## 3 Results and Discussion  
### Simulation Results  
Figures 1(a), 2(a) and 3(a) show the 2D electric field intensity profiles corresponding to arrangement 1, arrangement 2 and arrangement 3, respectively. In all three arrangements a very good electric field confinement inside the treatment chamber was obtained. Moreover, it can be inferred that the honeycomb filters effectively shield the electromagnetic field from escaping into the external environment. The corresponding temperature profiles at residence  
times of 80 s, 140 s and 200 s are shown in Figures 2b-d, 3b-d and 4b-d, too. Arrangements 1 and 2 exhibit a non-uniform temperature distribution having hot spots located in the regions of space close to the sections where the microwave power is started within the treatment chamber. Furthermore, the thermal non-uniformity increases as the residence time increases. On the other hand, arrangement 3 ensures a quite uniform temperature distribution inside the polypropylene tube filled with almonds even for long treatment times. Figure 2: **(a)** Numerical simulation of electric field and temperature distributions after **(b)** 80 s, **(c)** 140 s, and **(d)** 200 s for arrangement 1. Frequency f = 2.45 GHz and total MW power \(\mathrm{P_{T}}\) = 7.5 kW. Figure 3: (**a**) Numerical simulation of electric field and temperature distributions after (**b**) 80 s, (**c**) 140 s, and (**d**) 200 s for arrangement 2. Frequency \(\mathrm{f}=2.45\) GHz and total MW power \(\mathrm{P_{T}}=7.5\) kW. Figure 4: **(a)** Numerical simulation of electric field and temperature distributions after **(b)** 80 s, **(c)** 140 s, and **(d)** 200 s for arrangement 3. Frequency f = 2.45 GHz and total MW power \(\rm P_{T}\) = 7.5 kW. Considering that the simulations refer to multiport feeding, the design was carried out with the aim to maximize the overall system efficiency. To this aim, the incoming and outcoming microwave powers pertaining to the five active ports of the A3 set up are reported in Table 2. It is worth noting that with respect to the total power released by magnetrons (7.5 kW), about 7 kW came into the microwave applicator, thus ensuring an efficiency of about 93%. To evaluate the uniformity of MW heating, numerical data were post-processed. A first temperature data processing step of the treatment tube cross section was carried out as follows: (1) grouping the temperature data along the longitudinal direction in the center of the cross section, (2) grouping the temperature data along the longitudinal direction of the inner ring with diameter d\({}_{1}\) = 40.3 mm, and (3) grouping the temperature data along the longitudinal direction of the outer ring diameter d\({}_{2}\) = 90.6 mm. The data obtained show that for all arrangements at any residence time of the almonds in the treatment chamber between 80 and 200 s, there were no significant differences in the simulated temperature in the center, inner and outer sections. Simulation results for the mean temperature, standard deviation and the COV and pertaining the different arrangements are shown in Figure 5. \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Incoming Power (W)** & **Outcoming Power (W)** \\ \hline Port 1 & 1419.60 & 80.40 \\ Port 2 & 1358.23 & 141.77 \\ Port 3 & 1403.45 & 96.55 \\ Port 4 & 1395.64 & 104.36 \\ Port 5 & 1382.40 & 117.60 \\ TOTAL & 6959.33 & 540.67 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Microwave power pertaining to each waveguide port of the A3 set up. Figure 5: _Cont._  
Figure 5a highlights that in arrangement A3, after 150 s of treatment the final temperature exceeded 60 \({}^{\circ}\)C (goal of the design). The arrangements A1 and A2 had a similar temperature trend, but the temperature of 60 \({}^{\circ}\)C could only be reached after 200 s. Even if A3 had a standard deviation trend central to the other two conditions (see Figure 5b), it had the lowest trend of the COV, thus proving the configuration with better thermal uniformity (see Figure 5c). As a result, the A3 appears to be the most effective.