Micro-droplet of Particulate Suspension Generated by a Pneumatic Ejection System

Micro-droplet generation for solid particle suspensions is studied experimentally over a wide range of volume fraction of solid (η), using a home build pneumatic ejection system. Ejection is actuated by a solenoid valve, setting to “conduction” state for short period of time Δt. Pressurized gas of Po enters the reservoir, creating a pressure pulse P(t), forcing the liquid out via a tiny nozzle to produce a micro-droplet. Here, P(t) is measured by a high-speed sensor, and the ejection process is examined by high speed photography and image processing. Single droplet can be ejected for suspensions with η up to 33%. For η less than about 18%, the required pressure amplitude increases roughly linearly with η. With η increased above 18%, the demand for pressure amplitude is significantly higher than the linearly increasing trend. Especially as η is increased above 24%, the liquid band stretches much longer, and the break-up is delayed drastically.