Thermal modeling of a cylindrical LiFePO4/graphite lithium-ion battery

A lumped-parameter thermal model of a cylindrical LiFePO₄/graphite lithium-ion battery is developed. Heat transfer coefficients and heat capacity are determined from simultaneous measurements of the surface temperature and the internal temperature of the battery while applying 2 Hz current pulses of different magnitudes. For internal temperature measurements, a thermocouple is introduced into the battery under inert atmosphere. Heat transfer coefficients (thermal resistances in the model) inside and outside the battery are obtained from thermal steady state temperature measurements, whereas the heat capacity (thermal capacitance in the model) is determined from the transient part. The accuracy of the estimation of internal temperature from surface temperature measurements using the model is validated on current-pulse experiments and a complete charge/discharge of the battery and is within 1.5 °C. Furthermore, the model allows for simulating the internal temperature directly from the measured current and voltage of the battery. The model is simple enough to be implemented in battery management systems for electric vehicles.     

The energy performance improvement of a PEM fuel cell with various chaotic flowing channels

To improve the energy performance of a proton exchange membrane fuel cell (PEMFC), novel chaotic structures are proposed and numerically evaluated for replacing straight types in the serpentine gas diffusion flow channels. The numerical model is verified by the available experimental data. Nine cases (chaotic channels, Cases A2, B1, B2, C1, C2, D1, D2, E1, and E2) and a baseline case (straight flow channel, Case A1) are evaluated, and the detailed temperature and the flow characteristics are presented and analyzed. The influences of the main design parameters including the corner angle, bends number, and datum surface number are also analyzed and concluded. It is found that the newly proposed chaotic structures can improve not only the temperature uniformity, but also the maximum output power and the energy efficiency of the PEMFC. Compared with a traditional PEMFC, the power output of the new PEMFCs with chaotic flowing channels can be improved by 6.26% and the efficiency of PEMFC can be promoted by 8.40%.     

Performance assessment of a passive core cooling design for cylindrical lithium‐ion batteries

Battery thermal management (BTM) system is an indispensable component for large‐sized lithium‐ion battery packs used in aerospace and automotive applications. Besides providing a proper temperature range for batteries to operate, thus improving their efficiency, lifespan, and safety, the BTM system also needs to be well designed with considering the cost, weight, and practicability. In this paper, an internal passive BTM system is proposed for the cylindrical Li‐ion batteries. The design embeds a phase change material (PCM) filled mandrel inside the battery to achieve the cooling effect. A thermal test cell is first fabricated and tested in a wind tunnel under different cooling scenarios, and it is also used to verify a numerical thermal model. The proposed BTM system is further examined through the model and found to be able to create a preferable environment for batteries to operate. Specifically, the core BTM system consumes less PCM and achieves lower temperature rises and more uniform temperature distributions than an external BTM system. The proposed design can also exert its full latent heat to manage the heat generated from the battery without having a thermally conductive matrix, which is usually composite with PCM in external BTM systems. In addition, experiments show that the battery equipped with the proposed BTM system is ready for intensive cycling tests.     

多孔介质太阳能吸热器性能分析

采用4种多孔骨架中辐射传输模型,包括:忽略多孔骨架内部辐射模型(模型A)、Rosseland模型(模型B)、均匀内热源模型(模型C)与吸热器中辐射传输满足Beer定律的模型(模型D),推导得到了局部非热平衡条件下4种模型所对应的吸热器中多孔骨架温度、空气温度和吸热器热效率的解析解,分析了多孔骨架孔隙率、导热系数和孔隙直径对吸热器性能的影响。结果表明,对模型A和模型B,吸热器中最高温度位于吸热器进口处;对模型C,吸热器中最高温度位于吸热器出口处;而在模型D中,吸热器中吸热器内部或吸热器的出口处温度最高。吸热器效率取决于多孔骨架导热系数、孔隙率和孔隙直径等参数,当吸热器中内热源均匀分布时,吸热器效率是最高的。     

Dynamic modeling of high temperature PEM fuel cell start-up process

High temperature proton exchange membrane fuel cells (HT-PEMFCs) are considered to be the next generation fuel cells. Compared with standard low temperature proton exchange membrane fuel cells (LT-PEMFCs) the electrochemical kinetics for electrode reactions are enhanced by using a polybenzimidazole based membrane at an operation temperature between 160 °C and 180 °C. However, starting HT-PEMFCs from room temperature to a proper operation temperature is a challenge in application where a fast start of the fuel cell is required such as in uninterruptible power supply systems. There are different methods to start-up HT-PEMFCs. Based on a 3D physical model of a single HT-PEMFC, the start-up process is analyzed by comparing the start-up duration of the different start-up concepts. Furthermore, the temperature distribution in the HT-PEMFC is also analyzed. Finally, an optimal start-up method is proposed for the given cell configuration.     

Modeling and validation of temperature changes in a pouch lithium-ion battery at various discharge rates

This paper deals with the thermal modeling of temperature rise in a pouch lithium-ion battery with LiFePO₄ (also known as LFP) cathode material. The developed model represents the main thermal phenomena in the cell in terms of temperature change. The proposed model is validated with the collected experimental data from a module composed of 11 cells. In the conducted experiments, the different charge and discharge rates of 1/2C, 1C, 2C and 2.5C are applied. It is seen that, the increased discharge rates result in increased temperature on the surface of the battery. When the discharge rate is doubled, from 1C to 2C, cell temperatures have risen by 3.5 times. A simplified model for determining the heat generation is developed and validated with the test results.     

Simulation and experiment of thermal energy management with phase change material for ageing LiFePO4 power battery

Thermal energy management performance of ageing commercial rectangular LiFePO₄ power batteries using phase change material (PCM) and thermal behavior related to thermal conductivity between the PCM and the cell are discussed in this paper. The heat sources are simplified according to the experimental results of the cells discharged at 35 A (≈5 C). 3-D modules of a single cell and battery pack are formulated, respectively. The results show that the thermal resistance in the cell leads to an inevitable temperature difference. It is necessary to improve the thermal conductivity and to lower the melting point of the PCM for heat transfer enhancement. The PCM with a melting point lower than 45 °C will be more effective for heat dissipation, with a desired maximum temperature below 50 °C. The temperature difference in the whole unit before PCM melting will be decreased significantly. In addition, a proper k_PCM:k_c is necessary for a well designed battery thermal energy management system.     

Measurements and application of thermal characteristics of soft-packed NCM lithium-ion power battery

锂离子电池的极化内阻是不可逆热测试的关键参数。为了更准确地计算极化内阻,针对三元软包锂离子动力电池,进行了HPPC测试、熵热系数测试、充放电温升测试,采用两种方法对极化内阻进行了计算,一种是通过电压变化量除以电流得到,另一种是通过建立二阶RC模型,结合HPPC测试工况辨识得到。根据两种方法得到的极化内阻,结合Bernardi生热速率模型公式对电池进行了1C充电和0.5C、1C、2C放电下的温度场仿真,并与红外热成像仪记录到的温度分布进行了对比。结果表明：根据二阶RC模型得到的极化内阻进行的仿真与实验数据吻合较好,说明利用二阶RC模型得到的极化内阻更加适用于电池持续充放电过程中的热分析。模型很好地模拟了电池不同充放电倍率下的温度场信息,对电池热分析及热管理可起到指导作用。     

Performance assessment of thermal management systems for electric and hybrid electric vehicles

Thermal management systems (TMS) are one of the key components of electric and hybrid electric vehicles to achieve high vehicle efficiency and performance under all operating conditions. Current improvements in electric battery technology allow vehicles to have relatively long ranges, fast acceleration, and long life while keeping low‐maintenance costs and considerably lower emissions. However, the vehicle performance is significantly affected by the battery operating conditions. Moreover, the cell life cycle, safety, and possibility of thermal runaway significantly depend on peak temperature rise and temperature uniformity of the battery. Therefore, various TMSs are created to keep batteries within ideal operating ranges. In this article, three different TMS systems—passive cabin cooling (via air), active moderate liquid circulation (via refrigerant), and active liquid circulation (via refrigerant and coolant)—are analyzed and compared with electric and hybrid electric vehicles. A second law analysis is used to examine the areas of low exergy efficiency in each system and minimize the entropy generation based on the system configuration. Moreover, TMS systems are compared on the basis of battery temperature increase and temperature uniformity. Various parametric studies are conducted to compare the TMS in different ambient and operating conditions. On the basis of the analysis, the active liquid circulation (via refrigerant and coolant) is determined to have the lowest battery temperature increase (3.9 °C in 30 min) and most cell temperature uniformity (2.5 °C median) as well as the lowest entropy generation rate (0.0121 W/K) among the compared systems. Copyright © 2012 John Wiley & Sons, Ltd.     

Axially symmetric problems of heat conduction in a periodically laminated layer with vertical cylindrical hole

The distributions of temperature and heat fluxes in a periodically laminated layer with a vertically located cylindrical hole are obtained approximately within the homogenized model with microlocal parameters. The method of solution is based on the Weber-Orr integral transforms. The effects of geometrical and mechanical parameters of the composite structure on the thermal fields are discussed and presented in graphical form.     

Thermal analysis of a Li‐ion battery module under realistic EV operating conditions

The thermal behavior of a Li‐ion battery module that belongs to the battery system of an actual electric vehicle prototype was numerically investigated. Realistic driving loads and passive cooling conditions were considered. A combination of a vehicle dynamics model, an equivalent electric circuit battery model, and a 3D finite‐element thermal model was used in the analysis. Temperature and electric potential measurements, performed at the cell and module levels, were first used for model calibration. Electric currents, associated with the ARTEMIS driving cycles, were then calculated and applied in the battery model to predict the heat sources for the thermal model. It was found that the temperature increase corresponding to urban transportation requirements in European countries is tolerable. Nevertheless, road and highway applications would result in a temperature increase that accelerates cell ageing, and an active cooling strategy is required. Copyright © 2012 John Wiley & Sons, Ltd.     

A comprehensive investigation on thermal management of large‐capacity pouch cell using micro heat pipe array

A proper and effective battery thermal management system (BTMS) is critical for large‐capacity pouch cells to guarantee a suitable operating temperature and temperature difference. Hence, in this paper, a micro heat pipe array (MHPA) is utilized to build the thermal management system for large‐capacity pouch cells. In order to study the property of BTMS in depth, experimental and numerical investigation are carried out by considering the C‐rate, working medium, air velocity and duty. The experimental results present that the T_max can be maintained below 43.7°C and the ΔT is below 4.9°C at the discharge rate of 3C in the battery module with MHPA‐liquid. Moreover, the T_max of the battery module with MHPA‐liquid falls as the air velocity increases. The simulation results show that the variation and distribution of temperature matched well with experimental results. It demonstrates that the MHPA‐based BTMS is viable and effective for large‐capacity pouch cell battery, even at high C‐rate and cycle duty.     

THERMOELASTICITY OF A REGULARLY NONHOMOGENEOUS THIN CURVED LAYER WITH RAPIDLY VARYING THICKNESS

A regularly nonhomogeneous (composite), anisotropic, thin curved layer with rapidly oscillating material parameters and thickness is considered for the case when mean thickness and period scale have small magnitudes of the same order. A three-dimensional thermoelasticity problem for this layer is reduced to a homogenized shell model by means of an asymptotic homogenization method for periodic structures. The effective thermoelastic and thermal material parameters of this shell are expressed in terms of solutions for auxiliary local problems in the cell of periodicity. Using the solution of the boundary-value problem for the homogenized shell and the solutions of the local problems, one can obtain a three-dimensional microstructure of the stresses, displacements and temperature with a high accuracy

This general model is applied to the derivation of thermoelastic and thermal constitutive equations for network periodic shells. The relations obtained lay the foundation for a new continuous model of thermoelasticity and heat conductivity for network periodic shells and plates.     

An alternating current heating method for lithium‐ion batteries from subzero temperatures

An alternating current (AC) heating method for lithium‐ion batteries is proposed in the paper. Effects of current frequency, amplitudes and waveforms on the temperature evolution and battery performance degradation are respectively investigated. First, a thermal model is established to depict the heat generation rate and temperature status, whose parameters are calibrated from the AC impedance measurements under different current amplitudes and considering battery safe operating voltage limits. Further experiments with different current amplitudes, frequencies and waveforms on the 18650 batteries are conducted to validate the effectiveness of the AC heating. The experimental data recorded by appropriate measurement instrument are of great consistence with simulation results from the thermal model. At high frequency, the temperature rises prominently as the current increases, and high frequency serves as a good innovation to reduce the battery degradation. However, efficient temperature rise can be obtained from high impedance at low frequencies. Typically, 600 s is needed to heat up the battery from ?24 °C to 7.79 °C with sinusoidal waveform and approximately from ?24 °C to 25.6 °C with rectangular pulse waveform at 10A and 30 Hz. The model and experiments presented have shown potential value in battery thermal management studies for electric vehicle (EV)/hybrid electric vehicle (HEV) applications at subzero temperatures. Copyright © 2016 John Wiley & Sons, Ltd.     

Reciprocating air flow for Li-ion battery thermal management to improve temperature uniformity

The thermal management of traction battery systems for electrical-drive vehicles directly affects vehicle dynamic performance, long-term durability and cost of the battery systems. In this paper, a new battery thermal management method using a reciprocating air flow for cylindrical Li-ion (LiMn₂O₄/C) cells was numerically analyzed using (i) a two-dimensional computational fluid dynamics (CFD) model and (ii) a lumped-capacitance thermal model for battery cells and a flow network model. The battery heat generation was approximated by uniform volumetric joule and reversible (entropic) losses. The results of the CFD model were validated with the experimental results of in-line tube-bank systems which approximates the battery cell arrangement considered for this study. The numerical results showed that the reciprocating flow can reduce the cell temperature difference of the battery system by about 4 °C (72% reduction) and the maximum cell temperature by 1.5 °C for a reciprocation period of τ = 120 s as compared with the uni-directional flow case (τ = ∞). Such temperature improvement attributes to the heat redistribution and disturbance of the boundary layers on the formed on the cells due to the periodic flow reversal.     

CAO垃圾焚烧系统热力模型研究

将CAO垃圾焚烧系统的两个燃烧室划分为：加热干燥区（A）、热解气化区（B）、残碳燃烧区（C）、可燃气燃烧区（D）。用多孔介质有效导热系数法，建立了A、B区中垃圾升温的传热模型；用不规则孔隙网络法，建立了B、C区中碳的气化和燃烧反应模型；用均相动力控制反应模型，分析了D区中多种化合物燃烬规律。最后讨论了CAO系统稳定燃烧的规律。     

An experimental investigation of liquid cooling scheduling for a battery module

The thermal safety of electric vehicle battery modules attracts public concern; controlling the severe temperature rise and ensuring uniform temperature distribution are essential to addressing this problem. In this research, a liquid cooling-based cooling structure equipped with minichannels is proposed to prevent a battery module's overheating. A novel cooling scheduling study is proposed to arrange the coolant flow rates at different cooling stages. The temperature rise, temperature difference, and energy consumption of all the cooling schedules are measured in experiments. Experimental findings indicate that appropriate cooling scheduling achieves the thermal objectives and reduces energy consumption through scheduling the coolant flow rate in the cooling process. A comprehensive cooling schedule selection is carried out to select the optimal cooling schedule with the highest cooling efficiency through evaluating both the thermal and energy consumption objective parameters under different discharging current rates (0.5C, 1C, and 1.5C). The optimal cooling schedule maintains the maximum temperature of the battery module within 26°C, 32°C, and 40°C under 0.5C, 1C, and 1.5C discharging current rates, respectively. Moreover, the temperature SD and the energy consumption of the liquid cooling-based battery pack can be controlled within 3.5°C and 40 J, respectively.     

Fatigue Analysis on Thermal Characteristics for PBGA by Using Finite Element Method

The stress and strain of Plastic Ball Grid Array (PBGA) is investigated for reliability evaluation, failure analysis, or manufacturing. A one-eighth model is built to estimate the thermal stress and strain of PBGA under thermal cycling temperature (0°C–100°C). The different 3D elements such as Visco107 and Solid45 were selected for modeling of material 37Sn63Pb and Print Circuit Board (PCB), silicon die, substrate, and Epoxy Molding Compound (EMC), respectively. The results show that the maximum equivalent stress and equivalent plastic strain occur in the second outer solder joint and close to the position of chip. The key solder joint can be obtained and the key node of solder joint is 41402. The results indicate that the integrating 3D model can provide a more comprehensive profile for the thermal investigation of the PBGA package than from using any 2D model. The investigation provides a basis for improving reliability of PBGA product in engineering design.     

A study of thermodynamic cycle and system configurations of hydrogen combustion turbines

A hydrogen combustion turbine is powered by steam generated from the internal combustion of hydrogen as a fuel mixed with stoichiometric oxygen. As it is possible to use a closed cycle system, benefits in cycle efficiency and a reduction of environmental pollution effects.Three different closed hydrogen combustion turbine cycles are evaluated. These are the Bottoming reheat cycle (A), the Topping extraction cycle (B) designed by Jericha and Ratzesberger, and the Rankine cycle (C).Calculations have been carried out to investigate the best cycle. This investigation consists of the comparison of thermodynamic efficiency, first stage turbine vane height of the high temperature, high pressure turbine, and maximum operating temperature of the heat exchangers. In these investigations, the component efficiencies are assumed to be the values which are expected to be achieved in the near future. As a result, the thermal efficiency of cycles (A) and (B) is the same value of 61.5%. That of cycle (C), which has the feed water heating with optimized pressure ratio of the intermediate turbine, is 58.8%. Cycle (B) has the largest first stage turbine vane height of the high temperature/high pressure turbine.The larger vane height has an advantage from the point of view of both the manufacturing of the complex cooling passage inside the vane and the turbine aerodynamic efficiency. The maximum operating temperature of the heat exchanger of cycles (A) and (B) is 870 °C, while that of cycle (C) is more than 1000 °C where some problems are anticipated in the feasibility of this heat exchanger.This investigation shows that the Topping extraction cycle (B) is considered to be the best cycle from the point of view of both the thermal efficiency and the feasibility of manufacturing.     

Measurement of heat generation in a 40 Ah LiFePO4 prismatic battery using accelerating rate calorimetry

Accurate characterization of the heat generation behavior of a battery is crucial to a good design of its thermal management system. Concerning the thermal properties, much attention has been paid to small-sized batteries such as the 18650- or button-type and little information is available for large-capacity Li-ion prismatic cells under adiabatic conditions. In this work, heat generation of a commercial 40 Ah prismatic LiFePO₄/C battery is evaluated using an accelerating rate calorimeter under an adiabatic condition. The battery cell is charged or discharged at an initial temperature from ?12.5 to 40 °C and a current rate from 0.2C to 2C. The experiment results show that heat generated in the battery is highly dependent on its operating temperature, state of charge and current rate. Internal resistance and entropy coefficient of the battery cell are also determined by the Hybrid Pulse Power Characterization method and potentiometric method, respectively. Relationship between the internal resistance and the heat generation behavior is highlighted. Entropy coefficient and volumetric heat generation rate of the battery cell obtained in this work are compared with those of other Li-ion batteries reported in literature.