| With the increasing intensification of energy and environment problems, countries allover the world have been enforced more and more energy on research and development ofnew energy vehicles. As the heart of new energy vehicles, batteries ushered in the newdevelopment opportunity, also faced with enormous challenges. The temperature and thetemperature uniformity are very important for batteries, because they are electrochemicalreaction devices. And the difficulty to control the temperature is fold increase for batterypacking. So it is a key technical bottleneck whether people can develop an efficient batterythermal management system (BTMS) or not.This study is based on the study of batteries development, summarized the progress ofresearch work about battery thermal management technology at home and abroad.According to the heat transfer medium, BTMS can divide into three types, they are air-typeBTMS, liquid-type BTMS and PCM (phase change materials)-type BTMS. Air-type BTMSis the mainly form for engineering applications, liquid-type BTMS is gradually replacingthe former due to its high heat transfer efficiency and good temperature consistency.At present, cooling plates is the mainstream of BTMS. There are a few researches onheating and mainly for PTC heating. The author designed two types of liquid-typeheating/cooling devices with the objective of light-weighting battery pack. The flat tubebundle device for flake batteries and the tube bundle soft contact device for columnarbatteries. And liquid flow circulation experiment system was set up to do thermal controlexperiment. Focus on seeking the most effective battery group cooling/heating device and acontrol method that could ensure the heat transfer effect and the temperature distributionuniformity in different heat load/discharge ratio and the initial temperature conditions bychanging the flux and inlet temperature of circulating fluid. After the performance experiment about the flake batteries flat tube bundle device, theauthor put forward a measure that laid a high thermal conductive pad between flat tube andbattery to improve the temperature homogeneity in the battery pack. It turned out that thebalance response time for cooling and preheating time were shortened by about55%,temperature homogeneity were increased by78%. And then done the basic characteristicexperiment on the improved flake batteries flat tube bundle device and the columnarbatteries tube bundle soft contact device. The result show that, the equilibrium temperatureis33℃, the maximum temperature difference is2.3℃, the preheating time is90s for theimproved flake batteries flat tube bundle device, and the equilibrium temperature is27℃,the maximum temperature difference is3.4℃, the preheating time is5.5min for thecolumnar batteries tube bundle soft contact device.The thermal control experiments have been carried out by changing the fluid mediumflux and inlet temperature. Through experiments found that flux factors effect on coolingperformance is weak, while greater influence on preheating characteristics, when fluxincreased from3L/min to7L/min, preheating time can be shortened by about30%inselected range of flux conditions. Liquid flow inlet temperature has significant influence oncooling and preheating for flat tube bundle and tube bundle soft contact structures, thelower the inlet temperature the faster the response of cooling and lower equilibriumtemperature when cooling and the higher the inlet temperature the faster the response ofheating when preheating. But the inlet temperature too low or too high will go against thebattery temperature homogeneity or the heat exchange efficiency for tube bundle structures.So it need further weighing the lightweight battery pack and the affect of temperaturehomogeneity and thermal response between flat tube structure and plate structure.The initial temperature mainly affects battery preheating characteristics, the higher theinitial temperature the quicker the battery preheating. So the battery pack needs thermalinsulation to improve the time utilization efficiency of drivers and reduce the waste of heatenergy. The two kinds of structure can still meet the requirements of the BTMS whenbatteries in the case of big heat load/discharge ratio.Cold shock phenomenon will occur during cooling experiments when there is a large difference between the inlet temperature and the battery temperature. So in order to avoidthe occurrence of cold shock, the author put forward a step cooling manner to cooling thebattery pack. |
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