| Pure electric vehicles don’t consume fossil energy and don’t emit exhaust.,which is an important way to effectively solve the two major problems of energy shortage and environmental pollution effectively.Power battery is the power core of pure electric vehicle.Appropriate working temperature and temperature difference are the premise of its high performance and long life span,so it is particularly important to develop an efficient thermal management system.The flat heat pipe has strong heat dissipation ability and high equivalent thermal conductivity.Phase change materials can absorb a lot of heat while keep a constant temperature which have good temperature uniformity.The organic combination of the two can just meet the requirements of the power battery pack for the cooling system.In this paper,a battery thermal management system based on flat heat pipe and phase change material is designed,and its performance under different working conditions is tested by experiments and simulations method,and the heat transfer process is analyzed in detail.In this paper,a flat heat pipe cooling system is designed for multiple battery packs connected in parallel.The heat dissipation characteristics of the thermal management system under different charge and discharge currents,different cooling conditions and different tilt angles were studied experimentally.The results show that the cooling system of flat heat pipe has the phenomenon of "cold start" at a low discharge rate（1.5 C or 2 C）,the maximum temperature difference in the battery pack presents a "hump" like fluctuation.With the increase of cooling water temperature,the phenomenon of "cold start" is alleviated,the temperature uniformity of the battery pack is better,but the maximum temperature is increased.With the increase of incline angle,the heat transfer performance of the heat pipe deteriorates,and the maximum temperature and maximum temperature difference of the battery pack increase.Under 3 C high discharge rate and 298.15 K cooling water temperature,the flat heat pipe cooling system can maintain the maximum temperature and maximum temperature difference of the battery pack of 318.6 K and 3.74 K,respectivelyIn order to improve the heat dissipation of flat heat pipe at high discharge rate and "cold start" at low discharge rate,the composite heat dissipation system of flat heat pipe with eicosane phase change material was designed in this paper.Compared with the flat heat pipe cooling system,it can not only avoid the phenomenon of "cold start",but also improve the temperature uniformity of the battery pack and reduce the maximum temperature of the battery pack.Under298.15 K cooling water and 3C discharge rate,the maximum temperature and maximum temperature difference of the battery pack in the composite cooling system are reduced by 6.3K and 1.18 K,respectively,compared with the flat heat pipe cooling system.Under different cooling conditions and angle of inclination,the cooling effect of the composite cooling system is better than that of the flat heat pipe cooling system.The composite heat dissipation system can meet the heat dissipation requirements of the battery pack under all discharge rate conditions at 5° inclination and cyclic charge and discharge conditions.In order to analyze the role of each part of the composite cooling system in the cooling process in detail,this paper adopts CFD method to carry out numerical analysis on the cooling process.The results show that the flat heat pipe is the only way for the battery to dissipate heat in the flat plate heat pipe cooling system.At the 3 C discharge rate,the heat taken away by the flat heat pipe only accounts for 87% of the heat generation rate of the battery,and the battery temperature continues to rise.In the composite cooling system,in addition to the flat heat pipe,the phase change module can also effectively dissipate heat.Under the condition of low discharge rate,the copper box with high thermal conductivity in the phase change module transfers more heat to the flat heat pipe at the beginning of discharge,which accelerates the start of the heat pipe and inhibits the "cold start" phenomenon.The heat taken away by flat heat pipe and phase change module at 3 C discharge rate accounts for more than 95% of the heat generation rate of the battery.The melting of eicosane increases the heat dissipation capacity of the phase change module rapidly,and the heat dissipation rate increases from 20% of the total heat production rate before melting to 44% after melting,which effectively inhibits the temperature rise. |
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