## 2 Materials and Methods
### Description of the Experimental System
The schematic diagram of the experimental system is shown in Figure 2.  
Figure 1: Solar dryer: (**a**) 2D side and cross-sectional view; (**b**) 3D view; (**c**) experimental solar dryer: (**c1**) rear view solar dryer; (**c2**) side view of the solar dryer and sensor connection; (**c3**) front view of temperature sensors, solar collector; (**c4**) connection of the data acquisition card; (**c5**) fan for air extraction; (**c6**) view of the product to dry and fan; (**c7**) rear view of the dryer with the drying tray; (**c8**) drying tray; (**c9**) solar dryer. To measure the mass of evaporated water, a kilogram of fruit was sliced, placed in trays, and subsequently introduced to the solar dryer. The samples were left in the dryer for a period of 8 h. During this time, the set of all samples was weighed every 15 min and returned to the tray, identifying the evaporated water from the samples through weight loss. For practical terms, in each measurement, the mass of all the slices was quantified each measurement interval. In this period, the mass of water evaporated from the product \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Type** & **Parameter** & **Symbol** & **Unit** & **Sensor** & **Range** & **Accuracy** & **Resolution** \\ \hline \multirow{4}{*}{**Solar irradiance**} & Solar irradiance & \(G_{T}\) & W\(\cdot\)m\({}^{-2}\) & Solar energy meter & 0-1999 W\(\cdot\)m\({}^{-2}\) & \(\pm\)10 W\(\cdot\)m\({}^{-2}\) & 0.1 W\(\cdot\)m\({}^{-2}\) \\  & Room temperature & \(T_{a}\) & \({}^{\circ}\)C & Hypo- & \(-\)20–60 \({}^{\circ}\)C & \(\pm\)2 \({}^{\circ}\)C & 0.1 \({}^{\circ}\)C \\  & Relative & \(RH\) & \% & Thermometer & 10-95\% & \(\pm\)3.5\% & 0.1\% \\  & Humidity & & & Extech RH101 & & & \\  & & & Fin anemometer & & & \\  & Wind velocity & \(w_{v}\) & m/s & Extech & 0.30–45.00 m/s & \(\pm\) (3% + 0.1 m/s) & 0.01 m/sz \\  & & & & 451126 & & & \\ \hline \multirow{4}{*}{**Solar irradiance**} & Inlet temperature & \multirow{2}{*}{\(T_{i}\)} & \({}^{\circ}\)C & Thermocouple & \multirow{2}{*}{0–400 \({}^{\circ}\)C} & \multirow{2}{*}{\(\pm\)2.2 \({}^{\circ}\)C} & \multirow{2}{*}{0.1 \({}^{\circ}\)C} \\  & in the & & & K type & & & \\ \cline{1-1}  & drying chamber & & & & & \\ \cline{1-1}  & outlet temperature & \(T_{o}\) & \({}^{\circ}\)C & & & & \\ \cline{1-1}  & Air velocity at the & & & Fin anemometer & & & \\ \cline{1-1}  & inlet of the & \(v_{id}\) & m/s & Extech & 0.30–45.00 m/s & \(\pm\) (3% + 0.1 m/s) & 0.01 m/s \\ \cline{1-1}  & drying chamber & & & 451126 & & & \\ \cline{1-1}  & Product mass & \(m_{p}\) & kg & Weighing scales & & & \\ \cline{1-1}  & & & & Torrey L-PCR 20 & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Environmental and operational parameters measured for the evaluation of the solar dryer. Figure 2: Schematic diagram with the instrumentation of the indirect solar dryer prototype with forced convection implemented in the present study. was recorded to calculate the drying rate. This procedure was performed separately for both plantain and taro. The experimental drying velocity was estimated as the ratio between the mass of evaporated water of the product and the drying time interval of the same. These values were obtained by measuring the loss mass of the fruit and the time elapsed between each sampling. This relationship is expressed by the following equation [34]:  
\[v_{d}=\frac{m_{w}}{\Delta t}, \tag{1}\]  
where \(m_{w}\) is the mass of evaporated water of the product (g), \(\Delta t\) is the drying time interval (min), and \(v_{d}\) the drying velocity (g/min).