Abstract:

Liquid argon on the nano-copper substrate was taken as the research object to investigate the effect of heated surface wettability on the pool boiling heat transfer. The bubble nucleation of hydrophobic/hydrophilic surface was explored to reveal the enhanced mechanism of heat transfer from the microscopic point of view. A Cu-Ar pool boiling model was built by the large-scale atomic/molecular massively parallel simulator (LAMMPS). The degree of surface wettability was adjusted by changing the interfacial energy coefficient α. The effect of α(hydrophobicity α=0.2, 0.4, 0.5, neutral α=1.0 and hydrophilicity α=1.5, 2.0) on the bubble growth, combination and breakup was investigated at a temperature of 160 K. The heat transfer mechanism of liquid argon pool boiling on the surface was revealed through the bubble volume, heat flux absorbed from liquid argon, and interface thermal resistance. The results showed that no bubbles were observed under α = 0.2 (super hydrophobic), due to weak heat transfer and large interfacial thermal resistance. Moreover, as α increased from 0.4 to 2.0, the bubble nucleation and detachment time of liquid film shortened from 7ns to 4ns, and increased 8.5ns to 7ns, respectively. At the same time, the bubble volume and heat flux increased from 291.1nm³ to 373.4nm³ and 130kW/cm² to 161.3kW/cm², with the increment of 22.1% and 19.4%, respectively. It indicates that compared to hydrophobic surface, stronger liquid-solid interaction of hydrophilic surface continuously absorbs heat energy to grow the coalesce bubbles, which increases the bubble volume. Before forming the gas film, more heat of liquid film is absorbed from the hydrophilic surface, leading lower interface thermal resistance. Consequently, more favorable boiling conditions can be provided from the hydrophilic surface to shorten the transition time from liquid phase to gas phase, accelerate the formations of bubble nucleation and gas film, and improve the efficiency of bubble nucleation and boiling heat transfer.

Key words: bubble nucleation, surface wettability, boiling process, heat transfer enhancement, molecular dynamic

摘要：

为了研究加热表面润湿性对传热的影响，以纳米铜基板上液氩的池沸腾过程为研究对象，从微观角度探究疏水/亲水性表面的气泡成核过程，进而揭示微纳尺度下池沸腾强化传热机制。使用大规模原子/分子并行模拟器LAMMPS构建Cu-Ar池沸腾模型，通过改变界面能量系数α调节表面润湿性程度。在加热温度160K下，研究了α（疏水性α=0.2、0.4、0.5，中性α=1.0以及亲水性α=1.5和2.0）对气泡生长、合并及破裂过程的影响规律。通过气泡核体积、液氩吸收的热流密度以及界面热阻从微观角度分析了铜基板表面液氩池沸腾中的传热机制。结果表明:当α=0.2（超疏水性）时，加热表面向液体的传热量小，界面热阻较大，无气泡生成；当α从0.4增大到2.0时，气泡成核和液膜脱离基板时间分别从7ns缩短到4ns、从8.5ns提前至7ns；在沸腾起始时刻，当α从0.4增大到2.0时，气泡核体积从291.1nm³增大到373.4nm³，热流密度从130kW/cm²增大到161.3kW/cm²，分别提高了22.1%和19.4%。说明亲水表面比疏水表面具有更强的液固相互作用，在沸腾过程中液氩持续吸收热能，促进了气泡的生长和合并，使气泡成核体积增大。同时，亲水性表面的液膜在气膜形成前吸收了更多的热能，界面热阻更低。总之，亲水性表面提供了更有利的沸腾条件，缩短液-气相的转变时间，加速了气泡成核以及气膜的形成，提高了气泡成核及沸腾传热的效率。

关键词: 气泡成核, 表面润湿性, 沸腾过程, 强化传热, 分子动力学