Shen Yang, Cheng Yongpan, Xu Jinliang, Zhang Kai, Sui Yi
Beijing Key Laboratory of Multiphase Flow and Heat Transfer for Low Grade Energy, North China Electric Power University, Beijing 102206, China.
Beijing Key Laboratory of Emission Surveillance and Control for Thermal Power Generation, North China Electric Power University, Beijing 102206, China.
Langmuir. 2020 May 26;36(20):5618-5625. doi: 10.1021/acs.langmuir.0c00850. Epub 2020 May 14.
Sessile droplet evaporation is widely encountered in nature, and it has numerous applications in industrial and scientific communities; therefore, the accurate prediction of droplet evaporation has great significance in practical applications. In this paper, for the first time, a comprehensive theoretical model is built up for diffusion-controlled heat and mass transfer for sessile droplet evaporation on a curved substrate in toroidal coordinates. The evaporative mass transfer is coupled with the heat transfer across the gas-liquid droplet interface, as well as the heat transfer across the solid-liquid interface of the curved substrate. The effects of interfacial cooling and thermal conductivity of the droplet and substrate as well as their initial shapes on the droplet evaporation are provided in details. It is found that the evaporative flux usually increases sharply near the droplet edge due to the short distance for heat conduction from the substrate to the droplet; however, it can be reversed from sharp increasing to decreasing at a low thermal conductivity ratio < 0.3 of the substrate over droplet or large initial droplet contact angle θ > 30°. The interfacial evaporative cooling effect can always suppress the droplet evaporation. The lifetime of evaporative droplet can be prolonged with the decreasing thermal conductivity ratio, increasing evaporative cooling number, and increasing initial droplet contact angle or tangential angle of a curved substrate. These findings may be of great significance in the applications of droplet evaporation on the curved substrate.
静态液滴蒸发在自然界中广泛存在，并且在工业和科学界有众多应用；因此，准确预测液滴蒸发在实际应用中具有重要意义。本文首次建立了一个全面的理论模型，用于环形坐标系下弯曲基底上静态液滴蒸发的扩散控制传热传质。蒸发传质与气液滴界面的传热以及弯曲基底固液界面的传热相耦合。详细给出了界面冷却、液滴和基底的热导率及其初始形状对液滴蒸发的影响。研究发现，由于从基底到液滴的热传导距离短，蒸发通量通常在液滴边缘附近急剧增加；然而，当基底与液滴的热导率比 < 0.3 或初始液滴接触角 θ > 30° 较大时，蒸发通量可能会从急剧增加转变为减少。界面蒸发冷却效应总是会抑制液滴蒸发。随着热导率比降低、蒸发冷却数增加、初始液滴接触角或弯曲基底的切向角增大，蒸发液滴的寿命可以延长。这些发现可能对弯曲基底上液滴蒸发的应用具有重要意义。
