## 7 Thermal Analysis of an Air Cooler and Airflow Model  
When the inverter is fully loaded during DC to AC voltage inversion, the inefficiency causes high waste heat. However, increasing the operating temperature of the inverter reduces its efficiency. Therefore, it is necessary to maintain the optimum operating temperature of the inverter. The numerical software Ansys 2022 R2 Icepak is used by researchers to develop and solve thermal management systems of modern electric vehicles [44; 45] as well as thermal and fluid flow analysis in integrated circuits. Ansys Icepak provides a powerful simulation workspace for electronic cooling solution development that utilizes Ansys Fluent's industry-leading computational fluid dynamics (CFD) methods [46]. Therefore, this study investigates the thermal analysis and airflow of the newly designed air cooler (Figure 15) using Ansys Icepak numerical software. Figure 14: Model of an active air cooler with circular cross-section (**a**) and rhombic cross-section (**b**). Figure 13: Conventional inverter assembly (**b**) including inverter and passive air cooler (**a**). The thermal and fluid flow analyses in the integrated circuits were performed in several steps. In the first step, the model was prepared in PTC Creo 7.0 software (Figure 16). In the next step, the CAD model was loaded into the Ansys Icepak environment. Here, the heat generation points on the printed circuit board were defined. In total, 11 heat sources were defined on the printed circuit board according to the specification of the individual electronic components with a total power of 8 kW (Figure 17). Figure 16: The active inverter cooling system model (PTC Creo 7.0). Figure 17: The active inverter cooling system model (Ansys 2022 R2 Icepak) with boundary conditions. Figure 15: The active inverter cooling system model. In addition to the heat sources, the inverter cooling was defined. The fan was defined as a 2D fixed flow type with a total airflow of 0.4 m\({}^{3}\cdot\)s\({}^{-1}\). After defining the boundary conditions, a finite element mesh was generated; the number of elements was 2,350,311, and the number of nodes was 2,587,468 (Figure 18). After defining the boundary conditions, the basic calculation parameters were defined. The variables that were calculated were flow (velocity/pressure) and temperature. Radiation (surface to surface radiation model) was included in the calculation, and the flow regime was set to turbulent (two equation k-epsilon). With these parameters set, two models were created--an air cooler with ducts of a circular cross-section and an air cooler with ducts of a rhombic cross-section. The first phase of the investigation was a thermal analysis of an air cooler with ducts of a circular cross-section. The airflow from the fan to the active air cooler was set to a flow rate of 0.4 m\(\cdot\)s\({}^{-1}\). The manufacturer of the three-phase inverter states in the technical documentation that a maximum power of 8 kW can be provided to the electric motor to ensure the speed of the electric vehicle to a maximum of 120 km\(\cdot\)h\({}^{-1}\). During the inverting simulation with a maximum output of 8 kW, the inverter generated a temperature that the air cooler could maintain at the temperature of 192.5 \({}^{\circ}\)C (Figure 19). Figure 19: Temperature profile of an inverter’s air cooler with a circular hole. Figure 18: The active inverter cooling system model (Ansys 2022 R2 ICPeak) with finite element mesh. The airflow rate was most significant at the beginning of the duct (2000-2500 m\(\cdot\)s\({}^{-1}\)), where the exhaust from the fan connects to the narrow circular duct of the air cooler. At this point, the diameter of the duct narrows, which causes the air velocity to increase. However, the airflow velocity is almost constant along the entire length of the active heatsink with a velocity of 1000-1500 m\(\cdot\)s\({}^{-1}\) (Figure 20). Thermal and airflow analysis in the air cooler with rhombic cross-section tubes were generated in a second step (Figure 21).