## 2 Materials and Methods
### Experimental Apparatus  
The heat and moisture transfer test of the wheat grain pile in the silo adopts the multi-field coupling simulation test platform built by the research group. The platform is composed of six parts: the grain storage silo, ventilation regulation system, servo flexible loading control system, constant temperature control system, temperature detection system, and computer control system. There is a cavity region at the bottom of the silo, and ventilation cages near the silo walls were connected to that area. Small circular holes with a diameter of 3 mm were evenly distributed on the surface of the ventilation cage. The air flow was pressed by the fan and filled the cavity region at the bottom of the silo. Then, the air flow entered the ventilation cage near the wall of the silo and continued to move upwards along the height of the ventilation cage, entering the interior of the grain pile from the holes on the surface of the ventilation cage. Finally, the air flow was discharged through the air outlet on the top of the silo (as shown in Figure 1c).  
As is shown in Figure 1b, the grain storage silo consists of a cylindrical body and a conical roof. The inner diameter of the silo is 1.5 m, the height is 3.0 m, and the maximum grain loading height is 3.0 m. Four sensor cable outlets and five sampling ports were installed on the wall of the soil. The height of the warehouse top was 0.8 m, with a slope of 45\({}^{\circ}\). Two vents and servo flexible loading control system loading ports were reserved. The insulation materials were used on the outer surface of the experimental silo to ensure the heat insulation performance. Four air ducts with a height of 2.2 m and an aperture of 3 mm at equal intervals were set into the inner wall of the silo. To eliminate errors caused by the sensor's movement during grain loading, a horizontal bracket was installed on each layer inside the silo to fix the position of the temperature sensor.  
The drying method used in this paper was low-temperature ventilation drying. The temperature control system regulated the temperature and humidity of the ambient air sucked in by the axial flow fan. After reaching the set target temperature and stabilizing it, the ventilation system was activated to send cold air into the interior of the grain pile through a ventilation cage at the inner wall of the silo, and the cold air supplied to the wheat piles exchanged the heat with the grain particles to achieve the cooling effect in the grain pile. To ensure that the temperature of the ventilation air was lower than that of the wheat pile, a refrigeration machine was used to control the ventilation temperature. To reduce the impact of the environmental temperature on the supply air temperature and humidity inside of external pipelines during the ventilation process, insulation treatment was carried out on it. The outer walls of the silo and its bottom were also thermally insulated to reduce the impact of the environmental temperature.  
To study the variation in temperature and water content inside the wheat grain pile under ventilation, each system of the test platform was inspected and debugged using  
Figure 1: Schematic diagram of the composition of the multi-field coupling test platform for the grain storage environment: (**a**) platform system; (**b**) grain storage cylinder; (**c**) ventilation path.  
measuring instruments before testing. The temperature sensors were arranged according to the test plan. A total of fourteen temperature sensors are arranged inside the silo to record temperature changes at different positions. One temperature and one humidity sensor in the air inlet at the bottom of the silo were installed to record the temperature and humidity of the diffuser, respectively. The sensors position was shown by the red dot in Figure 2. Of note, the measured data were also used as the inlet boundary conditions for numerical simulation research in a later section. The measurement point positions are shown in Figure 2.