Sun and artificial air drying kinetics of some agricultural products

Drying of agricultural products look place by traditional means using solar energy and a new large tray air dryer of 5000 kg capacity. Drying experiments for various products, such as Sultana grapes, currants, Jigs, plums and apricots, were conducted and the drying rates were found for both solar and industrial drying operations. Air and product temperatures were measured for the whole industrial drying process. It was proved that most materials were dried in the falling rate period, while currants, plums, apricots and Jigs exhibited two drying rare periods, a first slowly decreasing (almost constant) and a second fast decreasing (falling) drying rate period. Based on the findings of preliminary runs the drying cycle of this fully automated industrial dryer was designed to give maximum quality of dried products with reasonable energy costs. A high air velocity and medium temperature were utilised for the beginning of the process, while for the second falling drying rate period a medium air velocity, a high air temperature and a partial recirculation of the air stream were used. The industrial drying operation resulted in a product of superior quality compared to products dried by solar dehydration. (C) 1997 Elsevier Science Limited. All rights reserved.