58-5 |
Mathematical simulation of convection food batch drying with plug flow and complete mixed assumptions |
M. A. GARCÍA-ALVARADO, Chemical and Biochemical Dept., Instituto Tecnologico de Veracruz, Miguel A. de Quevedo No.2779, Col. Formando Hogar, Veracruz, Ver., 91897, Mexico, E. Herman-Lara, Chemical and Biochemical Dept., Instituto Tecnológico de Tuxtepec, PO Box 69, Tuxtepec, Oax., 68360, Mexico, G. C. Rodríguez-Jimenes, Chemical and Biochemical Dept., Instituto Tecnológico de Veracruz, Miguel A. de Quevedo No.2779, Col. Formando Hogar, Veracurz, Ver., 91897, Mexico, and M. A. Salgado-Cervantes, UNIDA, Instituto Tecnólogico de Veracruz, Av. Miguel Angel de Quevedo 2779, P.O. Box 1420, Veracruz, 91860, Mexico. JUSTIFICATION Mathematical modeling of convective fix bed drying for foods has been traditionally modeled with air plug flow assumption. However, some deviations from this assumption may be presented due to air mixing in the flow direction. The extreme deviation is represented by the complete mix of the air in the bed. OBJECTIVE In this work a mathematical simulation of convection food drying in fix bed were developed with plug flow and complete mixed assumptions. METHODS The plug flow model was a system of four coupled non-lineal partial differential equations that represented the temperature and moisture of solid and air as function of time and bed position. The complete mixed model was a system of four coupled ordinary differential equations that represented the same state variables only as function of time. These systems were solved numerically using the finite difference and Runge-Kutta methods. Experimental drying of cassava slices bed was developed in a plant pilot dryer with 0.1 m2 transversal section chamber and 1000 kg-h-1 of air flow. Different drying treatments were carried out at 50 and 60 C for inlet air, and 0.01 and 0.005 m for slice thickness. RESULTS No difference was found by simulation between plug flow and complete mixing when the process is diffusion controlled. However some difference was appreciated when process is convection controlled. The model predict a diffusion controlled process, at the conditions stated for experimental treatments, for a slice thickness greater than 0.003 m. Then, the whole of experimental drying was diffusion controlled. The simulator reproduces the experimental moisture and temperature evolution satisfactorily. SIGNIFICANCE The results show that plug flow is and acceptable assumption for fix bed drying of foods, if the process is diffusion controlled. In the case of different products or conditions, the simulator may predict when the process is diffusion controlled.
Session 58, Food Engineering: Transport processes and kinetics
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