Ultrasonic Piezoelectric Atomizers: Electromechanical Modeling and Performance Testing

Abstract

Ultrasonic atomization of bulk liquids has received extensive attention in the past few decades due to the ability to produce controlled droplet sizes, a necessity for many industries such as spray coating and aerosol drug delivery. Despite the increase in attention, one novel application of this technology has been overlooked until recently, and that is the moisture removal capabilities of atomization. The first ever ultrasonic dryer, created by researchers at Oak Ridge National Lab in 2016, applies the mechanisms of atomization to mechanically remove moisture from clothing. The process utilizes the ultrasonic vibrations created by a piezoelectric transducer in direct contact with a wet fabric to rupture the liquid-vapor boundary of the retained water. Once ruptured, smaller droplets are ejected from the bulk liquid and are actively removed from the fabric pores. The mechanisms of droplet ejection from this event are related to both capillary waves forming on the liquid surface (Capillary Wave Theory), as well as the implosion of cavitation bubbles formed from the hydraulic shocks propagating from the transducer (Cavitation Theory). In this work, we present an analytical model for predicting the moisture removal rate of a wet fabric exposed to ultrasonic vibrations, and connect the atomization events to a global variable, acceleration, in order to decouple the relationship between the transducer and applied voltage. The acceleration governing atomization is predicted using a verified numerical model. The numerical model is shown to assist in developing ultrasonic drying by means of efficiently evaluating transducer design changes.