Measuring moisture diffusivity of potato and carrot (core and cortex) during convective hot air and isothermal drying

Moisture transfer during drying of hygroscopic non-porous materials (potato, carrot core and carrot cortex) was investigated. Drying curves and temperature profiles were obtained from cylindrical samples (0.7 and 1.4 diameter) under convective hot air drying (40, 50, 60, and 70 °C and 1.5 and 3 m/s air velocity). The effective moisture diffusivity of these materials were in the range of reported values. Temperature dependence of the effective moisture diffusivity was found to follow the Arrhenius relationship. However, the prediction of moisture loss failed to follow experimental drying curves. Temperature profiles during convective hot air drying showed temperature gradients, which explains the discrepancy between experimental data and model predictions. Therefore, an isothermal drying apparatus that combines microwave energy and convective hot air was used to quantify the drying kinetics. Using effective moisture diffusivity experimentally determined under isothermal conditions, Fickian model was found to accurately predict moisture loss during isothermal drying.