Effective Thermal Management System Research Articles

Experience in the development of an effective thermal management system for the high-voltage battery of the vehicle

For the effective operation of the vehicle, which includes a high-voltage battery (HVB), it is first necessary to understand what conditions it is designed for. There are a number of criteria for the selection of HVBs for vehicles. One of them is the thermal management system, which ensures the operation of a HVB in optimal temperature mode. In HVBs, it is necessary to maintain an optimum temperature for maximum efficiency and service life. The article discusses the preferred thermal management system of the main manufacturers of vehicles with HVB. The technical solutions, the applied designs and the development trends of the designs of the temperature control of HVBs are described. On the basis of the considered structures, operating conditions and prospects for the development of the market for such vehicles, the concept of creating an effective thermal management system for HVBs for projected vehicles has been proposed. A classification of the thermal management system of HVBs as part of a vehicle, depending on the climatic conditions of operation, is proposed. One of the developed variants of perspective designs of high-voltage batteries of a vehicle operated in a wide range of temperatures is presented.

Form-stable phase change materials based on polyolefin elastomer and octadecylamine-functionalized graphene for thermal energy storage

Latent heat storage using organic phase change materials (PCMs) have the potential to alleviate the contradiction between supply and demand in energy. However, the usage of PCMs is compromised by deficiencies including liquid leakage during liquidation and solidification, poor thermal conductivity and inferior thermal stability. Herein, we successfully fabricated a series of novel form-stable phase change materials (FSPCMs), using the polyolefin elastomer (POE) along with the octadecylamine-functionalized graphene (C18-rGO) acted as the supporting networks and paraffin as the thermal energy storage material. The octadecyl chain incorporated on the surface of graphene not only prevented from the graphene aggregation, but also endowed excellent structural stability to the composite FSPCMs. Meanwhile, the toughness of the composites was further improved with the addition of POE. Paraffin was tightly imprisoned in the frameworks formed by POE and the C18-rGO, resulting in no leakage even above their phase change temperature. As expected, the composite FSPCMs demonstrated reliable thermal stability and high thermal energy storage capacity. In particular, the composite FSPCMs was capable of absorbing or releasing stored thermal energy at a high rate, illustrating a great potential to be used as the effective thermal energy storage and thermal management systems.

EFFECT OF SURFACE WETTABILITY AND SURFACE ROUGHNESS ON SiO2 AND COPPER HYBRID THIN-FILM-COATED SURFACES FOR NUCLEATE BOILING PERFORMANCE

The present scenario shows that the usages of electronics equipment are very extensive because of its performance and compactness. The concept of boiling heat transfer is applied to cool the equipment for better thermal management system. In the present experimental investigation, the copper substrates were coated by SiO2 and copper hybrid thin film by the radio frequency sputtering method. The thickness of the coating was selected as 250 nm, 500 nm, and 750 nm. The contact angle of the SiO2 and copper-coated hybrid surface was measured by goniometer, and structural studies were conducted by images from a scanning electron microscope and a stylus profilometer. The wettability of surfaces was improved significantly because of active nucleation sites created by thin-film coating. The nucleate boiling test was carried out by the pool boiling experimental setup for deionized (DI) water at saturation temperature and atmospheric pressure. The critical heat flux (CHF) and boiling heat transfer coefficient (HTC) were calculated, and compared with bare copper substrate. The results showed that the critical heat flux was enhanced by 45%, 53%, and 62%, whereas the boiling heat transfer coefficient was 63%, 97%, and 130% for 250-nm-, 500-nm-, and 750-nm-thick surfaces, respectively. The reason for this enhancement was due to increased nucleation site density which deals with the bubble formation and departure. The critical heat flux and boiling heat transfer enhancement at low wall superheat reveals a better heat transfer mechanism for an effective thermal management system.

Experimental investigation on thermal management of cylindrical Li-ion battery pack based on vapor chamber combined with fin structure

In electric vehicles, the performance of the power battery is closely related toits operating temperature, which makes it necessary to develop an effective and compact thermal management system. In this paper, a novel battery thermal management system for cylindrical Li-ion battery pack based on vapor chamber combined with fin structure is developed. A set of experiments concerning temperature control performance of the system under different discharge rates (2C, 3C, 5C) at ambient temperature of 25 °C is conducted. Subsequently, the effects of heat dissipation area, flow rate and way of condensation (air-forced cooling and water cooling) on cooling performance of the system are investigated and analyzed. The results show that the vapor chamber can notably alleviate the average temperature rise and improve the uniformity of temperature distribution within the battery pack. Furthermore, with the rising of dissipation area, the temperature control effect of the system becomes more effective. In addition, comparing to air-forced cooling, the system hybridized with water cooling exhibits lower maximum temperature and more uniform temperature distribution. However, flow rate has little effect on cooling performance. The above results indicate that applying vapor chamber combined with fin structure is a viable solution to thermal management of Li-ion battery pack.

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 Tmax 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 Tmax 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.

Dynamic thermal behavior of micro heat pipe array-air cooling battery thermal management system based on thermal network model

An effective battery thermal management system is crucial for electric vehicles because the performance of lithium ion battery is sensitive to its operating temperature. In this study, a thermal management system equipped with micro heat pipe array (MHPA) is designed. An equivalent thermal resistance model is developed for MHPA based on thermal circuit method. The accuracy of the proposed model is validated by comparing the simulation results with experimental data under steady and dynamic and operating condition. A validated lumped thermoelectric model is adopted for prismatic lithium ion battery. The proposed thermal resistance model is combined with the battery model in order to predict the transient temperature distribution of a battery pack based on MHPA cooling. Simulations are conducted for air-cooled MHPA thermal management system. Temperature rise and temperature gradients of the designed cooling system are compared with direct forced convection. Simulation results demonstrate that the MHPA-based battery thermal management provides a quick response to ensure the temperature stability during rapid changing operating condition.

Boundaries of high-power charging for long-range battery electric car from the heat generation perspective

High-power charging (HPC) has been associated with a great potential to shorten the charging time, relative to increasing the all-electric range (AER) of battery electric cars (BECs). Such promise of applicability is however restrained by setbacks attributed to the high-voltage system of BECs, its negative influence on the battery performance, and a higher requirement of charging infrastructures. More importantly, the core issue is the functionality of the battery, as research has found that HPC may cause a high charging rate on the battery cell that consequently promotes its heat generation and eventually results in a significant loss of functionality and safety degradation. Considering these elements, the thermal reaction of a battery under HPC is seemingly the key toward the design of an effective thermal management system. Thus, we conducted the present study with a focal objective of examining the thermal reaction of a traction battery to the HPC, to evaluate the gap between existing battery technologies and HPC to find the suitable condition. We investigated the heat generation characteristics of Nickel–Cobalt–Manganese (NCM) and lithium iron phosphate (LFP) batteries by HPC testing in non-adiabatic and adiabatic conditions, respectively, for different charging rates from 0.5 to 5.0C. We analyzed and incorporated the test results to establish a model of battery heat generation, which could predict temperature rise under specified conditions. Moreover, we proposed an HPC operating boundary by considering the present battery technologies. The findings herein indicate that the increased charging rate leading to higher heat generation and lower charge efficiency can be effectively handled through specific thermal management, which, with the boundary, provides a limit for the optimal operation region to avoid safety risk. More practically, a good thermal management system is required to control the boundary setting and extend the operation region of battery charging.

Heat Generation and Thermal Management of a Rapid-Fire Electromagnetic Rail Launcher

The pulse current can raise the bulk temperature of rails in the electromagnetic rail launcher (EMRL) during each shot. Quantifying the energy deposited in the rails and implementing an effective thermal management system are the key to tactical applications of the EMRL. This paper acquired the spatial distribution characteristics of total heat in the rails by using an analytical model and a multiphysics coupled model based on the hybrid finite-element/boundary-element method. The rail segment that produces the most heat is located where the armature arrives near the end time of the rising edge of pulse current. Since the rails suffer the severest stress when the armature passes, the key to the thermal management is to control their residual temperature rise when the armature passes. Therefore, the horseshoe cooling grooves dug on the back of the rails, which have low-stress concentration effect and good engineering feasibility avoiding internal drilling problem, are enough to effectively cool the rails. The experimental data measured by the fiber Bragg grating sensors in the tests of a single shot and a rapid firing of two agree well with the simulation results, which verifies the validity of the thermal management strategy. Furthermore, through prediction, the maximum residual temperature rise is only 2.57 K in the stage of heat balance at a sustained firing rate of 12 shots per minute for the 30 mm $\times30$ mm rectangular caliber launcher presented in this paper. These conclusions are also adaptive to large-scale launchers and have guiding significance to the engineering application of the EMRL.

(Invited) Understanding Downstream Risk from Lithium-Ion Battery Thermal Runaway & Designing for Safety

With continued advances in battery technologies, batteries have become one of the leading solutions for not only portable power applications but also energy storage applications. Because of the high energy density in advanced batteries, one key safety goal is preventing the unintended release of stored energy. A catastrophic failure of a battery pack can occur if one or more cells in the battery pack undergo a thermal runaway event that results in a rapid release of the stored energy in the battery. Thermal runaway can lead to a release of flammable gases and heat, which can potentially result in fire and explosions. The design of effective thermal management systems or fire mitigation systems requires proper quantification of the thermal failure characteristics. This presentation will detail several research activities that have been developed to analyze and quantify thermal safety aspects of batteries, as well as to identify/quantify potential toxicology hazards. This process involves real-time gas analysis from lithium-ion battery failure events, as well as post-failure composition analysis and identification of gas combustion properties. The implications of this work toward designing for safety and integration into risk analyses will be discussed.

Decoupling of heat generated from ejected and non-ejected contents of 18650-format lithium-ion cells using statistical methods

Effective thermal management systems, designed to handle the impacts of thermal runaway (TR) and to prevent cell-to-cell propagation, are key to safe operation of lithium-ion (Li-ion) battery assemblies. Critical factors for optimizing these systems include the total energy released during a single cell TR event and the fraction of the total energy that is released through the cell casing versus through the ejecta material. A unique fractional thermal runaway calorimeter (FTRC), designed to characterize said critical factors, was utilized to examine the TR behavior of 18650-format Li-ion cells representing a variety of manufacturers, chemistries, capacities, and safety features. Primarily, the impacts of bottom vent (BV) safety features, varied cell casing thickness, and Dreamweaver cellulose based separators were assessed for select cell types. A subset of cells also had an imbedded internal short circuiting (ISC) device to allow examination of TR behavior initiated at lower temperatures (i.e. closer to field failure conditions). The impact of bottom rupture on TR behavior was also examined for experiments that resulted in this non-standard failure mechanism. Statistical analysis of the results for each cell configuration reveals that a lognormal distribution effectively characterizes the variation of total TR energy release. Typically 20%–30% of the total energy yield is released through the cell casing with the remainder through the ejecta material. Higher energy cells tend to exhibit more violent ejections and less predictable TR events. Inclusion of a BV feature reduces the overall severity of the TR event and can increase the predictability. Results also suggest that the magnitude of the TR event may not be directly proportional to the stored electrical energy, but rather has additional dependence on other design and failure mode factors.

Analysis of Passive Temperature Control Systems Using Phase Change Materials for Application to Secondary Batteries Cooling

Abstract Temperature control is one of the most significant factors to improve the performance and extend the cycle life of a battery. It is, therefore, important to design and implement an effective battery thermal management system (TMS). Phase change materials (PCMs) can be used as a cooling means for batteries. In the present paper, a preliminary analysis of the thermal behavior of PCMs used to cool down a heated metal surface was carried out. Tests have shown that pure PCMs are able to limit the temperature increase, but only for relatively low-heat fluxes. At higher values of the heat produced, the thermal conductivity of the PCM was increased by using solid foams characterized by higher thermal conductivity; it was, thus, possible to keep the surface temperature within safe limits for longer times. A computational fluid dynamics (CFD) model of the composite material (PCM + solid foam) was also developed, which allowed to predict the temperature trend within the system under different boundary conditions. However, the average thermal conductivity of the composite system that best fitted the experimental results was found to be much lower than that theoretically predicted by using common semiempirical correlations.

Investigation into the effectiveness of nanofluids on the mini-channel thermal management for high power lithium ion battery

An effective thermal management system that can maintain the maximum temperature and temperature difference in a desired range is needed to ensure a good performance and safety of lithium-ion batteries. In this paper, a mini-channel cooling system for high-power prismatic battery thermal management is investigated numerically using a three dimensional CFD model. The thermal performances of the cooling system when using different base fluids (i.e. water, ethylene glycol and engine oil) and their corresponding nanofluids as coolants are compared. The thermal conductivities of nanofluids are calculated using a semi-empirical correlation and the dynamic viscosities of nanofluids with different base fluids are obtained by curve fitting using experimental data. Due to its high thermal conductivity, water achieves a much better cooling effect than ethylene glycol and engine oil. However, the impact of adding nanoparticles is more remarkable for fluids with lower thermal conductivity, especially for engine oil. The nanoparticle addition is able to greatly reduce the cell maximum temperature but has a limited effect on the temperature uniformity. In addition, an evident performance enhancement is observed by increasing the suspended nanoparticles volume fractions despite that the required power cost is increased at the same time. Different influencing factors including the flow velocity and coolant inlet temperature on the mini-channel cooling performance and the enhancement of adding nanoparticles are also studied. It is observed that all of these influencing factors have significant impacts on the mini-channel cooling effects.

Multi-objective genetic optimization of the thermoelectric system for thermal management of proton exchange membrane fuel cells

As a clean power system with a narrow temperature range of typically 60–95 °C, the low temperature (LT) proton exchange membrane fuel cell (PEMFC) requires an effective thermal management system to enhance its efficiency and durability. This paper focuses on a genetic algorithm based optimization of the thermoelectric generator (TEG) as applied to the PEMFC system. The genetic algorithm approach is advantageous over similar previous research in that it enables multi-objective optimization where the various TEG module parameters can be configured towards critical objectives such as maximum output power, minimal mass and maintaining the PEMFC within its operating temperature range. A second case study is also studied where the combined efficiency of the PEMFC and TEG is selected as an objective in replacement of the maximum TEG output power. Optimization results suggest that, in both cases, there is a trade-off situation between maximum output TEG power or maximum system efficiency with respect to system mass. It is also shown that the most important benefit of increasing the cooling convection coefficient is that it increases the system’s specific power where the heat sink areas can be smaller to achieve the same cooling rate.

Temperature uniformity of a heated lithium-ion battery cell in cold climate

At low temperatures, charge–discharge performances of lithium-ion batteries decline rapidly. Preheat is essential for an effective battery thermal management system. Temperature uniformities of lithium-ion battery cells heated by the self-heating lithium-ion battery structure (SHLB) method and the wide-line metal film (WLMF) method are studied by the transient three-dimensional heating finite element models. Under the same condition, the temperature of a lithium-ion battery cell heated by SHLB heating method is three times more uniform than that heated by the WLMF heating method. However, temperature uniformity of a lithium-ion battery cell heated by SHLB method still is poor. Effects of environment temperature, heating time, heating power, thickness of a lithium-ion battery cell and stand time after heating on temperature distribution of a lithium-ion battery cell heated have been analyzed. For the two heating methods, heating power, thickness of a lithium-ion battery cell and stand time after heating have remarkably influences on temperature distribution of a heated lithium-ion battery cell. For SHLB heating method, temperature uniformity of a heated lithium-ion battery cell is acceptable by decreasing heating power and thickness of a lithium-ion battery cell if there is no safety issue on the structure. Meanwhile, for WLMF heating method, temperature uniformity of a heated lithium-ion battery cell is also acceptable by decreasing heating power, thickness of a lithium-ion battery cell or increasing stand time after heating.

Heat generation in lithium-ion batteries with different nominal capacities and chemistries

Heat generation in lithium-ion batteries (LIBs), different in nominal battery capacity and electrode materials (battery chemistry), is studied at various charge and discharge rates through the multiphysics modeling and computer simulation. The model is validated using experimental results obtained in lab and the results reported by other researchers in literature. All sources of heat generation – including reversible heat generation and irreversible heat generation due to activation, concentration, and ohmic (electronic and ionic) polarizations – in LIBs with graphite/LiFePO4, graphite/LiMn2O4, and graphite/LiCoO2 electrode materials are quantified and the effects of the battery nominal capacity at various charge and discharge rates are studied. This study determines which sources of heat generation are significant and which sources of heat generation are negligible at different LIBs design and operating conditions. The contribution of LIB’s different components including cathode, anode, separator, and current collectors in heat generation in LIBs is also determined. The results of this study assists battery engineers and researchers to characterize the thermal behavior of LIBs and have a much more exact prediction over the battery heat generation, leading to designing effective thermal management systems and providing accurate battery management systems for different applications of LIBs as well as cell design optimization and operation.

Optimization of a phase change material based internal cooling system for cylindrical Li-ion battery pack and a hybrid cooling design

An effective and compact thermal management system is essential for modern lithium-ion (Li-ion) battery powered vehicles, which involve rigorous constraints on weight and volume. In this paper, a phase change material (PCM) based battery internal cooling system is proposed by replacing the hollow mandrel in cylindrical battery with a PCM-filled mandrel, and it is tested on a fabricated steel cell. With verifying its effectiveness in cooling, as well as the accuracy of the thermal model, numerical studies are carried out on a Li-ion battery submodule consisting of 40 cylindrical batteries. Variables including PCM species (n-octadecane, n-eicosane, and n-docosane), PCM core size, and PCM core size distribution are used in the simulations to optimize the design by examining the performance indices involving temperature, temperature difference, PCM solidification time, and pack compactness. The numerical results show that the PCM cores can effectively alleviate the temperature rise inside the battery pack, and a uniform temperature distribution can be obtained when thicker PCM cores are embedded in the interior batteries. A pack compactness study indicates that the internal cooling is a space-saving design that facilitates the achievement of the high energy density of the battery pack.

Numerical Analyses on Aluminum Foams Cooling Plate for Lithium-ion Batteries

Successful implementation of electric vehicle relies strongly on its energy storage systems. Li-ion battery is the best candidate for the energy storage systems due to its energy density, power density and low maintenance. Temperature will affect the power availability, driveability and cycle life of the battery. Hence, effective thermal management system is needed to prolong cycle life and ensure balance charging/discharging among the cell in the battery pack. In this study, a battery module comprised three pieces of Li-ion pouch cell is arranged side by side and attached to aluminum foam heat sink to extract heat generated. The performance of two different type of pores density aluminum foams with different porosity were investigated numerically. Experimental correlation of Nusselt Number, permeability and resistance loss coefficient from the literature was extracted and used in the steady state CFD simulation. Among the metal foams, 10 PPI aluminum foam with 0.918 porosity offered the highest thermal performance and lowest flow resistance. Hence, it was shown that aluminum foam can be used to replace heat sink in the battery pack.

하이브리드 차량의 엔진 및 배터리 냉각팬 구동용 BLDC모터 개발

Hybrid Electric Vehicles(HEVs) have seriously come into prevalence recently as car manufacturers and consumers have become more aware of the environmental and economic problems of conventional vehicles. For the alternative power-train and battery cooling systems in HEVs, an effective thermal management system is required, and many automakers are interested in using Brushless DC(BLDC) motors for cooling fans for the overall traction unit's performance and energy saving capability. This paper presents the development status of BLDC motors as major parts of the power-train, i.e. the engine cooling and battery cooling fans of HEVs. A design that uses BLDC motors for the power-train and each battery cooling fan, is successfully implemented through using electro-magnetic analysis, and prototype BLDC motors are examined. As experimental results, the BLDC motors achieved an efficiency of 85% as engine cooling fans and 72% as a battery thermal management fan motor. The electric cogging noise is significantly reduced by changing the skew of the slot pitch angle and optimizing the magnetic shape.

An experimental study of heat pipe thermal management system with wet cooling method for lithium ion batteries

An effective battery thermal management (BTM) system is required for lithium-ion batteries to ensure a desirable operating temperature range with minimal temperature gradient, and thus to guarantee their high efficiency, long lifetime and great safety. In this paper, a heat pipe and wet cooling combined BTM system is developed to handle the thermal surge of lithium-ion batteries during high rate operations. The proposed BTM system relies on ultra-thin heat pipes which can efficiently transfer the heat from the battery sides to the cooling ends where the water evaporation process can rapidly dissipate the heat. Two sized battery packs, 3 Ah and 8 Ah, with different lengths of cooling ends are used and tested through a series high-intensity discharges in this study to examine the cooling effects of the combined BTM system, and its performance is compared with other four types of heat pipe involved BTM systems and natural convection cooling method. A combination of natural convection, fan cooling and wet cooling methods is also introduced to the heat pipe BTM system, which is able to control the temperature of battery pack in an appropriate temperature range with the minimum cost of energy and water spray.

Analysis of electric and thermal behaviour of lithium-ion cells in realistic driving cycles

A substantial part of electric vehicles (EVs) powertrain is the battery cell. The cells are usually connected in series, and failure of a single cell can deactivate an entire module in the battery pack. Hence, understanding the cell behaviour helps to predict and improve the battery performance and leads to design a cost effective thermal management system for the battery pack. A first principle thermo electrochemical model is applied to study the cell behaviour. The model is in good agreement with the experimental results and can predict the heat generation and the temperature distribution across the cell for different operating conditions. The operating temperature effect on the cell performance is studied and the operating temperature for the best performance is verified. In addition, EV cells are examined in a realistic driving cycle from the Artemis class. The study findings lead to the proposal of some crucial recommendation to design cost effective thermal management systems for the battery pack.