Abstract
High power cylindrical Ni-MH battery cells have a heavy heat load because of their high discharge rate and large equivalent internal resistance. This heavy heat load, together with an imbalanced flow in parallel liquid cooling systems, can lead to variances in the temperature of each cell in the entire battery pack, thereby reducing the life cycle of the battery pack. In this paper, a parallel-series combined liquid cooling system for a 288V Ni-MH battery pack was designed, and several parameters that influence the flow balance of the system by heat transfer and fluid dynamics were calculated. Then, a thermal-fluid simulation was executed with different parameters using StarCCM+ software, and the simulation results were validated by a battery pack temperature experiment on a bench and in a vehicle. The results indicate that the cell’s temperature and temperature differences can be kept within an ideal range. We also determined that within the battery power requirements and structural spacing limits, the total flow rate of the cooling liquid, the cross-sectional area ratio of the main pipe to the branch pipes, and the number of internal supporting walls in each branch pipe need to be large enough to minimize the cell’s maximum temperature and temperature differences.
Highlights
In recent years, the market of novel energy vehicles, including electric vehicles and hybrid electric vehicles, has grown fast [1,2]
Pesaran et al [12] noted that Ni-MH and Li-ion batteries’ ideal operating temperatures range from 25 to 40 ◦ C, and the temperature differences between the cells within a battery pack should be below 5 ◦ C
Plenty of works have been done in the field of battery thermal management system for commercially sold electric vehicles (EVs) and hybrid electric vehicles (HEVs) in the market, such as direct air cooling, liquid cooling, phase change material, heat pipes, hybrid cooling system and other emerging cooling technologies
Summary
The market of novel energy vehicles, including electric vehicles and hybrid electric vehicles, has grown fast [1,2]. A large quantity of battery cells will generate a large amount of heat and cause temperatures to rise during the charge and discharge process [5,6]. A cell’s voltage, energy, efficiency, and life cycle are deeply influenced by its operating temperature [7,8]. At temperatures exceeding 50 ◦ C, charging efficiency and battery life deteriorate the most rapidly due to heat [10,11]. It is necessary to pay more attention to the research of battery thermal management system (BTMS), which is very important for battery performance, life and safety. Pesaran et al [12] noted that Ni-MH and Li-ion batteries’ ideal operating temperatures range from 25 to 40 ◦ C, and the temperature differences between the cells within a battery pack should be below 5 ◦ C
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