| Electric vehicles have attracted more and more attention due to their advantages of energy saving and environmental protection.The key to the development of electric vehicles is power batteries.The performance,lifespan,safety and reliability of power batteries are closely related to temperature.Therefore,it is especially important to design a suitable battery thermal management system.In this paper,the method based on combination of theoretical analysis,numerical simulation and experimental study was taken.Two kinds of thermal management systems based on mini-channel were proposed with square and cylindrical Li-ion batteries as the research object.The three-dimensional model of battery pack was established in CFD.The temperature field was analyzed in Fluent.And design scheme was optimized according to the cooling effect of several different conditions,to ensure safe and effective operation of battery pack at the most suitable temperature.At the same time,energy consumption of battery thermal management system under different cooling schemes was studied.The main conclusions are as follows:（1）The mini-channel cold-plate thermal management system provides good cooling efficiency in controlling the square battery pack temperature.The more channels are,the better the cooling efficiency is,the increasing trend slows down.The suitable number of channels is 5.The maximum temperature and temperature difference can be reduced by the way of increasing inlet mass flow rate which is more efficient than other methods.Taking the energy consumption into account,the optimal mass flow is 1×10-3kg/s.Increasing the channel width can reduce the energy consumption.Because of the higher heat generation rate in near-electrode area and different cooling effects on each battery,it is very difficult to decrease the temperature difference under 5℃.Besides,the advanced design is proposed to improve the temperature uniformity of the pack.The result indicates that compared to original design,the maximum temperature and temperature difference in advanced design decreases 13.3%and 43.3%,respectively,when the inlet mass flow rate is 1×10-3kg/s.The temperature uniformity is improved.Therefore,each battery needs to be cooled by two cold plates.（2）A novel battery thermal management system is designed for cylindrical Li-ion batteries.Constant contact surface（aluminum blocks with constant l）is firstly adopted in the cooling system.The results show that both maximum temperature and temperature difference decrease with the increases of l and inlet velocity.The cooling performance is best when l is 24 mm.The maximum temperature of the battery pack is well controlled under 40℃when inlet velocity is 0.05m/s.To further improve the temperature distribution in the battery pack,variable contact surface（aluminum blocks with linear changeable l）is proposed and its performance is compared with constant contact surface.Three slopes k=1mm,2mm,3mm are studied.Temperature distribution in the case of k=3mm is the most uniform when inlet velocity doesn’t exceed 0.1m/s,but it gets worse when inlet velocity is more than 0.2m/s.Taking the system weight and pump power consumption into consideration,system with variable contact surface is superior to system with constant contact surface.Compared to the case of l=24mm,the maximum temperature can decrease to the same value and temperature difference decreases by 6%,14%and 28%when inlet velocity is 0.05m/s,while system weight decreases by 20%,29%and 47%.Among the three slopes,the case of k=3mm is the optimal design for the system.（3）The heat transfer and energy consumption characteristics of battery thermal management system under cooling schemes are studied.The mini-channel cooling system can effectively decrease the average temperature and temperature difference of battery pack.Without cooling,the average temperature can be up to 56.5℃and 69.5℃,temperature difference can be up to 12.3℃and 15.4℃at 1C and 1.5C discharge rates.With cooling of case 1,the average temperature and temperature difference decrease by 43.7%and 65.9%at 1C discharge rate,47.3%and 63.6%at 1.5C discharge rate.As cooling system works under on-off control,the energy consumption saves by 83.2%and 49%at the discharge rates of 1C and 1.5C.Meanwhile,the temperature of battery pack is still controlled in optimal range.The maximum temperature appears on different cells in the battery pack during charge and discharge process.Thus,temperature dynamic comparison mechanism is very necessary. |
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