Showing papers in "International Journal of Heat and Mass Transfer in 2022"

A CNN-ABC model for estimation and optimization of heat generation rate and voltage distributions of lithium-ion batteries for electric vehicles

Abstract: Accurate estimation of battery voltage and heat generation rate (HGR) at different conditions is critical to manage a battery system on behalf of making safe and efficient operations for electric vehicles (EVs). However, due to malfunction structures within the battery cell, it is extremely challenging task to estimate the HGR and voltage by measuring the external parameters. Although there are many parameter estimation algorithms, it has become essential to make better estimations with deep networks. In this study, we propose a novel scheme, namely convolutional neural network (CNN)-artificial bee colony (ABC) leveraged from CNN and ABC algorithm for HGR and voltage estimation. Unlike other CNN methods, in this proposed CNN model, hidden features in the data are dynamically revealed and thanks to artificial feature extraction. The Voltage and HGR data are used as inputs of the proposed model after the preprocessing operation is terminated. To optimize the HGR and voltage estimates and minimize the error functions, new objective and fitness functions are introduced using the ABC algorithm. The proposed model is tested with several experiments that are carried on 20Ah Lithium phosphate (LFP) battery at different discharge rates of 1C, 2C, 3C, and 4C, and various temperature ranges of 5°C, 15°C, 25°C, and 35°C, and voltage distributions, as making long-term HGR and voltage predictions. The proposed methods are compared with artificial intelligence methods such as Linear Regression (LR), Multi Linear Regression (MLR), Decision Tree (DT), Random Forest (RF), Support Vector Machine (SVM), Artificial Neural network (ANN), Long Term Short Memory (LSTM), and basic CNN. The performance results strikingly show that the proposed CNN-ABC scheme is better than others. The proposed scheme produces 1.38% and 99.72% root mean square error (RMSE) and R2 in HGR estimation, while 3.55% and 99.82% in voltage data estimation, respectively, when applying the ABC to the proposed CNN architecture.

A novel study on a micromixer with Cantor fractal obstacle through grey relational analysis

Abstract: • The Poiseuille number is proposed to evaluate the safety and reliability of the micromixer. • Orthogonal experiment is used to ensure that the number of experiments is small and evenly distributed. • Grey relational analysis is used to find the micromixer with the best overall performance. • A new type of micromixer with Cantor fractal baffle is proposed. This paper proposes a multi-objective optimization method for a micromixer with Cantor fractal baffles through grey relational analysis, and evaluates the comprehensive performance of the micromixer through two aspects. The height of the baffle (h), the distance of the baffle (p), the width of the microchannel (L) and the height of the microchannel (H) are selected as design variables, and the orthogonal experiment table L 16 (4 4 ) is obtained. The optimized performance characteristics take into account the mixing index and Poiseuille number. Numerical simulations are used to obtain the results of each experimental design group. We use the grey relational degree as an index to evaluate the comprehensive performance of the multi-objective of the micromixer, and optimize to find a set of optimal design variables. Finally, we judge the influence of the four design variables on the two performance characteristics respectively, so as to obtain the importance of different design variables. The results show that the optimized micromixer, namely CFM-11, has a maximum increase of 23.75% in mixing index and a maximum decrease in Poiseuille number of 34.40%. Among all the parameters, the h and the L have a greater impact on the performance characteristics. This work can provide a good analysis method for multi-objective research and structural optimization related to micromixers.

A novel study on a micromixer with Cantor fractal obstacle through grey relational analysis

Abstract: This paper proposes a multi-objective optimization method for a micromixer with Cantor fractal baffles through grey relational analysis, and evaluates the comprehensive performance of the micromixer through two aspects. The height of the baffle (h), the distance of the baffle (p), the width of the microchannel (L) and the height of the microchannel (H) are selected as design variables, and the orthogonal experiment table L16(44) is obtained. The optimized performance characteristics take into account the mixing index and Poiseuille number. Numerical simulations are used to obtain the results of each experimental design group. We use the grey relational degree as an index to evaluate the comprehensive performance of the multi-objective of the micromixer, and optimize to find a set of optimal design variables. Finally, we judge the influence of the four design variables on the two performance characteristics respectively, so as to obtain the importance of different design variables. The results show that the optimized micromixer, namely CFM-11, has a maximum increase of 23.75% in mixing index and a maximum decrease in Poiseuille number of 34.40%. Among all the parameters, the h and the L have a greater impact on the performance characteristics. This work can provide a good analysis method for multi-objective research and structural optimization related to micromixers.

Coarse-grained CFD-DEM modelling of dense gas-solid reacting flow

Abstract: Dense gas-solid reacting flow is practised in many industrial processes where the particle number may be huge and cannot be modelled using the conventional CFD-DEM approach. In this paper, a coarse-grained CFD-DEM model (CGM) is developed to simulate dense gas-solid reacting flow involving multiphase flow and heat and mass transfers. The CGM is first validated against the conventional CFD-DEM simulation results and experimental results. The CGM is then applied to simulate a reacting flow case of biomass gasification in a bubbling fluidised bed gasifier (BFBG) for capability demonstration. The results show that the size- and density-induced particle segregation and bubble evolution affect the hydrodynamics and thermochemical behaviours of biomass gasification in the BFBG significantly. The non-uniform distribution of gaseous species along with the radial and axial directions is captured. Compared with the conventional CFD-DEM, the CGM can reduce the computational cost significantly in the simulation of dense gas-solid reacting systems. The present work provides a cost-effective tool to simulate dense gas-solid reacting flow in various chemical reactors.

A review on passive and active strategies of enhancing the safety of lithium-ion batteries

Abstract: Lithium-ion battery (LIB) becomes the dominant candidate for electric vehicles (EVs) and energy storage systems (ESSs); nevertheless, as its popularization, the number of safety (fire) accidents regarding with LIB thermal runaway increases, undermining the public confidence. Safety turns into one of the main concerns in the widespread usage of LIBs. In this review paper, various faults in LIBs which have a potential risk leading to safety accidents are scrutinized firstly, followed by the presentation of recent progress in strategies of improving the safety of LIBs. Faults in large-scale LIB-based systems like EVs and ESSs for power grids include battery faults, sensor faults and actuator faults. The battery faults can be triggered by mechanical abuse, electrical abuse, thermal abuse as well as aging or degradation. This paper classifies the safety strategies into active safety strategies and passive safety strategies. Passive safety strategies pursue inherent safety in LIBs via material modification and alleviate the hazard level of faults through taking timely countermeasure like fire suppression or extinguishment once the LIB fire accident occurs. On the contrary, the active safety strategies aim to prevent the abuse conditions from developing into uncontrollable thermal runaway or fire accidents by effective state estimation and monitoring, fault diagnosis and early warning, thermal management, equalization technology, etc.

Heat transfer efficiency and electrical performance evaluation of photovoltaic unit under influence of NEPCM

Abstract: • A 3D model of PVT/PCM has developed to analyze the performance of the system • The effect of using different types of nanofluid and NEPCM is assessed. • Escalation of nanofluid concentration reduces the liquefaction rate of PCM. • NEPCM is capable to store more energy compared to pure PCM. • Electrical yield of PVT-TE/PCM reaches 13.93% which is 0.75% more than PVT/PCM. In present study, a design of PVT unit involving PCM has been analyzed. The influence of several types of nanofluids and NEPCMs at different concentrations on the system efficaciousness is assessed. The SiC, ZnO, MCNT (multi-walled carbon nanotube), Al 2 O 3 , Cu, and Ag nanoparticles are utilized within water and phase change material at concentrations of 0, 0.02, 0.04. The impact of different flow rates and various solar radiation intensities are also evaluated. In addition, the influence of using multilayer of PCMs (including OM35, RT35HC, and eicosane) with different combinations inside the PCM receptacle on the productivity of component is assessed. At last, a comparison study between PVT, PVT/PCM, PVT-TE (thermoelectric module), and PVT-TE/PCM collector is conducted to assess the impact of TE module integration with the PVT systems from the electrical and thermal perspectives. To simulate the procedure of the charging of paraffin, the enthalpy-porosity approach is used. In addition, a transient solver and pressure-based finite volume approach are selected to perform the simulation. Based on the acquired results, enhancing the flow rate of coolant from 3.77 to 7.54 ml/s leads to 7.21% reduction in liquid fraction. It also de-elevates the average PV temperature, average outlet temperature, and the PCM temperature by 7.06%, 35.13%, and 3.62%, respectively. Enhancement of the NEPCM concentration from 0 to 4% improves the escalating charging rate, however, it de-elevates the temperature of PV unit and the T out of coolant slightly.

Thermal management and performance improvement by using coupled effects of magnetic field and phase change material for hybrid nanoliquid convection through a 3D vented cylindrical cavity

Abstract: In this study, effects of using magnetic field and packed bed phase change material (PCM) system in a 3D cavity having ventilation ports on the performance improvements are analyzed during hybrid nanoliquid convection. Two different locations of inlet port is considered while the numerical study is conduced for various values (Reynolds number (Re, between 250 and 750), Hartmann number (Ha, between 0 and 100), size of the inlet (wd, between 0.15H and 0.85H) and nanoparticle loading amount (between 0.02% and 0.1%). When PCM is used in the vented cavity, 13% and 16.5% enhancements of average Nusselt (Nu) number are obtained as compared to no-PCM case at Ha=0 and Ha=100. A critical Ha is obtained beyond which the phase transition time (tc) is reduced and the value depends upon the inlet port location. The location of the inlet port has significant impacts on phase change dynamics and transition time. When it is closer to the wall (case-C2), tc is reduced. 65% and 80% of reductions in the tc are observed at the highest Re for configurations C1 and C2. The higher port size resulted in fast phase transition while reduction of 89% in tc is obtained at Re=750 for case C1. Nanoparticle loading accelerates the phase transition and tc is reduced by 10.4% and 9% for cases C1 and C2. However, the average Nu variation with PCM shows different behavior for cases C1 and C2. At the highest particle loading, 11% (t=52 min) and 13% (t=250 min) increments in the average Nu are achieved C1 and C2. A polynomial type correlation for tc is obtained in terms of Ha and nanoparticle amount in the heat transfer fluid.

Structure optimization of a heat pipe-cooling battery thermal management system based on fuzzy grey relational analysis

Abstract: An efficient thermal management system is essential to maintain its good performance of a power battery pack. Evaluating the impacts of influential factors on the system cooling performance helps guide the design of the battery thermal management system. In the present work, a battery thermal management system based on heat pipes combined with a liquid-cooling plate is proposed. Orthogonal design and fuzzy grey relational analysis are employed as evaluating methods, and numerical simulations are carried out to investigate the influence of four structure parameters of the aluminum sheet (the height, the thickness, the covering angle to battery, and the covering angle to heat pipe) on the temperature distribution of the battery pack. Results show that, in order to keep a good operating temperature range of the battery, the values of the height, the thickness, the covering angle to battery and the covering angle to heat pipe of the aluminum sheet are suggested to be above 50 mm, 2 mm, 75° and 60°, respectively. The covering angle of aluminum sheet to battery has the most influential impact on the system cooling performance, and the covering angle to heat pipe has the slightest influence. The optimal value of the maximum temperature is 37.58 °C and the temperature difference is 3.67 °C.

Structure optimization of a heat pipe-cooling battery thermal management system based on fuzzy grey relational analysis

Abstract: An efficient thermal management system is essential to maintain its good performance of a power battery pack. Evaluating the impacts of influential factors on the system cooling performance helps guide the design of the battery thermal management system. In the present work, a battery thermal management system based on heat pipes combined with a liquid-cooling plate is proposed. Orthogonal design and fuzzy grey relational analysis are employed as evaluating methods, and numerical simulations are carried out to investigate the influence of four structure parameters of the aluminum sheet (the height, the thickness, the covering angle to battery, and the covering angle to heat pipe) on the temperature distribution of the battery pack. Results show that, in order to keep a good operating temperature range of the battery, the values of the height, the thickness, the covering angle to battery and the covering angle to heat pipe of the aluminum sheet are suggested to be above 50 mm, 2 mm, 75° and 60°, respectively. The covering angle of aluminum sheet to battery has the most influential impact on the system cooling performance, and the covering angle to heat pipe has the slightest influence. The optimal value of the maximum temperature is 37.58 °C and the temperature difference is 3.67 °C.

Experimental study on heat transfer performance of sCO2 near pseudo‐critical point in airfoil‐fin PCHE from viewpoint of average thermal‐resistance ratio

Abstract: The printed circuit heat exchanger (PCHE) is one of the leading heat exchanger candidates in the supercritical carbon dioxide Brayton cycle, which has high efficiency and compactness. In the present paper, a novel type of PCHE with airfoil fins was proposed and tested. The effect of the thermal resistance variation on the heat transfer performance near the pseudo-critical point was analyzed. Meanwhile, a non-dimensional factor defined as the ratio of bulk temperature to the pseudo-critical temperature was applied to evaluate the heat transfer performance. The results indicate that the variation of the heat transfer performance can be attributed to the different average thermal-resistance ratios, where a larger the average thermal-resistance ratio corresponds to a better heat transfer performance. When the non-dimensional factor is around 1.03, the heat exchanger exhibits the highest heat transfer performance. In this regard, a working condition analysis method based on the non-dimensional factor and the average thermal-resistance ratio is suggested. Finally, a modified heat transfer correlation considering the non-dimensional working parameters near the pseudo-critical point is obtained.

Experimental and numerical studies on the heat transfer improvement of a latent heat storage unit using gradient tree-shaped fins

Abstract: To improve the thermal performance of horizontal latent heat storage (LHS) units, this study investigates two innovative LHS units using uniform and gradient tree-shaped fins. By coupling visualization experiments and three-dimensional numerical simulations, the melting/solidification behavior and thermal properties of innovative LHS units are comprehensively analyzed and compared with traditional LHS units. The results show that tree-shaped fins facilitate heat diffusion from point to area, breaking the heat transport hysteresis in traditional LHS units, thus accelerating the melting/solidification rate. During the melting process, the gradient tree-shaped fins strengthen the heat transfer in lower parts of the LHS unit and extend the convective heat transfer duration in upper regions, promoting the synergistic strengthening of natural convection and heat conduction in the late melting stage. Compared to the uniform fin layout, the gradient tree-shaped fins effectively increase the melting rate, shortens the melting duration by 9%, and further improve the overall temperature uniformity of LHS units. However, the non-uniform transport path of gradient tree-shaped fins is not conducive to solidification heat transfer with conduction as the primary thermal regime, which increases the temperature gradient of LHS units and prolongs the solidification duration by 57.4% compared to the uniform tree-shaped fins.

Three-dimensional numerical study of a cathode gas diffusion layer with a through/in plane synergetic gradient porosity distribution for PEM fuel cells

Abstract: This study proposes a through-plane (TP) and in-plane (IP) synergetic (SYN) gradient porosity distribution (GPD) in the cathode gas diffusion layer (CGDL) to enhance the mass transfer and water removal of a polymer electrolyte membrane (PEM) fuel cell. The novel SYN-GPD CGDL is comparatively evaluated with TP-GPD, IP-GPD and uniform porosity distribution (UPD) CGDL by implementing a three-dimensional multiphase fuel cell model. The results show that a higher porosity within CGDL near the cathode flow channel (CFC) for TP-GPD CGDL, however, a higher or lower porosity near the cathode outlet for IP-GPD CGDL improves the mass transfer and water removal within fuel cell, which benefitting the uniform distributions of oxygen and current density, and the cell performance. Additionally, as compared with the TP-GPD, IP-GPD and UPD CGDL, the SYN-GPD CGDL has a greater advantage in the enhancement of mass transfer and water removal, consequently resulting in much more homogeneous internal physical quantity profiles and a higher overall cell performance. Ultimately, the optimal SYN-GPD CGDL improves the maximum power density by 6.73%, while reducing the coefficient variations (CVs) of the oxygen mass fraction and current density by approximately 10.24% and 40.69%, respectively, compared with those of the UPD CGDL.

Experimental investigation on the performance of RT-44HC-nickel foam-based heat sinks for thermal management of electronic gadgets

Abstract: A large amount of heat is generated during the operation of electronic gadgets. Efficient thermal management is crucial for their safe operation and reliability. Phase change materials serve the role to maintain almost constant temperature during the phase change process by absorbing the generated heat. Therefore, the present experimental investigation is performed to single out the thermal performance of nickel foam-based heat sink embedded with RT-44HC paraffin as phase change material (PCM). Nickel foam is used for a high heat transfer area with a minimum reduction in the latent heat of a composite PCM. Results revealed that at the end of the charging process, the heat sink base temperature is reduced by 18.6% when a PCM volume fraction of 0.6 was added to the nickel foam. Furthermore, as the PCM fraction increased, the base temperature decreased further. An 11.6% additional decrease in temperature of the PCM was observed for volume fraction increment from 0.6 to 0.8. The effective thermal conductivity of the composite PCM was noticed to be enhanced by six times as that of a pristine PCM. The discharging process of the composite PCM was delayed compared with that of nickel foam without PCM. However, the sink temperature lies within the safe limits for the composite PCM. The latent heat of the composite PCM was diminished by 23% when effective thermal conductivity was enhanced. Thus, a nickel foam-PCM based heat sink is an efficient source to maintain the electronics temperature within the safe limits.

Canopy-to-canopy liquid cooling for the thermal management of lithium-ion batteries, a constructal approach

Abstract: With the growing interest on electric vehicles comes the question of the thermal management of their battery pack. In this work, we propose a thermally efficient solution consisting in inserting between the cells a liquid cooling system based on constructal canopy-to-canopy architectures. In such systems, the cooling fluid is driven from a trunk channel to perpendicular branches that make the tree canopy. An opposite tree collects the liquid in such a way that the two trees match canopy-to-canopy. The configuration of the cooling solution is predicted following the constructal methodology, leading to the choice of the hydraulic diameter ratios. We show that such configurations allow extracting most of the non-uniformly generated heat by the battery cell during the discharging phase, while using a small mass flow rate.

A comprehensive study on 21st-century refrigerants - R290 and R1234yf: A review

Abstract: Prolonged use of environment unfriendly refrigerants in high-grade energy systems has resulted in increased greenhouse gas emissions and ozone layer depletion. This has resulted in increased global warming. Therefore, it is important to analyze all the studies of any refrigerant before its use for the sustainable development of any system. The present review paper is an attempt to report all studies related to 21st-century refrigerants comprising sustainable refrigerants for longer use. In this regard, the historic evolution of refrigerants and their potential effect on global warming and ozone layer depletion are presented. Further, R290 and R1234yf are found to be promising alternatives amongst all refrigerants to be used as 21st-century refrigerants. An attempt has been made to provide a comprehensive study for these refrigerants, including their thermophysical properties, leakage in the compressor, leakage in the evaporator, leakage in the condenser, explosion characteristics due to leakage, and consequences due to leakage and explosion. In addition, a thorough study has been made for the use of oils, their importance, and their consequences in a refrigeration system. The study has also been made for the use of these refrigerants in flow boiling and condensation. The increased commercialization of electric vehicles and refrigerant use in electric vehicles may increase global warming in near future. Therefore, the discussion has been included to use these refrigerants in electric vehicle air conditioning systems. Finally, a short conclusion with the future scope is presented for the various aspect of 21st-century refrigerants.

Numerical analysis of single-phase liquid immersion cooling for lithium-ion battery thermal management using different dielectric fluids

Abstract: Lithium-ion battery (LIB) cells are responsible for powering most electric vehicles. LIB is still a superior battery available in the market because of its high energy density, specific power, and long cycle life. However, LIB comes with the challenges like thermal management as it is highly sensitive to temperature. Amongst different cooling methods, direct liquid cooling, also known as immersion cooling, can deliver a high cooling rate mainly because of its complete contact with the heat source. The single-phase liquid immersion with dielectric fluids (DELC) offers safety and cooling performance with lower parasitic power consumption and space requirements. This research involves studying and comparing different DELC's for the direct cooling of lithium-ion batteries. A numerical analysis of the 4S1P arrangement of LIB cells with direct cooling is conducted with three different DELC's including deionised water, mineral oil, and an engineered fluid. The transient behaviour of the battery module for various mass flow rates of DELC and at 1C,2C,3C-discharge rates are examined. All DELC maintains an excellent temperature homogeneity within the individual cells and LIB cells. The DELC with higher specific heat and thermal conductivity is suitable for cooling the LIB cells during high discharge conditions. However, all the dielectric fluids studied here effectively limit the temperature rise below 5 °C at 2-C discharging operation when the mass flow rate is increased to 0.05 kg/s. This improvement in thermal performance comes at the expense of extra power consumption. Even though both DELC-2 and DELC -3 delivered almost similar temperature rise values of 6.1, 5.2 °C, respectively during 2C discharging operation, the latter consumed 76.43% less power at a mass flow rate of 0.05 kg/s. For this reason, engineered fluids with lower viscosity values can be preferred over mineral oils. The deionised water is more effective for limiting the temperature rise below 2.2 °C for 3C discharging with the least parasitic power consumption of 0.52 mW at a mass flow rate of 0.05 kg/s. A variable cyclic load matching HWFET-driving cycle has been applied to the battery pack with all three DELCs, and all three fluids limited temperature rise below 1 °C.

Numerical analysis of lithium-ion battery thermal management system using phase change material assisted by liquid cooling method

Abstract: In this paper, a novel design for hybrid battery thermal management systems (BTMS) is proposed and evaluated from the economic and engineering perspectives. Numerical models are compared with phase change materials (PCM) BTMS. Further, the suggested hybrid cooling system’s thermal performance at the pack level is investigated considering cell-to-cell variation. A three-dimensional thermal model is used for the numerical simulation of the battery cooling system. The probability distributions is utilised for the cell-to-cell variations of a 168-cell battery pack. Results shows that for a 53 Ah lithium-ion battery (LIB) under a 5 C discharge rate, a hybrid cooling system with two-sided cold plates can reduce the maximum temperature from ∼ 64 ∘ C to 46.3 ∘ C with acceptable system weight and power consumption, which is used for further pack level simulation. It is concluded that the two-sided cold plate hybrid design system can manage the maximum average temperature as well as temperature difference of cells in the desirable range at extreme cases.

Numerical analysis of lithium-ion battery thermal management system using phase change material assisted by liquid cooling method

Abstract: In this paper, a novel design for hybrid battery thermal management systems (BTMS) is proposed and evaluated from the economic and engineering perspectives. Numerical models are compared with phase change materials (PCM) BTMS. Further, the suggested hybrid cooling system’s thermal performance at the pack level is investigated considering cell-to-cell variation. A three-dimensional thermal model is used for the numerical simulation of the battery cooling system. The probability distributions is utilised for the cell-to-cell variations of a 168-cell battery pack. Results shows that for a 53 Ah lithium-ion battery (LIB) under a 5C discharge rate, a hybrid cooling system with two-sided cold plates can reduce the maximum temperature from ∼64 ∘C to 46.3 ∘C with acceptable system weight and power consumption, which is used for further pack level simulation. It is concluded that the two-sided cold plate hybrid design system can manage the maximum average temperature as well as temperature difference of cells in the desirable range at extreme cases.

Multi-objective optimization design for a double-direction liquid heating system-based Cell-to-Chassis battery module

Abstract: Sub-zero temperature causes performance degradation, lifespan shortage, and even some safety issues of Li-ion battery cells, such as the internal short circuit. Preheating has become a critical issue for electric vehicle (EV) promotion in the high-latitude area or cold temperatures. To address this issue, a double-direction liquid heating-based Cell-to-Chassis (CTC) battery module is proposed for an extreme low-temperature environment (-40°C). Two cooling plates and the battery module are embedded in the chassis to reduce the component number. Besides, the volume energy density gets increased by 26.3%. The numerical calculation indicates that the proposed system is more efficient than the commonly utilized battery thermal management system (BTMS) in EVs. Moreover, the preheating effect with different heating intervals is compared; eight-minutes-preheating is proved to be more effective in preheating the battery module to 0°C with less energy consumption. Furthermore, a multi-objective optimization design is further carried out considering the heating rate, thermal safety, thermal uniformity, and energy cost. The impact of the mass flow rate in the mini-channels and the PTC heating film power are analysed through sensitivity analysis. Finally, the optimal design scheme is selected. The minimum, maximum, and volume average temperatures of the battery module are 273.2K, 296.7K, and 286.9K, respectively. Moreover, the temperature standard deviation is further reduced to 8.8K without much energy cost increment. This study guides for combing the efficient BTMS with the EV chassis for all-climate applications, especially with integrated preheating/cooling functions, which is feasible for the fast charging and cold environment applications, both the thermal management efficiency and the volume energy density can be effectively enhanced.

Multi-objective optimization design for a double-direction liquid heating system-based Cell-to-Chassis battery module

Abstract: Sub-zero temperature causes performance degradation, lifespan shortage, and even some safety issues of Li-ion battery cells, such as the internal short circuit. Preheating has become a critical issue for electric vehicle (EV) promotion in the high-latitude area or cold temperatures. To address this issue, a double-direction liquid heating-based Cell-to-Chassis (CTC) battery module is proposed for an extreme low-temperature environment (-40°C). Two cooling plates and the battery module are embedded in the chassis to reduce the component number. Besides, the volume energy density gets increased by 26.3%. The numerical calculation indicates that the proposed system is more efficient than the commonly utilized battery thermal management system (BTMS) in EVs. Moreover, the preheating effect with different heating intervals is compared; eight-minutes-preheating is proved to be more effective in preheating the battery module to 0°C with less energy consumption. Furthermore, a multi-objective optimization design is further carried out considering the heating rate, thermal safety, thermal uniformity, and energy cost. The impact of the mass flow rate in the mini-channels and the PTC heating film power are analysed through sensitivity analysis. Finally, the optimal design scheme is selected. The minimum, maximum, and volume average temperatures of the battery module are 273.2K, 296.7K, and 286.9K, respectively. Moreover, the temperature standard deviation is further reduced to 8.8K without much energy cost increment. This study guides for combing the efficient BTMS with the EV chassis for all-climate applications, especially with integrated preheating/cooling functions, which is feasible for the fast charging and cold environment applications, both the thermal management efficiency and the volume energy density can be effectively enhanced.

Canopy-to-canopy liquid cooling for the thermal management of lithium-ion batteries, a constructal approach

Abstract: With the growing interest on electric vehicles comes the question of the thermal management of their battery pack. In this work, we propose a thermally efficient solution consisting in inserting between the cells a liquid cooling system based on constructal canopy-to-canopy architectures. In such systems, the cooling fluid is driven from a trunk channel to perpendicular branches that make the tree canopy. An opposite tree collects the liquid in such a way that the two trees match canopy-to-canopy. The configuration of the cooling solution is predicted following the constructal methodology, leading to the choice of the hydraulic diameter ratios. We show that such configurations allow extracting most of the non-uniformly generated heat by the battery cell during the discharging phase, while using a small mass flow rate.

Fundamental and estimation of thermal contact resistance between polymer matrix composites: A review

Abstract: The thermal contact resistance (TCR) between polymer matrix composites (PMCs) imposes the significant impacts on the design, processing and application of these materials. This paper reviews the fundamental of the interfacial thermal conductance mechanism by analyzing the effects of inherent material properties, surface topography and working conditions of PMCs on TCR. Experimental measurement and numerical modeling methods are addressed to identify the distinct characteristics for estimating the TCR between PMCs. The main challenges for the accurate estimation are summarized, mainly including the complex interfacial thermal conductance due to the addition of fillers, the anisotropic thermal and mechanical responses due to the heterogeneity of PMCs, the uncertain contact mechanics due to the special mechanical properties. Finally, the multiscale estimation and machine learning methods are proposed for the further study on TCR between PMCs. This review is important because it provides guidance for the future studies in the interfacial thermal conductance between PMCs and thus the wide applications of emerging composites.

Thermal transport in planar <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si16.svg"><mml:msup><mml:mtext>sp</mml:mtext><mml:mn>2</mml:mn></mml:msup></mml:math>-hybridized carbon allotropes: A comparative study of biphenylene network, pentaheptite and graphene

Abstract: • The thermal conductivities κ of three carbon allotropes were investigated by HNEMD, EMD, and NEMD methods. • The κ of biphenylene network is only about one-thirteenth of the value of graphene. • The great reduction in κ of biphenylene network and pentaheptite arises from the decline of structural symmetry. • Phonon MFP, phonon group velocity, elastic modulus and ELF are analyzed to reveal the mechanism. The biphenylene network with periodically arranged four-, six-, and eight-membered rings has been successfully synthesized in very recent experiments. This novel two-dimensional (2D) carbon allotrope has potentials in applications of lithium storage and carbon-based circuitry. Understanding the thermal transport properties of biphenylene network is of critical importance for the performance and reliability of its practical applications. To this end, the thermal transport in biphenylene network is comprehensively investigated in this paper with the aid of molecular dynamics simulations together with first-principles calculations. For the sake of comparison, the thermal conductivities of other 2D sp 2 -hybridized carbon allotropes including graphene and pentaheptite are also investigated using the same method. It is found that the thermal conductivities of biphenylene network and pentaheptite are, respectively, only about one-thirteenth and one-eighth of graphene. Through the analysis of phonon property, mechanical property and electron density distribution, it is demonstrated that the great reduction in the thermal conductivity of biphenylene network and pentaheptite arises from the decline in their structural symmetry, which leads to the decrease of phonon group velocity and the reduction of phonon mean free path.

Thermal transport in planar sp2-hybridized carbon allotropes: A comparative study of biphenylene network, pentaheptite and graphene

Abstract: The biphenylene network with periodically arranged four-, six-, and eight-membered rings has been successfully synthesized in very recent experiments. This novel two-dimensional (2D) carbon allotrope has potentials in applications of lithium storage and carbon-based circuitry. Understanding the thermal transport properties of biphenylene network is of critical importance for the performance and reliability of its practical applications. To this end, the thermal transport in biphenylene network is comprehensively investigated in this paper with the aid of molecular dynamics simulations together with first-principles calculations. For the sake of comparison, the thermal conductivities of other 2D sp 2 -hybridized carbon allotropes including graphene and pentaheptite are also investigated using the same method. It is found that the thermal conductivities of biphenylene network and pentaheptite are, respectively, only about one-thirteenth and one-eighth of graphene. Through the analysis of phonon property, mechanical property and electron density distribution, it is demonstrated that the great reduction in the thermal conductivity of biphenylene network and pentaheptite arises from the decline in their structural symmetry, which leads to the decrease of phonon group velocity and the reduction of phonon mean free path.

Melting and energy storage characteristics of macro-encapsulated PCM-metal foam system

Abstract: In this study a novel encapsulated phase change material (PCM)-metal foam hybrid system is proposed for energy storage applications. The idea is to improve the melting rate of PCM in encapsulated PCM systems with the introduction of metal foam structures inside the capsules. The main objective of the work is to develop a numerical model which can simulate the melting of PCM in this hybrid system due to the flow of heat transfer fluid (HTF) around the capsule with the resolution of the metal foam geometry at the pore-scale level. The developed model couples geometry creation, phase change and fluid flow models. The foam geometry is created using overlapping circular pores with random location, radii, and overlap. The phase change model is developed by modifying the enthalpy method to incorporate the presence of four phases – HTF, metal, solid PCM, and liquid PCM. This is coupled with an implicit flow solver within a finite volume framework. An in-depth analysis of a base case is conducted by fixing different geometrical parameters such as capsule size, porosity, pore size distribution and shell thickness. The results of the base case are then compared in subsequent parametric studies, by varying one geometrical parameter at a time. The parametric studies reveal that the structure of the metal foam plays an important role in determining the melting pattern and the energy storage characteristics because of its net-like large inner surface area. It is found that the melting time is reduced for lower capsule size, lower porosity, and higher shell thickness. The average pore size and range are crucial in determining the rate of melting.

Experimental and numerical studies on the heat transfer improvement of a latent heat storage unit using gradient tree-shaped fins

Abstract: To improve the thermal performance of horizontal latent heat storage (LHS) units, this study investigates two innovative LHS units using uniform and gradient tree-shaped fins. By coupling visualization experiments and three-dimensional numerical simulations, the melting/solidification behavior and thermal properties of innovative LHS units are comprehensively analyzed and compared with traditional LHS units. The results show that tree-shaped fins facilitate heat diffusion from point to area, breaking the heat transport hysteresis in traditional LHS units, thus accelerating the melting/solidification rate. During the melting process, the gradient tree-shaped fins strengthen the heat transfer in lower parts of the LHS unit and extend the convective heat transfer duration in upper regions, promoting the synergistic strengthening of natural convection and heat conduction in the late melting stage. Compared to the uniform fin layout, the gradient tree-shaped fins effectively increase the melting rate, shortens the melting duration by 9%, and further improve the overall temperature uniformity of LHS units. However, the non-uniform transport path of gradient tree-shaped fins is not conducive to solidification heat transfer with conduction as the primary thermal regime, which increases the temperature gradient of LHS units and prolongs the solidification duration by 57.4% compared to the uniform tree-shaped fins.

A comprehensive study on 21st-century refrigerants - R290 and R1234yf: A review

Abstract: Prolonged use of environment unfriendly refrigerants in high-grade energy systems has resulted in increased greenhouse gas emissions and ozone layer depletion. This has resulted in increased global warming. Therefore, it is important to analyze all the studies of any refrigerant before its use for the sustainable development of any system. The present review paper is an attempt to report all studies related to 21st-century refrigerants comprising sustainable refrigerants for longer use. In this regard, the historic evolution of refrigerants and their potential effect on global warming and ozone layer depletion are presented. Further, R290 and R1234yf are found to be promising alternatives amongst all refrigerants to be used as 21st-century refrigerants. An attempt has been made to provide a comprehensive study for these refrigerants, including their thermophysical properties, leakage in the compressor, leakage in the evaporator, leakage in the condenser, explosion characteristics due to leakage, and consequences due to leakage and explosion. In addition, a thorough study has been made for the use of oils, their importance, and their consequences in a refrigeration system. The study has also been made for the use of these refrigerants in flow boiling and condensation. The increased commercialization of electric vehicles and refrigerant use in electric vehicles may increase global warming in near future. Therefore, the discussion has been included to use these refrigerants in electric vehicle air conditioning systems. Finally, a short conclusion with the future scope is presented for the various aspect of 21st-century refrigerants.

Heat transfer and flow visualization of pulsating heat pipe with silica nanofluid: An experimental study

Abstract: As heat transfer device with two-phase flow, pulsating heat pipe (PHP) has a widely application prospect in the fields of improving energy efficiency and thermal management. In order to optimize the heat transfer performance of PHP, a visualization experiment was carried out with a high-speed camera, and detailed characteristics of flow pattern variations in nanofluid PHP were obtained. The effect of SiO2-H2O nanofluid with different concentrations (0.5 wt%, 1.0 wt%, 1.5 wt% and 2.0 wt%) were experimentally investigated to analyze the thermal performance of PHP. Results demonstrate that the addition of nanoparticles on the one hand promotes the phase transition of the working fluid in the PHP, and on the other hand increases the instantaneous velocity and the driving force of working fluid. These are all benefit for the reflux of condensed liquid and effectively avoid the phenomenon of ′dry out′. Additionally, the results also indicate that there exists an optimum concentration of dispersed nanoparticles in base fluid to enhance heat transfer. The maximum heat transfer enhancement efficiency with nanofluid concentration of 1.0 wt% can reach 40.1 % at the heating power of 50 W. The present results can provide useful inspiration for the development and application of new type pulsating heat pipe.

Heat transfer and flow visualization of pulsating heat pipe with silica nanofluid: An experimental study

Abstract: As heat transfer device with two-phase flow, pulsating heat pipe (PHP) has a widely application prospect in the fields of improving energy efficiency and thermal management. In order to optimize the heat transfer performance of PHP, a visualization experiment was carried out with a high-speed camera, and detailed characteristics of flow pattern variations in nanofluid PHP were obtained. The effect of SiO2-H2O nanofluid with different concentrations (0.5 wt%, 1.0 wt%, 1.5 wt% and 2.0 wt%) were experimentally investigated to analyze the thermal performance of PHP. Results demonstrate that the addition of nanoparticles on the one hand promotes the phase transition of the working fluid in the PHP, and on the other hand increases the instantaneous velocity and the driving force of working fluid. These are all benefit for the reflux of condensed liquid and effectively avoid the phenomenon of ′dry out′. Additionally, the results also indicate that there exists an optimum concentration of dispersed nanoparticles in base fluid to enhance heat transfer. The maximum heat transfer enhancement efficiency with nanofluid concentration of 1.0 wt% can reach 40.1 % at the heating power of 50 W. The present results can provide useful inspiration for the development and application of new type pulsating heat pipe.

Melting and energy storage characteristics of macro-encapsulated PCM-metal foam system

Abstract: • Novel macro-encapsulated PCM-metal foam hybrid system proposed. • Pore-scale model developed to simulate melting in the hybrid system. • Melting and energy storage is faster in hybrid system compared to pure PCM system. • Melting rate is higher for smaller capsules and larger shell thickness. • Lower foam porosity, mean pore size and pore size range increases melting rate. In this study a novel encapsulated phase change material (PCM)-metal foam hybrid system is proposed for energy storage applications. The idea is to improve the melting rate of PCM in encapsulated PCM systems with the introduction of metal foam structures inside the capsules. The main objective of the work is to develop a numerical model which can simulate the melting of PCM in this hybrid system due to the flow of heat transfer fluid (HTF) around the capsule with the resolution of the metal foam geometry at the pore-scale level. The developed model couples geometry creation, phase change and fluid flow models. The foam geometry is created using overlapping circular pores with random location, radii, and overlap. The phase change model is developed by modifying the enthalpy method to incorporate the presence of four phases – HTF, metal, solid PCM, and liquid PCM. This is coupled with an implicit flow solver within a finite volume framework. An in-depth analysis of a base case is conducted by fixing different geometrical parameters such as capsule size, porosity, pore size distribution and shell thickness. The results of the base case are then compared in subsequent parametric studies, by varying one geometrical parameter at a time. The parametric studies reveal that the structure of the metal foam plays an important role in determining the melting pattern and the energy storage characteristics because of its net-like large inner surface area. It is found that the melting time is reduced for lower capsule size, lower porosity, and higher shell thickness. The average pore size and range are crucial in determining the rate of melting.