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A Liquid Cold Plate Design for Electric Vehicle Lithium Battery

Views: 142     Author: Site Editor     Publish Time: 2022-12-02      Origin: Site

Design a liquid-cooled plate for soft-pack lithium batteries of electric vehicles. Based on the determined internal channel direction and the orthogonal test design method, CFD software is used to study and analyze the effects of coolant flow rate (V), number of runners (N), runner width (W), and runner height (H) on the heat dissipation performance and pressure drop performance of the liquid cooled plate. The optimized structure of the liquid cooling plate is determined through the results of experimental design and simulation calculation, and its related performance is tested. The results show that the battery is in a reasonable temperature range and has an excellent temperature gradient under the heat dissipation state with an optimized structure, so the optimization is complete. On the basis of the optimization results, the alternate flow direction arrangement is studied, and the influence of the flow direction on the working performance of the liquid cold plate is analyzed. The comparison shows that the use of alternate flow scheme can make the battery have a better working temperature environment, which provides a reference for the design of the battery's liquid cooling plate.

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Battery thermal management has always been a hot topic of Winshare Thermal, which is divided into air, liquid and phase change material BTM. Air BTM has cost and structural advantages. However, studies have found that air cooling not only cannot effectively control the temperature gradient of battery cells, but also cannot cope with extreme conditions such as battery thermal runaway. BTM works through the latent heat of phase change and are currently limited to theoretical research ,but not widely used commercially. Liquid BTM have been widely adopted in recent years due to their advantages such as high heat transfer coefficient, large heat dissipation, and compact structure. A large number of experiments and simulations have found that liquid cooling has obvious advantages over air cooling.


A clamp-type liquid cooling plate with built-in micro-channels is designed for pouch batteries. The battery information and module layout are shown in Table 1 and Figure 1.

Liquid Cold Plate Design for Electric Vehicle

The surface size of the cold plate is the same as that of the battery, the thickness is 10 mm, and the material is aluminum alloy. Keep the direction and relative position of the central basic pipeline, and increase the number of pipelines at intervals of 2 mm. The lengths of each parallel pipeline are the same and the center is symmetrical, which is beneficial to simplify the follow-up flow direction research work.


The self-generated heat of lithium batteries includes internal reaction heat, polarization internal resistance heat, Ohms internal resistance heat and side reaction heat. The heat generation of the target battery is mainly Ohms internal resistance heat, so the Ohms internal resistance heat is approximately simplified as the total heat generation. The design working condition is that the battery is discharged at 2C rate from 100% SOC at 27°C.


The simulation model is mainly constructed based on ANSYS Fluent16.0. The boundary condition of the simulation is an initial ambient temperature of 300 K. The inlet port of the coolant is the flow rate inlet condition, and the temperature is consistent with the ambient temperature. The outlet port is under the pressure outlet condition, and the return pressure is 0 kPa. Except for the two sides that represent the heat generation of the battery, the other surfaces are set as adiabatic walls, which meaning the heat flux is 0.

liquid-cold-plate

The four parameters of coolant flow rate (V), number of runners (N), runner width (W), and runner height (H) are simulated in different combinations. The highest temperature, the largest temperature difference, and the pressure loss are used as indicators for evaluation. Considering cost and computational efficiency, an orthogonal experiment design widely used in practice is adopted to achieve ideal results.


Using 4 factors within a reasonable range constitutes an orthogonal table. According to the table, testing the level of each factor to examine the influence of each factor on the index and the interaction between factors, and find the optimal combination. The evaluation index adopts maximum temperature, maximum temperature difference and pressure loss to characterize the heat dissipation and hydraulic performance. The maximum temperature and maximum temperature difference refer to the maximum temperature and range of the battery surface at steady state. The pressure loss is the pressure difference between the inlet and outlet of the cold plate at this moment.


In order to independently study the influence of the number of runners on the cooling performance,changing the number of runners does not affect the flow of coolant while maintaining the other three factors. Different from common runner width studies, the actual runner width is expressed by the following formula.

Liquid Cold Plate Design for Electric Vehicle-1


As shown in Table 2, in the runner width column, previous data are the different levels of runner factor, and the data in the back brackets are the actual runner width.

Liquid Cold Plate Design for Electric Vehicle-2

The 4 sets of simulation results in Figure 2 show that the standard deviation fluctuations of maximum temperature, average temperature and pressure loss are less than 2%. In order to obtain more accurate results and surface temperature distribution,the gird with 251193 elements is selected for simulation.

Liquid Cold Plate Design for Electric Vehicle-3


It can be known from Table 2 that 16 groups of cold plates need to be simulated and compared. Comparing the data of maximum temperature, maximum temperature difference and pressure loss, it is found that the design of No. 16 can make the maximum temperature of the battery the lowest, No. 14 achieves the smallest temperature difference, and No. 3 liquid cold plate has the smallest pressure loss.


In addition, the influence degree of available factors on the corresponding indicators can be obtained by analyzing the mean value and mean range of each indicator. Figure 3 shows the extreme difference of the mean value of each indicator under different factors, and Rx (x=a, b, c) corresponds to the three indicators in turn. From the analysis results, it can be concluded that changing the number of flow channels can improve the control of the maximum temperature of the cold plate, and changing the flow rate can also realize the control of the maximum temperature difference Tdifference and pressure loss Ploss.

Liquid Cold Plate Design for Electric Vehicle-4


Figure 4 shows the fluctuation of each index with the change of factor level. The abscissa in the figure is sorted in order of value. As shown in the figure, the maximum temperature decreases monotonically with the increase of coolant flow rate, number of runners, and runner width. The analysis results can prove that for the maximum temperature index, the number of runners and the flow rate are the main factors. The increase of the flow rate will cause a rapid increase of the pressure loss, and increasing the width of the flow channel can improve this situation.

Liquid Cold Plate Design for Electric Vehicle-5

It is worth mentioning that, based on the good pipeline layout scheme and the physical properties of the coolant, the temperature difference data of each factor is less than 2K, showing good uniformity. The factors of pressure loss have mutual offset effect. Therefore, in the optimization design, the index reference sequence when selecting the level of each factor should be the highest temperature , pressure loss and maximum temperature difference.


To sum up, the optimized level combination adopted in this paper is V=0.3 m/s, N=4, W=6 mm, H=5 mm, and named as optimum. Figure 5 is a data comparison of the maximum temperature, maximum temperature difference, pressure loss and other indicators obtained by optimization and other 16 groups of structural simulations. Under the heat dissipation work of the optimized structure, the maximum temperature and temperature difference of the battery surface are both within the suitable working range of the battery. Although the optimized structure is in the middle of the pressure loss, the value is less than 5 kPa, which is still in a reasonable range. After index comparison, the optimal structure can keep the maximum temperature of the battery within a reasonable range and the temperature gradient is small. At the same time, it can also meet the actual application requirements in the current engineering field in terms of voltage drop. Therefore, the effect of optimizing the design of the liquid cooled plate by using the orthogonal test design method is ideal. The current setting only considers the working performance when the ambient temperature is 300K, and other extreme working conditions need to be further explored.

Liquid Cold Plate Design for Electric Vehicle-6Liquid Cold Plate Design for Electric Vehicle-7Liquid Cold Plate Design for Electric Vehicle-8


The influence of flow direction on cooling performance is studied by optimizing structure of the cold plate, and the practical application of alternate flow direction arrangement scheme is explored.


From the comparison of 16 alternative flow direction schemes, it is found that when the inlet flow rate is constant, the use of alternate flow direction schemes can improve the uniformity of battery temperature to a certain extent, but the extreme temperature changes are small.


The reasons are as follows

(1) Improve the battery temperature non-uniformity caused by the inlet and outlet settings by changing the flow direction of some pipelines. When the flow rate is constant, the amount of coolant participating in heat exchange per unit time does not change. Due to the physical properties of the coolant, the alternative solution cannot improve the absolute heat dissipation capacity, so the effect on extreme temperatures is limited.

(2) The optimized structure above improves the effective heat dissipation area and has better cooling performance. The improvement of extreme temperature is not obvious by adopting the alternating scheme, but the improvement of temperature difference is relatively obvious.

(3) Although the structure of the liquid cold plate itself can make the temperature difference of the battery within the ideal range, the comparison can still find the optimal case, and the temperature uniformity of the initial case has increased by about 20%.


Battery Cooling Plate

Through the experimental data and temperature conditions, it is found that the alternate scheme of double-tube counterflow can improve the temperature uniformity of the battery surface. Considering that the alternate arrangement scheme of clamping cold plates is not conducive to grouping, this optimization scheme keeps the original flow direction instead of using the alternate scheme. For the exploratory experiments of alternative schemes, a direction for optimization of liquid-cooled plates is provided. For larger batteries, the alternate flow direction scheme is a scheme that can improve the uniformity of the cells, which can provide better battery thermal management for long strip batteries such as blade batteries, and ensure safe operation of the battery.


Taking the soft-packed lithium-ion battery of electric vehicles as the object, the design and parameter optimization of the liquid cooling plate are carried out, and the influence of different parameters on the cooling performance is studied.

(1) Design and establish the geometric model of the liquid cold plate. Study the heating principle of lithium-ion batteries and analyze the heat transfer process. Complete the preliminary work of the initial liquid cold plate structure design and simulation.

liquid-cooling-plate

(2) Orthogonal experimental design was used to optimize the cold plate. Taking the maximum temperature, maximum temperature difference and pressure loss as evaluation indicators, coolant flow rate (V), number of runners (N), runner width (W), runner height (H) and four different levels are selected to form an orthogonal table. Using ANSYS Fluent 16.0 simulation to comprehensively analyze the influence of each factor on the index, the optimal parameter combination is determined to be V=0.3 m/s, N=4, W=6 mm, H=5 mm. Through comparison, the optimized design performed well in terms of heat dissipation performance and pressure drop, so that the battery was at a reasonable temperature and the gradient was suitable, and the optimized design was completed. However, the working performance and performance of the cold plate at other extreme ambient temperatures still needs to be further explored.


(3) Based on the optimized design structure, research is carried out on the alternate flow direction arrangement scheme, and the influence of flow direction on the heat dissipation performance is explored. The simulation test analysis found that the alternate flow direction arrangement can improve the temperature uniformity of the battery. This solution can be applied to new types of batteries that generate more heat and require higher temperature uniformity in the future.

 
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