Simulation of heat and mass transfer of wheat particles in a small-scale gas-solid fluidized bed based on CFD-DEM

Fluidized beds are widely used for drying agricultural products because of their uniform and efficient drying effect, making it crucial to deeply study the physical phenomena during the drying process. A heat and mass transfer model for gas-solid two-phase flow in fluidized beds was established based on CFD-DEM (Computational Fluid Dynamics-Discrete Element Method). The solid dispersion and heat and mass transfer of wheat under different fitting models were analyzed, revealing the influence of air parameters on heat and mass transfer. It was shown that the drying inhomogeneity in the fluidized bed gradually increased with time, while the heating rate gradually decreased. The larger heat flux of the particles in the bottom region indicates a higher heat transfer efficiency between the gas and solid phases, which is the main reason for the drying inhomogeneity. The solid dispersion coefficients varied from 1.41×10^-3 m²/s to 1.64×10^-1 m²/s in different fitted models, while 1S had the fastest heat and mass transfer rates. For the 5S and 7S models, the physical fields of the fluidized bed during the whole drying process were extremely similar in spatial and temporal distributions, and the frequency distribution curves of the temperatures and moisture contents were approximately overlapping, suggesting that the 5S fitted model can accurately simulate the heat and mass transfer behavior of wheat. Air temperature is a key factor regulating the heat and mass transfer rate, while the variation of air flow rate could reduce the inhomogeneity of fluidized bed drying. These findings provide a theoretical basis for optimizing fluidized bed drying processing and holds important guiding significance for engineering practice.