Parametric Study of High-Intensity Ultrasound in the Atmospheric Freeze Drying of Peas

Abstract

Atmospheric freeze drying (AFD) is a dehydration process that can be used to produce high-end products for the food, pharmaceutical, and biological industries. Evaporation or sublimation at the drying temperatures used for these processes is generally low. Airborne ultrasound can be used to increase drying rates. This parametric study investigates the influence of the drying temperature, drying time, and ultrasonic power for atmospheric freeze drying in the presence of an airborne ultrasonic field. Accelerated effective diffusion of up to 14.8% was obtained for atmospheric freeze drying with a fluid bed. The faster drying in ultrasonic-assisted atmospheric freeze drying is assumed to be due to a higher mass transfer rate at the solid-gas interface, caused by a reduced boundary layer due to a higher turbulent interface. Thus high intensity, airborne ultrasound used with modern drying systems has great potential to accelerate drying, reduce investment and production costs, and improve product quality.

Keywords:

• Acoustic field drying
• Airborne ultrasound
• Atmospheric freeze drying
• Convective freeze drying
• Fluid bed drying
• High intensity ultrasound
• Mass transfer enhancement

ACKNOWLEDGMENTS

This work was supported by the Research Council of Norway's Projects 172641-S40 (New marine resources) and 195182-S60 (CREATIVE). Thanks to all the members of our Food Technology group, and especially to Christopher Rundel, for their support.