The Research Of Structural Optimization And Secondary Heat Dissipation Enhancement Of Phase Change Material Battery Thermal Management Module

With the increasing environmental pollution and energy depletion,promoting electric vehicles（EVs）is considered as an effective strategy to deal with the critical issues of fossil fuel shortages and global warming.Apart from the driving mileage,the thermal safety performance of the power battery pack still restricts the promotion of the EVs greatly.An excessive high temperature and/or temperature difference（ΔT）will accelerate the lifespan degradation of the battery,and lead to thermal hazards of the battery modules.In this context,various battery thermal management（BTM）technologies emerge as times require,aiming to strictly control the temperature rise andΔT of the module.Among them,phase change material（PCM）cooling technology has been treated as a potential substitute to the current BTM technologies by virtue of its simple structure,low cost and excellent cooling performance.To meet the engineering requirements,pure PCM is usually blended with shape-stabilized additives like polythene and epoxy resin（ER）,obtaining composite PCM（CPCM）,to enhance the forming stability.The resultant CPCMs are easily processed into rectangular plates and sandwiched alternately with prismatic or pouch cells,thus achieving orderly cooling structures.Unfortunately,for cylindrical cells,much more complicated situations are encountered because of the curve surface of the cells.In general,cuboid-like CPCM modules with orderly arranged cylindrical holes are prepared to match the curve surface of cylindrical cells.Nevertheless,there remain inherent defects of this kind of compact block-shaped CPCM modules,which inevitably limit their practical applications.The most important aspect is that compact CPCM module is short of outer heat-exchange surface and air flow channels,leading to a low secondary heat dissipation capability to the air.In view of this,this dissertation mainly solves the problems in the application process of PCM through structural optimization and secondary heat dissipation enhancement.The main research contents are as follows:（1）Preparation of CPCM.CPCM was prepared with paraffin（PA）as the phase change material,expanded graphite（EG）as thermal conductivity additive,and epoxy resin（ER）as the shape-stabilized additive.Stability test,mechanical test,DSC test and thermal conductivity test were performed.The test results show that the stability,mechanical properties,latent heat and thermal conductivity of the CPCM prepared after adding EG and ER meet the temperature control and mechanical requirements of BTM.（2）Structural optimization of CPCM BTM module.The traditional bulk CPCM（b-CPCM）module and the novel tubular CPCM（t-CPCM）module were designed using CPCM based on PA/EG/ER.Compared with b-CPCM module,t-CPCM module uses less CPCM,and possesses the advantages of higher energy density and larger heat dissipation area.The experimental results show that,compared with the b-CPCM module,the t-CPCM module has better performance.For example,at a fan velocity of 5 m s^-1,the T_max of the b-CPCM module is 51.3℃,and theΔT_max is 5.0℃,While the T_max of the t-CPCM module is 47.2℃,and theΔT _max is 1.0℃.（3）Flow field simulation of CPCM model.Two-dimensional b-CPCM model and t-CPCM model were established respectively,and the flow channel distribution of the two models was studied and calculated using Fluent.Numerical calculation results show that the flow field of the b-CPCM model is distributed only on both sides of the module,while the t-CPCM model’s is distributed uniform throughout the whole module.Theoretical calculation of heat transfer thermal resistance found that the convective heat transfer thermal resistance of the t-CPCM model was only 0.8 K W^-1,which was 1/20 of the b-CPCM model.（4）Secondary heat dissipation enhancement of the CPCM module.The CPCM module,the CPCM coupled with forced air cooling（CPCM-FAC）module and the CPCM coupled with liquid cooling（CPCM-LC）module were designed using CPCM based on PA/EG/ER.The experimental results showed that the T_max andΔT_max of the CPCM module at high enviroment temperature exceed 70℃and 15℃,respectively.The CPCM-FAC module was unable to simultaneously meet the demands of T_max andΔT_max.The T_max of CPCM-LC module is controlled below 50℃,and theΔT_max is controlled within 5℃.