Thin Film Evaporation Modeling of the Liquid Microlayer Region in a Dewetting Water Bubble
Thin Film Evaporation Modeling of the Liquid Microlayer Region in a Dewetting Water Bubble
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DOI：
10.3390/fluids8040126
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发表时间：
2023-04
期刊：
影响因子：
1.9
通讯作者：
Ermiyas Lakew;Amirhosein Sarchami;G. Giustini;Hyungdae Kim;K. Bellur
中科院分区：
文献类型：
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作者：
Ermiyas Lakew;Amirhosein Sarchami;G. Giustini;Hyungdae Kim;K. Bellur
了解气泡生长机制对于模拟沸腾传热和开发技术应用至关重要，例如依赖沸腾来实现运行所需的高热通量的能源系统和热管理过程。本文介绍了对“微层”蒸发的分析，即在大气压沸水成核的加热表面生长的蒸汽气泡下方存在的超薄液体层。微层蒸发被认为是相变传热的主要贡献者，但其演化、时空稳定性以及对宏观气泡动力学的影响仍然知之甚少。微层中的质量、动量和能量传递采用润滑理论方法进行建模，该方法考虑了毛细管力和分子间力以及界面质量传递。该模型体现为三阶非线性薄膜演化方程，并进行数值求解。在固液界面应用可变壁温边界条件，以解释由于液汽界面蒸发热损失而产生的共轭传热。用当前方法获得的预测与微层蒸发的实验测量结果相比毫不逊色。通过比较单个气泡的沸腾循环中一系列时间的薄膜轮廓，推断出蒸发传热系数的可能值，并发现其落在先前报道的估计范围内。结果表明，系数可能不是如之前假设的常数，而是在沸腾周期中随时间变化的系数。
Understanding the mechanism of bubble growth is crucial to modeling boiling heat transfer and enabling the development of technological applications, such as energy systems and thermal management processes, which rely on boiling to achieve the high heat fluxes required for their operation. This paper presents analyses of the evaporation of “microlayers”, i.e., ultra-thin layers of liquid present beneath steam bubbles growing at the heated surface in the atmospheric pressure nucleate of boiling water. Evaporation of the microlayer is believed to be a major contributor to the phase change heat transfer, but its evolution, spatio-temporal stability, and impact on macroscale bubble dynamics are still poorly understood. Mass, momentum, and energy transfer in the microlayer are modeled with a lubrication theory approach that accounts for capillary and intermolecular forces and interfacial mass transfer. The model is embodied in a third-order nonlinear film evolution equation, which is solved numerically. Variable wall-temperature boundary conditions are applied at the solid–liquid interface to account for conjugate heat transfer due to evaporative heat loss at the liquid–vapor interface. Predictions obtained with the current approach compare favorably with experimental measurements of microlayer evaporation. By comparing film profiles at a sequence of times into the ebullition cycle of a single bubble, likely values of evaporative heat transfer coefficients were inferred and found to fall within the range of previously reported estimates. The result suggests that the coefficients may not be a constant, as previously assumed, but instead something that varies with time during the ebullition cycle.