AIR-DRYING CHARACTERISTICS, EFFECTIVE MOISTURE DIFFUSIVITY AND ACTIVATION ENERGY OF GRAPE LEAVES

Grape leaves were dried in a thin layer under hot air at 40, 50 and 60C m/s in the a cabinet dryer. The drying rate curves showed that the drying of grape leaves was characterized by a single falling rate period. Drying of grape leaves was greatly influenced by air temperature. Eight mathematical models available in the literature were fitted to the experimental data. The Wang and Singh and Midilli et al. models gave the best fits for each drying curve; based on the statistical tests, namely, coefficient of determination (R2), mean relative percent error (P), reduced chi-square (?2) and root mean square error (RMSE). Fick's second law model was used to calculate the effective moisture diffusivity, which increased with temperature from 4.13 x 10-10 to 1.83 x 10-9 m2/s, with estimated activation energy value of 64.56 kJ/mol. The rehydration capacity was found to decrease with an increase in rehydration temperature.