## 3 Results and Discussion  
### Verification of Numerical Simulation Method  
The following was carried out in order to verify the effectiveness of numerical simulation methods and study the influence of porosity distribution on the temperature and moisture content distribution of a wheat grain pile under the thin-layer drying model. First, the simulation results were compared with the experimental results. Figure 4 shows the comparison of the experimental and simulated temperature of each layer and the overall average temperature of the wheat pile after 88 h of mechanical ventilation. Overall, the numerical results at various layers agree with the experimental measurements, while the results show that the non-uniform porosity distribution is improved with the trend in the experiment compared with the uniform porosity distribution. The difference in the predicted results between the two porosity distribution models gradually increases as the ventilation time increases, especially at the first layer (Figure 4a). The maximum difference occurs at the moment after the end of ventilation, where the predicted values of the non-uniform porosity distribution model are basically consistent with the experimental results, while the uniform porosity distribution model overestimates a cooling of approximately 1 \({}^{\circ}\)C. The reason for the above differences is that the first measurement point is closest to the bottom of the silo, with the smallest porosity under non-uniform porosity distribution (value 0.37), while the corresponding value of the uniform porosity distribution model is 0.40. Therefore, during the ventilation process, the decrease in porosity increases the airflow resistance of ventilation, and the increase in density also increases the heat absorbed by the wheat during drying in this area. Ultimately, the predicted results for the cooling of the non-uniform porosity distribution model during ventilation and cooling are slower compared to the uniform distribution model. For the other layers, as the depth of the grain layer decreases, the difference in porosity distribution between the two models decreases, resulting in the predicted difference between the two porosity distributions also decreasing. The maximum temperature differences from the first layer to the fourth layer were 1 \({}^{\circ}\)C, 0.67 \({}^{\circ}\)C, 0.45 \({}^{\circ}\)C, and 0.27 \({}^{\circ}\)C, respectively. The cooling rate of two porosity distribution models was faster compared with the experimental results. However, the non-uniform porosity distribution model showed better  
Figure 4: Experiment and simulation comparison of wheat grain pile temperature: (**a**) average temperature of the first layer; (**b**) average temperature of the second layer; (**c**) average temperature of the third layer; (**d**) average temperature of the fourth layer; (**e**) overall average temperature. agreement with the experiment during the entire ventilation process. This was particularly true in the first and second layers of the wheat pile, where the predicted results of the two models differed significantly. For the model with non-uniform porosity distribution, there was a small difference between the simulated and experimental results of each grain layer from 0 h to 10 h and from 60 h to 88 h. The maximum error occurred in the fourth layer with a value of 0.9 \({}^{\circ}\)C, while the maximum error value at that area of the uniform porosity distribution was 1.18 \({}^{\circ}\)C. During the ventilation period from 10 h to 60 h, there was a relatively large difference between the simulated and experimental results. For the non-uniform porosity distribution, the maximum error occurred in the fourth layer with a value of 1.68 \({}^{\circ}\)C, while the corresponding value for the uniform porosity distribution was 1.94 \({}^{\circ}\)C. The reason for this is that the experimental conditions were not stable due to environmental factors, the silo structure, and the internal air duct layout.