Visualization and Measurements of Microdroplet Impact Dynamics on a Curved Substrate

Abstract

The basic problem of the impact of a microdroplet on a curved substrate is of central importance to micromanufacturing and targeted spray cooling of microdevices. The transient fluid dynamics involved in the droplet spreading and eventual splashing drastically influence the heat transfer involved in these processes. Although the fluid dynamics and heat transfer related to microdroplet impact on flat substrates is well documented, there is a lack of systematic study concerning microdroplet impact on a substrate of comparable curvature. Such a study is reported in this paper. Droplets of typical diameter and velocity of respectively 80 micrometer and 9 m/s were produced with a piezoelectrically-driven generator. The fluids used were filtered water and isopropanol. The size, velocity and temperature of the droplets were maintained constant. The primary variable is the substrate curvature, which was varied using a collection of spheres with diameters ranging from 60 micrometer to 10 millimeter. The dynamic behavior of the microdroplet during impact is visualized and quantified in this paper. Based on the experimental results, an existing analytical correlation that predicts the spreading temporal evolution is extended to account for substrate curvature.