Experimental Investigation of Droplet Spreading on a Stationary and Moving Solid Surface

Surface wetting by liquid droplets is ubiquitous in both natural and industrial applications, making it of great interest to researchers. Many surface-wetting studies have been conducted for gravity-driven droplet impingement, where the droplet freely falls through the stationary air onto a stationary solid surface. However, there are several industrial applications, such as machinery cooling, where the solid surface is in motion and makes an impact with a droplet. Unlike the gravity-driven droplet impingement, the motion of the ambient air relative to the impact surface is not stationary. The effect of this difference on surface wetting has not been fully investigated. In this study, an experimental setup is developed to simulate the surface wetting by a stationary water droplet impinging onto a moving surface. The droplet's spreading diameter is measured with the newly developed setup and a traditional gravity-driven impingement setup. A comparison between the two systems' effect on the droplet spreading diameter is made and discussed.