CFD-DEM simulation on flow behavior and heat transfer characteristics in a zigzag moving bed for soil disinfection

To solve the problem of crop soil-borne diseases caused by the direct return of crop straw and root stubble to the field and the application of heavy pesticides, the thermal-contact killing equipment was developed independently. Utilizing the high-temperature smoke generated from the combustion of crop stubble for heat exchange with the soil can deactivate soil-borne diseases. In this study, computational fluid dynamics (CFD) and discrete element method (DEM) were coupled to deeply explore the flow behavior and heat transfer characteristics of soil particles in a zigzag moving bed. The results showed that the zigzag structure significantly regulated the flow behavior and heat transfer of the particles. With the increase of gas velocity, the Y-direction velocity oscillated periodically in the range of 0-1.5 m/s. Compared with the vertical moving bed, the residence time distribution of particle in the zigzag moving bed changed from negative skewness to positive skewness, and the peak residence time increased by more than twice. In addition, an increase in the residence time of the particles was accompanied by an increase in the dispersion of their distribution. The increase of gas velocity or temperature leaded to the increase of the temperature and the distribution dispersion degree of particles along the Y-direction. However, the mass fraction of peak particle temperature was maintained at about 28 %. As the feeding rate increased, the particle temperature distribution became sharper and narrower. Under the conditions of gas velocity of 0.8 m/s, gas temperature of 443 K and feeding rate of 1.27 Kg/(m 2 ·s), the heat exchange reactor showed the final particle temperature distribution that met the requirements of soil-borne disease killing, and high thermal efficiency. The research can provide theoretical guidance for the optimal operation of equipment.