| In response to the energy crisis and industial upgrading,the new energy vehicle industry has been strongly supported by the Chinese government.Pure electric vehicles(PEVs)and hybrid electric vehicles(HEVs)equipped with lithium-ion(Li-ion)batteries have occupied more than 90%Chinese new energy vehicles market share.Along with the increase of Li-ion battery market permeability,safety accidents caused by Li-ion batteries are also rising,according to statistics,safety issues have become the primary reason that consumers refuse to choose PEVs.Therefore,the priority is how to make Li-ion batteries safer and more reliable,the safety accidents related to Li-ion are often related to the failure of battery thermal management.A good battery thermal management system can greatly reduce the safety accidents of PEVs.The study object of this paper is the module with 15 cylindrical Li-ion battery cells.On the basis of accurately obtaining the thermophysical parameters and boundary conditions of the cell,the thermal model of the cell is established.The three-dimensional thermal simulation of the cell is carried out,and the accuracy of the model is verified by the temperature rise experiment of the cell.A single channel with“S”shape of liquid cooling pipe is designed for the module heat dissipation.The effects of channel height ratio(β),mass flow rate(m_a),wrapping angle(θ)and number of channels(N)on the heat dissipation performance of the module are explored.Meanwhile,the influence of different fluid flow directions and control strategies on the heat dissipation characteristics of battery modules in the four-channel model is analyzed.The specific research contents are shown as follows:(1)Theoretical analysis of heat generation and heat transfer characteristics of Li-ion batteries,the internal resistance of the cell is measured by HPPC experiments at different ambient temperatures,Based on the accurate thermal parameters and boundary conditions of the battery,such as thermal conductivity and specific heat capacity,a three-dimensional(3D)thermal model of the battery is established.And the temperature rise experiments of the battery under different discharge rates are carried out to verify the accuracy of the model.(2)A S-shape liquid cooling pipe is designed for the battery module,and the 3D physical model of the battery module is established through Solidworks.The fluid control equation is established according to the basic theory of fluid mechanics.3D thermal simulation of the module is carried out by ANSYS software.The influence of the channel height ratio(β),mass flow rate(m_a),wrapping angle(θ)on the heat dissipation effect of the battery module under 3C discharge rate is analyzed.(3)Increasing the number of channel(N)of liquid cooling pipe,under the condition of keeping the total area of channel inlet unchanged,when the inlet mass flow rate(m_a)is0.01kg/s and the inlet temperature of coolant is 25℃,the influence of liquid cooling pipe with one,two,three and four channels on the heat dissipation performance of battery module under 3C discharge rate is analyzed.Meanwhile,the influence of different fluid flow directions on the temperature rise of battery module under differentβmodels is analyzed.(4)The fluid control strategy of the four-channel model is optimized.Under the condition of 3C discharge,the unidirectional flow is changed into a reciprocating flow that the flow direction is changed with the time,and the period T_q of the reciprocating flow is changed to 1200s,600s,300s,100s and 50s respectively.The effects of different flow strategies on the heat dissipation performance of the battery are studied.It is found that the shorter the cycle of reciprocating flow,the smaller the temperature difference between modules,which is beneficial to improve the temperature consistency of the battery module. |
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