Modelling of Thin-Layer Drying of Black Gram

Abstract

Thin layer drying characteristics of black gram were studied at three initial moisture contents (17.0, 21.8, 25.4% d.b), three drying air temperatures (45, 55, 65°C) and three air velocities (0.5, 1.0, 1.5 m.s-1). Drying characteristics of black gram was significantly affected by drying air temperature. Grain initial moisture content and velocity, both had a limited influence, and only during the initial stages of drying. Increase in airflow velocity greater than 1m.s-1 had no significant effect on moisture reduction. Out of the eight models evaluated, Midilli model was found to be the best fit. Effective moisture diffusivity varied from 2.96 x 10-7 to 1.08 x 10-6 m2 .s-1 and activation energy varied from 37.43 kJ.mol-1 to 48.36 kJ.mol-1 for black gram drying. The effect of air temperature and air velocity on drying constants was explained through an Arrhenius type relation, while the effect of initial moisture content on model constants could not be explained. The developed model could be used to predict the moisture ratio of black gram as affected by temperature and air velocity. Highest dehulling efficiency was found to vary between 72.3 and 72.8% when 21.8% (d.b.) initial moisture grains was dried at a temperature of 55°C.