Heterogeneous bubble nucleation dynamics
Heterogeneous bubble nucleation dynamics
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DOI：
10.1017/jfm.2020.761
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发表时间：
2021-01-10
影响因子：
3.7
通讯作者：
Casciola, Carlo Massimo
中科院分区：
文献类型：
--
作者：
Gallo, Mirko;Magaletti, Francesco;Casciola, Carlo Massimo
异质成核是相变开始的最有效机制。固体壁和杂质通过降低相变所需的活化能，充当形成新热力学相的催化剂，从而增强成核作用。这里通过利用介观尺度描述来解决接近固体（理想情况下平坦的壁）的蒸气泡的形成，该介观描述将两相汽液系统的扩散界面建模与波动流体动力学相结合，扩展了作者之前关于均匀成核的工作。这项工作的技术重点是通过符合波动耗散平衡的适当边界条件直接解释疏水或亲水壁，这是脉动流体动力学理论背景下的一个关键点。这种方法提供了成核过程的完整动力学，从多个气泡的产生到它们的长期宏观膨胀，其时间和空间尺度是成核标准技术（例如分子动力学）无法承受的。该分析主要关注壁润湿性对成核速率的影响，尽管在定性上与经典成核理论的预测一致，但它揭示了一些差异，这些差异归因于靠近边界的液体中的分层效应和气泡与气泡的相互作用。特别是，发现在接近中等亲水性表面时，最可能的成核事件通过均匀机制发生在远离壁的地方。
Heterogeneous nucleation is the most effective mechanism for the inception of phase transformation. Solid walls and impurities act as a catalyst for the formation of a new thermodynamic phase by reducing the activation energy required for a phase change, hence enhancing nucleation. The formation of vapour bubbles close to solid, ideally flat, walls is addressed here by exploiting a mesoscale description that couples diffuse interface modelling of the two-phase vapour-liquid system with fluctuating hydrodynamics, extending previous work by the authors on homogeneous nucleation. The technical focus of this work is to directly account for hydrophobic or hydrophilic walls through appropriate boundary conditions compliant with the fluctuation-dissipation balance, a crucial point in the context of fluctuating hydrodynamics theory. This methodology provides access to the complete dynamics of the nucleation process, from the inception of multiple bubbles up to their long-time macroscopic expansion, on time and spatial scales unaffordable by standard techniques for nucleation, such as molecular dynamics. The analysis mainly focuses on the effect of wall wettability on the nucleation rate, and, albeit qualitatively in agreement with classical nucleation theory predictions, it reveals several discrepancies to be ascribed to layering effects in the liquid close to the boundary and to bubble-bubble interactions. In particular, it is found that, close to moderately hydrophilic surfaces, the most probable nucleation events occur away from the wall through a homogeneous mechanism.