Theoretical Modeling of Levitated Clusters of Water Droplets Stabilized by Infrared Irradiation
Theoretical Modeling of Levitated Clusters of Water Droplets Stabilized by Infrared Irradiation
复制标题
红外辐射稳定的悬浮水滴簇的理论模型
DOI：
10.1115/1.4053415
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Brewster, M. Q.
中科院分区：
文献类型：
--
作者：
Brewster, M. Q.
本文展示了如何集群的辐射稳定的水滴悬浮在一个向上流动的空气和水蒸气加热的水面以上可以使用斯伯丁的自相似理论的热量和质量传递和斯特凡流建模。该模型描述了平衡液滴状态，包括稳定性条件，以及非平衡（准稳态）瞬态演变。平衡状态的存在时，斯蒂芬流过饱和度，它有一个二次样的变化与高度以上的水面，和辐射稳定的平衡过饱和度，这是几乎恒定的高度，是相等的。后者可以通过吸收的辐射通量（线性），液滴半径（线性，如果不透明），连续体热导率和热力学性质的基本推导函数来预测。事实上，所有的实验观察到的液滴行为可以预测使用简单的分析结果的基础上准稳态液滴能量和连续传输。不稳定的液滴能量，努森层传输，数值解，和曲线拟合的数值计算，如以前在建模这种行为，是不必要的。一个有趣的反转通常的质量传递对液滴阻力在低Re流时，悬浮液滴被照射不对称的显着的红外辐射也假定，这涉及到正常（压力）和切向（剪切应力）阻力的相对重要性。这种辐射增强的液滴蒸发、冷凝和运动气体中的相对运动的理论适用于云中的条件，其中液滴可以经历净辐射加热或冷却以及波动的上升气流或下降气流。
This paper shows how clusters of radiation-stabilized water droplets levitated in an upward flow of air and water vapor above a heated water surface can be modeled using Spalding's self-similarity theory of heat and mass transfer and Stefan flow. The model describes equilibrium droplet states, including stability conditions, as well as nonequilibrium (quasi-steady) transient evolution. Equilibrium states are shown to exist when Stefan-flow supersaturation, which has a quadratic-like variation with height above the water surface, and radiation-stabilized equilibrium supersaturation, which is nearly constant with height, are equal. The latter can be predicted by a fundamentally derived function of absorbed radiant flux (linear), droplet radius (linear if opaque), continuum thermal conductivity, and thermodynamic properties. In fact, all of the experimentally observed droplet behavior can be predicted using simple analytical results based on quasi-steady droplet energy and continuum transport. Unsteady droplet energy, Knudsen-layer transport, numerical solutions, and curve-fitting of numerical computations, as used previously in modeling this behavior, are not necessary. An interesting reversal of the usual effect of mass transfer on droplet drag in low-Re flow when levitated droplets are irradiated asymmetrically by significant infrared radiation is also postulated, which relates to the relative importance of normal (pressure) and tangential (shear stress) drag. This theory of radiation-augmented droplet evaporation, condensation, and relative motion in a moving gas has application to conditions in clouds, wherein droplets can experience either net radiative heating or cooling and fluctuating updrafts or downdrafts.