Effect of drying mode on drying kinetics of onion

Onion slices 3 mm thick were dried in different modes. Drying at 60 degrees C by convection was taken as a reference process. It has been shown that increase in air temperature increases the rate of drying. Effective diffusivity increases with increasing temperature, but it is strongly dependent on water content. Energy of activation for diffusion is also strongly affected by water content. Stepwise changes in temperature do not result in beneficial effects which could be expected. Extension of drying time was even observed in respect to that obtained at constant 60 degrees C. Drying with infrared energy or assisting convective drying with microwave energy results in increased drying rates and substantial shortening of the drying time.