positively skewed surface with micropillar arrays ( > 0). The results indicate that both microtextured surfaces contribute to a higher Leidenfrost temperature compared with the original smooth surface, which is consistent with previous studies. However, it is worth noting that the Leidenfrost points of the micropit and micropillar surfaces showed opposite trends with the microtexture area occupancy. Specifically, the Leidenfrost temperature on micropit surfaces increases with greater micropit area occupancy, while it decreases on micropillar surfaces under similar conditions, which is mainly attributed to the differential impact of area occupancy on droplet heat transfer efficiency. When the microtexture area occupancy is 50%, it is worth noting that the micropit and micropillar surfaces have nearly same roughness (), but the Leidenfrost temperature was notably higher on the micropit surface with negative skewness ( < 0), which was related to differences in vapor flow dynamics. We further find that the Weber number () significantly influences the Leidenfrost point, with the droplet impact wall behavior going through the states of film bounce back, ejecting tiny droplets and bounce back, and ultimately droplet breakup as the increases. The dynamic Leidenfrost point was found to be generally higher than the static point and increases with the . Finally, we compare the cooling efficiency of these surfaces, and it is found that the micropit surfaces with a negative skewness exhibit superior heat dissipation performance under the same conditions, which proved that the negatively skewed surface may have great potential in high-density heat dissipation technology.
本研究采用高速摄影和皮秒激光微加工技术，探索了在莱顿弗罗斯特温度下液滴撞击微纹理表面的动力学行为。研究聚焦于两种具有截然不同表面峰谷特征的微纹理表面：一种是具有微坑阵列的负偏态表面（<0），另一种是具有微柱阵列的正偏态表面（>0）。结果表明，与原始光滑表面相比，这两种微纹理表面都有助于提高莱顿弗罗斯特温度，这与先前的研究一致。然而，值得注意的是，微坑和微柱表面的莱顿弗罗斯特点随微纹理面积占有率呈现相反的趋势。具体而言，微坑表面的莱顿弗罗斯特温度随着微坑面积占有率的增加而升高，而在类似条件下微柱表面的莱顿弗罗斯特温度则降低，这主要归因于面积占有率对液滴传热效率的不同影响。当微纹理面积占有率为50%时，值得注意的是，微坑和微柱表面具有几乎相同的粗糙度（），但负偏态（<0）的微坑表面的莱顿弗罗斯特温度明显更高，这与蒸汽流动动力学的差异有关。我们进一步发现，韦伯数（）对莱顿弗罗斯特点有显著影响，随着的增加，液滴撞击壁面的行为经历膜反弹、喷射微小液滴并反弹以及最终液滴破碎的状态。发现动态莱顿弗罗斯特点通常高于静态点，并且随着的增加而升高。最后，我们比较了这些表面的冷却效率，发现在相同条件下，负偏态的微坑表面表现出优异的散热性能，这证明负偏态表面在高密度散热技术中可能具有巨大潜力。
