新能源汽车动力电池冷却系统热仿真及优化

动力电池的温度控制是新能源汽车发展中的一个难题,而电池冷却系统在动力电池的温度控制过程中起着相当重要的作用。利用Solidworks软件对电池包进行建模,利用ICEM CFD软件对电池包模型进行网格划分等前处理。利用Fluent软件并采用控制变量法分别对冷却管道截面宽度、冷却液质量流量和冷却液进口温度等3个对电池包散热性能影响较大的参数进行仿真计算和对比分析。根据仿真结果选择可优化电池包散热性能的参数,并在原方案基础上提出了一种新的冷却管道分布方案。经过仿真计算发现,该方案可有效降低电池在使用过程中的最高温度和温差,提高了电池冷却系统的散热性能。     

基于有限元分析的强迫对流条件下开关柜温升特性研究

12kV大电流开关柜广泛用于配电网中,一般采取强迫对流的方式进行散热。为研究开关柜在强迫对流条件下的散热过程,基于有限元仿真技术,分别分析了强迫鼓风和抽风两种条件下开关柜的散热能力。通过对开关柜进行三维建模、热源计算和边界条件设立,仿真分析了开关柜在强迫鼓风和抽风条件下的温升分布及气流场分布情况,并与试验结果进行对比。结果表明,开关柜在两种强迫对流条件下散热效果均较好,温升符合国标温升要求,但不同的散热方式对开关柜温升和气流场分布影响较大。     

Thermal analysis of lithium-ion batteries

A detailed three-dimensional thermal model has been developed to examine the thermal behaviour of a lithium-ion battery. This model precisely considers the layered-structure of the cell stacks, the case of a battery pack, and the gap between both elements to achieve a comprehensive analysis. Both location-dependent convection and radiation are adopted at boundaries to reflect different heat dissipation performances on all surfaces. Furthermore, a simplified thermal model is proposed according to the examination of various simplification strategies and validation from the detailed thermal model. Based on the examination, the calculation speed of the simplified model is comparable with that of a one-dimensional model with a maximum error less than 0.54 K. These models successfully describe asymmetric temperature distribution inside a battery, and they predict an anomaly of temperature distribution on the surface if a metal case is used. Based on the simulation results from the detailed thermal model, radiation could contribute 43–63% at most to the overall heat dissipation under natural convection. Forced convection is effective in depressing the maximum temperature, and the temperature uniformity does not necessarily decrease infinitely when the extent of forced convection is enhanced. The metal battery case serves as a heat spreader, and the contact layer provides extra thermal resistance and heat capacity for the system. These factors are important and should be considered seriously in the design of battery systems.     

圆柱形锂离子电池热管理实验研究

保持合适的运行温度是锂离子电池高效、安全、长寿命的保证,因而对其进行有效的热管理是非常有必要的。本文针对圆柱形锂离子电池,设计了嵌套电池表面的方形金属外壳,以强化电池散热和单体电池间传热。对比自然对流条件下电池单体加壳和无壳时不同放电倍率的温升情况、多个电池并联的温升情况,以及不同通风功率下多个电池并联时嵌套不同外壳的温升情况,发现加壳可以有效促进电池（组）散热。另外,设计了电池组内不同单体电池出现放电不均衡情况,以检验嵌套外壳对减小电池组内单体电池间温差的效果,结果表明,自然对流条件下,加壳后单体电池间最大温差可以降低10℃以上。     

Research on heat dissipation performance and flow characteristics of air‐cooled battery pack

With the depletion of fossil fuels and the aggravation of environmental pollution, the research and development speed of electric vehicles has been accelerating, and the thermal management of battery pack has become increasingly important. This paper selects the electric vehicle battery pack with natural air cooling as the study subject, conducts simulation analysis of the heat dissipation performance of battery packs with and without vents. Then this paper researches on the influence of internal flow field and external flow field. Field synergy principle is used to analyze the effect of velocity field and temperature field amplitude. The results show the following: it is found that the maximum temperature rise and the internal maximum temperature difference of the battery pack with vents are reduced by about 23.1% and 19.9%, raising speed value can improve the heat dissipation performance, and raising temperature value can decrease the heat dissipation performance. Reasonable design of the vents can make the inner and outer flow field work synergistically to achieve the best cooling effect. Then the reference basis for the air cooling heat dissipation performance analysis of electric vehicle, battery pack structure arrangement, and air‐inlet and air‐outlet pattern choosing are offered.     

An Experimental and Numerical Study on the Effects of the Flat Heat Pipe Wick Structure on Its Thermal Performance

This paper presents an experimental and numerical work on the effect of flat heat pipe construction on the cooling of an electronic component. The flat heat pipe is heated via 1-cm-diameter circular electrical resistance (the evaporator side), and the other side (the condenser side) is cooled by convection through a heat sink. In the experimental work, three types of wick construction are used in the heat pipe: (A) mesh + powder, (B) mesh, and (C) powder. A comparison is performed of the electronic component cooling from the heat pipe, copper block, and open heat pipe constructions. The numerical work studies the effect of wick porosity on the heat pipe performance for different wicks that we could not study experimentally. For forced convection, heat pipe A is more efficient for the electronic component cooling than the copper block and other heat pipe construction. For free convection, the copper block is the most efficient. The maximum variation of the heat pipe temperature is about 19% due to change of the heat pipe construction. When the wick porosity increases, the temperature increases and the pressure decreases. The rectangular groove construction produces the minimum temperature compared to the wrapped screen and packed sphere constructions.     

锂离子电池热管理技术

电动汽车在应对气候变化和减少碳排放方面显示出了巨大潜力,电池作为电动汽车的动力来源,在性能和安全方面受温度影响很大。一套有效的热管理控制系统能使电池组温度保持在最佳工作范围内,提高整车的续驶里程。主要总结了目前对电池进行散热和保温的主流电池热管理技术——风冷、液冷、相变冷却、热管冷却以及电池加热技术。提出电池热管理技术应往智能化、集成化、与机器学习相结合、能够自适应调节电池生态温度的方向发展,将会有很大的研究空间。     

Experimental study of a direct evaporative cooling approach for Li-ion battery thermal management

A desirable operating temperature range and small temperature gradient is beneficial to the safety and longevity of lithium-ion (Li-ion) batteries, and battery thermal management systems (BTMSs) play a critical role in achieving the temperature control. Having the advantages of direct access and low viscosity, air is widely used as a cooling medium in BTMSs. In this paper, an air-based BTMS is modified by integrating a direct evaporative cooling (DEC) system, which helps reduce the inlet air temperature for enhanced heat dissipation. Experiments are carried out on 18650-type batteries and a 9-cell battery pack to study how relative humidity and air flow rate affect the DEC system. The maximum temperatures, temperature differences, and capacity fading of batteries are compared between three cooling conditions, which include the proposed DEC, air cooling, and natural convection cooling. In addition, a DEC tunnel that can produce reciprocating air flow is assembled to further reduce the maximum temperature and temperature difference inside the battery pack. It is demonstrated that the proposed DEC system can expand the usage of Li-ion batteries in more adverse and intensive operating conditions.     

Simulation Studies on Multimode Heat Transfer from a Square-Shaped Electronic Device with Multiple Discrete Heat Sources

ABSTRACT

The results of a numerical study of the problem of multimode heat transfer from a square-shaped electronic device provided with three identical flush-mounted discrete heat sources are presented here. Air, a radiatively nonparticipating fluid, is taken to be the cooling medium. The heat generated in the discrete heat sources is first conducted through the device, before ultimately being dissipated by convection and surface radiation. The governing partial differential equations for temperature distribution are converted into algebraic form using a finite-volume based finite difference method, and the resulting algebraic equations are subsequently solved using Gauss-Seidel iterative procedure. A grid size of 151 × 91 is used for discretizing the computational domain. The effects of all relevant parameters, including volumetric heat generation, thermal conductivity, convection heat transfer coefficient, and surface emissivity, on various important results, such as the local temperature distribution, the peak temperature of the device, and the relative contributions of convection and surface radiation to heat dissipation from the device, are studied in sufficient detail. The exclusive effect of surface radiation on pertinent results of the present problem is also brought out.     

Lithium battery thermal management system for hybrid vehicles

为研究动力电池组的温度特性以及维持其工作在最佳的温度范围内,以锂离子电池为研究对象,设计了一种新型混合动力汽车的电池热管理系统,利用空调系统和发动机排气系统来调控电池组的温度。建立了锂电池组的三维瞬态产热数值模型,以电池组的三维尺寸和进风口流速为输入参数,以降低电池组的最大温升和提高电池组的温度均匀性为输出参数,利用FLUENT仿真软件和DesignXplorer模块进行联合优化设计了电池组的结构。优化后的电池组的温升比优化前降低了5.39 K,电池组温差降低了6.41 K。分析了恒倍率放电以及对流换热系数对单体电池温升的影响,研究表明：放电倍率越大电池温升越快,放电结束后电池的温度越高,在对流换热系数小于30 W/（m²·K）时,散热效果明显。对电池组在不同条件下加热或者冷却进行了仿真分析,验证了该电池热管理系统的可行性。     

防爆电池箱的相变散热分析

电动汽车电池在充放电过程中,会放出大量的热。防爆电动车上的防爆电池箱由于密闭性和防爆性,风冷和水冷散热模式会带来潜在风险,相变散热模式适应防爆性的要求,需要探索其可行性。通过对电池箱的相变散热进行设计和流动散热FLUENT仿真分析,发现了相变散热的局域不均匀性。针对问题导向,提出了利用相变材料对电池箱内部及外壁进行散热,仿真结果表明此方法达到了降低电池温度以及改善了其温度不均匀等问题。     

BUOYANCY-AIDED MIXED CONVECTION WITH CONDUCTION AND SURFACE RADIATION FROM A VERTICAL ELECTRONIC BOARD WITH A TRAVERSABLE DISCRETE HEAT SOURCE

This article presents the results of a comprehensive fundamental numerical study of the problem of buoyancy-aided mixed convection with conduction and surface radiation from a vertical electronic board provided with a traversable, flush-mounted, discrete heat source. Air, a radiatively transparent medium, is considered to be the cooling agent. The governing equations in primitive variables for fluid flow and heat transfer are first converted into stream function–vorticity form, and are later converted into algebraic form using the finite-volume method. The resulting finite-difference equations are solved by Gauss-Seidel iterative technique. The governing equation for temperature distribution along the electronic board is obtained by appropriate energy balance. The effects of pertinent parameters, viz., location of the discrete heat source, surface emissivity of the board, and modifiedRichardson number, on various results, including local temperature distribution along the board, maximum board temperature, and contributions of convection and surface radiation to heat dissipation from the board, are studied in great detail. The fact that any design calculation that ignores surface radiation in problems of this kind would be error-prone is clearly highlighted.     

Experimental study on rack cooling system based on a pulsating heat pipe

A rack cooling system based on a large scale flat plate pulsating heat pipe is proposed. The heat generated from IT equipment in a closed rack is transferred by the rear door pulsating heat pipe to the chilled air passage and is avoided to release into the room. The influence of the start-up performance of the heat pipe, the load of the rack and the load dissipation to the temperature and the velocity distribution in the rack are discussed. It is found that the temperature would be lower and the temperature distribution would be more uniform in the rack when the pulsating heat pipe is in operation. Also, the effect of rack electricity load on temperature distribution is analyzed. It is indicated that higher velocity of chilled air will improve heat transfer of the rack.     

Numerical investigation of thermal runaway propagation in a Li-ion battery module using the heat pipe cooling system

It is a promising cooling strategy to use the heat pipe for the Li-ion battery module, which can maintain the temperature of the battery module properly and prevent high temperature, triggering the thermal runaway among adjacent batteries. In this study, the thermal runaway model is simulated through the internal short circuit, which couples with Volume of Fluid (VOF) model of the heat pipe cooling and solves in ANSYS FLUENT to realize the heat and mass transfer between batteries and heat pipes. A user-defined function (UDF) code including mass source and energy source is used to calculate the heat and mass transfer in VOF model during the thermal runaway process. Numerical simulations are adopted to probe thermal runaway processes of a single battery under different operation conditions and the thermal runaway propagation from a battery to adjacent batteries. It is concluded that the heat pipe cooling system cannot prevent the thermal runaway of a single battery, but it can prevent the thermal runaway propagation from a battery to adjacent batteries.     

Numerical investigation on integrated thermal management for lithiumion battery pack with phase change material and liquid cooling

为满足3 C放电倍率下电池组散热要求,提出了PCM\液冷复合式散热方案,利用有限元分析了液体流速、流道排列方式、铝制框架鳍宽和环境温度对电池组温度的影响。结果表明,增加流速可优化电池组散热性能,但当流速大于0.08 m/s时,流速的增加对散热系统无明显优化;各流速下Type I散热方式效果均为最优且电池组满足散热要求;鳍宽为2 mm时可将电池组最高温度进一步降低1.6℃;当环境温度从38℃增至42℃时,复合式散热系统体现了良好的热稳定性能。     

A review on lithium-ion power battery thermal management technologies and thermal safety

Lithium-ion power battery has become one of the main power sources for electric vehicles and hybrid electric vehicles because of superior performance compared with other power sources.In order to ensure the safety and improve the performance,the maximum operating temperature and local temperature difference of batteries must be maintained in an appropriate range.The effect of temperature on the capacity fade and aging are simply investigated.The electrode structure,including electrode thickness,particle size and porosity,are analyzed.It is found that all of them have significant influences on the heat generation of battery.Details of various thermal management technologies,namely air based,phase change material based,heat pipe based and liquid based,are discussed and compared from the perspective of improving the external heat dissipation.The selection of different battery thermal management (BTM) technologies should be based on the cooling demand and applications,and liquid cooling is suggested being the most suitable method for large-scale battery pack charged/discharged at higher C-rate and in high-temperature environment.The thermal safety in the respect of propagation and suppression of thermal runaway is analyzed.     

Effects of viscous dissipation on the heat transfer in a forced pipe flow. Part 2: Thermally developing flow

In this part of the study, consideration is given to thermally developing laminar forced convection in a pipe including viscous dissipation. The axial heat conduction in the fluid is neglected. Two different thermal boundary conditions are considered: the constant heat flux (CHF) and the constant wall temperature (CWT). Both the wall heating (the fluid is heated) case and the wall cooling (the fluid is cooled) case are considered. The distributions for the developing temperature and local Nusselt number in the entrance region are obtained. Results show that the temperature profiles and local Nusselt number are influenced by the Brinkman number (Br) and the thermal boundary condition used for the wall. Significant viscous dissipation effects have been observed for large Br.     

Simulation Studies on Buoyancy-Aided Conjugate Mixed Convection With Radiation From a Vertical Plate With Multiple Nonidentical Heat Sources

This paper documents certain salient results of the simulation studies performed on conjugate mixed convection with surface radiation from a vertical electronic board equipped with multiple nonidentical flush-mounted discrete heat sources. Air that is assumed to be radiatively transparent with constant thermophysical properties subjected to the Boussinesq approximation is considered to be the cooling agent. The governing fluid flow and heat transfer equations without the boundary-layer approximations are initially transformed into vorticity-stream function form and are later appropriately normalized. The resulting equations, along with pertinent boundary conditions, are subsequently solved using a finite-volume-based finite-difference method coupled with Gauss–Seidel iterative technique. An extended computational domain has been used to capture the fluid flow and heat transfer adequately employing optimum combination of finer and coarser grids. A computer code is specifically written for the job. Effects of modified Richardson number, surface emissivity, and thermal conductivity on local temperature distribution, peak board temperature, and contributions of mixed convection and radiation in heat dissipation have been clearly elucidated. Two correlations that help in calculation of maximum and average nondimensional plate temperatures have also been developed.     

Thermal management of lithium‐ion batteries for electric vehicles

Thermal issues associated with electric vehicle battery packs can significantly affect performance and life cycle. Fundamental heat transfer principles and performance characteristics of commercial lithium‐ion battery are used to predict the temperature distributions in a typical battery pack under a range of discharge conditions. Various cooling strategies are implemented to examine the relationship between battery thermal behavior and design parameters. By studying the effect of cooling conditions and pack configuration on battery temperature, information is obtained as to how to maintain operating temperature by designing proper battery configuration and choosing proper cooling systems. It was found that a cooling strategy based on distributed forced convection is an efficient, cost‐effective method which can provide uniform temperature and voltage distributions within the battery pack at various discharge rates. Copyright © 2012 John Wiley & Sons, Ltd.     

平流层电子设备温度数值模拟

分析了平流层电子设备内外部热环境,考虑平流层大气对流、设备内部自然对流、太阳直射辐射、大气辐射、地面反射太阳辐射、地球红外辐射以及设备自身辐射等因素的基础上,建立了计算电子设备温度分布特征的对流、辐射耦合模型,模拟了其在不同功率、不同对流换热、不同环境条件下的温度分布。结果表明:对于平流层电子设备散热,对流换热和辐射换热都会影响电子设备的温度分布,尽管由于平流层大气压力低、对流换热弱,但对流换热量占到散热总量的60%以上,是散热的主要方式。因此,在平流层电子设备热设计时,可以优先考虑采取开孔等强化对流散热方法来控制设备的温度。最后,开展了平流层模拟环境的实验验证,典型工况实验值与计算值吻合较好,验证了计算模型的正确性。对平流层电子设备热设计有重要的指导意义。