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 to simulate the drying process. Special attention was placed on the interfacial conditions. A system of four couple nonlineal partial differential equations in conjunction with three nonlineal algebraic equations was applied and Solved numerically by both finite differences and Runge-Kutta methods. Simulations were compared with experimental data from carrot slabs in deep fixed-bed drying. Slab thicknesses were 1.0 and 0.1 cm, and air drying temperatures were 50-60 degreesC. Simulation predicted that water transport was controlled by internal diffusion in slabs with 1.0 cm of thickness; therefore, the interfacial conditions may be considered in steady state. Nevertheless, the predominant phenomenon in slabs with 0.1 cm of thickness was by convection; therefore, the interfacial conditions varied with respect to space and time. In the proposed phenomenological representation of fixed-bed drying, the properties and variables of the system defined the type of mechanism controlling of the drying process without previous assumptions.