Evaluation of species transfer models in the cfd simulation of fixed bed soybean drying

Abstract

The drying is fundamental to the preservation of materials, particularly food, which is sensible to damaging related to moisture because of its hygroscopic nature. The drying increases the shelf life of these products and reduces their overall weight, which facilitates the logistics and aggregates value to the product. Computational Fluid Dynamics is a potentially facilitating tool for the analysis of drying variables, such as velocity, air temperature, and particle temperature, which have great influence on the drying rate. This work aimed at studying different numeric models for the simulation of a fixed bed drying operation, analyzing the influence of the equilibrium ratio and water diffusivity in the solid on the results. The computations were made in the software FLUENT 19.2, using the Multiphase Eulerian Granular Model with packed bed configuration and different mass transfer models: Constant, Species-Constant, Species-Sherwood, Ranz-Marshall, and Hughmark, as well as heat transfer models: Constant Heat Transfer Coefficient, Constant Nusselt Number, Ranz-Marshall, and Hughmark. The mass transfer models with the best performance were the Ranz-Marshall and Hughmark models. A strong influence of the equilibrium ratio was observed for both models, and a moderate influence of the water diffusivity. The influence of equilibrium ratio and water diffusivity was not observed for the other models. The heat transfer models did not present expressive difference, and the system reached thermal equilibrium quickly. The overall study of the models and the influence of different parameters was effective, and was able to document the obtained results for future optimization and further investigation of the numeric model.