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 onion (Allium cepa L., cv. Southport White Globe) slices. Twenty seven single-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 humidity range of 0.0093-0.0442 kg of water/kg of dry air: and a slice thickness range of 0.002-0.005 m. The single-term exponential model adequately described the single-layer drying behaviour of the onion slices. The dependence of the drying rate constant on air temperature, absolute humidity, velocity and on slice thickness was best explained by an Arrhenius-type relationship The drying rate constant in which moisture diffusion and shrinkage effects are lumped was greatly influenced by the sample thickness and drying air temperature, and to a lesser extent, by the air humidity and velocity.