Influence of Pulse Signal Spike and Liquid Characteristics on Performance of Uniform-Droplet Generator

The performance of a pulsed-chamber, uniform-droplet generator was enhanced through the development of a digital pulse generator system. A trapezoidal pulse signal, variable in terms of peak voltage, rise time, dwell time, and fall time, actuated a piezoelectric disk to force droplets through a precision orifice. Variable pulse control enabled precise delivery of either paraffinic oil or water droplets. The effects of each pulse variable on droplet size and velocity were examined using a phase-Doppler particle analyzer and a photographic technique. Droplet size increased with increased voltage, rise time, dwell time, fall time, and integrated area under the pulse curve. Air bubbles in the chamber did not prevent droplet delivery, except for certain combinations of bubble size and location. Dwell time was statistically the most important variable affecting oil droplet size and delivery. Liquid reservoir height was most important for water. Increased pulse voltage tended to increase droplet size and velocity because of increased impulse and momentum.