Influence of process variables on hot air drying assisted by power ultrasound

Abstract

Power ultrasound application on convective drying of foodstuffs may be considered an emergent technology. Acoustic energy may improve drying rate without significantly heating the material due to phenomena affecting mass transfer resistances. As a consequence, ultrasound application on the drying of heat sensitive materials or in process carried out at low temperatures is quite interesting.

The aim of this work was to address the influence of the main processing variables on the convective drying assisted by power ultrasound (21.7 kHz) of different foodstuffs. The influence of air velocity and temperature, raw material characteristics, mass load density and ultrasonic power applied was addressed.

From the experimental results, a significant influence of the application of power ultrasound on both external and internal resistance to mass transfer has been found. Nevertheless, the ultrasonic effects depended strongly on the experimental conditions used. In the case of carrot drying at different temperatures, the application of power ultrasound increased the effective moisture diffusivity by 55% at experiments carried out at 30ºC, however the improvement was non significant at experiments conducted at 70ºC.