Study on the influence of the shape of silica gel on the thermal performance of liquid cooled batteries Liu Yifan Liu Yifan 1, Zhou Jie 1, Huang Rui 1, sun Tianfei 1, Wang Huawen 2
(1. Shenzhen Graduate School of Tsinghua University, Shenzhen 518055, Guangdong; 2. Xinwangda Electronic Co., Ltd., Shenzhen 518108, Guangdong)
Liu Yifan (1995 -), male, born in Anhui Province, master's degree, mainly focuses on the structural design and optimization of battery thermal management of electric vehicles.
In the first issue in 2020, Liu Yifan, et al. From Shenzhen Graduate School of Tsinghua University, published the research on the influence of the shape of thermal conductive silica gel on the thermal performance of liquid cooled batteries
The main content of this article:
Starting from the application scenario of power battery pack, the finite element model of liquid cooled battery pack is established, and the influence of four kinds of conductive silica gel shapes on the thermal performance of battery pack is simulated and analyzed. It is found that with the decrease of the contact area between the conductive silica gel and the battery pack, the temperature of the battery pack increases, but the temperature difference is small. The main points of this paper are as follows:
1. Design a new type of liquid cooling structure
2. To evaluate the influence of different silica gel shape on the maximum temperature and temperature difference of liquid cooled battery module by model building and simulation analysis
Part of the excerpt is as follows:
At present, air, liquid or phase change materials are the main heat transfer media in the heat management design of power battery. For the liquid cooled type, the research focuses on the influence of the structure shape of the liquid cooled plate, serpentine tube and harmonica tube combined with the battery pack on the heat transfer efficiency [4]. In fact, the contact between the liquid cooled heat exchange structure and the battery interface is not completely close, and there is heat transfer resistance. Therefore, in order to maintain a good contact interface and reduce the contact heat resistance, the heat transfer components are used in the liquid cooled heat exchange structure. At present, the research on thermal conductivity components mainly focuses on the influence of new material components and their proportions on thermal conductivity. For example, the design of new graphene component thermal conductivity silica gel is used to enhance its thermal conductivity [5]. In fact, the shape of heat conduction component is very important for the design, application and evaluation of thermal management system of power battery. In this paper, a liquid cooling plate with "single in and single out" channel structure is designed for the square power battery module. The heat dissipation characteristics are studied under the condition of high temperature discharge. On the premise that the working temperature of the battery meets certain requirements, the influence of the shape of the heat conduction silica gel on the heat transfer effect of the battery group is studied. Figure 1 is the power battery group model.
1 theoretical analysis
The motion and heat transfer process of the fluid in the liquid cooled plate meet the laws of conservation of mass and energy [6].
2 model establishment and simulation analysis
2.1 model establishment
The square lithium-ion power battery pack developed by a battery company is adopted, and its appearance is shown in Figure 1. The battery module is composed of 12 monomers and fasteners in series. The nominal capacity is 37 ah, the nominal voltage is 43.8 V, the length × width × height is 355 mm × 151.5 mm × 108 mm. At the same time, in order to better monitor the temperature changes in the working process of the module, two temperature sensors need to be set on the surface of the module, and the location and number of the temperature sensors are shown in Figure 2.
For the battery module, a liquid cooling plate with single inlet and single outlet channel for heat transfer is designed, as shown in Figure 3. Based on the thermal conductivity of the fluid medium, glycol water solution with the ratio of 1:1 was selected as the coolant. In order to ensure the good contact between the battery module and the liquid cooling plate, the gap is filled with heat conducting material. The influence of the ratio, thickness and shape of heat conducting materials on the heat conducting effect. In order to achieve the compact structure of the battery thermal management system, the design requires that the material thickness is between 1-2 mm; the material components can be thermal conductive silicone grease, phase change material and thermal conductive silica gel, etc., and finally the thermal conductive silica gel with good adhesion and thermal conductivity stability is selected. Figure 3 shows the combination of the liquid cooling plate and the battery pack. The material is designed into different characteristic shapes (see Figure 4) for the battery pack, and its influence on the thermal characteristics of the battery pack is investigated.
2.2 simulation analysis
After the geometric model is established and repaired in the space claim software, HyperMesh software is imported for surface mesh generation and quality control. Because the size of thermal insulation pad and insulating film is small, which is not conducive to surface mesh generation, it is converted into equivalent thermal resistance for processing according to the principle of numerical heat transfer. Finally, the volume mesh is divided and solved in star-ccm + software. Among them, the turbulent flow of fluid is very complex, and the selected model equation depends on the specific situation. Table 1 shows the thermophysical parameters of each component.
3 results and discussion
After the numerical analysis of the liquid cooled battery module is carried out with different shape design scheme, the temperature field distribution of the battery module is shown in Figure 5. It can be seen from the figure that the square battery module has poor internal heat dissipation performance, which shows the trend of the highest temperature of the middle monomer and the lower temperature of the monomer on both sides of the module. With the decrease of the contact area between the conductive silica gel and the battery module, the lowest temperature of the battery module increases.
Although the distribution of the battery temperature field can be analyzed by the simulation results, the process of heat generation and heat dissipation of the battery can not be directly measured in the engineering application. Therefore, in order to further approach the engineering practice, this paper simulates the engineering application scenario of real-time recording the temperature change of the module by setting the temperature measuring points corresponding to the location of the temperature sensors of the battery module, so as to achieve the heat loss of the battery Provide reference for control design and prevention. Figure 6 shows the temperature measurement point value and temperature difference change under different design schemes.
It can be seen from Fig. 5 to Fig. 6 that the change trend of simulation results of schemes 1 to 3 is basically the same, but too large temperature difference of temperature measuring points of scheme 1 will shorten the cycle life of battery. Although the temperature difference of scheme 4 is the smallest, it will lead to the high temperature of the cell on the secondary side of the battery module, and also lead to the significant reduction of the cycle life of the battery. Compared with the change range of temperature difference in scheme 2, the change level of temperature difference in scheme 3 is only half of that in scheme 2. Therefore, the shape of silica gel designed in scheme 3 is the best scheme.
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