喷嘴入口条件对微液滴生成的影响

Effects of nozzle inlet conditions on micro-droplet formation

利用数值计算的方法对微液滴的喷射过程进行研究.描述在1个完整周期内液滴的形成发展,并通过系统改变速度周期、平均速度、速度幅值、壁面接触角的对比模拟试验,对液滴喷射与液滴形成阶段的流动特性进行分析;在不同惯性比重下探究均匀、稳定液滴的形成区域.结果表明:雷诺数Re、弛豫时间CH、速度脉动幅值ZF对液滴喷射行为特征有显著影响,而且在一定条件下可以形成均匀稳定的液滴;通过减小Re,CH,ZF这3个量纲一化参数,可以获得较小的液滴喷射速度,但当Re<9时,在喷嘴出口处将无法形成液滴;疏水性壁面(润湿角θ=175°)液滴的断裂时间比亲水性壁面(润湿角θ=10°)迟.

The purpose of this work is to investigate the liquid ejection process of a micro droplet generator by applying a numerical approach. The time evolution of droplet shape characteristics is predicted. The flow behavior in the liquid ejection and droplet formation processes are examined with water as a baseline test fluid in a full ejection cycle. Numerical experiments are conducted to determine droplet ejection characteristics by systematically varying the velocity period, magnitude and amplitude as well as the contact angle at the nozzle inlet. The uniform and steady droplet formation region is ex- ploited at different inertial proportions. The simulations results reveal that the dimensionless number Re, CH, ZF have a significant influence on the behavior of the droplet ejection characteristics, and the uniform and steady droplets can be formed under certain conditions. A lower velocity of the first droplet can be achieved by reducing the three dimensionless numbers. However, the ejection velocity is too low to form the droplet as Re is smaller than 9. The droplet through a hydrophobic surface breaks up later than one through a hydrophilic surface.