Effective moisture diffusivity, activation energy and kinetic models of microwave-assisted-foam-mat-drying of berry pulp

The drying kinetics of blue honeysuckle pulp subjected to microwave-assisted-foam-mat drying (MFD) were studied. The independent variable levels were 4, 7, and 10 kW in a continuous microwave dryer and 140-700 W in a microwave oven for microwave power, and 80, 100, 160, 360, 480 g/min for input rate, and drying rate, effective moisture diffusivity and activation energy were objective indexes. The results show drying kinetic constants k of foamed berry pulp increase with the increase of microwave power, but decreases with the increase of the input rate during microwave drying proceed. At low microwave power of 140-700 W, the drying rate change trends are determined by a critical microwave intensity of 14.0 W/g. Below the critical value, three stages include the preheating period, and constant and falling rate drying periods. The other drying processes consist of the heating up and falling rate stages. Effective moisture diffusivity of foamed blue honeysuckle pulp varied from 5.5206×10-7 to 1.5706×10-7 m2/s in given input rate range, and 1.2135×10-7 to 5.6541×10 -7 m2/s in given microwave power range with corresponding activation energy is 89.2 W/g. Both two-term exponential and Sigmoid model were found to satisfactorily describe the drying behaviour of foamed blue honeysuckle pulp under microwave power and input rate, respectively.