Proton exchange membrane fuel cells (PEMFCs) are highly susceptible to performance limitations at high current densities due to competing gas and liquid transport mechanisms. While microporous layers (MPLs) reduce contact resistance, they often exacerbate the risk of flooding. This study leverages the topological advantages of highly interconnected cage-like MPLs. By integrating X-ray computed tomography (X-CT) with digital techniques (reconstructed geometry and numerical simulation), it reveals the mass transfer mechanisms within cross-scale composite microstructures. Considering in-situ compression and surface wettability, the research delves into the influence of MPL thickness and crack morphology on multiphase flow dynamics. The results indicate that despite the significant non-steady-state velocity fluctuations and reduced liquid permeability caused by cascading Haines jumps due to increased MPL thickness, its unique high-porosity cage-like network structure still maintains robust oxygen diffusion performance. In-situ compaction further weakens the macropore transport capacity of the gas diffusion layer (GDL), leading to a significant reduction in permeability. In contrast, fractures effectively break through transport bottlenecks. Vertical through-holes maximize oxygen diffusion efficiency through the shortest path effect, while 45 degrees inclined fractures optimize gas-liquid convective permeability while enabling directed high-speed drainage of liquid water. This study elucidates the regulation mechanism of microstructural parameters across scales, providing theoretical guidance for designing next-generation gas diffusion layers that combine high gas-phase diffusion with efficient drainage capabilities.

With the rapid development of flash boiling spray technology, a thorough investigation into the spray characteristics of flashing flows has become increasingly important. This study focused on a refrigerant mixture (R410A) composed of 50% difluoromethane (CH2F2) and 50% pentafluoroethane (C2HF5) and developed a closed-loop spray experimental system to investigate the effects of critical parameters, including nozzle height, injection pressure, ambient pressure, and refrigerant temperature on the spray cone angle using a pressure-swirl nozzle configuration. Experimental results demonstrate that nozzle height and injection pressure have a negligible influence on the cone angle under the pressure-swirl nozzle structure. Conversely, ambient pressure and refrigerant temperature significantly affect the near-field cone angle through their influence on gas density and superheat. Moreover, a quadratic relationship is identified between the tangent value of half cone angle and the degree of superheat (R-p), expressed by the equation tan(theta/2) = 0.102R(p)(2) - 0.648R(p) + 1.357. It implies that the flash spray cone angle does not vary monotonically with R-p. This study provides new insights into this phenomenon by incorporating the rapid vapor expansion surrounding the liquid column. In contrast, the far-field cone angle is predominantly influenced by ambient pressure. These findings provide experimental evidence of the combined effects of superheat and aerodynamic interaction associated with the flow structure induced by the pressure swirl. Based on experimental data, the present study developed a dimensionless correlation for predicting the tangent value of half cone angle of flash boiling spray under low superheat conditions (R-p < 3.33). The proposed correlation predicts the tangent of the near-field spray half-angle with a mean relative error of 7.2%. This research has introduced novel insights into flash boiling spray morphology and provided a solid foundation for future studies of liquid film boiling and heat transfer mechanisms.

The gas diffusion layer (GDL) of proton exchange membrane fuel cells (PEMFCs) is a critical component for the transport of reactants. The efficiency of reactant gas transport remains a major technical challenge in the field today. The anisotropic structure of the GDL gives rise to substantial variations of gas diffusion as well as permeability in different directions. The study employs X-CT technology to obtain the actual GDL's geometry, aiming to investigate a spatial structure at the microscale and its gas transport characteristics. The computational fluid dynamics (CFD) method is used to simulate and study the gas diffusivity and gas permeability of GDL with four different thicknesses. The numerical simulation results show that the diffusivity and permeability in the through-plane (TP) direction are lower than those in the in-plane (IP) direction. Moreover, the effective diffusion coefficient (EDC) decreases with increasing thickness, but is also dependent on the solid fibre structure of GDL. Horizontal alignment of the carbon fibers and the disc-shaped adhesive contributes to the anisotropy between the TP and IP directions, resulting in anisotropic gas transport. The purpose of the study is to supply critical references for manufacturing techniques and optimization of gas transport in GDLs.

Traditional designs of liquid cooling plates using single thermally conductive material are either constrained by predefined topologies or fail to adequately mitigate hotspot issues, which remain insufficient for design freedom and performance trade-offs. To overcome these limitations, we propose a density-based topology optimization model that simultaneously optimizes the layout of flow channels and spatial distribution of two thermally conductive solids-enabling functional structures tailored to poorly ventilated areas. The tri-material liquid cooling plate integrates conjugate heat transfer modeling with a multi-physics battery model to accurately capture the electrochemical-thermal-hydrodynamic interaction in 46.59 kWh battery module. The optimized design yields bifurcated flow patterns that reduce fluid energy dissipation by up to 19.5 and 12.6 %, respectively, compared to straight-channel and single-solid designs at Reynolds number of 900, while improving thermal diffusion performance by over 10 % in terms of performance evaluation criterion. The comparative analysis further reveals that side-mounted composite cold plate outperforms the bottom-mounted counterpart under high discharge rates of 0.5-1C, achieving comprehensive evaluation improvements of 0.09-0.12 due to shorter heat transfer paths and increased thermal contact areas. These results demonstrate that tri-material topology optimization enables co-design of structure and material distribution, offering a scalable solution for high-efficiency and cost-effective liquid cooling design in energy storage systems.

The performance of solid oxide electrolysis cells (SOECs) is closely related to its flow channel structure, stoichiometric ratio, and operating temperature. In this study, multiphysics numerical models were developed, incorporating coupled heat and mass transport alongside electrochemical reaction processes. The model validity was confirmed by comparing simulated results with experimentally measured I-V curves. The impacts of the fuel-to-air stoichiometric ratio (F:A from 2:1 to 2:4), channel aspect ratio (L:W from 1:1 to 4:1), temperature (from 873.15 K to 1073.15 K), and flow arrangements (co-current vs. counter-current) on the performance of a single-channel electrolyzer were systematically investigated, complemented by an analysis of multi-channel behavior under cross-flow conditions. The findings reveal that among the investigated parameters, temperature exerts the most significant influence on cell performance. Increasing the temperature facilitates the substitution of electrical energy with thermal energy, reducing the cell voltage from 1.5364 V to 1.1142 V at 1.2 A/cm2. Furthermore, varying the stoichiometric ratio effectively improves the oxygen partial pressure in the catalyst layer, thereby reducing concentration polarization. At the same current density, the required cell voltage decreased from 1.5364 V to 1.5153 V. Increasing the channel aspect ratio improves mass transport, reducing the required cell voltage from 1.5444 V to 1.5053 V. In contrast, flow arrangements were found to have a negligible impact on overall performance, though the counter-flow arrangement demonstrated marginal superiority over the co-flow arrangement.

Cryogenic spray cooling (CSC) is widely used in laser dermatology to protect the epidermis from thermal damage, but conventional refrigerants like R134a suffer from high global warming potential (GWP) and limited cooling efficiency. This study introduces R454B (GWP = 467) as a sustainable alternative and systematically evaluates its transient cooling performance on a skin phantom. Experiments were conducted using an open-loop flashing spray system to assess the effects of spray pressure (p), distance (d), spurt duration (tsd), nozzle diameter (D), and nozzle length (L). High-speed imaging and binarization were employed to analyze spray morphology. Optimal cooling performance - a maximum surface heat transfer coefficient of 10.08 kW & sdot;m- 2 & sdot;K- 1 - was achieved at d = 30 mm, p = 1.5 MPa, D = 0.8 mm, tsd = 100 ms, and L = 40 mm. Among several machine learning models evaluated, the Gradient Boosting Regression Tree (GBRT) model performed best in capturing nonlinear feature interactions within the experimental data. SHAP analysis revealed that tsd (33.8%), d (28.6%), and D (21.6%) were the most influential parameters. This study validates R454B as an effective, eco-friendly alternative to R134a for clinical CSC and introduces a data-driven framework for optimizing spray cooling performance.

The lithium plating reaction in graphite electrodes acts as a root cause for the accelerated degradation and the internal short circuits in lithium-ion batteries. Here, an electrochemical model based on multi-scale microstructural images was established to identify lithium plating-stripping processes, thereby supporting the predictive outcomes of electrochemical monitoring techniques. Experiments revealed that the open-circuit voltage differential curve (dOCV/dt) led to ambiguous delineation of the safe state-of-charge (SOC) operating range. The established lithium plating-stripping model was used to compare with experimental results, revealing the dynamic evolution of electrode-scale kinetics and quantified the impact of lithium metal residue on electrode performance. Ex situ X-ray computed tomography (XCT) captured micrometer-resolution microstructural details of graphite electrodes and plated lithium, enabling further correlation of spatially heterogeneous lithium plating-stripping reactions with electrode microstructure. The sensitivity of lithium plating to electrode microstructure was examined at the particle scale, attributed to competition between electrode kinetic rates and active reaction areas. Theoretical mechanism analysis and experimental results from high-energy-density electrodes demonstrated that positioning small particles on the current collector side effectively mitigates solid-state diffusion polarization while confining side reactions to a limited area. The integration of experiments and multiscale modeling elucidates the relationship between lithium plating-stripping reactions and electrode structure, providing mechanistic insights for similar structural optimization designs.

Spray cooling is an effective thermal management method for high-heat-flux electronic systems, and the droplet evaporation strongly influences the heat transfer performance. This study experimentally investigates the evaporation behavior of Perfluoro-4-methyl-2-pentene (FCM-47) droplets under ambient temperatures ranging from 50 to 200 degrees C and pressures between 0.1 and 2.0 MPa. The results indicate that a higher ambient temperature increases both the gas-liquid temperature gradient and the interfacial vapor-pressure difference, thereby enhancing convective heat transfer and diffusive mass transfer. As a result, the evaporation rate increases markedly and the droplet lifetime becomes shorter. The influence of ambient pressure on droplet evaporation exhibits a clear temperature dependence. At relatively low temperatures, the effect of pressure on droplet evaporation shows a non-monotonic trend. In the low-pressure range, increasing pressure promotes evaporation, mainly because the higher gas density enhances heat transfer. However, in the high-pressure range, the interfacial vapor mass fraction and the vapor diffusion coefficient decrease, which weakens the evaporation enhancement effect. Under high temperatures, increasing pressure consistently accelerates evaporation. In this case, the dominant mechanism shifts to the substantial reduction in latent heat together with the enhancement of gas-phase thermal conductivity. These effects overcome the resistance of mass diffusion and lead to a significantly higher evaporation rate. This work reveals the non-linear evaporation behavior of FCM-47 droplets under high pressure, including a regime shift from diffusion-dominated to heat-conduction-dominated evaporation. These findings provide new insight into refrigerant droplet evaporation under combined high-temperature and high-pressure conditions, helping to optimize spray-cooling performance.

Carbon corrosion induced by anode localized flooding severely compromises the durability of proton exchange membrane fuel cell (PEMFC). Limited by the computational stability and efficiency, existing simulations are always in 2D or single-channel scales, which overlooks the influence of the actual flow field structure in commercial PEMFC on carbon corrosion behavior. In this study, a performance-coupled 3D carbon corrosion model is established to investigate the carbon corrosion behavior and performance degradation in a 306 cm2 commercial-scale PEMFC under anode localized flooding conditions. The research demonstrates that the carbon corrosion zone exhibits a quasi-trapezoidal distribution influenced by hydrogen transport and in-plane proton conduction. Carbon loading undergoes rapid loss during the initial flooding phase, followed by a gradual leveling off. After 120 min of local flooding, the PEMFC exhibits an electrochemically active surface area (ECSA) loss of 23.97 % and an output power loss of 16.83 %. This model provides deeper insights into carbon corrosion behavior under localized flooding in large-scale PEMFC and offers a valuable reference for formulating carbon corrosion mitigation strategies.

Gelled fuels have gained attention for their enhanced safety and higher energy density in aerospace propulsion, yet their complex rheological behavior poses challenges for atomization modeling and performance prediction. This study develops a constitutive model for thixotropic organic kerosene gel and integrates it with a VOF-LESbased numerical framework to investigate the primary atomization characteristics under varying inlet conditions and Reynolds numbers. The simulations explore breakup mechanisms, jet penetration, fuel-air mixing, and atomization efficiency, with conventional kerosene as a baseline for comparison. Under uniform inlet conditions, atomization is predominantly driven by the frontal impact between the jet tip and the quiescent ambient gas, leading to lateral dispersion and front-end ligament breakup with relatively stable liquid core structures. In contrast, turbulent inflows introduce strong perturbations and turbulent kinetic energy, intensifying surface instabilities, promoting earlier and more complete breakup, and producing more numerous and smaller droplets. Increasing Reynolds number enhances inertial forces and weakens the suppressive effects of gel rheology, though efficiency gains diminish at high values due to energy dissipation and droplet coalescence. Compared to conventional kerosene, gel fuels demonstrate lower atomization efficiency and mixing due to higher viscosity and internal structural resistance. These findings offer valuable insights into the atomization dynamics of gelled propellants, supporting improved injector design and combustion performance optimization.

Even though thermal management systems have been widely developed to maintain the thermal stability and safety of lithium-ion battery, a comprehensive comparison remains insufficient for large-scale battery module, particularly across wide temperature ranges. For this purpose, a numerical framework that includes electrochemical-thermal coupled model, aging model, thermal runaway model, and hydrodynamic model is established for 46.592 kWh battery module. The aim of this study is to comprehensively assess the thermal management efficiency of different methods under low-temperature preheating, normal cooling, and thermal runaway protection scenarios. Results found that under the given configuration, battery heating rate is ordered as immersion heating > film heating > liquid heating plate, and the latter two approaches show larger thermal inhomogeneities due to battery anisotropy and longer heat transfer paths. For normal cooling condition, immersion cooling needs more power consumption to maintain the same inlet flow rate than air cooling and liquid cooling plate, but its superior cooling performance can slow down battery capacity fading after long-term cycling. Additionally, liquid cooling plate and immersion cooling allow for delaying thermal propagation after onset of thermal runaway, whereas boiling-based system can effectively prohibit thermal runaway from local overheating due to its phase change cooling effect.

The gas diffusion layer (GDL) is a critical component for gas transport in proton exchange membrane fuel cells (PEMFCs). Gas transport efficiency significantly impacts PEMFC performance. This study employs integrated micro-computed tomography (Micro-CT) for 3D reconstruction of the GDL and utilizes computational fluid dynamics (CFD) to investigate gas diffusion and convection in GDLs with varying perforation/thickness ratios. Results indicate that perforations enhance the effective diffusion coefficient (EDC) of GDLs, while GDL thickness has minimal impact on EDC. EDC variations are primarily influenced by internal geometric structures. The anisotropy arising from fiber orientation during carbon paper manufacturing results in higher diffusion rates in the in-plane (IP) direction than in the through-plane (TP) direction. Perforations reduce inlet pressure and improve gas flow, thereby increasing GDL permeability; conversely, permeability decreases with increasing GDL thickness. High-velocity regions in the GDL correspond to large pore areas, indicating that pore distribution influences gas transport. This study aims to elucidate the fundamental mechanisms of gas transport in GDLs as functions of thickness and perforation, thereby providing crucial theoretical guidance for GDL design.

Temperature variations significantly affect the performance and safety of lithium-ion batteries (LIBs), particularly under extreme conditions and high charge/discharge rates. Uneven heat generation, limited heat dissipation, and residual energy accumulation exacerbate thermal effects, leading to capacity degradation, reduced efficiency, and safety hazards. Addressing these challenges requires a multiscale understanding of the thermal behavior of LIBs. This review provides an integrated, multiscale perspective on battery thermal safety, spanning material-level design, cell-level modeling and state estimation, and system-level thermal management. We first examine the fundamental thermal mechanisms and modeling approaches governing heat generation, transport, and accumulation across varying operating conditions at the cell level. We then explore material-level strategies to mitigate low-temperature degradation and enhance high-temperature stability, enabling reliable all-climate operation. Building on these insights, we assess system-level thermal management approaches, including internal and external preheating, as well as active and passive cooling methods. Particular attention is given to immersion cooling, which offers superior heat dissipation, improved temperature uniformity, and enhanced safety. We comprehensively review immersion cooling technologies, including system configurations, fluid selection, operational parameters, and recent advances in both single-phase and two-phase cooling. By bridging physical mechanisms, modeling frameworks, and engineering solutions across scales, this review highlights key challenges, identifies critical research gaps, and outlines future directions for achieving adaptive and robust thermal safety in LIBs. The insights provided aim to support the development of safer, more reliable, and thermally resilient LIB systems for transportation and large-scale energy storage applications.

Water in Proton Exchange Membrane Fuel Cells (PEMFCs) holds significance and complexity. The study of water is crucial for enhancing the efficiency and extending the lifespan of the batteries. This study used micro-CT technology to obtain tomographic images of the gas diffusion layer (GDL) in PEMFCs. Subsequently, the samples were reconstructed in three dimensions using Avizo, and the internal fluid flow in the GDL was simulated using the Volume of Fluid (VOF) method. The local and average porosities of all sample types were calculated, providing insight into the distribution of the internal pore structure of the GDL. Analyzed the impact of the pressure difference at the inlet and outlet(Delta P), contact angle, and the thickness of the model on the flow of liquid. The research results indicate that for the TGP-H-60 model of GDL, the Delta P must be at least 6 kPa to allow liquid water to flow from one end to the other. The contact angle within the GDL significantly impacts the removal of liquid water. In practical applications, the selection of GDL thickness must ensure mechanical strength while also considering fluid transport efficiency to enhance battery performance. An overly thick can make the flow of water more difficult, resulting in flooding phenomena.

Refrigerant-induced noise near the electric expansion valve (EEV) is a critical concern for automotive acoustic comfort, yet its underlying mechanisms remain poorly understood due to limited experimental accessibility. This study presents a numerical investigation of flow-induced noise in EEVs under both single-phase and two-phase inflow conditions using an integrated approach combining multiphase, turbulence, cavitation, and broadband noise models to characterize the distributions of velocity, pressure, phase, turbulent kinetic energy, and noise power. The results reveal that noise intensity scales positively with pressure drop across the valve, and regions of elevated noise coincide with areas of high turbulent kinetic energy. Under liquid-phase inflow, cavitation occurring downstream of the throttling orifice generates pronounced noise predominantly on the right side of the valve needle. In contrast, when two-phase flow enters the valve, the high-velocity gas jet accelerates through the orifice, producing strong noise on both sides of the needle. Two distinct noise generation mechanisms are identified based on upstream flow conditions. The first is cavitation-induced noise, localized near the needle tip, where rapid phase change creates intense unsteadiness that decays quickly as cavitation subsides. The second is backflow-induced noise, originating at the valve bottom where the impinging jet generates large-scale recirculation and momentum exchange with the mainstream, producing sustained noise over an extended region that gradually dissipates downstream. The overall variation trend of noise through flowing direction firstly decreases, then increases and finally decreases. The maximum average noise power in selected planes reaches 112 dB with annular flow appearing before EEV.

Thermal runaway (TR) is a severe challenge to the widespread commercial adoption of high energy-density lithium-ion batteries (LIBs). Nonetheless, the current strategies lack responsiveness for both extreme heat dissipation and explosion suppression. Here, a thermal safety protection strategy based on liquid immersion cooling (LIC) is proposed. The peak temperature of overcharge-induced TR is decreased below 300 degrees C through boiling heat exchange of FS49, rapidly (3 min) stabilizing the LIB temperature around 49 degrees C. Simultaneously, critical radicals are captured by FS49 in the combustion chain reaction, reducing emissions of combustible toxic gases by approximately 62.65%. This effectively prevents LIB explosions and secondary re-ignition disasters. Surprisingly, when applied as 1 mm interlayers between cells for a pack with four LIBs, the FS49 not only suppresses the TR propagation but also maintains the adjacent LIB temperature at 53.89 degrees C. Additionally, it is further demonstrated that the thermal safety of a large-scale 36-cell LIB pack through finite volume method simulations. This strategy can represent a critical step forward in enhancing the safety performance of electric vehicles and grid-scale energy storage systems.

To meet the increasing demands for high energy density and safety in aerospace propulsion, gel propellants have drawn significant attention due to their dual solid-liquid characteristics. However, their high viscosity and complex rheology suppress interfacial instabilities and hinder jet breakup, posing critical challenges to efficient atomization. This study develops a high-fidelity numerical framework coupling the VOF method, large eddy simulation (LES), and adaptive mesh refinement (AMR), incorporating a thixotropic shear-thinning model based on experimental data for 5 % organic kerosene gel. Considering the strong mechanical vibrations in rocket engines, the primary atomization behavior under periodic perturbations with varying amplitude and frequency is systematically investigated, with a focus on jet evolution, breakup mechanisms, droplet characteristics, and mixing efficiency. Under high-speed injection, periodic forcing intensifies upstream core instability and promotes downstream fragmentation, generating numerous fine droplets. Increased perturbation amplitude enhances radial spreading and multiscale breakup, while frequency primarily adjusts droplet size uniformity but contributes little to penetration, with a saturation effect observed. Despite large number of small, slow droplets are generated near the jet core and upstream, the jet remains largely dominated by an unbroken liquid core and ligaments. Compared to kerosene, the gel exhibits significantly poorer atomization performance, producing larger, slower, and more localized droplets due to its rheological resistance to instability growth and spatial dispersion. This work provides quantitative insights into the atomization dynamics of gel fuels and establishes a theoretical foundation for rheological control strategies in propulsion applications.