Mathematical modeling for fixed-bed drying considering heat and mass transfer and interfacial phenomena

A mathematical model for fixed-bed drying with air crossflow was obtained t o simulate the drying process. Special attention was placed on the interfac ial conditions. A system of four couple nonlineal partial differential equa tions in conjunction with three nonlineal algebraic equations was applied a nd Solved numerically by both finite differences and Runge-Kutta methods. S imulations were compared with experimental data from carrot slabs in deep f ixed-bed drying. Slab thicknesses were 1.0 and 0.1 cm, and air drying tempe ratures were 50-60 degreesC. Simulation predicted that water transport was controlled by internal diffusion in slabs with 1.0 cm of thickness; therefo re, the interfacial conditions may be considered in steady state. Neverthel ess, the predominant phenomenon in slabs with 0.1 cm of thickness was by co nvection; therefore, the interfacial conditions varied with respect to spac e and time. In the proposed phenomenological representation of fixed-bed dr ying, the properties and variables of the system defined the type of mechan ism controlling of the drying process without previous assumptions.