Effect of air velocity on airborne ultrasound application in pork liver drying

Airborne ultrasound is considered a feasible emerging technology for the intensification of the drying of biological materials due to its mild thermal effect avoiding the degradation of heat sensitive compounds. The effects brought about by airborne ultrasound on the drying are largely dependent on both the product structure itself and the process variables used. Thus, the present study examines the effect of the air velocity and the application of airborne ultrasound during the low-temperature convective drying of pork liver. For this purpose, drying experiments were carried out at 50 °C on pork liver cylinders using different air velocities, ranging from 1 to 6 m·s⁻¹, without (AIR) and with ultrasound application (US). The modelling of the drying kinetics was approached using the diffusion theory, evaluating both the contribution of external convection and shrinkage. The experimental results demonstrated that the application of airborne ultrasound only increased the drying rate at air velocities below 3 m·s⁻¹, shortening the drying time by up to 30 %.