Effective Thermal Management System Research Articles

Recent Progress on Air, Liquid, PCM, Heat Pipe, and Hybrid Modes of Thermal Management in Lithium-Ion Batteries

This study emphasises lithium-ion batteries, which have been the subject of extensive research due to their wide range of benefits, including extended life cycle, minimal discharge, and high energy density. However, the temperature sensitivity of the batteries presents a notable obstacle that can negatively impact their performance and longevity when operating under extreme conditions. To overcome this challenge, implementing an effective battery thermal management system (BTMS) is imperative. Battery thermal management is crucial for ensuring the safety and longevity of lithium-ion batteries, especially in high-demand applications like electric vehicles. This comprehensive review explores a variety of BTMS technologies, including air-cooling methods, liquid-cooling techniques, heat pipes, and PCM materials. While air-cooled BTMS is a safe and straightforward design, its lower heat capacity and thermal efficiency limit its use to low-capacity batteries. However, forced air-cooled BTMS is an excellent solution for high charging/discharging rates, as air flows through channels within the battery packs to optimize cooling. Liquid-cooled BTMS also shows promise, although designers must ensure the sealing cover is secure to prevent leaks. Heat pipes (HP) offer a unique approach to controlling battery temperature, while Phase change materials (PCM) thermal management is notable for its ability to absorb significant heat by latent heat. Hybrid cooling combines fins, nanofluids, PCM, and microchannels-based cooling and can significantly enhance battery performance under high charging/discharging rates. Furthermore, lithium-ion batteries are extensively used in various applications, including the Electric vehicle industry. Keeping the lithium-ion battery temperature within the optimal range is important and is accomplished by a suitable BTMS. Different methods, such as air cooling, Liquid cooling, Heat pipe, and PCM materials, are used in BTMS. An effective thermal management system and efficient battery model are absolutely necessary. Each of the techniques in BTMS has its own benefits and drawbacks. The effectiveness of thermal management configurations and methods can vary. Thus, evaluating performance and optimal configuration is crucial before implementation.

Thermal management of lithium-ion batteries based on the coupling of liquid cooling and composite phase change materials

ABSTRACT Effective thermal management techniques for lithium-ion batteries are crucial to ensure their optimal efficiency. This paper proposes a thermal management system that combines liquid cooling with composite phase change materials (PCM) to enhance the cooling performance of these lithium-ion batteries. A numerical study was conducted to examine the impact of various factors on the battery module’s thermal management performance, including the number of flow channels, the distance between these flow channels and the upper and front surfaces, fluid flow rate, coolant inlet temperature, and material’s phase change temperature. The simulation results indicate that at a discharge rate of 6C and a flow channel count of 5, the maximum temperature and the maximum temperature difference of the battery module decrease by 6.44% and 34.35%, respectively, when PCM is coupled with liquid cooling, compared to the pure liquid cooling. However, as the flow rate increases, the rate of temperature reduction slows down, while the pressure drop increases. When the flow rate reaches 0.4 m/s, the maximum temperature only drops by 0.57°C while the pressure drop increases by nearly two times. Furthermore, an increase in the PCM’s melting temperature leads to a larger maximum temperature difference in the battery module. This effect is more pronounced with higher coolant inlet temperatures. Therefore, careful consideration of both flow rate and coolant inlet temperature is essential for designing an effective thermal management system for batteries.

Thermal and hydrodynamic effects in variable geometry nanofluid transport with Thermo-Responsive liquid Composites: Dynamics of entropy generation

In this communication, the authors focused on energy loss during the flow of hybrid nanofluid in expanding/contracting channels. The goal is to determine how, in real-world applications, hybrid nanofluids can maximize energy efficiency and reduce entropy production, hence assisting in the development of more effective and sustainable thermal management systems. It is well documented that heat transfer is enhanced due to the presence of nanoparticles in a base fluid and hence decreases energy loss in the system. The second law of thermodynamics defines that heat transfer is not ideal; hence, entropy in a system always rises. Suitable measures can be taken to minimize energy loss. One method is to use a nanofluid, if multiple nanosized particles are used; it is named a hybrid nanofluid. In this communication, a comparative analysis of simple and hybrid nanofluids is provided. A mathematical model outlining the dynamics of the flow is provided. The upper plate acts as a porous plate that is contracting/expanding and through which coolant hybrid nanofluids enter the channel. The lower plate remains stationary and is heated externally. The equations governing the flow are converted into ordinary differential equations by employing the similarity transformation. These ODEs are then solved analytically to get the series solution by using HAM along with the given boundary conditions. The entropy equation is modelled using the Clausius Duhem inequality. Copper and silver nanoparticles are combined with water. The impacts of different dimensionless parameters on stream function, velocity profile, Nusselt number, entropy, and Bejan number are discussed, and their results are shown graphically.

Design and Simulation of eVTOL Aircraft Thermal Management System

Abstract Vertical Take-off and Landing (VTOL) aircraft with hybrid or fully-electric propulsion systems are becoming popular for Urban Air Mobility (UAM) applications. However, they face challenges such as limited power and energy density, stringent operating temperature constraints, and the generation of low-grade waste heat. These issues emphasize the need for effective Thermal Management Systems (TMS) design. In light of the above, this paper aims to design the TMS for a parallel hybrid electric XV-15 aircraft, a widely known civil tiltrotor concept. The TMS is integrated into the aircraft system to assess its impact on energy efficiency and emissions at both aircraft and mission levels. This study considers current state of the art technology and expected advancements over the next two decades to identify the benefits of electrification. In the designed TMS, liquid cooling cold plates serve as the main heat acquisition and cooling system for each electric component. An air-coolant heat exchanger is also incorporated to dissipate the accumulated heat load. The study conducts a comparative analysis to determine the optimal TMS design point. It involves a comparison between two design scenarios: one focused on the cruise condition, which constitutes a significant portion of the flight mission, and another designed specifically for peak heat load conditions. This ensures a holistic evaluation of the TMS's performance across various flight phases, balancing efficiency and resilience to peak demands. Finally, the energy efficiency and emission penalty associated with the TMS integration are quantified and discussed in the study.

Research Progress of Battery Thermal Management Systems with Minichannels

With the developing technology, energy storage systems, especially lithium-ion batteries (LiBs), play a critical role in electric vehicles and renewable energy applications. However, the performance and life of batteries are significantly affected by their operating temperatures. In this context, battery thermal management systems (BTMS) are of vital importance to ensure temperature control of batteries and to create a safe operating environment. BTMSs are divided into main two groups active and passive which require and does not require extra energy consumption, respectively. In this review, the basic principles, design criteria and application areas of battery thermal management systems are examined. First of all, the components of BTMS, passive and active cooling methods, heat dissipation and temperature monitoring techniques are detailed. In addition, the effects of different BTMS approaches on efficiency and performance are compared. The analysis of existing studies in the literature reveals the positive contributions of BTMS on battery life, charge-discharge efficiency and safety. In addition, future research areas and development opportunities are also highlighted. In conclusion, an effective thermal management system is a critical factor in the development of battery technology and has great potential in terms of sustainability of energy systems.

Numerical investigation and optimization of battery thermal management systems based on phase change material coupled with heating plates in low temperature environment

Low temperature environment has a significant impact on the performance and reliability of lithium-ion batteries (LIBs), particularly in terms of capacity, posing challenges to their safety and availability. However, existing studies primarily focus on cooling technologies for high temperatures, while less attention is paid to the preheating and heat preservation performance under low temperatures. In this study, a simple and effective battery thermal management system (BTMS) combines phase change material (PCM) and heating plates (HPs) is developed. The influence of structures, PCMs, composite phase change material (CPCM), and battery spacing is investigated. Additionally, the essential of insulation is emphasized. Furthermore, the utilization of natural thermal insulation material in BTMS is explored, and the influence of insulation thickness during both preheating and insulation stages are researched. The results indicate that the proposed BTMS can preheat the batteries to 20 °C under four typical low temperatures of 0 °C (480 s), −10 °C (720 s), −20 °C (900 s), and − 30 °C (1200 s). The temperature differences can be controlled below 3 °C. Moreover, the temperature can be maintained above 10 °C for approximately 4 h in the parking stage. A thickness of 10 mm is found to be sufficient. Overall, the energy compensation value above 5 is achieved under most low temperatures.

Thermal characterization of pouch cell using infrared thermography and electrochemical modelling for the Design of Effective Battery Thermal Management System

Lithium-ion (Li-ion) cells are the optimal choice of energy storage for battery electric vehicles. As the Li-ion cells must operate in a temperature range of 15–45 °C for optimal performance and life, thermal control of the cells is paramount. The study uses infrared imaging to investigate the temperature dynamics of two lithium-ion pouch cells with two energy capacities, 60 Ah and 20 Ah under different operational scenarios with natural convection. Experimental analysis conducted at ambient temperatures of 27 °C, 35 °C, and 40 °C reveals the necessity of cooling for the 20 Ah cell at temperatures exceeding 40 °C and C-rates beyond 1C. Similarly, thermal management is recommended for the 60 Ah cell at ambient temperatures of 35 °C and above, as temperatures surpass the 45 °C desirable threshold during charging and discharging rates of 1C and higher. Further studies are concentrated on the 60 Ah cell due to its increased cooling demands in comparison to the 20 Ah cell. The 60 Ah cell is modelled using NTGK and ECM electrochemical models and validated against experimental data, showing a good agreement within ±10% between both models and the experimental study. Finally, numerical simulations explain the efficacy of localized cooling with forced convection of liquid and performance metrics are introduced to evaluate the cooling efficiency of design configurations. Based on performance metrics, the T-shaped cold plate design, with an inlet coolant temperature of 30 °C, achieved the highest performance index of 1.13. This design notably decreased the maximum temperature and maximum temperature difference by 41.8% and 31.8%, respectively, compared to natural convection. This improvement is observed during the discharge of 60 Ah cell at 2C in a 40 °C environment, where the cell demands substantial cooling measures. Therefore, implementing localized cooling for the cell demonstrates its effectiveness in regulating temperature increase, leading to a significant decrease in the infrastructure requirements and weight of the thermal management system.

Thermal network for breeding blanket analysis and design in fusion reactor

Achieving carbon neutrality in energy production has become crucial and fusion energy is a promising way to a sustainable energy future. Breeding blanket is a critical component of a fusion reactor, ensuring tritium self-sufficiency and heat recovery for power generation. Breeding blanket needs an effective thermal management system as it operates under the high plasma in fusion reactors and the heat generated by the breeding reaction, which should be collected for power conversion. In this study, a thermal circuit model is used to analyze the design of a breeding blanket cooling system; in this model, each component is regarded as a thermal resistance element. Numerical simulations, empirical correlations, and equations are used to compute each resistance element. The thermal circuit results are then integrated into power conversion system using GateCycle for a basic analysis of power generation efficiency of a breeding blanket. Furthermore, we investigated the modified jet impingement design by changing thermal circuit elements to enhance cooling performance. The use of protrusions enhances the thermal performance of the impinging jet by 11 %, contributing to an overall enhancement in system efficiency. These findings could offer valuable insights for advancing the development of efficient, sustainable fusion energy systems.

Investigation of the immersion cooling system for 280Ah LiFePO4 batteries: Effects of flow layouts and fluid types

The widespread use of high-capacity LiFePO4 batteries (LFPB) is crucial for meeting the growing demand for energy storage systems (ESSs). This requires effective thermal management systems, and single-phase immersion cooling (SPIC) is emerging as a promising option due to its superior cooling capability. This paper investigates the effects of flow layout and fluid type on 280 Ah LFPB under SPIC through experimental and numerical analyses. Three flow layouts (opposite sides, same side, and jet impingement) are proposed, and six fluids are used for simulations. Results show that the jet impingement achieves the lowest temperature and pressure drop. During 1P discharge with DF1 flowing at 0.006 m/s, the maximum temperature, temperature difference, and pressure drop are 317.67 °C, 4.71 °C, and 0.09 Pa, respectively. Varying flow velocities within 0.006–0.053 m/s significantly impact battery temperature in the same-side layout. The volatility due to different fluid types, including CV,ΔP (pressure drop), CV,Tmax (maximum temperature) and CV,ΔT (temperature difference) are presented. As the flow velocity increases, CV,ΔP decrease by 35.9 %, 39.4 %, and 36.2 % for opposite sides, jet impingement, and same side, respectively. CV,Tmax increases with the P-rate, and the same-side layout has the lowest CV,Tmax, below 0.9 % at 0.5P and 0.6 % at 1P. This study emphasizes that the effect of fluid type should be considered in the design of flow layouts, especially at low flow rates. Experimental observation indicates that no ignition or explosion occurred during battery thermal runaway under SPIC. The maximum battery temperature during thermal runaway is 241.9 °C. This research provides valuable insights into SPIC application and fluid selection for ESS.

A Review of Thermal Management and Heat Transfer of Lithium-Ion Batteries

With the increasing demand for renewable energy worldwide, lithium-ion batteries are a major candidate for the energy shift due to their superior capabilities. However, the heat generated by these batteries during their operation can lead to serious safety issues and even fires and explosions if not managed effectively. Lithium-ion batteries also suffer from significant performance degradation at low temperatures, including reduced power output, a shorter cycle life, and reduced usable capacity. Deploying an effective battery thermal management system (BTMS) is crucial to address these obstacles and maintain stable battery operation within a safe temperature range. In this study, we review recent developments in the thermal management and heat transfer of Li-ion batteries to offer more effective, secure, and cost-effective solutions. We evaluate different technologies in BTMSs, such as air cooling, liquid cooling, phase change materials, heat pipes, external preheating, and internal preheating, discussing their advantages and disadvantages. Through comparative analyses of high-temperature cooling and low-temperature preheating, we highlight the research trends to inspire future researchers. According to the review of the literature, submerged liquid BTMS configurations show the greatest potential as a research focus to enhance thermal regulation in Li-ion batteries. In addition, there is considerable research potential in the innovation of air-based BTMSs, the optimization of liquid-based BTMSs, the coupling of heat pipes with PCMs, the integration of PCMs and liquid-cooled hybrid BTMSs, and the application of machine learning and topology optimization in BTMS design. The application of 3D printing in lithium-ion battery thermal management promises to enhance heat transfer efficiency and system adaptability through the design of innovative materials and structures, thereby improving the battery’s performance and safety.

Enhancing efficiency and sustainability: Utilizing high energy density paraffin-based various PCM emulsions for low-medium temperature applications

This research investigated the potential of high-energy-density Paraffin-based four different phase change materials (PCMs) (Paraffin 56/58, n-Eicosane, n-Octadecane, and n-Heptadecane) emulsions as a promising heat transfer fluid for low and medium-temperature applications at different concentrations. The primary focus is on elevating efficiency and sustainability within this domain. The investigation revolves around formulation and characterizations of these PCM emulsions, meticulously assessing their thermal attributes and stability. The results showed that producing these PCM emulsions using a high-energy manufacturing method with surfactant achieved superior dispersion stability and uniform size distribution throughout PCM emulsions. Among the pristine PCMs, n-Eicosane exhibited the highest latent heat of 252.7 kJ/kg during the melting process. In comparison, other PCMs, Paraffin 56/58, n-Octadecane, and n-Heptadecane demonstrated latent heat fusions of 197.7, 244.3, and 221.3 kJ/kg, respectively. Moreover, the energy storage density of PCM emulsions increased with increasing PCM concentration in basefluid. The highest energy storage density was observed in the case of 70 wt% n-Eicosane PCM emulsion, which is 401.1 kJ/kg. By examining the effectiveness of Paraffin-based PCM emulsions, this research aims to contribute to advancing eco-conscious and effective thermal management systems across diverse applications.

Analysis and design of module-level liquid cooling system for rectangular Li-ion batteries

To promote energy conservation and emission reduction, the electric vehicles (EVs) are developing rapidly. An effective battery thermal management system (BTMS) can extend the service life of batteries and avoid thermal runaway. In this study, a liquid-cooling management system of a Li-ion battery (LIB) pack (Ni-Co-Mn, NCM) is established by CFD simulation. The effects of liquid-cooling plate connections, coolant inlet temperature, and ambient temperature on thermal performance of battery pack are studied under different layouts of the liquid-cooling plate. Then, A new heat dissipation scheme, variable temperature cooling of the inlet coolant, is proposed. Results indicate that connecting two sets of liquid coolant plates in a 3-series, 1-parallel configuration can effectively reduce the maximum temperature of the battery pack from 48.73 ℃ to 30.75 ℃, while controlling the maximum temperature difference to 3.98 ℃ at the end of discharge. Simultaneously, the proposed cooling scheme reduces the maximum temperature difference within the battery pack by 36.09 % at the beginning of the discharge period. This study provides a valuable reference into advancing BTMSs of battery pack-level for EVs.

Enhancing thermal management in cylindrical Li-ion battery through PCM integration with variable contact area

Cylindrical Li-ion batteries are widely embraced in various sectors, notably electric vehicles and renewable energy storage systems. An effective thermal management system is vital for their safe and dependable operation, enhancing both the performance and reliability of the system. This study employs a distinctive hybrid cooling strategy consisting of a phase change material (PCM) at the centre of the battery and liquid cooling at the surface of the cylindrical batteries. The contact area between the coolant and the battery’s surfaces varies to make sure same heat transfers from each battery. This approach is instrumental in maintaining thermal uniformity and regulating the maximum temperature. In the numerical analysis, we employed ANSYS Fluent 2022 R1 to create the computational model encompassing the Li-ion battery, PCM, and liquid cooling system. This arrangement utilized eight 18650Li-ion batteries, with each battery housing a 2 mm radius PCM rod at the centre of the batteries. A heat-conducting element (HCE) was introduced to facilitate contact between the battery and the coolant channel. Water was selected as the coolant, and the coolant channel cross-sectional area is 65 × 2 mm2. The relationship governing the variable contact area is determined by fixing the velocity and the first battery contact area. The variable contact geometry maintains thermal uniformity throughout the battery module, resulting in a 74% enhancement in thermal uniformity. Nevertheless, the integration of PCM inside the battery effectively prevents individual batteries from surpassing specified temperature limits. It yields a remarkable 36.64% enhancement in thermal uniformity compared to situations in which PCM is not present, albeit with a 3.75% capacity loss. Furthermore, the study investigates the effects of coolant flow rates and performs an extensive analysis of temperature variation and melting fraction.

Employing extended surfaces for a hybrid battery thermal management system comprising PCM and refrigerated cooling air: An experimental investigation

If electric vehicles (EVs) are to supersede a larger share of the automobile market, developing safer battery packs with longer life and larger energy and power capacities is crucial. An effective battery thermal management system (BTMS) can promise many critical attributes of an EV battery pack, such as safety, life, and reliability. This article presents an effective BTMS with a novel hybrid design in which phase change material (PCM) is hybridized with a refrigerated air stream equipped with fins. The presented hybrid design is investigated experimentally and the role of fin structure and environmental conditions are examined. In addition, active and passive cooling strategies are also investigated to provide a more comprehensive analysis. The results show that the pure passive BTMS cannot control the module temperature in hot environments. On the other hand, although an active BTMS incorporating the refrigerated air provides a fast cooling process, the maximum temperature difference exceeds the improper value of 15 °C. The results demonstrate that the hybrid BTMSs can effectively control the temperature as well as minimize the maximum temperature difference. Furthermore, employing fins in the hybrid BTMSs leads to faster cooling. Among the three investigated fin structures, the spiral structure shows the best performance in controlling the average temperature of the module with a 4.2 °C temperature reduction relative to a similar case with no fin. The results of this study show that in long-term operation, a hybrid cooling strategy requires about one-third less energy in comparison to an active cooling strategy.

Parametric investigation of battery thermal management system with phase change material, metal foam, and fins; utilizing CFD and ANN models

The focus on developing an effective battery thermal management system (BTMS) to maintain optimal temperatures for lithium-ion batteries (LIBs), especially in electric vehicle (EV) applications, has grown significantly. The effective BTMS not only enhances the cooling performance of LIBs but also contributes to increased passenger safety and mileage of EVs. This study investigates BTMS configurations with fins, metal foam, and phase change material (PCM) to minimize temperature of battery during 3C discharging in varying conditions. Additionally, the study explores the impact of different BTMS material combinations and various fins lengths on system performance as a parametric investigation. Moreover, to streamline the analysis process and introduce novelty, artificial intelligence is explored as an alternative to computational fluid dynamics for predicting liquid fraction of PCM and temperature of battery, enhancing the innovative aspect of this study. Numerical simulations, using a non-equilibrium thermal model for metal foam modeling, reveal that the fourth case, integrating all three passive approaches, maintains the lowest temperature and enhances LIB cooling. The optimum BTMS shows a reduction of 3 K compared to BTMS utilizing pure PCM. During discharge process, the temperature difference in the battery decreases by approximately 75 % and 66 % in the fourth case compared to the first case (with pure PCM) under normal and harsh environmental conditions, respectively. Applying copper metal foam and copper fins yields the best results in reducing battery temperature. Increasing the length of fins and adding more fins effectively lower the battery temperature. Finally, an artificial neural network model is developed using the backpropagation learning technique coupled with the gradient descent optimization algorithm. The model exhibits excellent predictive capabilities, achieving high R-squared values of 0.98 for PCM liquid fraction and 0.99 for battery temperature.

Preventing Thermal Runaway Propagation in Lithium-ion Batteries using a Passive Liquid Housing

Lithium-ion batteries (LIBs), due to their high energy density, long lifespan, and low self-discharge, are widely used in various applications. However, they are challenged by the risk of thermal runaway and thermal degradation, so they require effective thermal management system. In this study, we investigated the application of a water-inclusive housing structure to battery modules to prevent thermal runaway propagation and enhance thermal management. The thermal and electrochemical behaviors of the batteries were analyzed using the ANSYS Fluent simulator. Through simulations, we determined the optimal cell spacing of the water-housing module that maximizes energy density while ensuring thermal stability. Our results indicate that a water housing module composed of 20 cylindrical cells(10s2p) with a cell spacing of 4 mm can effectively prevent thermal runaway propagation and reduce cell temperature by approximately 60% during normal discharge, while maintaining 80% of the volumetric energy density of a conventional module. Furthermore, the reliability of our simulation results was validated through thermal runaway and normal discharge tests. The proposed water housing method holds great promise in preventing thermal runaway propagation and enhancing thermal stability of LIB modules, thereby mitigating the risk of fire and thermal degradation during normal discharge.

Optimizing BESS performance: Anisotropic thermal properties and innovative parallel-flow cooling solutions

As the demand for efficient energy storage solutions intensifies, container-type battery energy storage systems (BESS) have gained prominence. BESS usually utilizes large-format laminated lithium-ion battery (LIB) modules, which inherently possess unique anisotropic thermal properties. Specifically, the surface regions with elevated temperatures exhibit high thermal conductivity, while the cooler zones at both ends manifest reduced conductivity. Such disparities emphasize the challenge of developing an effective battery thermal management system (BTMS) for these modules. To address this, our study introduces an innovative BTMS configuration wherein the batteries are aligned in series, while cooling air flows parallel to them. This parallel-flow cooling approach capitalizes on the anisotropic properties, intensifying airflow over the surfaces and recirculating cooling air to optimize heat dissipation from hotspots. Consequently, our system reduces the peak temperature from 42.3 °C to 37.5 °C, as well as the temperature difference (ΔT) from 14.3 °C to 10.2 °C across the entire BESS, respectively representing 11.3 % and 28.7 % changes. This leads to a substantial 75.9 % enhancement in the performance index, significantly augmenting both the safety and commercial viability of the BESS.

A Review of Thermal Runaway Prevention and Mitigation Strategies for Lithium-ion Batteries

Lithium-ion batteries are widely considered the leading candidate energy source for powering electric vehicles due to their high energy and power densities. The thermal runaway of lithium-ion batteries is the phenomenon of chain exothermic reactions within the battery. These reactions cause a sharp rise in the internal battery temperature causing the inner structures of the battery to destabilize and degrade, which eventually leads to the failure of the battery. This study thermal runaway initiation mechanisms, thermal runaway propagation, Thermal runaway is a major safety concern; therefore, the development of mathematical and numerical experimental models to predict thermal runaway is reviewed, which provides useful data to design and develop battery packs with thermal runaway safety features.It explores the importance of effective battery thermal management systems to prevent thermal runaway and reviews strategies for mitigating damages in case of an occurrence.

Thermal Performance Enhancement of Lithium-Ion Batteries Using Phase Change Material and Fin Geometry Modification

The rapid increase in emissions and the depletion of fossil fuels have led to a rapid rise in the electric vehicle (EV) industry. Electric vehicles predominantly rely on lithium-ion batteries (LIBs) to power their electric motors. However, the charging and discharging processes of LIB packs generate heat, resulting in a significant decline in the battery performance of EVs. Consequently, there is a pressing need for effective battery thermal management systems (BTMSs) for lithium-ion batteries in EVs. In the current study, a novel experimental BTMS was developed for the thermal performance enhancement of an LIB pack comprising 2 × 2 cells. Three distinct fin configurations (circular, rectangular, and tapered) were integrated for the outer wall of the lithium-ion cells. Additionally, the cells were fully submerged in phase change material (PCM). The study considered 1C, 2C, and 3C cell discharge rates, affiliated with their corresponding volumetric heat generation rates. The combination of rectangular fins and PCM manifested superior performance, reducing the mean cell temperature by 29.71% and 28.36% compared to unfinned lithium-ion cells under ambient conditions at the 1C and 2C discharge rates. Furthermore, at the 3C discharge rate, lithium-ion cells equipped with rectangular fins demonstrated a delay of 40 min in reaching the maximum surface temperature of 40 °C compared to the unfinned ambient case. After 60 min of battery discharge at the 3C rate, the cell surface temperature of the rectangular fin case only reached 42.7 °C. Furthermore, numerical simulations showed that the Nusselt numbers for lithium-ion cells with rectangular fins improved by 9.72% compared to unfinned configurations at the 3C discharge rate.

A novel thermal history sensor for thermal barrier coatings based on europium (III) ion self-reduction in barium aluminate

Thermometry of thermal barrier coatings (TBCs) is essential for designing effective thermal management systems and prolonging the service life of components in aeroengines and gas turbines. However, conducting on-line thermometry in these systems is challenging because it requires physical or optical access to components during operation. A promising alternative is off-line thermometry, in which phosphorescent thermal-history sensors are used to record exposure temperatures after operation. In this study, we synthesized europium (III)-ion-doped barium aluminate (BaAl2O4:Eu3+) via a solid-state reaction and confirmed its ability to function as a thermal history sensor. Subsequently, we developed a new thermal-sensing strategy based on the self-reduction of Eu3+ to Eu2+ in a BaAl2O4:Eu3+ phosphor exposed to high temperatures (900–1300 °C) in ambient air. The Eu3+ concentration decreased as the heat exposure temperature increased due to self-reduction of Eu3+ to Eu2+, which irreversibly changed the phosphorescence of BaAl2O4:Eu3+, i.e., its spectra, the ratio of the phosphorescence intensities of Eu3+ and Eu2+, and the lifetime of Eu3+. As the heat exposure temperature increased, the ratio of the phosphorescence intensities of Eu3+ and Eu2+ monotonically decreased due to self-reduction, whereas the phosphorescence lifetime of Eu3+ initially gradually increased until the heat exposure temperature reached 1000 °C because of the degeneration of concentration quenching, and then decreased as the temperature exceeded 1000 °C because of the degeneration of lattice distortions. This demonstrates that heat exposure temperatures exceeding 1000 °C can be quantitatively evaluated through off-line analysis of Eu3+ and Eu2+ phosphorescence intensity ratios and Eu3+ lifetime at room temperature. Thus, BaAl2O4:Eu3+, a self-reducing phosphor, is a potential sensor for off-line thermometry of TBCs.