ID 56

Impregnation of a water droplet between two parallel glass plates: Influence of gap spacing

 

Abstract:

The penetration of a water droplet into a gap between two parallel plates has been studied experimentally. A deionized water droplet (2 mm diameter) impacted the plates at velocities of 0.06, 0.5, 1.0, and 1.5 m/s (Weber numbers ranging from 0.1 – 63); the spacings of the parallel glass plates were 50, 100, and 150 μm. We photographed the experiment using a high-speed camera and processed the images in MATLAB to measure the growth rate of the liquid film between the plates. We observe that liquid penetration commences immediately upon or shortly after impact. Consequently, the flow rate of the liquid entering the plates has two distinct regimes: an impact regime, where the flow rate rapidly increases and decreases; and a capillary regime, where flow rate is constant and dependent on the spacing of the plates. The faster flow rates in the capillary regime are found when the gap spacing is larger. Within the velocities tested, a higher impact velocity resulted in a higher initial flow rate and an overall faster droplet depletion time. However, a smaller fraction of the initial droplet volume penetrates because a high velocity impact on the gap cleaves the drop into two. We develop and present a mathematical model that predicts these findings.