Department of Energy and Resources Engineering, College of Engineering, Peking University, Beijing 100871, China.
Department of Energy and Mineral Engineering, Pennsylvania State University, University Park, PA16802.
Proc Natl Acad Sci U S A. 2021 Apr 27;118(17). doi: 10.1073/pnas.2024069118.
In geologic, biologic, and engineering porous media, bubbles (or droplets, ganglia) emerge in the aftermath of flow, phase change, or chemical reactions, where capillary equilibrium of bubbles significantly impacts the hydraulic, transport, and reactive processes. There has previously been great progress in general understanding of capillarity in porous media, but specific investigation into bubbles is lacking. Here, we propose a conceptual model of a bubble's capillary equilibrium associated with free energy inside a porous medium. We quantify the multistability and hysteretic behaviors of a bubble induced by multiple state variables and study the impacts of pore geometry and wettability. Surprisingly, our model provides a compact explanation of counterintuitive observations that bubble populations within porous media can be thermodynamically stable despite their large specific area by analyzing the relationship between free energy and bubble volume. This work provides a perspective for understanding dispersed fluids in porous media that is relevant to CO sequestration, petroleum recovery, and fuel cells, among other applications.
在地质、生物和工程多孔介质中，气泡（或液滴、聚集体）在流动、相变或化学反应之后出现，其中气泡的毛细平衡会显著影响水力、传输和反应过程。在多孔介质中对毛细作用的普遍理解已经取得了很大的进展，但对气泡的具体研究却很缺乏。在这里，我们提出了一个与多孔介质中自由能相关的气泡毛细平衡的概念模型。我们量化了由多个状态变量引起的气泡的多稳定性和滞后行为，并研究了孔隙几何形状和润湿性的影响。令人惊讶的是，通过分析自由能和气泡体积之间的关系，我们的模型对气泡在多孔介质中尽管具有较大的比表面积，但仍能在热力学上稳定的反直觉观察结果提供了一个简洁的解释。这项工作为理解多孔介质中的分散流体提供了一个视角，这与 CO2 封存、石油回收和燃料电池等应用有关。
