Cross-flow drying of wheat. A simulation program with a diffusion-based deep-bed model and a kinetic equation for viability loss estimations.

A mathematical model of heat and mass transfer for fixed beds was developed according to the modern theory of process simulation and standard laws of thermodynamics and transport phenomena. The mass transfer grain-air was predicted with simplified diffusional expressions together with an equation for the static equilibrium moisture content. Four differential equations were obtained for a grain layer and they were integrated along the bed depth and time with second and a fourth-order methods, respectively. The model was validated by comparing drying time predictions with experimental values, being the average error of 6%. The model was extended into a program for continuous cross-flow drying-cooling, which included a kinetic equation for viability losses, and validated against published tests of cross-flow dryers. On average, the error in dryer throughput was 11.4% while that in outlet germination, of only 5.7% germination units. The program can be used to optimize dryer design.