Drying Kinetics of Onion Slices in a Hot-air Dryer

Abstract

Onion slices were dehydrated in a single layer at drying air temperatures ranging from 50～70℃ in a laboratory scale convective hot-air dryer at an air velocity of 0.66 m/s. The effect of drying air temperature on the drying kinetic characteristics were determined. It was found that onion slices would dry within 210～460 min under these drying conditions. Moisture transfer during dehydration was described by applying the Fick's diffusion model and the effective diffusivity changed between 1.345×10?? and 2.658×10?? ㎡/s. A non-linear regression procedure was used to fit 9 thin layer drying models available in the literature to the experimental drying curves. The Logarithmic model provided a better fit to the experimental drying data as compared to other models. Temperature dependency of the effective diffusivity during the hot-air drying process obeyed the Arrhenius relationship with estimated activation energy being 31.36 kJ/㏖. The effect of the drying air temperature on the drying model constants and coefficients were also determined.