# Thermal Evaluation of a Hybrid Dryer with Solar and Geothermal Energy for Agroindustry Application
## 2 Materials and Methods  
After the design and construction of the experimental prototype, the dryer was tested for operation. The first experimental tests were carried out under controlled conditions in a laboratory at constant ambient temperature with artificial irradiation produced by halogen lamps placed at different distances from the drying chamber. The objective of this test was to study each of the variables that will influence the operation of the prototype separately such as the chamber temperature, hot air flow, stability time, system homogeneity, and energy consumption, among other. It should be added that the above-mentioned procedure was replicated under environmental conditions, where irradiation conditions, humidity, and environmental temperatures are variable  
Initially, a measurement protocol was performed as a standardized procedure, developed for the continuous recording of information throughout the different experimental tests. The main parameters measured in the system were:  
Figure 1: Scheme of the complements that are part of the hybrid dryer. * Hot air temperature. * Ambient air temperature. * Air velocity. * Flow of hot or drying air circulating through the tray assembly. * Air flow the solar collector. * Humidity at the inlet and outlet of hot air
* Ambient air humidity. * Time. * Solar irradiation. * Energy consumption. (a) Measuring instruments
* K-type thermocouples, connected to a data acquisition system datalogger brand \"Pico Technology\", model TC-08. * The internal humidity of the chamber and external environment was measured with a RH/temperature datalogger and dew point \"Lascar EL-USB-2\". * Air velocity was measured with the digital equipment \"Testo 404-V1\", Thermo hot wire anemometer. * Global pyranometer connected to a digital multiple (mV). * Automatic control system connected to the dual channel thermostat (T2S+2C DIGIT), 6-channel temperature and humidity control inside the chamber, electrical fan control, and photovoltaic system protections. (b) Drying chamber and solar collector  
The drying chamber had an area of \(150\times 100\times 100\) cm. Constructed of 304 stainless steel of 4 mm thickness. Internally, the camera was insulated with 10 cm thick glass wool. The front wall and ceiling were formed of 6 mm polycarbonate plates. The solar collector was built of 430N4 stainless steel of 0.040 cm and internally insulated with 10 cm thick glass wool. On the surface of the collector, we placed a commercial steel plate of 0.03 cm, covered with black anticorrosive paint (black body). The cover of the collector was 3 mm thick transparent glass with a low iron content. The manifold was attached to the dryer chamber via a 3-inch tube. (c) Photovoltaic systems  
The photovoltaic system will supply a 65 W fan, dual channel thermostat (T2S+2C DIGIT) with a consumption of 5 W, and an information acquisition system of 20 W. It is estimated that 90 W of energy is needed. Therefore, a photovoltaic panel of 110 W peak power, voltage of 12 V, short-circuit current Isc of 6.78 A, and Voc open circuit voltage of 22.41 V was selected with a 12/24 regulator, 250 W inverter, and 100 Ah battery. (d) Aerothermia or buried horizontal catcher  
This consists of a heat exchange probe with the subsurface constructed with 55 m of PVC tube with a diameter of 11 cm. The exchanger was buried homogeneously in the subsoil at an approximate depth of 70 cm, occupying an area of 21 m\({}^{2}\). The installation will act as an auxiliary system for pre-heating the ambient air before it enters the drying chamber. The distance between the air inlet and outlet pipe was 3.5 m. The air entering the exchanger is a forced flow that is generated through a blower with the size of 2\", a voltage of 110 V, 4 A, and 3000/3600 rpm. (e) Controlled conditions in the laboratory  
The first test was to determine the stabilization time and uniformity of the temperature of the drying chamber and the collector, passing an airflow (forced convection) by using a ventilation system.