固着液滴蒸发薄液膜区传质传热特性数值研究

Numerical Study on Mass and Heat Transfer Characteristics of Evaporation Thin Liquid Film of a Sessile Droplet

本文基于扩展Young-Laplace方程和动力学理论,以水为工质,建立固着液滴蒸发薄液膜区、宏观弯月面区、固体基底内部及气液、液固、气固界面的耦合传热模型,并探究固体基底厚度和热物性对蒸发薄液膜区传热特性的影响。结果表明,由于液滴蒸发过程中的冷却效应,三相接触线附近的基底温度低于周围固体温度;蒸发速度越快,温度差越大。蒸发薄液膜的长度、最大质量流量和传热量与基底厚度与液滴半径比值h_r有关;当h_r=0.4时,薄液膜区传热对总体传热贡献最大;基底的热导率越小,蒸发液滴具有更长的蒸发薄液膜长度及更强的界面传热,薄液膜区传热对总体传热影响越显著.

Based on the augmented Young-Laplace equation and the kinetic theory,the conjugated heat transfer model,including the evaporating thin liquid film,intrinsic meniscus,the solid substrates and the interface between three phases,is developed to study the heat and mass transfer characteristics in the evaporating thin liquid film of a sessile droplet of water.The effects of substrate thickness and thermal properties on the heat transfer characteristics of the evaporating thin film are investigated. The results show that a temperature valley value exists in the thin film on the substrate,corresponding to a peak value of heat flow rate,due to the cooling effect of evaporation.The thin film length, maximum mass flux and heat flux of the evaporating thin film are related to the ratio of the substrate thickness to the droplet radius,hr.Meanwhile,the thin film contribution can be maximized at a critical ratio hr=0.4,and a smaller substrate thermal conductivity can lead to a longer thin film length and thus higher heat transfer rate.