# Compression and Fungal Heat Production in Maize Bulk Considering Kernel Breakage
## 3 Results and Discussion
### Estimation of Fungal Heat Production  
Fungal growth decomposes organic matter in maize, thereby developing heat energy, and biochemical heat production is assumed to be heat production due to fungi development [21]. In the estimation of fungal heat production, some of the heat (\(E_{T}\)) is used to raise the temperature of the system, some heat is likely lost due to conduction (\(E_{C}\)) and convection (\(E_{V}\)), and some may be consumed during the water phase change (\(E_{E}\)), e.g., from liquid to vapor. In this study, \(E_{C}\) was not considered, as the sample was nearly sealed. \(E_{E}\) was also considered ignorable because the moisture content of the four samples lost only 1.1%-1.3% after being stored for 7 d. Therefore, the heat produced by fungi in the maize bulk can be determined as follows:  
\[Q=f(\Delta T^{\prime})=E_{T}+E_{C} \tag{9}\]  
where \(\Delta T\)' is the temperature difference in the maize bulk before and after fungus emergence. Heat absorbed by maize and the specific heat capacity of maize bulk were calculated using the following formula [21; 26]:  
\[E_{T}=\frac{c_{b}\rho_{b}\Delta V\Delta T^{\prime}}{\Delta V}=c_{b}\rho_{b} \Delta T^{\prime} \tag{10}\]  
where \(\Delta V\) is the spatial range affected by fungal activity (m\({}^{3}\)).  
The conduction heat loss (\(E_{C}\)) was determined by considering heat transfer from the geometric center of the maize sample to the wall of the testing box. The calculation space is \(\Delta x=0.12\) m,\(\Delta y=0.12\) m, and \(\Delta z\) is the height of the sample at the corresponding time (\(\Delta V=\Delta x\Delta y\Delta z\)). Taking into account the sum of the conduction heat loss on the six sides of the testing box, according to [PERSON]'s law, \(E_{C}\) can be calculated as follows:  
\[E_{C}=\frac{k_{b}\Delta t}{\Delta x\Delta y\Delta z}\sum_{i=1}^{6}\frac{A_{i} \Delta T_{i}}{l_{i}} \tag{11}\]  
where \(\Delta t\) is the storage time, \(A_{i}\) is the area of one of the six faces of the testing box, and \(\Delta T_{i}\) is the temperature difference between the center of the geometric center of the maize sample and the corresponding face \(A_{i}\) measured at a given time \(t\). \(l_{i}\) is the distance between the center of the geometric center of the maize sample and the corresponding face \(A_{i}\).  
In this investigation, the value of temperature difference before and after fungi emergence (\(\Delta T\)) can be equivalently regarded as the difference between the test and numerical results (\(\Delta T\)). As mentioned above, the reason for \(\Delta T\) between test and simulation is whether the biochemical effect or fungi was considered. The numerical result from COMSOL Multiphysics can only include the physical factors in the simulation. Using the test and numerical temperature difference, heat production (\(Q\)) by fungi was evaluated, as shown in Figure 10. \(Q\) was the least in WK\({}_{150}\), and in HK\({}_{50}\), HK\({}_{150}\), and WK\({}_{50}\), the values were 33.7%, 29.7%, and 1.4% higher than it on average. Additionally, it is clear that this variation in \(Q\) with time agreed very well with the APC and temperature results (Figures 7 and 9).  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Material Property** & **Value** \\ \hline Moisture content (\(M\)) & 21\% \\ Mass (\(m\)) & 0.4 kg \\ Initial height (\(l_{0}\)) & HK & 0.042 m \\ WK & 0.045 m \\ Maize bulk density (\(\rho_{\text{b}}\)) & \(m/0.0144\times(l_{0}-s)\) \\ Particle Density (\(\rho_{\text{s}}\)) & 1230.2 kg\(\cdot\)m\({}^{-3}\) \\ Porosity (\(\phi\)) & \(1-\rho_{\text{b}}/\rho_{\text{s}}\) \\ Thermal conductivity (\(k_{b}\)) & \(0.0902+1.165\times 10^{-4}\,\rho_{\text{b}}\)[16] \\ \hline \hline \end{tabular}
\end{table}
Table 2: The parameters involved in FE simulation for maize.