Ejection Process Simulation for a Piezoelectric Microdroplet Generator

Abstract

The purpose of this work is to investigate the liquid ejection process of a novel microdroplet generator applying a computational approach. In simulations, the theoretical model is based on the unsteady three-dimensional conservation equations of mass and momentum with the treatment of surface tension effect at the gas-liquid boundary by the continuous surface force scheme. The volume-of-fluid method along with the piecewise linear interface construction technique is implemented to describe the interfacial movements. The time evolution of droplet meniscus shape is predicted and compared to Shield’s microphotographed images for the computer code validation. To explore the practicability of the proposed new microdroplet generator, the flow behavior during the stages of liquid ejection and droplet formation are examined with water as the baseline test fluid for a full ejection cycle of 50μs. In addition, 12 numerical experiments were conducted to determine droplet ejection characteristics by systematically varying the ejection time period as well as surface tension and viscosity of liquids. Simulations reveal that a liquid strand with a shorter breakup time and a longer breakup length could be achieved by reducing the ejection time and decreasing the liquid surface tension and viscosity. For the ejection time greater than 4.0μs, the ejection velocity is too low to render a sufficient momentum for droplet breakup. The feasibility studies have demonstrated the potential of this proposed microdroplet generator in dispensing diverse liquids with the surface tension and the viscosity up to 0.08N∕m and 3.0cps.