| In order to solve the problem of increasingly serious air pollution and depletion of fossil energy,and overcome the problem of low combustion efficiency of fuel oil in low oxygen and high humidity environment,research and development the new energy electric engineering vehicles is a development direction of engineering vehicles.As the power source of electric excavator,power battery is the key equipment that restricts the development of excavator electrification.Due to its high energy density and long cycle life,lithium-ion battery has become one of the fastest growing and most widely used of the power batteries in electric vehicle field.However when the power battery is used in groups the accumulation of heat generated will cause the temperature to rise significantly,and the vehicle performance to decline.In severe cases,the power battery pack may be out of control,causing a safety accident.Therefore,adopting a reasonable power battery thermal management system,maintaining the electrochemical performance of the power battery and prolonging its service life,and ensuring the power,safety and reliability of the electric vehicle have become one of the current research hotspots.In this paper,based on the theoretical analysis and numerical simulation of the mobile power box for electric excavator of a company,the heat distribution of lithium iron phosphate power battery pack is studied.A liquid-cooled power battery heat exchanger structure is proposed.And optimized design,the main research contents are as follows:1.According to the rated working voltage,power and capacity of the excavator,the single battery is selected to build a power battery pack for the mobile power-operated electric excavator,and a liquid-cooled heat exchanger matched with it is designed structure.2.Based on the heat dissipation structure of the liquid-cooled excavator power battery pack heat exchanger,a fluid-solid coupling heat transfer calculation model of CFD was established,and the influence of the initial structural scheme on the thermal distribution of the power battery pack was analyzed.Through Fluent simulation combined with theoretical analysis,the optimization effect of structural optimization on the heat dissipation effect of liquid-cooled heat exchanger is expounded.It is proved that under the premise that the total length of the flow channel is not reduced,the method of increasing the number of liquid inlets of the liquid cooling plate and shortening the fluid flow can effectively reduce the maximum temperature difference between the maximum temperature of the battery and the single battery.3.The single variable control method is used to simulate and compare the flow path shape of the liquid cooling plate,the ratio of the length and width of the rectangular flow channel,the liquid cooling medium,the inlet flow rate of the coolant and the inlet temperature to the maximum temperature of the power battery pack,and the battery cell unit.The consistency,uniformity and flow resistance characteristics of the temperature between the batteries.the simulation results show that under the same hydraulic diameter,the circular cross-section flow path and the square cross-section flow path have little difference in controlling the temperature distribution of the battery pack,but the flow resistance characteristics under the circular crosssection flow path are poor;In the case where the height of the rectangular flow path is constant,increasing the width of the flow path can reduce the pressure loss of the fluid inlet and outlet;The heat exchanger using water as the liquid cooling medium has better heat exchange performance and flow resistance characteristics,but is inferior to the ethylene glycol aqueous solution having a mass fraction of 50% in controlling the temperature uniformity of the battery;Increasing the coolant inlet flow and lowering the coolant inlet temperature help to reduce the maximum temperature of the power battery pack;In a certain temperature range,the lower ambient temperature of the battery,the better temperature rise and temperature uniformity of the battery pack.4.From the perspective of improving the temperature uniformity of the power battery pack,a heat conduction enhancement scheme is proposed based on the shape of the cross section of the liquid cooling plate.And compare the influence of the positional arrangement,material selection and thickness of the thermal pad on the thermal distribution of the power battery pack.It is concluded that the arrangement of the heat conducting sheet in the X direction is superior to the Z direction in reducing the maximum temperature of the power battery pack and improving the temperature uniformity of the battery pack.Moreover,if the graphite sheet is used while maintaining the same weight or the thickness of the heat conductive sheet is increased when the same heat conductive material is used,the temperature uniformity of the battery pack can be improved.5.Through the Box-Behnken design method and response surface analysis,the main parameters of the liquid-cooled heat exchanger and their interactions on the temperature distribution of the battery were studied.Using the Design-Expert software to obtain the prediction model of the regression equation and perform the response surface analysis,the conditions for the optimal temperature distribution of the power battery pack and the minimum pressure loss of the fluid inlet and outlet. |
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