Numerical simulation of hot air drying of wheat grain piles based on CFD-DEM and experimental research

Abstract

In this study, a heat and mass transfer model for hot air drying of wheat grain piles based on the discrete-continuous medium assumption method was established to understand the wet heat transfer law inside the wheat grain pile during the drying process. Simulations using COMSOL Multiphysics software were then carried out to study the heat transfer and moisture migration in the porous pile structure of wheat under the conditions of 20 °C ambient temperature, 60 °C air temperature, and 1 m/s air speed. The model was validated in combination with wheat hot air-drying experiments. The experimental results showed that the established model can reflect the drying process of the grain pile well, and the experimental values were in good agreement with the predicted values. The temperature, humidity, and flow fields in the wheat pile were unevenly distributed. The temperature distribution of the wheat pile showed a high temperature in the edge region and a low temperature in the center region, the maximum temperature difference reached around 8 °C. The moisture distribution of the pile showed the opposite trend, with lower moisture in the edge region and higher moisture in the center region. The humidity of the upper layer of wheat in the grain pile showed an upward trend over a period of time due to the influence of rising steam, the maximum moisture difference reached about 15%. The velocity of the edge region with a large pore rate was large, and obvious vortex regions were found in the grain layer. The local speed reaches about 5 times the inlet wind speed. Based on the CFD-DEM medium coupling method, the complex pore structure within the grain stacking structure can be accurately constructed, and a mathematical model can be established on this basis, providing a new approach for simulating the moisture and heat transfer of grain stacking structures.