Three-dimensional model of phase transition of thin sucrose films during drying

A computer model was developed to predict crystallization during processing of thin sugar films on a porous support during drying of a bed of pieces in a through-flow dryer. The three-dimensional model analyzed simultaneous heat and moisture transfer in both the film and the porous support, accounting for shrinkage, with temperature and moisture-dependent transport properties. Kinetics of crystal growth at different solution conditions were determined experimentally. Predicted crystal growth rates were evaluated from crystallization kinetics based on supersaturation, temperature, and slate of the solution. The influence of growth on the solution concentration and drying rate were tal;en into account, The drying temperature (60-95 degrees C) and relative humidity (0-50%) of air had a significant impact on growth rate, whereas the velocity of drying air influenced growth rate only at low magnitudes (less than 1 m/s). Initial concentration of solution had no effect at the investigated conditions (70-85% TS). Concentration profiles around the growing crystals during drying of the thin films were evaluated. A phenomenon of case hardening was observed for dried films with high density of seeds on the surface. Simulation results were in agreement with theory and experimental results. (C) 2000 Elsevier Science Ltd. All rights reserved.