## 5 Results and Discussion
### System-Level and Component-Level Analysis for the Base Case  
The system-level and component-level comparison between the serial and parallel thermal module designs is presented in Figure 10; individual variations between cells will be described in Section 5.3. From Figure 10a, the battery heat dissipation for both designs is below zero at the beginning, which means that the battery does not generate as much heat as the motor and inverter, so the coolant temperature is higher than the battery temperature. After 200 s, the heat dissipation rate for both designs is above zero, and the heat dissipation rate of the serial design gradually exceeds that of the parallel design, as the gap between them widens over time. Therefore, the serial design proves to be more effective in achieving heat dissipation for the entire battery pack. This phenomenon is reflected in Figure 10b, where the maximum battery pack temperature for the serial design is 1.22 degrees lower than that of the parallel design. However, this comes at the cost of the maximum motor temperature being 0.59 degrees higher. Figure 10c conveys two key messages: one is the accumulative heat dissipation at the radiator end, which can be understood as the portion of total heat generated by all HV components that is carried away by the coolant and expelled to the outside by the radiator, and the other is the cooling system efficiency (\(\eta\)), which is calculated by the accumulative heat dissipation (\(Q_{dis,all}\)) divided by the accumulative heat generation (\(Q_{gen,all}\)) of all HV components [37], as Equation (22). It can be seen that the accumulative heat generation for both designs is almost the same, reaching 1.97 kWh at the end of riding. However, the serial design enables the entire cooling system to dissipate an additional 0.03 kWh of heat, resulting in a 1.36% higher cooling system efficiency compared to the parallel design. Figure 10: System-level and component-level thermal performances of the serial and parallel module designs. (**a**) Heat dissipation rate of the battery pack, (**b**) battery pack and motor temperatures, (**c**) accumulative heat dissipation and efficiency of the cooling system, and (**d**) coolant temperature at end of riding. Therefore, the serial design allows for the entire cooling system to dissipate more heat and be more efficient at a vehicle level. Figure 10d displays the coolant temperature at different points in the cooling system. At the end of riding, the coolant temperature in the serial design is generally higher than that in the parallel design, indicating that the coolant in the serial design more effectively absorbs the heat generated by the HV components. This observation can be explained as follows. In the serial design, the coolant sequentially absorbs heat from every cell in the battery module, gaining thermal energy and increasing in temperature progressively along the path. This results in a cumulative heat uptake and a higher exit temperature, demonstrating effective heat removal from the heat sources. Conversely, in the parallel design, the coolant is divided into four separate streams, and thus, the thermal energy gain in each stream is limited to the heat dissipated by the cells it serves. Hence, the parallel design does not utilise the full thermal absorption potential of the coolant in a cumulative manner as the serial design does. Therefore, it is expected that the outlet temperature in the parallel design will be lower, indicating less overall heat absorption per unit of coolant. For both designs, the battery pack contributes to an increase in coolant temperature of approximately 5.9 degrees, while the motor contributes to an increase of around 6.3 degrees. In contrast, the inverter contributes an increase of less than 0.2 degrees in coolant temperature.