Mathematical modeling of convective thin layer drying of basil leaves

Basil leaves are well known for the medicinal values and grown widely in India. To investigate the effect of different drying conditions on kinetics of basil leaves, the laboratory models of tunnel and tray dryers were employed and air temperatures of 55, 60 and 65°C were considered for the drying. Drying of basil leaves prominently occurred in falling rate period and it was found that basil leaves dried faster in tray dryer. Six thin layer-drying models were fitted to the experimental moisture ratio data. Among the mathematical models investigated, the logarithmic model satisfactorily described the drying behaviour of basil leaves with highest r2 values. The effective moisture diffusivity (Deff) of basil leaves increased with the increase in drying air temperature. The Deff values were higher for tray dryer than those dried in the tunnel dryer. Effective moisture diffusivity of basil leaves ranged from 2.65 x 10-10 to 5.69 x 10-10 m2/s. An Arrhenius relation was employed to ascertain activation energy for the samples dried in both types of dryers and activation energy for basil leaves drying ranged from 33.21 to 9.03 kJ/mol.   Key words: Activation energy, diffusivity, drying, models, basil leaves, tray dryer, tunnel dryer.

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