Practical design of ultrasonic spray devices: experimental testing of several atomizer geometries

Ultrasonic atomization generates a mist-like uniform spray. Each particular application (air conditioning, drugs delivery, combustion....) has specific requirements in terms of mean droplet size, spray shape, spray velocity and liquid flow rate. Forcing frequency and liquid properties are the main factors affecting mean droplet diameter and droplets size distribution. Physical and statistical modeling is applied to predict spray characteristics or to design specific atomizers for required droplets dimensions. Initial droplets velocity is mainly determined by input power. Flow rate is limited by atomizers active surface area. Present work is focusing on flow rate maximization. Several atomizer geometries have been designed in order to vary forcing wave parameters and to maximize atomizer active surface area. Tests involve droplets size distribution measurements by Fraunhofer diffraction. The maximum possible flow rate without affecting spray parameters is also investigated for each specific atomizer geometry. Present measurements add to past theoretical and experimental results in order to improve practical flexible design of ultrasonic atomizers with respect to operating condition and spray quality requirements. An adequate atomizer design will provide the complete required spray characteristics, droplets mean diameter and size distribution as well as initial velocity and maximum flow rate. (C) 2002 Elsevier Science Inc. All rights reserved.