Key Takeaways & Executive Findings
- •• • Under progressive acceleration at 35°C, the direct cooling system without fins fails: maximum surface temperature reaches 49.8°C and maximum temperature difference 16.5°C, exceeding safe control ranges and risking thermal runaway. • • Adding aluminum fins reduces maximum temperature from 49.8°C to 40.9°C (a 8.9°C drop) and temperature difference from 16.5°C to 5.0°C (a 11.5°C reduction), demonstrating effective thermal homogeneity improvement. • • Longitudinal temperature difference decreases from 11.2°C to 4.6°C (58.9% reduction) and transverse from 5.9°C to 1.2°C (79.7% reduction) with fins, indicating enhanced heat conduction in both directions. • • The direct cooling system with fins meets temperature control requirements under all tested dynamic conditions (steady, alternating load, progressive acceleration) at ambient temperatures of 25, 30, and 35°C, ensuring battery safety and longevity.
Abstract
Lithium-ion batteries are widely used in electric vehicles due to their high energy density, long cycle life, and stability. However, significant heat generation caused by power fluctuations under dynamic driving conditions poses substantial challenges to battery safety and longevity. Existing research often focuses on thermal behavior under fixed ambient temperatures or constant discharge rates, failing to replicate real-world dynamic operations. This study investigates the thermal performance of a 52 Ah battery pack under three typical dynamic operating conditions: steady operation, alternating load operation, and progressive acceleration. Experiments were conducted at ambient temperatures of 25, 30, and 35°C. Results show that the direct cooling thermal management system meets temperature control requirements during steady and alternating load operations at all tested temperatures. However, under progressive acceleration at 35°C, the battery pack's maximum surface temperature reaches 49.8°C with a significant temperature difference of 16.5°C, exceeding safe limits. After installing aluminum fins, the maximum temperature is reduced to 40.9°C, and the temperature difference drops to 5.0°C. Longitudinal temperature difference decreases from 11.2°C to 4.6°C, and transverse temperature difference from 5.9°C to 1.2°C. The fins enhance longitudinal heat conduction and mitigate transverse temperature imbalance. These findings underscore the importance of optimizing thermal management strategies and provide experimental data for developing more effective systems, contributing to improved battery safety and longevity under real-world driving conditions.
1. Introduction
Electric vehicles rely on lithium-ion batteries for their high energy density and long cycle life, yet dynamic driving conditions—such as rapid acceleration and deceleration—generate intense heat that can accelerate degradation and trigger thermal runaway. Conventional thermal management studies typically evaluate battery behavior under fixed ambient temperatures or constant discharge rates, which do not capture the fluctuating thermal loads encountered in real-world operation. This gap leaves commercial battery thermal management systems (BTMS) vulnerable to temperature inhomogeneity, leading to localized overheating and reduced pack lifespan.
This study addresses this bottleneck by experimentally evaluating a direct cooling BTMS on a 52 Ah battery pack under three representative dynamic operating conditions: steady operation, alternating load, and progressive acceleration. The research quantifies thermal performance using metrics such as maximum surface temperature (Tmax), cell-to-cell temperature difference (ΔTcell), and pack-level temperature difference (ΔTpack). Critically, the study introduces aluminum fins as a passive enhancement to improve thermal homogeneity. The experimental protocol directly replicates real-world dynamic loads, providing actionable data for designing robust BTMS that ensure safety and longevity under actual driving conditions.
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ZHU Xijiao, MA Xiaona, YAN Huaxia, CHEN Yi (2026). Improvement of Homogeneity for Direct Cooling Battery Thermal Management System in Electric Vehicles under Dynamic Operating Conditions. The Chinese Journal of Process Engineering. https://doi.org/10.12034/j.issn.1009-606X.225159
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Frequently Asked Questions
What are the specific thermal limits that the direct cooling system fails to meet under progressive acceleration, and how do fins address them?
Under progressive acceleration at 35°C, the system without fins reaches a maximum surface temperature of 49.8°C and a maximum temperature difference of 16.5°C, exceeding safe operational thresholds. Adding aluminum fins reduces the maximum temperature to 40.9°C and the temperature difference to 5.0°C, bringing the system within acceptable limits for battery safety and performance.
How do fins affect longitudinal and transverse temperature differences, and what are the quantitative improvements?
Fins reduce longitudinal temperature difference from 11.2°C to 4.6°C (a 58.9% reduction) and transverse temperature difference from 5.9°C to 1.2°C (a 79.7% reduction). This indicates enhanced heat conduction along the battery pack, mitigating both vertical and horizontal thermal imbalances.
Does the direct cooling system with fins maintain performance across different ambient temperatures?
Yes, with fins, the system meets temperature control requirements under all tested dynamic conditions at ambient temperatures of 25, 30, and 35°C. For example, at 35°C, the maximum temperature is 40.9°C, and the pack temperature difference is 5.0°C, demonstrating robust performance across a range of environmental conditions.
What are the implications of these findings for scaling up to larger battery packs or real-world EV applications?
The experimental data provide a benchmark for designing direct cooling systems with fins to ensure thermal homogeneity under dynamic loads. The quantitative improvements in temperature uniformity suggest that fin-enhanced direct cooling can be scaled to larger packs, potentially reducing the risk of thermal runaway and extending battery life in real-world driving scenarios.
What are the potential trade-offs of adding fins, such as increased weight or cost, and how do they compare to the thermal benefits?
While the study does not provide cost or weight analysis, the thermal benefits are substantial: a reduction of 8.9°C in maximum temperature and 11.5°C in temperature difference. In automotive applications, the added weight and cost of aluminum fins are likely justified by improved safety and longevity, but a detailed cost-benefit analysis would be necessary for commercial deployment.
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