Abstract:

Enhancement of nucleate boiling heat transfer using wettability modification on porous or micro-structured surfaces has been studied extensively. The CFD-VOF method is used to accurately study the nucleate boiling enhanced by surface temporary modulation in the growth and the departure regimes of single bubble boiling on silicon micropillar structured surface. To comparatively study the effect of wettability temporary modulation on bubble dynamics and heat transfer performance, initial contact angle is set at 48°, 60°, 90° and 110° respectively, then is modulated to 20° at t = 0.152 ms. The results show that the hydrophobicity can increase the bubble growing rate, the adhesion force between the bubble and micropillars, and promote the bubble spreading along the gaps between the micropillars. At t = 0.150 ms, the contact area between the bubble and the surface with the contact angle at 110° is increased by 1.3 times, and the microlayer evaporation rate is increased by 1.2 times. The hydrophilicity reduces the proportion of the detachment time in the whole cycle， the average evaporation power at the detachment time increases by 33.3%， and the surface heat transfer performance is enhanced throughout the process.

Key words: nucleate boiling, wettability, temporary modulation, numerical simulation, bubble dynamic

摘要：

基于多孔或微结构表面润湿性改性的核态沸腾强化传热，已得到广泛研究。利用CFD-VOF数值模拟方法，针对单晶硅微柱表面单气泡的生长及脱离过程，进行表面浸润性分段调控，实现气泡沸腾换热的全程强化。分别调控初始接触角为48°、60°、90°和110°后，同一时刻 （t = 0.152 ms） 变接触角为20°，对比研究分段调控浸润性对气泡动力学过程与表面换热性能的影响。结果表明：疏水性可提高气泡生长速率，增强微柱表面对气泡的黏附力，促进气泡在微结构缝隙内的横向铺展；t = 0.150 ms时接触角为110° 表面上气泡与底面接触面积增加1.3倍，微层蒸发功率增加1.2倍。需要指出的是，毛细效应随颗粒粒径变化趋势受到多孔介质复杂孔隙结构特征的影响。在当前粒径范围内，认为其具有正相关关系，但在更大范围内的对应关系，还需要在未来进一步深入揭示。

关键词: 核态沸腾, 浸润性, 分段调控, 数值模拟, 气泡动力学