Thermal Performance Of Battery Module Based On Microchannel Heat Sink

In recent years,new energy vehicles have developed rapidly under the strong support of the state.With the popularity of new energy vehicles,higher requirements are put forward for their safety and durability.However,the lithium-ion batteries in the battery module of new energy vehicles are very sensitive to temperature.Then high and uneven temperature will affect the battery life.As a new type of radiator,microchannel heat sink can promote energy saving,emission reduction and"carbon neutrality"on the basis of realizing efficient heat transfer.It was a microchannel structure with high efficiency,energy saving,compact structure and high reliability.Its application to the heat dissipation of electric vehicle has become a research hotspot.In view of the main problems faced by new energy electric vehicles in thermal management,this paper proposes a micro-channel heat sink with excellent cooling performance and low energy consumption by adding a cavity,rib and a combination of cavity and rib turbulence structures in the rectangular microchannel.This provides a new research idea for the development of battery heat transfer performance improvement.Based on the method of combining experiment and simulation,this paper studied the heat dissipation performance of battery liquid cooling system.The main research contents and conclusions are as follows:(1)Firstly,the structure,classification and thermal characteristics of lithium-ion batteries were introduced in order to understand the theoretical basis of battery thermal analysis.Then,the heat generation model of single battery was established,also the heat source of battery simulation was determined.Similarly,the physical parameters of battery were calculated,and the heat generation of single battery was simulated and analyzed.The simulation results of the battery surface temperature at different discharge rates were compared with the results of the battery temperature rise test.The results showed that the error was less than 10%,and the battery heat generation model was effective and reliable,which provides a basis for the following research of battery liquid cooling and thermal performance.(2)The liquid cooling heat dissipation experiment platform of lithium battery based on micro-channel heat sinks were built,at the same time the four different micro-channel heat sinks were designed and processed for comparative study.On the basis of verifying the validity of the test results of the micro-channel heat sink structure used in the battery liquid cooling heat dissipation experiment,the variation of the surface temperature of battery module with the Reynolds number under different micro-channel heat sinks at normal temperature was studied by comparison of experiment and simulation.The results showed that the experimental results of the four microchannel heat sink structures were in good agreement with the simulation results,and the maximum error was less than5%,which verifies the effectiveness of the battery liquid cooling heat dissipation model.The average temperature and temperature difference of cell surface with Reynolds number and coolant inlet temperature were analyzed by experiments.The results showed that increasing Reynolds number and decreasing the inlet temperature of coolant can improve the surface temperature of the battery.When using small rate discharge,the inlet temperature of coolant was between 20℃and 25℃.(3)The liquid cooling design and simulation analysis of lithium-ion battery module were carried out.The changes of the maximum temperature and temperature difference of the battery module under the condition of natural convection at different discharge rates were analyzed.It was found that when the discharge rate of the battery was 1.5C,the maximum temperature after discharge exceeded 40℃.At a higher discharge rate of 2C,the influences of flow channel distribution,flow channel internal structure,flow rate of coolant inlet,type of coolant,volume fraction of nanofluid and number of flow channels on battery performance were further investigated.It was found that the parallel rectangular channel with equal spacing had the maximum comprehensive performance factor value of 0.044,which was superior to the other 5 channel distribution forms.The microchannel heat sink with fan-shaped cavity structure had the best comprehensive performance,which could improve the comprehensive performance by 24%compared with the traditional rectangular channel heat sink.The optimal flow rate of coolant inlet is 0.58m/s.Adding nanoparticles to the base solution and increasing the volume fraction of the nano-fluid could improve the heat dissipation effect of the battery.Combining the pressure drop and the cooling effect of the battery,the number of six channels was selected for the study.(4)The influence of main structural parameters of microchannel heat sink was analyzed and optimized.The influence of W_c,H_c,L_fand H_f on the thermal performance of the battery module was studied by single factor analysis.The results showed that the maximum temperature of the battery module decreases with the decrease of L_f,and the temperature difference presented a first increases and then decreases trend.The increase of W_c and H_f will reduce the maximum temperature and temperature difference of battery module.With the increase of H_c,the maximum temperature and temperature difference of battery module decrease first and then increase.The Response Surface Methodology(RSM)was used to analyze the influence of interaction between structural parameters on different response values.It was found that the interaction effects between W_c and L_f was the most significant on the maximum temperature,and the interaction between W_c and H_f has more significant effects on the maximum temperature difference and the average pressure drop at the coolant inlet and outlet than other structural parameter combinations.(5)According to the uniform design method,the regression equations of heat resistance and pump power were built with multiple stepwise regression analysis with W_c,H_c,L_f,H_f as independent variables.The pareto optimal solution set combining heat resistance and pump power was obtained by multi-objective genetic algorithm,and a group of optimal solutions were selected from the optimal solution set by Topsis decision method.Through optimization calculation,we can know compared with the model before optimization,the temperature rise and temperature difference of the battery module were reduced by 11.5%and 7.7%,respectively.Meanwhile,the heat resistance and pump power decreased by 38.8%and 31.25%,respectively.