CFD Modeling of heat and mass transfer in a spouted bed dryer

For a description of the heat and mass transfer occurring during the drying of grain in a spouted bed dryer with a draft tube, a CFD modeling technique was used. The Eulerian-Eulerian multifluid modeling approach was applied to predict gas-solid flow behavior. A heat- and mass-transfer model was added as compiled executable code by means of UDF programming to FLUENT 6.1, expanding its abilities. Moisture was treated as UDS, and its transport in each phase and exchange between phases were predicted. The kinetics of drying was described by classical and diffusional models for periods I and II of drying, respectively. Results of the simulations were compared with experimental data and with values obtained from various correlations. CFD simulations predict very well the mass-transfer rate but underpredict the heat-transfer rate. Predicted values of the Nusselt and Sherwood numbers are above 2, in agreement with theory. The heat- and mass-transfer rates obtained from the correlations and CFD simulations were usually of the same order of magnitude, but the values obtained from the simulations were closer to the experimental data.