## 2 Materials and Methods  
### Measurement System and Equipment  
In this work, a D00-250-10 power diode (Lamina, Piaseczno, Poland) (\(I_{F}\) = 250 A, \(V_{F}\) = 1.5 V) was used. The design of this diode is similar to that of the D61-200-22-N0-ABG diodes (Poweralia, Barcelona, Spain) and SCDR0240N12M diodes (Poweralia, Barcelona, Spain). The diode D00-250-10 is shown in Figure 1.  
The diode was placed in a heat sink. The dimensions of the heat sink and the placement of the diode are shown in Figure 2.  
Figure 1: D00-250-10 diode dimensions in millimeters. The diode, together with the heat sink, was placed in a measurement system that allowed the measurement of the power dissipated in the diode. The value of the \(I_{F}\) current that flowed through the observed diode was forced with the use of a CSU 600 A power source (Megger, Dover, England). The voltage drop across the terminals of the diode was measured using a UT55 voltmeter (UNI-T, Dongguan, China). In the work carried out, the temperature at the surface of the diode case was measured with an Optris Xi 400 thermal imaging camera (Optris, Berlin, Germany) with a telephoto lens (Instantaneous Field of View = 0.9 mrad). The accuracy of measurement was equal to 2 \({}^{\circ}\)C or 2%. The parameters of this thermographic camera were described in reference [34]. A schematic diagram of the part of the measurement system that allowed for forcing the current through the diode under test, measuring the power, and performing the measurement system is shown in Figure 3.  
Figure 3: Schematic diagram of a section of the measurement system that allowed the current to be forced through the diode under testing, the measurement of the power dissipated at the junction, and the thermal imaging of the diode case temperature. Figure 2: Diode D00-250-10 mounted in a heat sink. Dimensions in millimeters. To force the air flow around the observed diode, the diode, together with the heat sink, was placed in a tube. The tube was made of stainless steel, a material that has a low emissivity value \(\varepsilon\). For this reason, the inside of the tube was lined with black polyurethane-made foam. The structure of the foam used was porous. There is a similarity between the single pore foam and the black body model. Therefore, the walls of the chamber that was prepared were characterized by a high emissivity value of \(\varepsilon\) = 0.95 [35]. Additionally, the value of their reflectance p was low. For this reason, part of the measuring system, placed inside the chamber, was optically isolated. The tube was mounted in a vertical orientation. A holder for a thermal imaging camera was placed inside the tube. Below this, a diode holder with a heat sink was placed. A fan was placed at the bottom of the resulting test rig to force air flow. The speed of the fan was controlled by a stepper motor controller, which in turn was controlled by a PLC (programmable logic controller) (Siemens S7-1200, 1215 DC/DC/DC). An HMI (Human Machine Interface) panel was attached to the PLC. A section of the measurement system that was responsible for the air flow around the diode under testing is shown in Figure 4.  
The air velocity in the tube was measured using GM 8903 (Benetech, Kalisz, Poland). By analyzing the system shown in Figure 4, it can be seen that the top of the tube was open. The heat sink and parts of the diode case were made of low-emissivity material. For this reason, markers were applied to the diode and the heat sink case using Velvet Coating 811-21 paint. The value of the emissivity coefficient of the paint used is known and is in the  
Figure 4: Schematic diagram of a section of the measurement system that allowed air to be forced around the diode under testing.