## 3 Thermal Analysis Methods
### Numerical Analysis-CFD Analysis for Water Jacket  
The CFD model was applied to studying the convective cooling inside the 72/48 SRM due to the flowing water, therefore calculating \(h_{cv}\) for the water jacket (WJ). The 3D CFD is the best alternative for the flow process in an electrical machine. The 3D numerical simulations of CFD mode for four WJ \begin{table}
\begin{tabular}{l l l} \hline
**WJ Channel** & **H [mm]** & **W [mm]** \\ \hline
1 channel & 47 & 380 \\
5 channels & 47 & 74.4 \\
9 channels & 47 & 40.44 \\
17 channels & 47 & 20.47 \\ \hline \end{tabular}
\end{table} 
Table 6: The proposal dimensions of the water jacket configuration. Figure 8: Variations of the convection heat transfer analysis of WJ when changing the channel height and number of a channel simultaneously. (**a**) Fluid velocity; (**b**) Reynolds number; (**c**) convection heat transfer; (**d**) the water head losses. configurations with different numbers of channels were performed. The geometrical modelling was carried out on an ANSYS-Design-Modeler, the unstructured, and structured grids are used in the paper. The SRM was meshed by a structured grid due to complex structures. There were 27,265,153 mesh cells in the simulations. With the use of the spiral WJ type, the coolant flows along the cylinder vertically, the coolant enters the cylinder from the bottom side and flow out from the head of the opposite side. The coolant used in this calculation was water at a temperature of 26 \({}^{\circ}\)C and the ambient temperature was 26 \({}^{\circ}\)C. The convection heat transfer coefficient between the motor's outside surface and the air is 5 W/m\({}^{2}\)\({}^{\circ}\)C. The inlet and outlet boundary conditions of the coolant are defined as a mass flow inlet (0.6 L/s) at a temperature of 26 \({}^{\circ}\)C and pressure outlet respectively. The wall boundary conditions as solid regions including stator, rotor and winding are set to heat flux boundary conditions. These wall boundary conditions were set to heat flux boundary conditions in our model. The winding's heating power was 6560 W, stator and the rotor's core heating power were 1445 W and 650 W, respectively. The losses of the stator, the rotor with winding copper loss were mapped directly to the model. For the application described in this research, the \(k\)-\(\varepsilon\) model was used for its robustness and simplicity. WJ is widely used for the high-power induction motor (IM) and interior permanent synchronous motor (IPMSM) [39; 40]. Based on the same principle, an analytical method and numerical method were used in this work to obtain the machine's temperature rise. The temperature rise for the 72/48 SRM was achieved under the rated load and the rated speed. Figure 9 shows the 3D model structure of WJ configurations, with four different numbers of channels, such as 1, 5, 9 and 17 channels. Moreover, the direction of the arrow shows the direction of water flows. Figures 10 and 11 show the 3D models' steady-state temperature profile of WJ configurations, with four different numbers of channels; 1, 5, 9 and 17 for a water flow rate of 0.6 L/s. The most significant temperature zone inside the SRM was at the stator winding close to the outlet towards where the fluid exits the cooling jacket. The rate of heat transfer is specifically proportionate to the temperature difference, and as the water flows from the inlet towards the outlet, it absorbs heat, which increments its temperature. This leads to lesser temperature differences towards the end. Hence, it decreased the amount of heat transfer as water flows toward the outlet, resulting in the most significant temperature zone towards the end of the coolant flow loop. Figures 10a and 11a show the outer portion of the stator winding displays are asymmetric. The temperature of the side of end winding near the inlet and outlet is (78 \({}^{\circ}\)C) and (94 \({}^{\circ}\)C), respectively. This situation can be explained based on water flow behavior in the casing of the water jacket for 1 channel.