THE THIN-LAYER DRYING CHARACTERISTICS OF WHITE ONION SLICES

A batch-type experimental dryer with a computer-aided data acquisition system was designed and built for the thin layer drying studies of on ion (Allium cepa L., cv. Southport White Globe) slices. Twenty seven s ingle-layer drying curves were established for a temperature range of 42.5-90 degrees C, an air velocity range of 0.6-1.4 m/s, an air humidi ty range of 0.0093-0.0442 kg of water/kg of dry air: and a slice thick ness range of 0.002-0.005 m. The single-term exponential model adequat ely described the single-layer drying behaviour of the onion slices. T he dependence of the drying rate constant on air temperature, absolute humidity, velocity and on slice thickness was best explained by an Ar rhenius-type relationship The drying rate constant in which moisture d iffusion and shrinkage effects are lumped was greatly influenced by th e sample thickness and drying air temperature, and to a lesser extent, by the air humidity and velocity.