Airborne power ultrasonic transducers with stepped circular radiator for lyophilization at atmospheric pressure

Roque Rubén Andrés, Alberto Pinto, Juan Andrés Cárcel, and Enrique Riera
Proc. Mtgs. Acoust. 38, 030011 (2019). Published by the Acoustical Society of America

The application of airborne power ultrasounds to enhance freeze drying processes has become a promising, green and efficient technology. It has been proved that this technology accelerates drying kinetics obtaining a good quality final product. The effectiveness of this process comes from the generation of a high-intensity ultrasonic field by an airborne power ultrasonic transducer (APUT) with an extensive radiator. A stepped circular plate, vibrating flexurally with seven nodal circles, has been used for this purpose. Its use allows a good impedance matching with the gas media because of the high surface of the radiator; and a coherent ultrasonic field due to the steps applied in the surface of the radiator and the high vibration amplitude of this surface.

The aim of this work is to present the integration of this ultrasonic system within the dehydration chamber for lyophilization at atmospheric pressure of food samples, and to show the efficiency of this novel technology in freeze drying of apple slices.