Numerical simulation of rough rice drying in a deep-bed dryer using non-equilibrium model

In this study, a non-equilibrium model of the grain fixed deep-bed drying for rough rice has been presented. The model was developed by using mass and energy balance inside a control volume of the bed and a proper rate equation for the thin-layer drying. The control volume was composed of two thermodynamical systems: intergranular air and grains. In most of the models reported in the literature, authors simplified the physical description by neglecting the accumulation terms from the energy and moisture balance equations without a relevant justification. Accurate modeling of the drying process is an important factor from design point of view as well as optimizing the operation. In the proposed model, in this work the accumulation terms were kept in both energy and mass balance equations. The set of coupled partial differential equations derived from the model was solved simultaneously by using the backward implicit method. Based on the discrete set of equation, a computer program was developed and implemented in MATLAB environment to simulate the grain drying process. The technique was capable to predict correctly the temperature of the air and grains, the air humidity and moisture content of the grains at different locations of the dryer at any time. The results of simulation were also compared with the experimental data. The results clearly show that the proposed method can predict the characteristics of the deep-bed dryer with a very good degree of accuracy. (C) 2009 Elsevier Ltd. All rights reserved.