The main points of liquid-cooled channel design are channel length-to-width ratio, channel shape and number, and solving the temperature difference between inlet and outlet. The research on these problems for conventional channels shows that increasing the number of channels can reduce the temperature difference between the maximum temperature and the battery module, but the improvement is limited and the energy consumption increases when increasing the number of channels. Increasing the aspect ratio of the channel within a certain range can also effectively reduce the maximum temperature of the lithium-ion battery pack and reduce the temperature difference. At the same time, the proposed wavy pipe can increase the contact area and improve the heat dissipation efficiency. In order to solve the temperature difference between the water inlet and the water outlet, the pipe can be split into two, and the direction of the water inlet is set to the opposite. In addition, when the number of batteries in the battery module is large, a parallel cooling structure should be used. A liquid cooling channel with longitudinal ribs is studied, and the effects of different rib length to width ratio and number on the performance of the cooling system are compared. The cross-section diagram is shown in FIG. 3. The four schemes designed are shown in Table 5. The paper compares the heat transfer coefficient, hydrothermal performance, mass flow rate, pumping power and power consumption ratio, in which the hydrothermal cooling performance index is calculated by equation. As shown in Table 6, the effect of scheme 4 is the best, which proves the feasibility of the design. Moreover, with the increase of the number of ribs, the heat dissipation efficiency is improved, while the improvement caused by the change of the aspect ratio of ribs is small.
Diagram of ribbed coolant channel
Ribbed coolant channel parameters
Liquid cooling and heat management systems generally use water, ethylene glycol or water-ethylene glycol mixture as the cooling medium. Changing the flow rate of coolant is an important factor in the research of liquid cooling system, and changing the flow rate can achieve different heat exchange efficiency, which is a key factor in the design of liquid cooling system. A battery thermal management system combining phase change material (PCM) and liquid cooling was studied. The latent heat of PCM was removed by coolant. The effects of different coolant flow rates on the performance of the thermal management system were compared. The experiment compared the maximum temperature and temperature difference of the lithium-ion battery pack at different flow rates between 0.05 and 0.4 m/s under the condition of charging rate of 0.5 C and discharge rate of 3 C (taking the average value of 3 cycles). The ambient temperature and inlet temperature are set to 40 °C. The experimental results show that as the flow rate increases from 0.05 m/s to 0.2 m/s, Tmax decreases from 49.17 ℃ to 47.5 ℃, and ΔTmax decreases from 7.43 ℃ to 6.41 ℃. When the speed is increased from 0.2 m/s to 0.4 m/s, the degree of reduction is reduced, and the increase in the flow rate can improve the heat dissipation performance of the system, but with marginal effect. Increasing the flow rate can reduce the maximum temperature of the battery module, but it may increase the maximum temperature difference between units of the battery, because the increase in the flow rate causes the coolant to take away more heat at the inlet, so that the battery near the outlet is not effective heat dissipation. In order to ensure the temperature consistency of the battery module, a set of gradient flow rate optimization strategy was proposed for the vertically distributed liquid cooling thermal management system. As shown in FIG. 4, the number of pipes around the battery is divided into three categories. Different categories of pipes are set with different flow rates, and a larger flow rate is set in the area with large heat dissipation demand. (2) The ambient temperature is 60 ° C, and the liquid medium temperature is 30 ° C. The experimental results show that there is little difference between Tmax and ΔTmax when the battery module reaches steady state. The heat exchange is mainly affected by the contact area and temperature difference, and the change of flow rate only affects the steady-state time of the battery module, but has little effect on the steady-state value. The experimental results show that increasing the flow gradient can reduce the ΔTmax of the module before the steady state stage, which is significantly improved compared with the case without the gradient flow rate. The gradient flow rate design also plays an obvious role in balancing the heat transfer efficiency of each part of the battery module.
Gradient flow rate liquid cooling system
Fuzzy PID cooling strategy
1.4 Application Mode of the liquid cooling systemThe three methods commonly used in the practical application of the liquid cooling cooling system are shown in Figure 6: First, the pipe containing the coolant is used to surround and contact each battery in the module to reduce the battery temperature and the temperature difference between batteries. This scheme is more suitable for cylindrical batteries [Figure 6(a)]; Second, the battery module is directly immersed in non-conductive coolant, which can cool all sides of the battery and help improve temperature consistency. Currently, it is commonly used in the server of supercomputing system, but it is rarely applied in the field of energy storage with high risk of leakage [Figure 6(b)]. Third, a cooling plate is placed between the battery or battery module, and there is a liquid microchannel in the cooling plate. This scheme is suitable for prismatic batteries or soft pack batteries [Figure 6(c)].
Three methods commonly used in the practical application of liquid cooled BTMS
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