Drying Kinetics and Modeling of Onion Slices in Two Stage Drying

The drying kinetics of onion slices were studied in a tray dryer. Response surface methodology (RSM) was used for designing the experiments with Incomplete Composite Block (Box-Behnken) Design. The independent parameters were drying temperature (70, 80 and 900C) during first stage, cut-off time (30, 50 and 70 min) and tempering period (0, 20 and 40 min).Temperature of second stage was kept constant at 600C. Empirical models namely Page's, exponential and logarithmic model were fitted to experimental drying data. The study indicates that drying time decreased with increase in temperature and cut-off time. Drying of onion slices took place in falling rate period only. The Page model of first stage and exponential model of second stage described the drying behaviour of onion slices well.