均匀与非均匀加热方式液滴蒸发流动与传热特性模拟分析*
摘要：
建立了二维轴对称模型,将动态接触角模型与瞬态两步动网格模型结合,实现了恒定接触半径(CCR)模式到恒定接触角(CCA)模式的转变,研究了固着在不同基材上的液滴在均匀与非均匀2种加热方式下以CCR模式蒸发的流动与传热特性。结果表明:基板底部均匀加热方式下,液滴在高导热系数基板上蒸发时,内部达到稳定流动所需时间最短,且表现出较高蒸发速率,低导热系数基板厚度越小,平均蒸发速率越大;基板底部非均匀加热方式下,温度梯度ΔT =-6 K时,液滴蒸发初始阶段内部为逆时针流动,接着在三相线附近产生顺时针流动的涡流,稳定流动时内部为单一顺时针流动;ΔT =-4 K时,液滴内部稳定流动时为2个方向相反的涡流;ΔT =6 K时,液滴内部始终为逆时针方向流动;随着ΔT 增大,液滴平均蒸发速率增大。
Abstract：
This paper establishes a two-dimensional axisymmetric model, and combines the dynamic contact angle model with a transient two-step moving mesh model to realize the transition from constant contact radius (CCR) mode to constant contact angle (CCA) mode. The flow and heat transfer characteristics of droplets fixed on different substrate surfaces evaporated in CCR mode under both uniform and non-uniform heating modes are studied.The results show that under the uniform heating mode at the bottom of the substrate, when droplets evaporate on a substrate with high thermal conductivity, the time to reach a stable internal flow is the shortest, and the average evaporation rate is the highest. The smaller the thickness of the substrate with low thermal conductivity, the higher the average evaporation rate.Under the non-uniform heating mode at the bottom of the substrate, when the temperature gradient ΔT is -6 K, the internal flow of the droplet in the initial stage of evaporation is counterclockwise flow, then a clockwise flow vortex is generated near the three-phase line, and the internal flow is a single clockwise flow when the flow is stable.When ΔT is -4 K, the stable internal flow of the droplet is two opposite vortices. When ΔT is 6 K, the internal flow of the droplet is always a counterclockwise flow. The average droplet evaporation rate increases with the increase of ΔT.
Keywords:droplet evaporation; heating mode; flow; heat transfer characteristic; temperature gradient; evaporation rate; dynamic contact angle; transient two-step moving mesh