Finite droplets vs long droplets: Discrepancy in release conditions in a microscopic constricted channel

Conditions of release of trapped droplets in constricted channels are of great significance in various domains, including microfluidic development and enhanced oil recovery. In our previous studies, a detailed and quantitative analysis of the threshold pressure needed to release a droplet from a constricted channel has been performed. However, droplets may exist in real applications as long droplets, which may exhibit different behavior than finite droplets. Therefore, in this study, direct numerical simulations, combining the fluid flow equations and the phase-field method, have been conducted on three-dimensional constrained channels to investigate discrepancies in release conditions of finite droplets and long droplets. The results have shown that for a finite droplet, the maximum pressure increases with the increase in the con-tact angle, whereas for a long droplet, the maximum pressure is almost the same both in the water-wet and neutral-wet conditions. Effects of droplet size on the release pressure have also been studied. For the finite droplet and at the water-wet condition (h 1/4 45 degrees), the minimum release pressure increases linearly with the droplet length, while for the long droplet at similar conditions, the minimum release pressure does not change much as the length of the droplet increases. Furthermore, the release pressure decreases with the increased tapering angle.

Automated summary

In this study, direct numerical simulations were conducted to compare the release conditions of finite droplets and long droplets in three-dimensional constrained channels. The results showed that for finite droplets, the maximum pressure increases with the increase in the contact angle, while for long droplets, the maximum pressure is almost the same in water-wet and neutral-wet conditions. The study also found that droplet size affects the release pressure, with the minimum release pressure of finite droplets increasing linearly with the droplet length in water-wet conditions, and the minimum release pressure of long droplets not changing much as the length increases. Furthermore, the release pressure decreases with the increased tapering angle.