Bubble dynamics and dry spot formation during boiling on a hierarchical structured surface: A lattice Boltzmann study

Y Yu,Y Qiu,R Z Huang,Q Li

doi:10.1063/5.0056894

Abstract

In this paper, the bubble dynamics and the mechanism of dry spot formation during boiling on a two-level hierarchical structured surface are numerically investigated using a three-dimensional thermal multiphase lattice Boltzmann model with liquid–vapor phase change. The hierarchical structured surface consists of three parts: a smooth surface basement, primary pillars on the basement, and secondary pillars overlaid on the primary pillars. It is found that the boiling heat transfer on the hierarchical structured surface is significantly dependent on the bubble departure frequency and the dry area fraction, which are in turn affected by the structural parameters of secondary pillars. Increasing the height or width of the secondary pillars is found to effectively increase the bubble departure frequency, but it may also enlarge the size of dry spots on the hierarchical structured surface. The numerical investigation shows that, in order to prevent the formation of dry spots on the hierarchical structured surface, an effective approach is to reduce the proportion of the contact line on the lateral walls of secondary pillars to the whole contact line, which can be realized by reducing the area of the lateral walls of secondary pillars or appropriately increasing the secondary pillar spacing. The optimum boiling performance on the hierarchical structured surface is found to be achieved under the situation that the bubble departure frequency is sufficiently high, but the dry spot area is as small as possible.

Highlights

Nucleate boiling is widely regarded as one of the most effective heat transfer modes, which has been commonly used in a broad range of industries such as thermal management of high-power electronics, nuclear reactors, chemical processing, and desalination.[1,2,3,4] The research on nucleate boiling can be traced back to an important study conducted by Nukiyama in 1934,5 who came up with the first boiling curve and studied the features of boiling heat transfer
We can see that the heat flux increases dramatically as the secondary pillar height increases from 5 to 12 l:u: After that, the heat flux increases relatively slowly and reaches its peak value at H2 1⁄4 20 l:u: a decrease in the normalized heat flux can be observed within 20 < H2 27 l:u: from Fig. 2, we can see that the variation of the heat flux is basically opposite to that of the dry area fraction, i.e., when the dry area fraction decreases with the increase in H2, the normalized heat flux increases and vice versa
III A, the present results show that promoting the bubble departure and suppressing the formation of dry spots can enhance the boiling heat transfer on the hierarchical structured surface

Summary

Introduction

Nucleate boiling is widely regarded as one of the most effective heat transfer modes, which has been commonly used in a broad range of industries such as thermal management of high-power electronics, nuclear reactors, chemical processing, and desalination.[1,2,3,4] The research on nucleate boiling can be traced back to an important study conducted by Nukiyama in 1934,5 who came up with the first boiling curve and studied the features of boiling heat transfer. It has been well recognized that a structured surface can promote the bubble nucleation and increase the bubble departure frequency.[7,8,9,10,11,12,13,14] Cooke et al.[15] have experimentally investigated the pool boiling on silicon chips textured by microchannels. They showed that liquid can be supplied to nucleation sites through microchannel conduits, which facilitates the rewetting of the heating surface and enhances boiling heat transfer. They observed that micro-structures can significantly increase the active nucleation sites, and nano-structures can increase the bubble departure frequency

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Conclusion