| Lithium-ion battery has become the main power source for electric vehicles because of the imprisonment in safety,specific energy and power,and cycle life.However,the temperature and local temperature difference of the batteries must be maintained within a suitable range to ensure the safety and ideal operating performance.An efficient battery thermal management system is deemed essential for this purpose.In this study,a compact cylindrical lithium-ion battery module was designed for a blade electric vehicle,and a liquid cooling scheme for the battery module was proposed by using multi-channel wavy tube.The battery module consists of 8 battery groups connected in series,with each group comprising 30 pieces of 18650 lithium-ion batteries connected in parallel.An aluminum wavy tube is embedded into the battery module to act as a separator and fixture between the batteries,and both sides of the wavy tube are in close contact with the cylindrical sides of 2 rows of batteries.The wavy tube has a wavy profile,and the curvature radius of each wavy contour is equal to that of the battery casing to guarantee reliable thermal contact with the cylindrical batteries.The inlet and outlet are set at the two ends of the wavy tube,and the coolant flows into the wavy tube from the inlet and is shunted into these parallel channels under working conditions.Three-dimensional transient simulations were conducted for the proposed battery module,based on the physical parameters and thermal model of the battery.Numerical optimizations were performed by varying the parameters that have great influence on the heat dissipation performance of battery module,namely,the wavy contact angle,channel quanlity and mass flow rate of the multi-channel wavy tube.An increase in wavy contact angle and mass flow rate positively affects the heat dissipation efficiency and temperature field homogeneity of the battery module.However,the positive effects decline as the same amount of wavy contact angle or mass flow rate is increased because the liquid cooling configuration reaches its limit in cooling the battery module.When the mass flow rate of each channel is constant,increasing the channel quantity can achieve similar results,but the optimal channel quantity exists in the case of the constant total flow rate.The 10-channel wavy tube shows apparent advantages at a mass flow rate of 4×10-3 kg/s,for example.When the battery module was discharged with 1C rate at 35?,the maximum temperature and local temperature difference of the battery module can be respectively kept down to 39.27? and 4.12? by using the10-channel wavy tube with a contact angle of 60°even at a low mass flow rate of4×10-3 kg/s.Experiments under corresponding working conditions were performed to validate the reliability of the simulation results,which turned out to be consistent with the experimental values.The simulation results have a maximum absolute error of0.37? and a maximum relative error 14.25%compared with the experimental values.Aiming at the fact that starting acceleration is often carried out during the driving process of the electric vehicles,the liquid-cooling characteristics of battery modules under short-term,frequent,and ultra-high C-rate discharge conditions are simulated.The results show that the liquid cooling system can fully meet the cooling requirements of frequent start acceleration under extreme conditions.In addition,the wavy tube with a progressively larger contact angle from the inlet to the outlet is proposed,and is superior to that with a constant contact angle of 60°in improving the temperature uniformity,under the same conditions,the temperature difference is further decreased by 18.2%.The simulation and experimental results in this paper provided specific reference values for the thermal management of cylindrical lithium-ion battery modules. |
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