Study On Supercapacitors Thermal Management For Tram

Tram vehicles have been vigorously developed and widely applied in China due to their advantages of energy saving,environmental protection,safety and speed.In extreme environments such as high traction power,high braking power,frequent and large fluctuations of tramcar,and high ambient temperature,supercapacitors will generate a large amount of heat,which will rapidly increase the temperature,affecting its performance and life,and bring great challenges to thermal management.In order to improve the performance of intermittently powered trams and reduce their energy storage costs,the energy storage system must be operated at a suitable temperature and a small temperature difference.This paper relies on the national key R&D project（task）（No.2017YFB1201004-12）and combines theoretical research,simulation analysis with experimental verification.A multi-physical field model of electric-thermal coupling of supercapacitor is established.Subsequently,the basic electrochemical and temperature characteristics of supercapacitor are studied.The space structure of the supercapacitor module oriented to high power density is optimally designed.Under different experimental conditions,the heat dissipation characteristics of various thermal management modes are studied through simulation and experiment.By comparing the temperature effects and economic cost of different thermal management modes,the practicability of thermal management based on heat pipe-cooling oil-forced air cooling is verified,which provides fundamental thermal management theory for the optimum design of supercapacitor for trams.The main research contents and conclusions are as follows:（1）The one-dimensional,three-dimensional geometric model and electro-thermal coupling model of supercapacitor are established.The electrochemical characteristics such as ohmic drop and electrolyte concentration polarization of supercapacitor are studied.The effects of different surface heat transfer coefficients and ambient temperatures on the maximum temperature of supercapacitors are analyzed.（2）Based on COMSOL simulation,the structure optimization of supercapacitor module space with natural convection and parallel air-cooling is carried out.The effects of single-gap（d_x,d_y,d_z）and single-distribution mode on the maximum temperature(T_max)and maximum temperature difference of supercapacitor module(（35）T_max)under natural convection in three-dimensional space were investigated.The influence of inclination angle of wedge-shaped ductθ,the bottom height of wedge-shaped duct b and single-gap d in parallel air-cooling structure is studied.The results show that d_y has the greatest influence on the T_maxax and（35）T_maxax under natural convection,while d_Z has the smallest effect on T_max.The distribution of 2 rows and 9 columns occupies slightly more space but has better temperature effect than that of 3 rows and 6 columns;The influence ofθ,b,d on parallel air cooling are successively weakened,and increasing their values in a certain range can effectively reduce T_max;Reducing T_inlet and increasing V_in can both reduce T_max,but increasing V_in will cause（35）T_max to become larger.Furthermore,when V_in increases to a certain value,the cooling effect decreases.（3）A heat dissipation structure based on heat pipe fin adapted to the overall layout of the 48V supercapacitor module is designed.The influence of thickness（d₁）and spacing（d₂）on the heat dissipation capability of the square fins is analyzed.The results show that the influence of d₂ is greater than d₁,and the optimized values of d₁ and d₂ are taken as 2mm and1mm respectively.The temperature changes of the module under the three thermal management schemes of phase change material（PCM）cooling,heat transfer oil cooling,heat pipe-heat transfer oil-forced air cooling are compared and studied.A heat management scheme which based on heat pipe-heat transfer oil-forced air cooling is proposed for the supercapacitor module of tramcar.This scheme has strong heat dissipation and uniform temperature performance.When the ambient temperature is 40℃,forced air is 2m/s and the circulated current is working condition,the maximum temperature and maximum temperature difference can be 45℃and 1.5℃,respectively.（4）A experimental platform for thermal management of supercapacitor is built.Under different thermal management modes,different ambient temperatures and different current conditions,the temperature effects of supercapacitor cells or modules are experimental analyzed.Compared with the experimental results,the simulation model is validated.The economic costs of three heat management modes are calculated.A control strategy is introduced for heat pipe-heat transfer oil-forced air cooling,which can not only guarantee the heat dissipation effect but also reasonably control the energy consumption of fan.As a result,the maximum relative error of T_max in simulation and experiment is about 7%,and（35）T_max is 3.179°C,which means simulation model has a certain feasibility.When the ambient temperature is 40°C,the cooling effect of natural convection,heat transfer oil cooling,PCM cooling,heat pipe-heat transfer oil-forced air cooling is enhanced in turn,the cost of the latter three thermal management schemes account for about 3%,30%and 13%of the price of the supercapacitor module,respectively.Heat pipe-heat transfer oil-forced air cooling can make T_max and（35）T_max under the working condition current or 100A current cycle less than50°C and 2.7°C respectively,which has the best practicability.