Coupled Transport Research Articles

Numerical investigation of PEMFC performance enhancement through combined design of anodic fishbone ridge groove channel and optimal gas diffusion layer porosity gradient

The flow field plate is one of the core components of proton exchange membrane fuel cells (PEMFC), and its structure significantly influences the thermo-electrochemical coupling transport characteristics of PEMFCs. Optimizing the parameters of the flow channels of bipolar plates is crucial for enhancing the mass transfer of reacting gas and improving water removal capacity. In this study, an anodal fishbone ridge groove combined flow channel (F-SFC) is designed to enhance the diffusion uniformity of anode hydrogen gas, and a 3D multi-phase model of PEMFC is established using the multiphysics simulation software COMSOL Multiphysics. The F-SFC was compared with traditional bipolar plates featuring symmetric anode and cathode flow channels in terms of overall output performance, and the results are presented. The findings indicate that the F-SFC design achieves an average increase of 28.78% in current density and 21.07% in power density compared to conventional fishbone flow channels. When compared to traditional serpentine flow channels, the F-SFC design shows a 13.5% increase in current density and a 10.42% increase in power density. Furthermore, adding multilayer porosity gradients to gas diffusion layers (GDLs) greatly improves internal mass transfer. A gradient porosity of 0.7, 0.5, and 0.3 along the Z-axis produces a more equal distribution of current density and water concentration on the membrane. This work sheds fresh light on optimizing PEMFC design for increased power density, providing useful theoretical advice for future advances.

Collaborative Optimization Framework for Coupled Power and Transportation Energy Systems Incorporating Integrated Demand Responses and Electric Vehicle Battery State-of-Charge

The growing adoption of electric vehicles (EVs) and advancements in dynamic wireless charging (DWC) technology have strengthened the interdependence between power distribution networks (PDNs) and electrified transportation networks (ETNs), leading to the emergence of coupled power and transportation energy systems (CPTESs). This development introduces new challenges, particularly as DWC technology shifts EV charging demand from residential plug-in charging to charging-while-driving during commuting hours, causing simultaneous congestion in both ETNs and PDNs during peak times. The present work addresses this issue by developing a collaborative optimization framework for CPTESs that incorporates integrated demand responses (IDRs) and EVs battery state-of-charge (SOC). In the ETN, a multiperiod traffic assignment model with time-shiftable traffic demands (MTA-TSTD) is established to optimize travelers’ routes and departure times while capturing traffic flow distribution. Meanwhile, effective path generation models with EVs battery SOC are proposed to optimize charging energy during driving and construct the effective path sets for MTA-TSTD. In the PDN, a multiperiod optimal power flow model with time-shiftable power demands (MOPF-TSPD) is formulated to schedule local generators and flexible power demands while calculating the power flow distribution. To enhance temporal and spatial coordination in CPTESs, a distributed coordinated operation model considering IDRs is proposed, aiming to optimize energy consumption, alleviate congestion, and ensure system safety. Finally, an adaptive effective path generation algorithm and an ETN–PDN interaction algorithm are devised to efficiently solve these models. Numerical results on two test systems validate the effectiveness of the proposed models and algorithms.

Coupled heat and fluid transport in pulled extrusion of optical fiber preforms

In the fabrication of optical fibers, the viscosity of the glass varies dramatically with temperature so that heat transfer plays an important role in the deformation of the fiber geometry. To date, models of fiber drawing processes have either assumed isothermal conditions or that advection is the dominant heat-transfer mechanism, with conduction therefore neglected. While advective heat transfer and neglect of conduction are valid in the fast process of drawing a preform to a fiber, heat conduction is also important in the slow process of extruding a fiber preform. In this paper, we derive and solve, in the context of pulled extrusion, a coupled heat and fluid flow model that incorporates heat conduction. The dramatic variation of viscosity with temperature means that this problem is extremely challenging to solve via standard numerical techniques and we therefore develop a novel finite-difference numerical solution method that proves to be highly robust. We use this method to show that conduction significantly affects the size of internal holes at the exit of the device and hence has important consequences for the process of manufacturing optical fibers.

Exploring the Coordination of Park Green Spaces and Urban Functional Areas through Multi-Source Data: A Spatial Analysis in Fuzhou, China

The coordinated development of park green spaces (PGS)with urban functional areas (UFA) has a direct impact on the operational efficiency of cities and the quality of life of residents. Therefore, an in-depth exploration of the coupling patterns and influencing factors between PGS and UFA is fundamental for efficient collaboration and the creation of high-quality living environments. This study focuses on the street units of Fuzhou’s central urban area, utilizing multi-source data such as land use, points of interest (POI), and OpenStreetMap (OSM) methods, including kernel density analysis, standard deviational ellipse, coupling coordination degree model, and geographical detectors, are employed to systematically analyze the spatial distribution patterns of PGS and UFA, as well as their coupling coordination relationships. The findings reveal that (1) both PGS and various UFA have higher densities in the city center, with a concentric decrease towards the periphery. PGS are primarily concentrated in the city center, exhibiting a monocentric distribution, while UFA display planar, polycentric, or axial distribution patterns. (2) The spatial distribution centers of both PGS and UFA are skewed towards the southwest of the city center, with PGS being relatively evenly distributed and showing minimal deviation from UFA. (3) The dominant type of coupling coordination between PGS and various UFA is “Close to dissonance”, displaying a spatial pattern of “high in the center, low on the east-west and north-south wings”. Socioeconomic factors are the primary driving force influencing the coupling coordination degree, while population and transportation conditions are secondary factors. This research provides a scientific basis for urban planning and assists planners in more precisely coordinating the development of parks, green spaces, and various functional spaces in urban spatial layouts, thereby promoting sustainable urban development.

Electric Vehicle Integration in Coupled Power Distribution and Transportation Networks: A Review

Integrating electric vehicles (EVs) into the coupled power distribution network (PDN) and transportation network (TN) presents substantial challenges. This paper explores three key areas in EV integration: charging/discharging scheduling, charging navigation, and charging station planning. First, the paper discusses the features and importance of EV integrated traffic–power networks. Then, it examines key factors influencing EV strategy, such as user behavior, charging preferences, and battery performance. Next, the study establishes an EV charging and discharging model, with particular emphasis on the complexities introduced by factors such as pricing mechanisms and integration approaches. Furthermore, the charging navigation model and the role of real-time traffic information are discussed. Additionally, the paper highlights the importance of multi-type charging stations and the impact of uncertainty on charging station planning. The paper concludes by identifying significant challenges and potential opportunities for EV integration. Future research should focus on enhancing coupled network modeling, refining user behavior models, developing incentive pricing mechanisms, and advancing autonomous driving and automated charging technologies. Such efforts will be essential for achieving a sustainable and efficient EV ecosystem.

Coupled Thermal and Power Transport of Optical Waveguide Arrays: Photonic Wiedemann-Franz Law and Rectification Effect.

In isolated nonlinear optical waveguide arrays, simultaneous conservation of longitudinal momentum flow ("internal energy") and optical power ("particle number") of the optical modes enables study of coupled thermal and particle transport in the negative temperature regime. Based on exact numerical simulation and rationale from Landauer formalism, we predict generic photonic version of the Wiedemann-Franz law in such systems, with the Lorenz number L∝|T|^{-2}. This is rooted in the spectral decoupling of thermal and particle current, and their different temperature dependence. In addition, in asymmetric junctions, relaxation of the system toward equilibrium shows apparent asymmetry for positive and negative biases, indicating rectification behavior. This Letter illustrates the possibility of simulate nonequilibrium transport processes using optical networks, in parameter regimes difficult to reach in natural condensed matter or atomic gas systems. It also provides new insights in manipulating power and momentum flow of optical waves in artificial waveguide arrays.

Nickel-Iron Layered Double Hydroxides/Nickel Sulfide Heterostructured Electrocatalysts on Surface-Modified Ti Foam for the Oxygen Evolution Reaction.

Electrochemical approaches for generating hydrogen from water splitting can be more promising if the challenges in the anodic oxygen evolution reaction (OER) can be harnessed. The interface heterostructure materials offer strong electronic coupling and appropriate charge transport at the interface regions, promoting accessible active sites to prompt kinetics and optimize the adsorption-desorption of active species. Herein, we have designed an efficient multi-interface-engineered Ni3Fe1 LDH/Ni3S2/TW heterostructure on in situ generated titanate web layers from the titanium foam. The synergistic effects of the multi-interface heterostructure caused the exposure of rich interfacial electronic coupling, fast reaction kinetics, and enhanced accessible site activity and site populations. The as-prepared electrocatalyst demonstrates outstanding OER activity, demanding a low overpotential of 220 mV at a high current density of 100 mA cm-2. Similarly, the designed Ni3Fe1 LDH/Ni3S2/TW electrocatalyst exhibits a low Tafel slope of 43.2 mV dec-1 and excellent stability for 100 h of operation, suggesting rapid kinetics and good structural stability. Also, the electrocatalyst shows a low overpotential of 260 mV at 100 mA cm-2 for HER activity. Moreover, the integrated electrocatalyst exhibits an incredible OER activity in simulated seawater with an overpotential of 370 mV at 100 mA cm-2 and stability for 100 h of operation, indicating good OER selectivity. This work might benefit further fabricating effective and stable self-sustained electrocatalysts for water splitting in large-scale applications.

(Keynote) Engineering Lead Halide Perovskite Nanocrystals for Fast Single-Particle and Collective Light Emission

Colloidal lead halide perovskite (LHP) nanocrystals (NCs), with bright and spectrally narrow photoluminescence (PL) tunable over the entire visible spectral range, are of immense interest as classical and quantum light sources. Fast (bright) and pure single-photon emission is key for many quantum technologies, from optical quantum computing to quantum key distribution and quantum imaging.The brightness of an emitter is ultimately described by Fermi’s golden rule, with a radiative rate proportional to its oscillator strength (intrinsic emitter property) times the local density of photonic states (photonic engineering, i.e. cavity). With perovskite NCs, we present a record-low sub-100 ps radiative decay time for CsPb(Br/Cl)3, almost as short as the reported exciton coherence time, by the NC size increase to 30 nm. The characteristic dependence of radiative rates on QD size, composition, and temperature suggests the formation of giant transition dipoles, as confirmed by effective-mass calculations for the case of the giant oscillator strength. Importantly, the fast radiative rate is achieved along with the single-photon emission despite the NC size being ten times larger than the exciton Bohr radius. NC self-assembly is a versatile platform for materials engineering, particularly for attaining collective phenomena with perovskite NCs, such as superfluorescence in perovskite NC superlattices. Thus far, LHP NCs have been co-assembled with building blocks that acted solely as spacers to promote the tuning of the mutual arrangement of LHP nanocubes [2]. However, the functionality of the second SL component can give rise to the enhancement of the LHP NCs properties or the emergence of new collective effects. We present the formation of multicomponent SLs made from the CsPbBr3 NCs of two different sizes. The diversity of obtained SLs encompassed the binary ABO6-, ABO3-, and NaCl-type structures, all of which contained orientationally and positionally confined NCs. For the selected model system, the ABO6-type SL, we observed efficient NC coupling and Förster-like energy transfer from strongly confined 5.3 nm CsPbBr3 NCs to weakly confined 17.6 nm CsPbBr3 NCs. Exciton spatiotemporal dynamics measurements reveal that binary SLs exhibit enhanced exciton diffusivity compared to one-component SLs across the entire temperature range (from 5 K to 298 K). Observed incoherent NC coupling and controllable excitonic transport within the solid NC SLs hold promise for potential applications in optoelectronic devices.[1]C. Zhu, S. C. Boehme, L. G. Feld, A. Moskalenko, D. N. Dirin, R. F. Mahrt, T. Stöferle, M. I. Bodnarchuk, A. L. Efros, P. C. Sercel, M. V. Kovalenko, G. Rainò. In review.[2] Ihor Cherniukh et al. Nature, 2021, 593, 535–542. [3] T. Sekh et al. Submitted

Investigation on thermochemical heat charging and discharging behavior of Ca(OH)2/CaO in a fixed bed reactor

Thermochemical heat storage (TCHS) technology plays a crucial role in the energy system, essential for maintaining the balance between energy supply and demand. The Ca(OH)2/CaO system holds significant promise for TCHS thanks to its high energy storage density, cost-effectiveness, and minimal heat loss. However, further research is required to elucidate the coupling mechanisms of the various physicochemical processes involved and to optimize the overall system performance. This paper focuses on assessing and elucidating the multi-physics coupled transport rules during both the charging and discharging stages in a fixed-bed reactor based on the developed numerical model. Results manifest the bed temperature rapidly increases to around 950 K, then slows down as the endothermic reaction predominates, completing dehydration in 1,900 s. During discharging, hydration conversion advances in a “U”-shaped pattern from the vapor inlet and side wall to the outlet, driven by the high vapor content near the inlet and the lower temperature near the wall. Furthermore, a thorough sensitivity analysis of the main parameters such as thermal conductivity and porosity is conducted to determine how different operating conditions affect the charging and discharging processes. Finally, a new reactor structure is proposed, in which a gas-guide duct is added at the central axis of the reactor to improve mass transport and uniformly distributed finned heating tube bundles to enhance heat transfer. These two functions can shorten the charging period by 9 % and 16 % respectively. The results can aid in predicting thermochemical conversion behaviors and multi-physic coupling transport processes, while also providing a foundational reference for the design of TCHS systems.

Off-target gradient-driven flows in 3D simulations of ADITYA-Upgrade tokamak scrape-off layer plasma transport

Coupled plasma-neutral transport simulations are performed on ADITYA-Upgrade tokamak scrape-off layer (SOL) plasma, where flows in the core and SOL were measured to reverse signs with density variation. The simulations performed using the EMC3-Eirene plasma-neutral code combination incorporate the toroidally continuous high-field-side belt limiter placed in a moderate circular tokamak equilibrium. The development of mutually counter-propagating toroidal plasma flows in the top and bottom regions of both the SOL and core is recovered for relatively high upstream density cases with high input power (300 kW and 3 m2 s−1). The origin of the flows is traced to the poloidal density variation introduced by high recycling on the inboard localized belt limiter. The results are compared with similar observations, for example, in Doppler-shifted passive charge exchange line emission on the ADITYA-Upgrade (ADITYA-U) tokamak, highlighting the role played by residual stress in the total Reynolds stress. The external stimuli, such as a localized gas puff, are discussed as potential drivers of flow, via residual stress, based on the existing resonant model of the tokamak plasma rotation.

Coupling coordination analysis on digital economy-tourism development-ecological environment

Growth-oriented tourism has caused global environmental degradation. The digital economy is widely regarded as a strategic engine of sustainable tourism, creating new potential for eco-environmental improvement by increasing innovation and efficiency, optimizing tourism sustainability management, and promoting sustainable tourist behavior. To reveal the coordination associations of the digital economy, tourism development, and ecological environment (DTE) and achieve sustainability in tourist destinations, this study aims to explore the DTE coupling coordination. We used the coupling coordination model to explore the coupling coordination degree of the DTE in 30 provinces in China from 2011 to 2021. Using Markov and modified gravity model, the dynamic evolution and spatial correlation intensity of the coupling coordination were examined, and influencing factors were determined by applying the GTWR model. The evaluation indices of the digital economy, tourism, and environment steadily increased but with significant spatial disequilibrium. The dominant trend was shifting from a lagging digital economy to lagging tourism development. Temporally, the coupling coordination state experienced a mild imbalance transformation to a near imbalance and a large gap with excellent coordination. Spatially, the coupling coordination is characterized by decreasing steps in the eastern, central, and western regions. The coupling coordination has regional diffusion and spatial correlation phenomena. Third, economic development, opening up, and government support positively affected the coupling coordination. Industrial structure had a fluctuating impact on the coupling coordination, and urbanization and transportation accessibility had a negative effect. Our study emphasizes the importance of DTE coordination development. Policymakers should consider these dynamics when promoting sustainable tourism practices in the digital age.

An Electroporation-Mediated Intracellular Delivery Model With Coupled Pore Currents and Solute Transport

An Electroporation-Mediated Intracellular Delivery Model With Coupled Pore Currents and Solute Transport

Nonequilibrium Lattice Dynamics of Individual and Attached PbSe Quantum Dots under Photoexcitation.

Quantum dot (QD) solids are emerging materials for many optoelectronic applications. To enhance interdot coupling and charge transport, surface ligands can be removed, allowing individual QDs to be attached along specific crystal orientations (termed "oriented attachment"). Optimizing the electronic and optical properties of QD solids demands a comprehensive understanding of the nanoscale energy flow in individual and attached QDs under photoexcitation. In this work, we employed ultrafast electron diffraction to directly measure how oriented attachment along ⟨100⟩ directions affects the nonequilibrium lattice dynamics of lead selenide QDs. The oriented attachment anisotropically alters the ultrafast energy relaxation along specific crystal axes. Along the ⟨100⟩ directions, both the lattice deformation and atomistic random motions are suppressed in comparison with those of individual QDs. Conversely, the effects are enhanced along the unattached ⟨111⟩ directions due to ligand removal. The oriented attachment switches the major lattice thermalization pathways from ⟨100⟩ to ⟨111⟩ directions.

Real-Time Hydrogen Refuelling of the Fuel Cell Electric Vehicle Through the Coupled Transportation Network and Power System

Real-Time Hydrogen Refuelling of the Fuel Cell Electric Vehicle Through the Coupled Transportation Network and Power System

Development of neutron-photon coupling transport code IMPC-NP and optimization of method for fabrication of neutron-photon multi-group cross section

This paper introduces a Monte Carlo code IMPC-NP which can realize the simulation of neutron-photon coupling transport. In IMPC-NP, Delta-tracking algorithm and Weight delta-tracking algorithm are used for neutron and photon transport. A new method of fabrication of photon multi-group cross sections named "Scattering merging" is proposed, which is implemented and on IMPC-NP. The results of multiple benchmarks show that the new method can greatly improve the accuracy of neutron and photon calculation in deterministic code.

A Reverse Nonequilibrium Molecular Dynamics Algorithm for Coupled Mass and Heat Transport in Mixtures.

We present a new method for introducing stable nonequilibrium concentration gradients in molecular dynamics simulations of mixtures. This method extends earlier reverse nonequilibrium molecular dynamics (RNEMD) methods, which use kinetic energy scaling moves to create temperature or velocity gradients. In the new scaled particle flux (SPF-RNEMD) algorithm, energies and forces are computed simultaneously for a molecule existing in two nonadjacent regions of a simulation box, and the system evolves under a linear combination of these interactions. A continuously increasing particle scaling variable is responsible for the migration of the molecule between the regions as the simulation progresses, allowing for simulations under an applied particle flux. To test the method, we investigate diffusivity in mixtures of identical but distinguishable particles and in a simple mixture of multiple Lennard-Jones particles. The resulting concentration gradients provide Fick diffusion constants for mixtures. We also discuss using the new method to obtain coupled transport properties using simultaneous particle and thermal fluxes to compute the temperature dependence of the diffusion coefficient and activation energies for diffusion from a single simulation. Lastly, we demonstrate the use of this new method in interfacial systems by computing the diffusive permeability of a molecular fluid moving through a nanoporous graphene membrane.

Bilevel Planning of Wireless Charging Lanes in Coupled Transportation and Power Distribution Networks

Bilevel Planning of Wireless Charging Lanes in Coupled Transportation and Power Distribution Networks

Bi-Level Continuous-Time Model for the Coordinated Operation of Coupled Electric Power Transmission and Energy Storage Transportation Systems

Bi-Level Continuous-Time Model for the Coordinated Operation of Coupled Electric Power Transmission and Energy Storage Transportation Systems

Heat and Mass Transfer Model for a Counter-Flow Moving Packed-Bed Oxidation Reactor/Heat Exchanger

Abstract Particle-based thermochemical energy storage (TCES) through metal oxide redox cycling is advantageous compared to traditional sensible and latent heat storage (SHS and LHS) due to its higher operating temperature and energy density, and the capability for long-duration storage. However, overall system performance also depends on the efficiency of the particle-to-working fluid heat exchangers (HXs). Moving packed-bed particle-to-supercritical CO2 (sCO2) HXs have been extensively studied in SHS systems. Integrating the oxidation reactor (OR) for discharging with a particle-to-sCO2 HX is a natural choice, for which detailed analysis is needed for OR/HX design and operation. In this work, a 2D continuum heat and mass transfer model coupling transport phenomena and reaction kinetics is developed for a shell-and-plate moving-bed OR/HX. For the baseline design, the model predicted ∼75% particle bed extent of oxidation at the channel exit, yielding a total heat transfer rate of 16.71 kW for 1.0 m2 heat transfer area per channel, while the same design with inert particles (SHS only) gives only 4.62 kW. A parametric study was also conducted to evaluate the effects of particle, air, and sCO2 flowrates, channel height and width, and average particle diameters. It is found that the respective heat transfer rate and sCO2 outlet temperature can approach ∼25 kW and >1000 °C for optimized designs for the OR/HX. The present model will be valuable for further OR/HX design, scale-up, and optimization of operating conditions.

Proxiome assembly of the plant nuclear pore reveals an essential hub for gene expression regulation.

The nuclear pore complex (NPC) is vital for nucleocytoplasmic communication. Recent evidence emphasizes its extensive association with proteins of diverse functions, suggesting roles beyond cargo transport. Yet, our understanding of NPC's composition and functionality at this extended level remains limited. Here, through proximity-labelling proteomics, we uncover both local and global NPC-associated proteome in Arabidopsis, comprising over 500 unique proteins, predominantly associated with NPC's peripheral extension structures. Compositional analysis of these proteins revealed that the NPC concentrates chromatin remodellers, transcriptional regulators and mRNA processing machineries in the nucleoplasmic region while recruiting translation regulatory machinery on the cytoplasmic side, achieving a remarkable orchestration of the genetic information flow by coupling RNA transcription, maturation, transport and translation regulation. Further biochemical and structural modelling analyses reveal that extensive interactions with nucleoporins, along with phase separation mediated by substantial intrinsically disordered proteins, may drive the formation of the unexpectedly large nuclear pore proteome assembly.