## 3 Results and Discussion
### Simulation Model Validation and Analysis  
The analysis of the correlation between the distance from the center of the compost pile and temperature change showed a significant variation in temperature from Day 0 to Day 1, reaching a peak before stabilizing. Based on these results, model validation was conducted  
Figure 6: A comparison of daily average compost temperatures, consisting of layers (bars) and the mean temperature (line): (B) bottom layer; (MB) middle bottom layer; (MT) middle top layer; (T) top layer.  
using Day 1 data, where microbial activity was highest and temperature diffusion from the center of the compost pile was most evident.  
A grid refinement study was conducted to evaluate the impact of grid size on the formation of structures within the model. To verify the shape of the grid formed inside according to the grid size, the model was filled with grids of different sizes to check the density. When the grid size was 1 mm, the number of grids was the highest at 840,403, while at 5 mm it was 34,125, and at 10 mm, it was 8742. Upon evaluating the density for each grid size, the result with the lowest skewness value of 0.46 at 5 mm suggests that a grid size of 5 mm is the most efficient (Figure 7a). Additionally, when the model was constructed with a grid size of 5 mm, the assessment of the shape and density by checking the grid composition at different locations revealed that the grids were well formed and robust at the outlet, compost pile, and inlet areas (Figure 7b).  
Figure 7: Evaluation of density and internal grid configuration by grid size: (**a**) internal density of the model by grid size; (**b**) grid formation at different internal locations with a 5 mm grid size.  
The results were found to be at a similar level to numerical analysis studies on reactor modeling using livestock manure. The structures built for processing livestock manure should prevent the accumulation of residues, and therefore, it is believed that most structures operating in the field have simple configurations [33; 34].  
The temperature simulation results of the model were implemented in the form of contour maps, which were compared with contour maps created based on actual measured temperature values. The legend was set identically, representing the temperature range with a maximum value of 70 \({}^{\circ}\)C in red and a minimum value of 30 \({}^{\circ}\)C in blue. Due to the inability to implement conductive heat in the map using measured temperature values, 20 mm on both sides was omitted when creating the map with model temperature values. The distribution of temperature changes was presented in a gradient form. Upon comparing the two maps, the high completeness of the model was evident. Both maps showed that the highest temperatures were at the center of the compost, gradually decreasing as the distance from the center increased. The low temperatures at the reactor's ceiling and floor due to the influx of external air and conductive heat were also well represented (Figure 8). The validation of the simulation model was conducted through an analysis of the correlation between the temperature values measured in the reactor and those calculated by the simulation model. The \(x\)-axis represented the measured temperature values, while the \(y\)-axis showed the simulation temperature values at the same locations. The analysis of the correlation between the two temperature values resulted in an R\({}^{2}\) value of 0.8 (Figure 9).  
Figure 8: Contour map for the comparison of measured and simulated temperature distributions: (a) measured in experiment; (b) computed in CFD.