Zou An, Chanana Ashish, Agrawal Amit, Wayner Peter C, Maroo Shalabh C
Department of Mechanical &Aerospace Engineering, Syracuse University, Syracuse NY 13244 USA.
Department of Electrical Engineering and Computer Science, Syracuse University, Syracuse NY 13244 USA.
Sci Rep. 2016 Feb 3;6:20240. doi: 10.1038/srep20240.
Boiling, a dynamic and multiscale process, has been studied for several decades; however, a comprehensive understanding of the process is still lacking. The bubble ebullition cycle, which occurs over millisecond time-span, makes it extremely challenging to study near-surface interfacial characteristics of a single bubble. Here, we create a steady-state vapor bubble that can remain stable for hours in a pool of sub-cooled water using a femtosecond laser source. The stability of the bubble allows us to measure the contact-angle and perform in-situ imaging of the contact-line region and the microlayer, on hydrophilic and hydrophobic surfaces and in both degassed and regular (with dissolved air) water. The early growth stage of vapor bubble in degassed water shows a completely wetted bubble base with the microlayer, and the bubble does not depart from the surface due to reduced liquid pressure in the microlayer. Using experimental data and numerical simulations, we obtain permissible range of maximum heat transfer coefficient possible in nucleate boiling and the width of the evaporating layer in the contact-line region. This technique of creating and measuring fundamental characteristics of a stable vapor bubble will facilitate rational design of nanostructures for boiling enhancement and advance thermal management in electronics.
沸腾是一个动态的多尺度过程，已经研究了几十年；然而，对该过程仍缺乏全面的理解。气泡沸腾周期发生在毫秒时间跨度内，这使得研究单个气泡的近表面界面特性极具挑战性。在这里，我们使用飞秒激光源在过冷水池中创建了一个可以稳定存在数小时的稳态蒸汽泡。气泡的稳定性使我们能够在亲水和疏水表面以及脱气水和普通水（含有溶解空气）中测量接触角，并对接触线区域和微层进行原位成像。脱气水中蒸汽泡的早期生长阶段显示气泡底部与微层完全湿润，并且由于微层中液体压力降低，气泡不会脱离表面。利用实验数据和数值模拟，我们获得了核态沸腾中可能的最大传热系数的允许范围以及接触线区域蒸发层的宽度。这种创建和测量稳定蒸汽泡基本特性的技术将有助于合理设计用于增强沸腾的纳米结构，并推动电子学中的热管理发展。
