【作者】 王浩东；

【导师】 高青；

【作者基本信息】 吉林大学 ， 动力工程及工程热物理， 2022， 硕士

【摘要】 随着电动汽车迅速发展其续航里程不断增加,作为其核心部件的动力电池的容量和产热也在不断增加,动力电池的热安全问题受到了广泛的关注,对大负荷、高温动力电池的应急管控技术已经成为当前研究的热点。因此,本研究在直冷式电池热管理系统的基础上进一步探究过热电池的应急冷却问题,和制冷剂直喷过程中动力电池的热安全问题。针对动力电池的应急热管理需求,本研究从喷管结构、系统特征参数、喷射模式等方面进行多角度、多工况的深入研究,以探究制冷剂直喷过程中热燃阻断的传热机制、控制机制。当动力电池发生过热时,将系统内高压液态制冷剂经喷管喷射至过热电池表面,制冷剂在电池表面蒸发、沸腾吸收电池产热,短时间内完成对过热电池的骤冷,排空电池包内原有空气,起到隔热稀氧的作用,增加电动汽车的热安全性。实验研究首先对直冷系统和应急喷射冷却系统进行设计,构建直冷整包应急冷却实验台架和电池组态喷射冷却实验台架,前者围绕整车进行宏观性能研究,后者用于细化研究应急冷却过程中的基本调控特性。在整包应急管控实验台架,开展对大负荷、高温电池的直冷基本传热特性研究,探究直冷式电池热管理系统的冷却性能和限度,和在直冷系统控制边界外的制冷剂直喷冷却的降温特性、稀氧性等,最终选取典型实验工况下的最佳喷射模式。基于电池组态喷射冷却实验系统,对喷射结构进行设计优化,提出孔式喷射与管式喷射两种喷射结构。以系统的瞬态降温能力、对制冷剂的利用效率、系统响应时间、电池模组的温度均匀性为评价指标,研究制冷剂导流管长度等喷管结构特征对系统应急冷却效果的影响,同时对电池模组初始温度、制冷剂喷射压力等系统结构参数也进行相关研究。实验结果表明,歧管具有极强的冷却能力,数秒内降温幅度达65℃,能够短时间内完成对过热电池的骤冷;非等直径喷管通过对喷孔直径进行设计优化,可以提升喷射冷却过程中电池模组的温度均匀性。基于上述典型喷射结构,开展动力电池间续性喷射控制特性实验研究,以探究包含喷射时间、喷射占空比、喷射频率等在内的主控因素的传热机理,并对两种典型喷管传热特性加以比较分析。通过对比分析发现,两种典型喷射结构热流变特性存在共性,系统的应急冷却能力均随着喷射时间的增加而增加,但单位质量制冷剂所能提供的最大温降存在先增加后减小的趋势。针对脉冲喷射,调整脉冲喷射的喷射占空比和喷射频率对系统冷却能力的影响各有不同,但是与喷射频率相比,喷射占空比对应急管控过程中系统的冷却效能起主要影响作用。依托实验研究获得的规律,可进一步提升应急热管理系统的冷却能力,并优选更佳的喷射时序。本文基于实车整包开展动力电池应急管控实验研究,设计并构建一种过热电池应急管控系统,在直冷式电池热管理系统基础上附加喷射冷却实验系统,开展喷射冷却对电池模组、电池整包热燃阻断机理的研究,为提升电动汽车热安全性开发了新的技术手段。更多还原

【Abstract】 The driving range of electric vehicles is increasing with their rapid development,as its core component,the capacity and heat production of the power battery is also increasing.The thermal safety of power batteries has received more widespread attention,and the emergency cooling and control technology for high-load,high-temperature power batteries has become a hot spot for current research.Therefore,this research further investigates the emergency cooling of overheated batteries based on the direct cooling battery thermal management system,and the thermal safety of power batteries during refrigerant spray cooling process.Aiming at the emergency thermal management requirements of the power battery,multi-angle and multi-conditions research is conducted from the nozzle structure,system characteristics parameters,spray mode to reveal the heat transfer mechanism and control mechanism of thermal combustion blocking during the spray cooling process in this paper.When the power battery gets overheated,the high-pressure liquid refrigerant from the system can be sprayed onto the surface of overheated batteries through the nozzle,and the refrigerant evaporates and boils on the battery surface to take away the heat produced by the battery,completing the sudden cooling of the overheated battery in a short time,exhausting the air in the battery pack,and playing the role of heat insulation and oxygen dilution to improve the thermal safety of the electric vehicles.The experimental study started with the design of the refrigeration system and emergency spray cooling system,and then constructed the direct-cooled battery pack emergency cooling experimental bench and the battery module spray cooling experimental bench,the former one was based on the performance of real vehicle applications to study the basic characteristics,and the latter one used to investigate the control characteristics during the emergency cooling process.In the direct-cooled battery pack emergency spray cooling experimental bench,the basic heat transfer characteristics of direct cooling for large load and overheated batteries are studied to define the cooling performance and limitations of the direct-cooled battery thermal management system,and the cooling characteristics,oxygen dilution characteristics of the spray cooling over the control boundary of the conventional direct-cooled battery thermal management system were investigated to determine the most powerful spray mode under different overheated states.Based on the battery module spray cooling experimental system,the nozzle structure is designed and optimized,and two types of nozzles,typical orifice nozzle,and typical tube nozzle are proposed.Using the transient cooling capacity of the system,the efficiency of refrigerant utilization,response time of the system,and the temperature uniformity of the battery module as the evaluation parameters to study the influence of the nozzle structure characteristics such as the length of the refrigerant guide tube on the emergency cooling effect of the system,the initial temperature of the battery module,refrigerant spray pressure and other system structural parameters are also studied.The experimental results show that the manifold has an extremely powerful cooling capacity,the temperature drop can be65℃ in seconds,which can complete the sudden cooling of overheated batteries;the non-equal diameter nozzle can improve the temperature uniformity of the battery module during the spray cooling process by optimizing the design of orifice diameter.Based on the above-mentioned typical nozzles,an experimental study of power battery emergency cooling spray mode is conducted to define the heat transfer mechanism of the main control factors such as spray time,spray duty cycle,and spray frequency,then a comparative analysis of the heat transfer characteristics of the two typical nozzles is conducted.It is found by comparison and analysis that there is a commonality in the thermal and flow characteristics of the typical nozzles,and the emergency cooling capacity of typical nozzles increases with the increase of the spray time,but there is a trend that the maximum temperature drop of unit mass refrigerant increases first and then decreases.For pulse spray,the effect of adjusting the spray duty cycle and spray frequency on the cooling capacity of the system is different,but compared with the spray frequency,the spray duty cycle plays a major role in the cooling capacity of the system during the emergency cooling process.Based on the results of the experimental investigation,the cooling capacity of the emergency thermal management system can be further improved and a better spray mode can be selected.Experimental research on power battery emergency cooling and control is carried out in this paper based on the battery pack of a real vehicle,and a power battery emergency thermal and control system is proposed and designed.On the basis of the direct cooling battery thermal management system,a spray cooling experimental system was added to carry out the research on the thermal and combustion blocking mechanism of spray cooling on battery modules and battery packs,which developed a new technical means to improve the thermal safety of electric vehicles.更多还原