## 2 Materials and Methods  
### Description of the Experimental System  
The experimental system used in the present study corresponds to a prototype of a solar dryer that operates by forced ventilation, designed mainly for drying plantain and taro. The prototype was evaluated in the Municipality of Cunduacan Tabasco, Mexico, at the facilities of the Chontalpa Campus, Academic Division of Engineering and Architecture of the Juarez Autonomous University of Tabasco (18\({}^{\circ}\)4\({}^{\prime}\)24.27\({}^{\prime\prime}\) N latitude and 93\({}^{\circ}\)9\({}^{\circ}\)52.72\({}^{\prime\prime}\) W longitude). Figure 1 shows the schematic diagram of the dryer used. It consists of a suspended absorber plate of stainless steel painted with a selective coating of nanostructured black nickel (\(\alpha\) = 0.91; \(\epsilon\) = 0.19), with a thickness of 4 mm and an area of 0.7 m\({}^{2}\). The dimensions of the solar collector are 1.0 m \(\times\) 0.7 m, with a fixed inclination angle of 18\({}^{\circ}\). In order to minimize the heat losses to the environment, the bottom and sides of the collector were built with a central piece of thermal insulation using polyurethane panels coated with galvanized steel, with a thickness of 3.81 cm and a coefficient of thermal conductivity (k) of 0.018 W\(\cdot\)m\({}^{-1}\cdot\)K\({}^{-1}\). The transparent cover is 3 mm thick clear glass (t\({}_{\rm c}\) = 0.84, \(\epsilon_{\rm c}\) = 0.9 and \(\alpha_{\rm c}\) = 0.06), to reduce heat loss at the entrance of solar radiation. The dimensions of the drying chamber are 0.7 \(\times\) 0.5 \(\times\) 0.8 m\({}^{3}\), whereas its walls are also made with polyurethane panel covered with galvanized steel. The inside of the chamber has a metal guide to place the drying trap with dimensions of 0.6 \(\times\) 0.45 m\({}^{2}\), constructed with galvanized steel mesh. Above the drying chamber, there is a 1 m high chimney, with an opening in the outlet to allow the circulation of humid air outside the dryer. Lastly, to generate forced ventilation, a direct current (DC) fan with nominal values of 60 W, 12 V, 5.0 A, and 1800 rpm was installed on top of the chimney. The solar dryer was instrumented to measure the environmental parameters that affect its performance and the operational parameters of interest. For the measurement of solar irradiance, an Amprobe Solar 100 pyranometer mounted on the solar dryer at an inclination of 18\({}^{\circ}\) was used. The temperature and relative humidity of the environment were sensed using an Extech RH101 Hygro-Thermometer hygrometer, while an Extech 451,126 fin anemometer was used for wind velocity. Concerning the operational parameters, the temperature inside the dryer was measured using type K thermocouples, distributed across the solar collector, the drying chamber, and the chimney. On the other hand, the air velocity inside the collector was measured using an Extech 451,126 anemometer, while the mass of the product to be dried was measured using a Torrey L-PCR 20 balance. Table 2 presents the technical information with the precision and operation ranges of these sensors. The sensors were connected to an ADAMS-4016 8-channel data acquisition card for the automated recording of information storage. The data were sent by network cable to a data logger, interconnected to a PC. The sampling period was 1 min with averages of 15 min. The selection of the sampling time at 15 min was carried out according to the design criteria for solar trackers, considering that the solar angle moves 1\({}^{\circ}\) every 15 min [12].