*3.1. LBM Simulation Results*

The effect of airflow configuration on temperature distribution within the battery pack was studied by varying the number of inlets and simulated using LBM-based CFD. A constant air inlet temperature of 30 ◦C was used to represent the average air temperature of the tropical region where the BTMS was intended to be used. The performance of air-cooled BTMS could be represented by the air velocity and the temperature inside the battery pack. The air velocity affected the convective heat transfer of the air and indicated the amount of air flowing and taking the heat generated by the batteries. Meanwhile, the temperature was the main objective of BTMS and represented its performance in providing an optimal operating condition for the batteries. In this section, the distributions and the average values of air velocity and the temperature inside the battery pack were compared.

The velocity and temperature contour, along with the batteries whose temperatures were maximum and minimum of one, two, three, and four-inlets configuration, are presented in Figures 3–6 respectively. The velocity contour described the velocity distribution of the air traveling across the battery pack and indicated how the air could reach every spot inside the battery pack. The temperature contour showed the temperature distribution inside the battery pack after being cooled by the air.

**Figure 3.** The contour of (**a**) velocity and (**b**) temperature of 1 inlet model.

**Figure 4.** The contour of (**a**) velocity and (**b**) temperature of 2 inlet model.

**Figure 5.** The contour of (**a**) velocity and (**b**) temperature of 3 inlet model.

**Figure 6.** The contour of (**a**) velocity and (**b**) temperature of 4 inlet model.

The air entered the battery pack through the inlet on the left side and exited through the outlet on the right side while taking the heat generated by the batteries in the process. The arrows on the left side of the figure indicate the number and locations of the inlet and the airflow direction. The air velocity had its maximum value around the inlet as the nearest area to the cooling fan. It gradually decreased as it reached the outlet due to the decreasing kinetic energy. On the contrary, the battery temperature was at the minimum value around the inlet and gradually increased as it got further. This happened because the convective heat transfer decreased due to the rising temperature of the air as it traveled through the battery pack while taking the heat from the batteries. This phenomenon led to the temperature difference that resulted in different charging/discharging rates between battery cells, causing a heavy workload for BMS. Excessive workload caused inefficient equalization, especially for BMS with an active balancing method, leading to non-optimal power generation and reducing the batteries' lifespan faster. Ideally, the simulation result needs to be validated with an experiment, but obtaining velocity and temperature contour from an experiment might be challenging. However, the current simulation result was sufficient to show the temperature distribution, which represents the performance from each configuration.

The overall velocity and temperature results were represented by their average value. The average value of air velocity and batteries temperature from each configuration are plotted in Figure 7. The results generated showed that air velocity increased while the temperature decreased with the increasing number of inlets. The increase in the number of inlets meant an increase in the number of cooling fans. This led to more power pushing the air from the inlet to the outlet, resulting in higher air velocity and more air particles transferring the heat from the batteries. This condition, in turn, caused a lower temperature as the number of inlets increased. The lowest average temperature of 36.4 ◦C was achieved by the four inlets configuration; however, the maximum battery temperature was still 42.2 ◦C, which is higher than the maximum optimal temperature range of 40 ◦C. Therefore, an additional optimization strategy was needed for the air-cooled BTMS to meet the optimal

temperature requirement. In the next section, we varied the inlet air temperature and the number of inlets to obtain the optimum cooling strategy.

**Figure 7.** The average values of velocity and temperature vs. the number of inlets.
