## 3 Results and Discussion
### Influence of Different Ventilation Conditions
#### 3.2.1 Influence of Different Ventilation Cage Heights  
This section investigates the effect of different ventilation cage heights on wheat drying, considering a non-uniform porosity distribution. The streamline diagrams of the ventilation cage on the inner wall of the silo at heights of 2.1 m, 1.4 m, and 0.7 m are shown in Figure 5.  
Overall, the external airflow under three conditions reaches the perforated ventilation cage on the inner wall of the silo along the ventilation duct, and the airflow inside the  
Figure 5: Flow field streamline and velocity distribution: (**a**) 2.1 m; (**b**) 1.4 m; (**c**) 0.7 m.  
cage is divided into two parts. A part of the airflow continues to flow along the height direction of the ventilation cage until it reaches the closed port at the top of the ventilation cage. After entering the interior of the wheat pile along the height direction of the silo, it is discharged from the outlet located at the silo roof. The other part of the airflow enters the interior of the wheat pile, travelling upward radially through the openings on the surface of the ventilation cage. The airflow then converges in the middle of the wheat pile and flows upward along the height direction of the silo, before being discharged from the top outlet of the silo. The difference is that the area affected by radial airflow inside the grain pile becomes larger as the height of the ventilation cage on the inner wall of the warehouse increases. From the perspective of streamline distribution, there is no ventilation dead angle problem in any of the three arrangements. The low-speed distribution area at the bottom of the silo gradually decreases with the decreases in the height of the ventilation. Compared with the other conditions, the airflow distribution inside the wheat pile was relatively uniform when the height of the ventilation cage was 0.7 m.  
Figure 6 shows the temperature distribution clouds inside the grain pile at different times when the ventilation cage height on the inner wall of the warehouse was 2.1 m, 1.4 m, and 0.7 m, respectively. The airflow velocity inside the wheat pile below the height of the ventilation cage was relatively small when the height of the ventilation cage was 2.1 m (Figure 6a). The low-temperature airflow entering the grain pile along the surface of the ventilation cage caused the wheat particles on the surface to cool down. Therefore, a phenomenon of a cold skin and a hot core caused by temperature accumulation formed in this region. Although the gathering area of high temperature decreased with the increase in ventilation time, the maximum temperature inside the wheat pile at the end of the ventilation was still as high as 26.9 \({}^{\circ}\)C. This indicates the relative inefficiency of the entire 96 h ventilation cooling cycle. The characteristics of the temperature distribution of the wheat pile when the height of the ventilation cage was 2.1 m were similar when the height of the ventilation cage was 1.4 m (Figure 6b). Although the gathering area of high temperature decreased with the decrease in the height of the ventilation cage, the highest temperature inside the wheat pile also reached 20.6 \({}^{\circ}\)C at the end of the ventilation. This indicates that the phenomenon of a cold skin and a hot core still did not disappear. The temperature inside the wheat pile decreased significantly faster than the other two cases when the height of the ventilation cage was 0.7 m (Figure 6c). The highest temperature inside the wheat pile was only 19.4 \({}^{\circ}\)C when it was continuously ventilated for 24 h; however, its high-temperature area was located in the middle and upper parts of the wheat layer (the other two cases were located in the middle and lower parts of the two layers). The reason for this is that the lower height of the ventilation cage causes the ventilation in the middle and lower parts of the wheat pile to be more sufficient (as shown in Figure 6).