ONION SLICES DEHYDRATION IN A DRYER WITH AIR DEHUMIDIFICATION BASED ON SILICA GEL

A drying solar tunnel was built with an auxiliary desiccant air recirculation system based on silica gel to adsorb moisture. Onion was cut in slices and dried inside the solar tunnel. Based on empirical data previously obtained, every fifteen minutes per hour, heat regeneration was applied to the auxiliary desiccant system to eliminate the moisture from the silica. Temperature and relative humidity were monitored during the process and drying data were compared with those of a drier that operated without the auxiliary desiccation system. In practical operation without considering initial conditions, the equipment with desiccant system dried the onion slices in 11.1 hours meanwhile the solar tunnel without the auxiliary system required 16.3 hours. A RGB (red green blue) color analysis was carried out for both drying treatments and a better quality was achieved on onions dried with the air-desiccant strategy, as the time exposed to high temperatures under low water quantity was reduced. Onion oxidation was evident when the blue value felt bellow below 100.