Analyzing airflow in dry grain storage silo with ventilation using CFD

Abstract: In order to ensure safe storage of highly moist grain after harvest and alleviate grain loss, we took a dry circular steel grain storage silo with a vertical ventilation tube in its center as an example and simulated airflow in the silo filled with highly moist wheat grain after harvest, using CFD. The effect of the wheat grain on airflow was approximated by a porous medium model, and the static and dynamic pressure in the silo was analyzed. The results showed that the static and dynamic pressure and the flow rate decrease exponentially with distance from the ventilation tube. Horizontally, the radial flow rate and the flow velocity (flow rate through per unit areas) both decreased with the distance from the ventilation tube in a power law. Vertically, both the flow rate and velocity decreased exponentially with the height of the grain. The ventilation in the grain stack area was more uniform in the vertical (longitudinal) direction than in the transverse (radial) direction, and the air velocity in the upper and lower part of the grain in the silo was higher than that in region from the vertical ventilation wall to 0.9m away from the central ventilation tube. It was found that the annular baffle with radius of 0.5 m and 0.9m could cover the upper surface and bottom of the silo respectively to improve uniformity of the ventilation. The airflow in the bottom of the silo was highest, followed by the upper surface. The minimum flow rate in the silo wall was only 24.6%, meaning that 1/4 of the flow was discharged from the silo wall and 3/4 was from the upper and low sides. The volume of the exhaust of the silo wall was on the low side. Wind speed test results were consistent with the simulations, with an average relative error of 16.35%. When pressurized air was flow into the ventilation, air flowed radially and the air velocity in the central silo was higher than that in region proximal to the silo wall. It was suggested that periodically ventilating the silo by blowing pressurized air followed by suction with vacuumed air can improved evenness of the air in the silo. The wind speed measurements in the silo were in good agreement with the simulations, proving that combing CFD with the porous media model was accurate to simulate airflow in the silo. The simulation results provide guidance for improving and optimizing silo management.