## 3 Results and Discussion
### Model Verification  
To verify the simulation results, the surface temperatures of almonds after microwave heating were measured using a thermal imager and compared with the simulation results.  
In Table 4, the mean temperature (\(\mu\)), standard deviation (SD) and both the simulated and experimental COV are summarized for each residence time.  
The relationships between the mean temperature value, both simulated and experimental, are shown in Figure 10.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**Residence Time (s)**} & \multirow{2}{*}{**RMSE**} \\ \cline{2-2} \cline{5-8}  & **80** & **100** & **120** & **140** & **160** & **180** & **200** \\ \hline \(\mu\) rilevated & 38.0 & 43.4 & 51.5 & 55.3 & 61.0 & 66.9 & 72.9 & \\ \(\mu\) simulated & 39.0 & 44.7 & 50.4 & 56.0 & 61.3 & 67.3 & 72.8 & \\ \(\sigma\) rilevated & 1.5 & 2.1 & 2.8 & 2.7 & 3.3 & 3.3 & 4.5 & \\ \(\sigma\) simulated & 9.0 & 11.2 & 13.3 & 15.5 & 17.5 & 19.8 & 21.9 & \\ COV rilevated & 0.07 & 0.08 & 0.08 & 0.07 & 0.07 & 0.07 & 0.08 & \\ COV simulated & 0.39 & 0.39 & 0.39 & 0.39 & 0.39 & 0.39 & 0.39 & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Simulated and experimental data of temperature of almond surfaces.  
Figure 10: Comparison between simulated and experimental temperature values.  
Figure 10 shows the comparison between the simulated and experimental temperature values. Considering the data shown in Table 4 and Figure 10, there was a perfect correspondence between the simulated and experimental values; this was also confirmed by the RMSE value; which was equal to 0.82. The results obtained prove that the numerical modeling can accurately predict the temperature trend.  
The standard deviation for experimental data was much lower than the simulated one, consequentially leading to a high RMSE value (13.02), as shown in Table 4. This means that there is no good match between the simulated and measured standard deviations. However, between them a strong linear regression was detected (R\({}^{2}\) = 0.91), as shown in Figure 11. This means that even the standard deviation can be predicted.  
It is important to remember that the numerical simulation was carried out in a static manner without considering the metal helix inserted in the treatment chamber. The helix has the function of transporting the almonds from the feed to the discharge, but also of mixing them. The lower standard deviation found during the experimental tests compared to that found in the numerical simulation confirms the effectiveness of the helix in mixing the almonds to guarantee their greater heating uniformity, as reported in [26; 27].  
In this study, the COV was used to evaluate the temperature uniformity of the outlet almond surface.  
The COV for the experimental data ranged between 0.07 to 0.08 but it was also up to more than five times less than the simulated data. This occurrence confirms the efficient heating uniformity of the developed prototype, as also shown by the thermographic images (Figure 12).  
Finally, the study demonstrated that the simulation results were in good agreement with the experimental findings and the operative process condition for almond disinfection. With the help of the numerical simulation, the complex process of interaction between microwaves and almonds during the treatments was understood.  
This study confirms that simulation is a powerful tool for the development of new technologies and above all for the investigation of heating uniformity, as also demonstrated in many other studies [33; 46; 47; 48; 49; 50].  
Figure 11: Simulated versus experimental temperature values.