The kinetics of forced convective air-drying of pumpkin slices

Air-drying characteristics of pumpkin slices were investigated in a laboratory scale hot-air dryer. The thin-layer drying was carried out under three air temperatures of 50, 55 and 60 degrees C at a constant air velocity of 1.0 m/s and relative humidity between 15% and 25%. Results indicated that drying took place in the falling rate period. Moisture transfer from pumpkin slices was described by applying the Fick's diffusion model. The effective diffusivity values changed from 3.88 x 10(-10) to 9.38 x 10(-10) m(2)/s within the given temperature range. An Arrhenius relation with an activation energy value of 78.93 kJ/mol expressed the effect of temperature on the diffusivity. The experimental moisture loss data were fitted to selected semi-theoretical and empirical thin-layer drying models. The mathematical models compared according to the three statistical parameters such as the coefficient of determination (R-2), reduced chi-square (chi(2)) and root means square error (RMSE) between the observed and predicted moisture ratios. In conclusion, the logarithmic and Verma et al. models satisfactorily described the drying characteristics of pumpkin slices. (c) 2006 Elsevier Ltd. All rights reserved.