Numerical study on dynamic behaviors of the coalescence between the advancing liquid meniscus and multi-droplets in a microchannel using CLSVOF method

The coalescence between the advancing liquid meniscus and multiple droplets is usually encountered in the liquid filling process and photothermal effect based microdevices. To shed light on how the coalescence between the advancing liquid meniscus and multiple droplets affects the liquid meniscus advancement, its dynamic behaviors are numerically investigated using the coupled level set and volume-of-fluid (CLSVOF) method along with the continuum surface force (CSF) model in this study. Particular attention is paid to the dynamic interfacial phenomena during the coalescence process. The effect of the droplet and its volume distributions is also investigated. The simulation results show that the coalescence between the advancing liquid meniscus and each droplet is able to instantly accelerate the original liquid flow as a result of the induced concave meniscus with large curvature. As compared to the coalescence with a single droplet, the fluctuation and deformation of the interface is stronger in the case of simultaneous coalescence with multiple droplets, which can further lower the average liquid pressure and thus show more significant advancement of the liquid flow. The velocity increment ratio is the largest when four droplets simultaneously coalesce with the advancing liquid meniscus. It is shown that the coalescence with large droplet can result in large velocity increment ratio because more surface energy is supplied. Large length of the advancing liquid segment before its coalescence with the droplets can weaken the advancing effect. It is also found that the overall variation trend of the simulation results is in agreement with that of the experimental results.