Design And Optimization Of Heat Dissipation System For Lithium-battery Of Electric Vehicle

With the increasingly serious energy crisis and environmental problems,the automobile industry has been affected in the international market.In order to solve the problem of sustainable development of automobile industry in the future,the research and development and production of electric vehicles have become an important way.Due to the complexity of road conditions,the vehicle will frequently switch back and forth in the process of charging and discharging,resulting in the rise of battery temperature.When the temperature is too high,the power and energy of the battery will be affected,the efficiency of charging and discharging cycle will also be reduced,and even lead to safety problems such as thermal runaway and explosion.Therefore,an effective battery thermal management system is of great significance for the development of electric vehicles.The research object of this paper is the square lithium iron phosphate battery for vehicle.The following research has been carried out:(1)The internal structure and working principle of square lithium iron phosphate battery,as well as the heat generation mechanism and heat transfer mechanism of single cell were introduced.This paper discusses the basic theory and parameters of the thermal model of the battery,establishes the electrochemical thermal coupling model of the lithium iron phosphate monomer battery,obtains the temperature rise curve and temperature distribution of the battery under different discharge rate,and paves the way for the structural design of the heat dissipation system.(2)According to the temperature distribution on the surface of the lithium battery,the heat dissipation structure of phase change material conical tube was designed.The traditional method of phase change material cooling combined with liquid cooling can reduce the surface temperature of the battery,but it can not reduce the temperature difference.In this paper,the surface area of the tapered tube is used to change the heat transfer efficiency,reduce the heat accumulated in the high temperature area of the battery,and improve the temperature uniformity.The influence of the diameter,quantity,the thickness of phase change material layer and the velocity of coolant inlet on the heat dissipation was analyzed by orthogonal test.The results show that for the maximum temperature and the maximum temperature difference of the battery surface,the change of the number of cooling pipes has the greatest influence on the heat dissipation effect,followed by the flow rate of the coolant inlet.For the highest temperature of the battery surface,the influence of the diameter of the tapered tube is the least.For the maximum temperature difference,the thickness of phase change material layer has the least influence.The optimal combination scheme can control the battery temperature in a safe and reasonable range under the condition of 5C high current continuous discharge.(3)When the battery generates heat,the high temperature mainly accumulates in the interior,and the external installation of cooling system is not direct and complex.For this reason,we designed a kind of internal heat dissipation structure of the battery.The cooling plate with cooling pipes is inserted into the battery to control the temperature from the inside.The orthogonal test method is selected to analyze the influence of the cooling pipe section size,the thickness of the cooling plate,the flow rate of the coolant and the arrangement of the pipes on the cooling plate on the cooling effect.The conclusion is that the influence of the four factors on the surface temperature performance of the battery is the same,the flow rate of the inlet coolant is the most important,the arrangement of the pipes on the cooling plate is the second,and the thickness of the cooling plate is the least.The temperature simulation of the better combination can effectively reduce the high temperature of the battery with a new battery structure with its own heat dissipation.The proposal of this new battery structure leads to a new direction in the field of heat dissipation research and battery design.(4)In the use of vehicle lithium battery,the single battery is composed of battery modules in series and parallel.Different heat exchange conditions in different positions of the module lead to poor temperature consistency between the single batteries,which affects many performance of the module.Two kinds of heat dissipating structures are respectively substituted into the battery module for further optimization.By contrast,the phase-change material cone tube cooling structure can better ensure the temperature uniformity of the module,while the internal cooling structure of the battery can effectively reduce the overall temperature of the module,and the space utilization rate is high.The two optimized cooling structures have their own characteristics,which meet the requirements of the battery thermal management system.