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汽泡成核在沸腾换热、微流控制设备中的气液分离以及生物医学中的气体传输等相变和流动过程中扮演关键角色，易受表面润湿性能和粗糙结构的影响。鉴于实验研究的局限，本文采用分子动力学方法系统研究了具有不同润湿性能和不同数量纳米凸起的恒热流过热表面对水中汽泡成核的影响规律和微观机制。结果表明，在相同表面润湿性能下，随纳米凸起数量增加，表面粗糙度增加，汽泡成核时间点提前；对具有相同粗糙度的表面，随表面亲水性增强，汽泡成核时间点提前；在本文研究范围内，具有最大粗糙度的亲水表面上水的汽泡成核最早。近壁面处水的密度和温度随时间的变化以及密度和温度的空间分布的分析表明：由于热量积聚，纳米凸起与底部平面连接拐角处最易成为汽化核心。Kapitza热阻的计算结果表明：亲水性越强的表面具有越低的固–液界面热阻，越有利于汽泡成核。本文为理解汽泡成核的微观机制及优化传热、传质和流体控制系统的设计提供了理论依据。Bubble nucleation plays a pivotal role in microscale heat conduction, boiling heat transfer, and liquid-vapor phase change processes, as it not only governs heat transfer efficiency but also strongly regulates bubble dynamics. The nucleation processes are highly sensitive to the surface morphology and wettability of solid substrates. However, due to the inherent limitations of conventional experiments in terms of spatial resolution and observation times, revealing the microscopic mechanisms of bubble nucleation at the nanoscale remains a significant challenge—particularly under conditions involving complex surface structures and diverse wettability states. In this study, molecular dynamics simulations were employed to systematically investigate the mechanisms by which surface roughness and wettability influence bubble nucleation behavior on nanostructured surfaces at the atomic scale. Five copper substrates featuring sinusoidal protrusions were designed to represent different degrees of surface roughness. The sinusoidal profile, characterized by mathematical continuity and smoothness, not only facilitates the observation of bubble coalescence and contact angle evolution but also ensures comparability among models by maintaining identical protrusion height and overall width, thereby keeping the protrusion volume constant. This design allows direct comparison of bubble growth rates and other physical quantities across different models. In addition, three distinct wettability conditions, namely hydrophobic, neutral, and hydrophilic, were achieved by modifying the interaction potential between oxygen and copper atoms. During the simulations, a constant heat flux was applied to the bottom copper substrate to trigger spontaneous bubble nucleation, local low-density regions were identified using density distribution analysis to track bubble nucleation sites; and a piston-like pressure control mechanism was introduced via the top copper plate, and the displacement of this plate over time was used to quantify bubble growth rates under varying roughness and wettability. Additionally, the Kapitza resistance between solid and liquid phases was calculated to evaluate interfacial heat transfer efficiency. The results demonstrate that increasing surface roughness significantly promotes the formation of local low-density cavities, thereby accelerating the bubble nucleation and subsequent growth. As the surface wettability transitions from hydrophobic to hydrophilic, the solid-liquid interfacial thermal resistance decreases, leading to earlier bubble nucleation. Moreover, under hydrophilic conditions, the contact angle of the bubbles increases significantly, indicating enhanced detachment and growth behavior. Overall, the findings of this work advance the fundamental understanding of the microscopic mechanisms of bubble nucleation and provide theoretical guidance and technical references for the design of high-efficiency heat transfer structures and tunable fluid-solid interfaces at the nanoscale.
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Keywords:
- molecular dynamics /
- bubble /
- roughness /
- wetting condition
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