Convective air drying characteristics of sweet potato cube (Ipomoea batatas L.)

The effects of drying conditions on the drying behavior of sweet potato (Ipomoea batatas L.) were investigated in a cabinet dryer. The convective air drying was carried out under five air temperatures; 50, 60, 70, 80 and 90 °C, five air velocities of 1.5, 2.5, 3.5, 4.5 and 5.5 m/s and three sweet potato cubes of 5, 8 and 12 mm thickness. Data were analyzed to obtain diffusivity values from the period of falling drying rate. Results indicated that drying took place in the falling rate period. Moisture transfer from sweet potato cubes was described by applying the Fick's diffusion model, and effective moisture diffusion coefficients were calculated. Effective diffusivity increased with increasing temperature. An Arrhenius relation with an activation energy value of 11.38 kJ/mol expressed effect of temperature on the diffusivity. Two mathematical models available in the literature were fitted to the experimental data. The page model gave better prediction than the first order kinetics of Henderson and Pabis model and satisfactorily described drying characteristics of sweet potato cubes.

► The values of calculated effective diffusivity for drying of sweet potato cubes at 50, 60, 70, 80 and 90 °C of air temperature and 1.5, 2.5, 3.5, 4.5 and 5.5 m/s of air flow rates ranged from 1.25890 × 10−9 to 8.79788 × 10−9 m2/s.
► The effective diffusivity increased as flow rate and temperature increased.
► The activation energy for moisture diffusion was found as 11.38 kJ/mol.
► Page's empirical model gave better prediction than the first order kinetics of Henderson and Pabi's model.