Simulation study on coupled heat and moisture transfer in grain drying process based on discrete element and finite element method

Abstract In present article, the soybean packed bed was generated based on the Discrete Element Method, and the distribution of radial porosity and airflow path of the packed bed were analyzed. The porosity distribution of the packed bed is not uniform, and it is larger near the wall. However, it is lower near the central axis, resulting in a larger airflow tortuosity in this area. Based on the thermal non-equilibrium principle, the double-diffusion heat and moisture transfer model of grain pile was developed. The double-diffusion model was verified and validated using experimental data from the relative literature on soybean thin-layer drying, and the mean relative deviation was 1.74–4.47% between the simulated and the experimental results. The model was applied to the drying process of soybean packed bed, and the influence of drying air temperature and inlet air velocity on drying was analyzed. It was shown that the moisture transfer rate of soybean is mainly affected by the drying air temperature and the moisture content of soybean. At constant air temperature of 35 °C, 45 °C, 55 °C, and 65 °C, and drying air relative humidity of 17%, 21%, 25%, and 30%, respectively, the drying rates were 0.086, 0.089, 0.093, and 0.098%(d.b.)/min, respectively (within the first 10 min). The drying with the stepwise temperature makes the drying rate curve abnormal. Compared with the constant temperature drying at 45 °C, when the drying air temperature changes from the initial value of 55 °C and 35 °C to the end value of 40 °C and 65 °C, respectively. It was observed that drying the packed bed moisture content to 14.5%(d.b.) saves time as much as 80, 110, and 130 min.