الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The model development and simulation approaches of this study were carried out in the Computer Laboratory of the Department of Biosystems Engineering, Ghent University, Belgium. The main objective of this work was to develop mathematical models to analyze the convective drying process of rough rice by means of the computational fluid dynamics (CFD). Finite element method was used to develop two mathematical models: (i) Single kernel model to analyze the heat and mass transfer inside a single rough rice kernel during drying. The CFD and diffusion models were coupled where all transfer coefficients were computed simultaneously with the external flow field and the internal diffusive field of the rice kernel, and (ii) A novel deep-bed model to analyze the drying behavior of rough rice in a deep bed. The predicted heat and mass transfer coefficients were used for coupling the moisture and heat fluxes inside the rough rice kernel with the external convective heat and mass transfers at the kernels surfaces in a complete rough rice bed.
The developed models were used successfully for describing the drying behavior of both single kernel and deep bed of rough rice. Also, the models successfully predict, with high accuracy, temperature and moisture distributions inside the single rice as well as the moisture contents and temperatures at different heights in the rice bed during drying. The simulation results were validated against experimental data. After the model validation, the effects of drying conditions on rough rice behavior during drying were analyzed. The models accuracy in predicting the average moisture content of rough rice during drying was very high with main relative deviation less than 7%.
The proposed models were capable of predicting temperature and moisture content distributions of rough rice reasonably at different temperatures and air velocities. The air temperature was the major variable that affected the drying rate of the rough rice. When the air temperature increased the drying rate of the rice increased. All tested drying conditions showed a clear effect on the drying rates of rice in deep bed. Whilst, air velocity showed no visible effect on the drying rates on the single rice kernel a due to the diffusion limitation on the drying rate for the single rice kernel.
The developed models in this study can be used as effective tools to design, optimize, and evaluating rice dryers as well as design and testing of new drying processes. The developed single kernel model can be used to study the effect of drying and tempering process on the grain quality by predicting the stress induced inside the kernels due to the moisture gradient. The developed deep-bed model can be used to optimize the energy consumption and dryer efficiency.
Key words Rice drying; CFD; Diffusion model; Heat and mass transfer; Mathematical modeling; Single kernel; Deep bed; Drying simulation.