Spreading of a Water Droplet for a Dynamic and Static Impact Surface

Surface wetting by liquid droplets is ubiquitous in both natural and industrial applications. 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, the surface wetting by a stationary water droplet impinging onto a moving surface is experimentally simulated. The droplet's spreading diameter is measured. A comparison between the stationary droplet impingement and the gravity-driven impingement is made with respect to the droplet spreading diameter.