In recent years, the rapid development of pure electric vehicles has placed increasing demands on charging infrastructure and grid stability. The intermittent nature of renewable energy sources such as wind and solar power necessitates the deployment of energy storage stations to perform peak shaving and frequency regulation. Lithium-ion batteries, owing to their high energy density, long cycle life, and lightweight characteristics, have become the primary choice for electrochemical energy storage systems. However, thermal management remains a critical challenge, as excessive temperature rise and uneven temperature distribution can significantly degrade battery performance and lifespan. My research focuses on an innovative cooling approach that combines spray cooling with forced ventilation to enhance the thermal management of energy storage batteries. In this study, I designed and constructed an experimental apparatus using deionized water as the cooling medium, and systematically investigated the effects of air velocity, spray flow rate, and discharge rate on battery temperature behavior. The experimental results demonstrate that the coupled spray and ventilation cooling system effectively suppresses temperature rise, and I have identified optimal operating parameters that balance cooling performance with energy consumption. This work provides valuable insights for the design and optimization of thermal management systems in practical energy storage applications.
Experimental System and Methodology
To investigate the thermal behavior of energy storage batteries under spray and ventilation coupled cooling, I designed a dedicated experimental setup. The test section consisted of an aluminum block with dimensions of 20 mm × 100 mm × 140 mm, corresponding to a volume of 280 cm³, which was used to simulate the heat generation of a real battery. The heating power was precisely controlled using a voltage regulator, and I set the power to 12.5 W for all experiments unless otherwise specified. This value was determined based on the theoretical heat generation rate of a lithium iron phosphate battery with a capacity of 11.2 Ah and a nominal voltage of 3.2 V under 3 C discharge conditions, which yields a theoretical power of approximately 10.752 W. The choice of 12.5 W as the experimental power point was made for several practical reasons: it corresponds to a standard adjustable power level on the regulator, facilitating precise control and experimental repeatability; moreover, the volumetric heat generation rate of 0.0446 W/cm³ falls well within the standard range of 0.03–0.08 W/cm³ specified for 3 C discharge of lithium iron phosphate batteries, ensuring that the thermal behavior observed in the experiments is representative of real-world conditions.
The cooling system comprised two main components: a spray generation unit and a variable-speed fan. The spray unit utilized deionized water as the working fluid, and the spray flow rate was controlled by adjusting the operating pressure. The actual spray flow rate was determined by measuring the mass change of the water reservoir before and after each experiment. The fan provided forced air flow through the test section, with the air velocity adjustable in the range of 0.5 to 3 m/s. The inlet air temperature was maintained at 300 K throughout the experiments.
Temperature measurements were performed using five T-type thermocouples placed at strategic locations on the battery surface: the four corners and the center. These thermocouples were connected to an Agilent 34972A data acquisition system, which recorded temperature readings at regular intervals throughout the experimental period. The discharge duration for all experiments was set to 1200 seconds, corresponding to a 3 C discharge rate unless otherwise specified. I conducted experiments under various combinations of air velocity, spray flow rate, and discharge rate to systematically evaluate the cooling performance.
The key experimental parameters and their ranges are summarized in Table 1.
| Parameter | Symbol | Unit | Range |
|---|---|---|---|
| Heating power | P | W | 12.5 |
| Inlet air temperature | Tin | K | 300 |
| Air velocity | v | m/s | 0.5 – 3.0 |
| Spray flow rate | ṁ | g/s | 0 – 0.5 |
| Discharge rate | C | — | 1, 2, 3 |
| Discharge duration | t | s | 1200 |
Data Processing and Uncertainty Analysis
To evaluate the thermal management performance, I defined two key temperature metrics based on the five thermocouple readings. The maximum temperature difference across the battery surface was calculated as:
$$
\Delta T = \max(T_{w1}, T_{w2}, T_{w3}, T_{w4}, T_{w5}) – \min(T_{w1}, T_{w2}, T_{w3}, T_{w4}, T_{w5})
$$
where Tw1 through Tw5 represent the temperatures measured at the four corners and the center of the battery surface, respectively. The average temperature was computed using:
$$
T_{ave} = \frac{T_{w1} + T_{w2} + T_{w3} + T_{w4} + T_{w5}}{5}
$$
These two metrics provide a comprehensive description of both the overall temperature level and the temperature uniformity of the energy storage battery surface.
Uncertainty analysis was performed to quantify the measurement errors. All instruments used in the experiments were of Grade 1 accuracy. The T-type thermocouples were calibrated against a thermometer with a minimum scale of 0.1 °C before the experiments. The data acquisition system had a specified accuracy of 0.3 °C. Based on the principle of random error propagation, the combined uncertainty of the temperature measurement system was calculated to be 0.32 °C. The uncertainty in spray flow rate measurement, determined from the mass change measurement, was estimated to be within ±2% of the measured value. Air velocity was measured using a hot-wire anemometer with an accuracy of ±0.1 m/s.
Results and Discussion
Effect of Air Velocity on Battery Temperature
I first investigated the effect of air velocity on the cooling performance under pure air cooling conditions (zero spray flow rate) at a discharge rate of 3 C. The inlet air temperature was maintained at 300 K. Figure 2 in the original study shows the variation of maximum temperature and maximum temperature difference with air velocity. As the air velocity increased from 0.5 m/s to 3 m/s, the maximum battery surface temperature decreased from 327.3 K to 308.3 K, representing a significant reduction of 19 K. This substantial temperature drop demonstrates the effectiveness of forced convection in removing heat from the battery surface.
The underlying mechanism is that increasing the air velocity enhances the turbulent intensity in the flow channel, thereby improving the convective heat transfer coefficient between the air and the battery surface. Additionally, higher air velocity brings a greater mass flow rate of cool air into contact with the battery, enabling more efficient heat removal. Conversely, at low air velocities, the airflow disturbance is weak, and the air remains in contact with the battery surface for a longer period, absorbing more heat and reducing the temperature difference between the air and the surface. This diminished temperature gradient leads to lower convective heat transfer efficiency, resulting in higher battery temperatures.
The maximum temperature difference across the battery surface also decreased with increasing air velocity, indicating improved temperature uniformity at higher flow rates. This is a critical observation because temperature gradients within an energy storage battery can lead to uneven aging and reduced cycle life. The quantitative relationship between air velocity and temperature metrics is summarized in Table 2.
| Air Velocity (m/s) | Maximum Temperature (K) | Maximum Temperature Difference (K) |
|---|---|---|
| 0.5 | 327.3 | 8.2 |
| 1.0 | 318.0 | 6.5 |
| 1.5 | 313.5 | 5.2 |
| 2.0 | 310.8 | 4.3 |
| 2.5 | 309.2 | 3.8 |
| 3.0 | 308.3 | 3.5 |
From Table 2, I observed that the rate of temperature decrease diminished as air velocity increased. The cooling enhancement from increasing velocity from 0.5 to 1.0 m/s was more pronounced than from 2.5 to 3.0 m/s. This diminishing returns behavior suggests that there exists an optimal air velocity range beyond which further increases yield marginal benefits while consuming more fan power. Considering the trade-off between cooling performance and energy consumption, I recommend an air velocity range of 1–2 m/s for practical applications.
Effect of Spray Flow Rate on Battery Temperature
To evaluate the additional benefit of spray cooling, I conducted experiments with varying spray flow rates while maintaining a constant air velocity of 1 m/s and a discharge rate of 3 C. The results are presented in Table 3. When only air cooling was applied (ṁ = 0 g/s), the maximum battery temperature reached 318.0 K. Introducing spray cooling at a flow rate of 0.1 g/s reduced the maximum temperature to 315.1 K, a decrease of 2.9 K. Increasing the spray flow rate further to 0.5 g/s brought the maximum temperature down to 314.1 K.
The cooling enhancement from spray cooling arises from two physical mechanisms: sensible heat absorption by the liquid water as it heats up from its initial temperature to the evaporation point, and latent heat absorption during the phase change from liquid to vapor. The latent heat of vaporization of water is approximately 2400 kJ/kg, which is about 9 to 11 times the latent heat of fusion of typical phase change materials like paraffin wax. This enormous heat absorption capacity makes evaporative cooling highly effective for thermal management of energy storage batteries.
| Spray Flow Rate (g/s) | Maximum Temperature (K) | Maximum Temperature Difference (K) |
|---|---|---|
| 0 | 318.0 | 6.5 |
| 0.1 | 315.1 | 4.8 |
| 0.2 | 314.6 | 4.7 |
| 0.3 | 314.3 | 4.6 |
| 0.4 | 314.2 | 4.6 |
| 0.5 | 314.1 | 4.6 |
Notably, the temperature reduction exhibited a diminishing returns pattern as the spray flow rate increased. The decrease from 0 to 0.1 g/s produced a significant temperature drop of 2.9 K, while the additional decrease from 0.1 to 0.2 g/s was only 0.5 K. Beyond 0.2 g/s, further increases in spray flow rate resulted in negligible temperature changes, with only 0.15 K reduction observed from 0.3 to 0.5 g/s. This saturation behavior can be explained by the limited evaporation capacity of the air at a given velocity and temperature. Once the air becomes nearly saturated with water vapor, additional spray droplets cannot evaporate effectively and simply fall to the bottom of the test section without contributing to heat removal.
The maximum temperature difference across the battery surface also decreased slightly with increasing spray flow rate, from 6.5 K at zero spray to approximately 4.6 K at spray rates above 0.2 g/s. This improvement in temperature uniformity is beneficial for extending the cycle life of energy storage batteries, as uneven temperature distribution is a known cause of accelerated aging.
Interaction Effects Between Air Velocity and Spray Flow Rate
In practical cooling systems, air velocity and spray flow rate do not act independently; rather, they interact in complex ways to determine the overall cooling performance. I conducted a series of experiments to investigate this coupling effect by varying both parameters systematically. Tables 4, 5, and 6 present the maximum temperature, average temperature, and maximum temperature difference, respectively, for different combinations of air velocity and spray flow rate.
| Spray Flow Rate (g/s) | v = 0.5 m/s | v = 1.0 m/s | v = 2.0 m/s | v = 3.0 m/s |
|---|---|---|---|---|
| 0 | 327.3 | 318.0 | 310.8 | 308.3 |
| 0.1 | 320.1 | 315.1 | 309.3 | 307.4 |
| 0.2 | 319.2 | 314.6 | 309.1 | 307.2 |
| 0.3 | 318.8 | 314.3 | 309.0 | 307.1 |
| 0.4 | 318.6 | 314.2 | 308.9 | 307.0 |
| 0.5 | 318.5 | 314.1 | 308.8 | 307.0 |
From Table 4, I observed that at low air velocity (0.5 m/s), the effect of spray cooling was most pronounced. Increasing the spray flow rate from 0 to 0.1 g/s reduced the maximum temperature by 7.2 K, and further increases continued to provide noticeable cooling benefits. This is because at low air velocity, the spray droplets have sufficient residence time in the air stream to evaporate fully and absorb heat effectively. In contrast, at high air velocities (2 m/s and above), the cooling benefit of spray was greatly diminished. At v = 3 m/s, increasing the spray flow rate from 0 to 0.1 g/s reduced the maximum temperature by only 0.9 K, and further increases had virtually no effect.
This interaction can be explained by the residence time of spray droplets in the flow field. At high air velocities, the droplets are rapidly swept away by the airflow before they have sufficient time to evaporate completely. Consequently, a significant portion of the sprayed water leaves the system without contributing to heat removal, resulting in inefficient water usage and limited cooling enhancement.
| Spray Flow Rate (g/s) | v = 0.5 m/s | v = 1.0 m/s | v = 2.0 m/s | v = 3.0 m/s |
|---|---|---|---|---|
| 0 | 324.8 | 316.2 | 309.5 | 307.1 |
| 0.1 | 318.4 | 313.7 | 308.3 | 306.5 |
| 0.2 | 317.6 | 313.3 | 308.1 | 306.3 |
| 0.3 | 317.3 | 313.1 | 308.0 | 306.2 |
| 0.4 | 317.1 | 313.0 | 307.9 | 306.2 |
| 0.5 | 317.0 | 312.9 | 307.9 | 306.1 |
The average temperature trends in Table 5 mirror those of the maximum temperature, confirming that the coupled cooling system provides uniform thermal management across the entire battery surface. The diminishing returns of spray cooling at high air velocities are again evident.
| Spray Flow Rate (g/s) | v = 0.5 m/s | v = 1.0 m/s | v = 2.0 m/s | v = 3.0 m/s |
|---|---|---|---|---|
| 0 | 8.2 | 6.5 | 4.3 | 3.5 |
| 0.1 | 5.8 | 4.8 | 3.6 | 3.2 |
| 0.2 | 5.5 | 4.7 | 3.5 | 3.1 |
| 0.3 | 5.3 | 4.6 | 3.5 | 3.0 |
| 0.4 | 5.2 | 4.6 | 3.4 | 3.0 |
| 0.5 | 5.2 | 4.6 | 3.4 | 3.0 |
Table 6 reveals that the maximum temperature difference across the battery surface is influenced by both air velocity and spray flow rate. Higher air velocities consistently reduced the temperature difference, indicating improved temperature uniformity. The addition of spray cooling also contributed to uniformity, particularly at low air velocities. For instance, at v = 0.5 m/s, increasing the spray flow rate from 0 to 0.1 g/s reduced the temperature difference from 8.2 K to 5.8 K, a substantial improvement. At higher air velocities, the effect of spray on temperature uniformity was less pronounced.
Based on the comprehensive analysis of these interaction effects, I determined that the optimal operating window for the spray and ventilation coupled cooling system is an air velocity range of 1–2 m/s combined with a spray flow rate of 0.1–0.2 g/s. Within this range, the system achieves effective cooling performance while minimizing water and energy consumption. Operating outside this window either wastes resources (excessive spray at low air velocity) or provides marginal benefits (high air velocity with excessive spray).
Effect of Discharge Rate on Battery Temperature
Energy storage batteries in practical applications must operate under varying load conditions, which translates to different discharge rates. I investigated the cooling performance of the coupled system under three different discharge rates: 1 C, 2 C, and 3 C, while maintaining a constant spray flow rate of 0.1 g/s. Tables 7, 8, and 9 present the maximum temperature, average temperature, and maximum temperature difference for these conditions.
| Air Velocity (m/s) | 1 C Discharge | 2 C Discharge | 3 C Discharge |
|---|---|---|---|
| 0.5 | 303.1 | 310.5 | 320.1 |
| 1.0 | 302.2 | 307.8 | 315.1 |
| 2.0 | 301.6 | 305.2 | 309.3 |
| 3.0 | 301.4 | 303.9 | 307.4 |
The data in Table 7 clearly demonstrate that the discharge rate has a profound impact on battery temperature. At the lowest air velocity of 0.5 m/s, the maximum temperature increased from 303.1 K at 1 C to 310.5 K at 2 C and further to 320.1 K at 3 C. This substantial temperature rise at higher discharge rates is due to the increased heat generation rate, which scales approximately with the square of the current. The cooling system must therefore be designed to handle the most demanding operating conditions.
Importantly, I observed that at 1 C discharge, even the lowest air velocity of 0.5 m/s with minimal spray cooling maintained the battery temperature at 303.1 K, which is well within the safe operating temperature range for lithium-ion batteries. This finding has practical significance: for low-rate applications, a simple air cooling system may suffice, and the spray cooling module can be deactivated to save energy and water. This provides a clear design boundary for dynamic cooling strategies in energy storage systems.
| Air Velocity (m/s) | 1 C Discharge | 2 C Discharge | 3 C Discharge |
|---|---|---|---|
| 0.5 | 302.3 | 309.1 | 318.4 |
| 1.0 | 301.6 | 306.6 | 313.7 |
| 2.0 | 301.1 | 304.3 | 308.3 |
| 3.0 | 300.9 | 303.2 | 306.5 |
The average temperature trends in Table 8 follow the same pattern as the maximum temperature, reinforcing the conclusion that higher discharge rates demand more aggressive cooling strategies. The coupled spray and ventilation system demonstrates its capability to handle the increased thermal load at 3 C discharge, albeit with higher energy and water consumption.
| Air Velocity (m/s) | 1 C Discharge | 2 C Discharge | 3 C Discharge |
|---|---|---|---|
| 0.5 | 2.4 | 5.0 | 5.8 |
| 1.0 | 1.8 | 3.6 | 4.8 |
| 2.0 | 1.4 | 1.8 | 3.6 |
| 3.0 | 1.2 | 1.3 | 3.2 |
Temperature uniformity, as quantified by the maximum temperature difference in Table 9, deteriorated at higher discharge rates. At 1 C discharge, the temperature difference remained below 2.5 K for all air velocities, indicating excellent uniformity. At 3 C discharge, however, the temperature difference reached 5.8 K at the lowest air velocity, which approaches the recommended limit of 5 K for maintaining battery health. Increasing the air velocity to 3 m/s reduced this to 3.2 K, demonstrating the effectiveness of forced convection in improving temperature uniformity even under high thermal load.
The quantitative data from these experiments provide clear guidance for the design of adaptive cooling strategies. For energy storage batteries that operate under variable load conditions, the cooling system should modulate both air velocity and spray flow rate in response to the real-time discharge rate. At low discharge rates (≤ 1 C), the spray module can be safely deactivated, and the fan speed can be reduced to minimize energy consumption. At high discharge rates (≥ 3 C), both air velocity and spray flow rate should be increased to prevent excessive temperature rise and maintain temperature uniformity within acceptable limits.
Engineering Challenges and Future Perspectives for High-Voltage Battery Pack Applications
The experimental results presented in this study demonstrate the thermal management efficacy of the spray and ventilation coupled cooling system at the single-cell level. However, translating this technology to practical high-voltage energy storage battery packs, which typically consist of hundreds of cells connected in series and parallel, requires careful consideration of electrical safety challenges, particularly those related to moisture-induced insulation degradation and high-voltage breakdown risks. The introduction of atomized water droplets into the battery enclosure inevitably increases the ambient humidity, which can reduce the dielectric strength of air and increase its electrical conductivity. In the presence of insulation defects, such as contaminated connectors or damaged cable insulation, the high-humidity environment can promote leakage currents and creepage phenomena, potentially leading to localized arcing or insulation failure that poses serious safety hazards to the entire energy storage system.
To ensure the safe application of spray and ventilation cooling technology in high-voltage battery packs, future system designs must incorporate multiple layers of safety redundancy. First, enhanced insulation design is essential: battery modules should be enclosed in housings with IP67 or higher protection ratings, and high-voltage components such as busbars and connectors must maintain adequate creepage distances and electrical clearances that comply with relevant safety standards. Second, material and process innovations can play a crucial role: applying hydrophobic or moisture-repellent coatings to the interior surfaces of the battery enclosure, module casings, and high-voltage components can effectively reduce water condensation and adhesion, physically preventing the formation of continuous moisture films that could create conductive paths. Third, system-level safety interlocking is necessary: the cooling control system should be deeply integrated with the battery management system and the energy storage converter. Real-time monitoring of both global and local humidity levels, as well as insulation resistance, should be implemented. Upon detection of humidity exceeding safe thresholds or insulation faults, the battery management system should execute a graded response strategy, such as first deactivating the spray system while enhancing ventilation, and if the situation does not improve, limiting the system power or performing a safe shutdown. Safety must always take precedence over cooling performance in the control logic.
In summary, while the spray and ventilation cooling technology is thermodynamically efficient for thermal management of energy storage batteries, its application in high-voltage systems presents significant electrochemical safety challenges. The ultimate engineering feasibility of this technology will depend on achieving a synergistic optimization between thermal management performance and the cost and complexity of the safety protection systems. Future research should focus on multi-physics coupling validation at the module and system levels, with particular emphasis on developing anti-condensation control strategies and addressing high-voltage insulation reliability in high-humidity environments. These efforts are essential to advance this promising cooling technology toward safe and reliable practical deployment.
Conclusions
Through systematic experimental investigation of the spray and ventilation coupled cooling system for energy storage batteries, I have drawn the following key conclusions. First, under 3 C discharge conditions, increasing the air velocity is an effective means of reducing both the maximum temperature and the temperature gradient across the battery surface. However, the cooling enhancement exhibits diminishing returns at high velocities, and I recommend an air velocity range of 1–2 m/s to balance cooling performance with fan energy consumption.
Second, the introduction of spray cooling provides significant additional temperature suppression compared to pure air cooling. The optimal spray flow rate was found to be 0.1–0.2 g/s, as further increases beyond this range yielded negligible cooling benefits due to the saturation of evaporation capacity in the air stream. The coupled cooling system achieves its best performance within the combined parameter window of 1–2 m/s air velocity and 0.1–0.2 g/s spray flow rate.
Third, the discharge rate has a substantial impact on battery temperature, with higher rates requiring more aggressive cooling. Importantly, I found that at discharge rates of 1 C and below, air cooling alone is sufficient to maintain battery temperatures within safe limits. This provides a clear design boundary for dynamic cooling strategies: the spray module can be deactivated when the discharge rate falls below 1 C, thereby improving overall system energy efficiency.
Fourth, while this study confirms the thermal management advantages of the spray and ventilation coupled cooling approach, its practical application in high-voltage energy storage battery packs must be preceded by thorough electrical safety design. Future work should focus on multi-physics coupling validation at the module and system levels, addressing critical issues such as anti-condensation control strategies and high-voltage insulation reliability under humid conditions. These efforts will be crucial for the safe and reliable transition of this technology from laboratory research to real-world engineering applications.