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Showing papers on "Transport phenomena published in 2018"


Journal ArticleDOI
Yueqi Luo1, Kui Jiao1
TL;DR: In this article, the authors defined cold start as the startup of proton exchange membrane (PEM) fuel cells from subfreezing temperatures and discussed experimental studies focusing on output performance degradation, water and ice visualization, and component damages during a cold start.

183 citations


Journal ArticleDOI
TL;DR: Recent progress in the theory and simulation of quantum transport in molecular junctions is discussed and challenges are identified, which appear crucial to achieve a comprehensive and quantitative understanding of transport in these systems.
Abstract: Molecular junctions, where single molecules are bound to metal or semiconductor electrodes, represent a unique architecture to investigate molecules in a distinct nonequilibrium situation and, in a broader context, to study basic mechanisms of charge and energy transport in a many-body quantum system at the nanoscale. Experimental studies of molecular junctions have revealed a wealth of interesting transport phenomena, the understanding of which necessitates theoretical modeling. The accurate theoretical description of quantum transport in molecular junctions is challenging because it requires methods that are capable to describe the electronic structure and dynamics of molecules in a condensed phase environment out of equilibrium, in some cases with strong electron-electron and/or electronic-vibrational interaction. This perspective discusses recent progress in the theory and simulation of quantum transport in molecular junctions. Furthermore, challenges are identified, which appear crucial to achieve a comprehensive and quantitative understanding of transport in these systems.

165 citations


Journal ArticleDOI
TL;DR: In this article, the authors provide a review of the fundamental physical phenomena in underground coal gasification and associated modeling efforts, including cavity growth at the sidewall and roof of the underground cavity and the transport phenomena and chemical reactions occurring in the permeable bed of char and ash and the void space.

73 citations


Journal ArticleDOI
TL;DR: In this paper, a theoretical study of nonsmoothy nonlinear convection on magnetohydrodynamic fluid in a suspension of dust and graphene nanoparticles is presented, and the numerical values of friction factor and heat transfer rate are tabulated numerically for various physical parameters obtained.
Abstract: This is a theoretical study of unsteady nonlinear convection on magnetohydrodynamic fluid in a suspension of dust and graphene nanoparticles. For boosting the heat transport phenomena we consider the Cattaneo-Christov heat flux and thermal radiation. Dispersal of graphene nanoparticles in dusty fluids finds applications in biocompatibility, bio-imaging, biosensors, detection and cancer treatment, in monitoring stem cells differentiation etc. Initially the simulation is performed by amalgamation of dust (micron size) and nanoparticles into base fluid. Primarily existing partial differential system (PDEs) is changed to ordinary differential system (ODEs) with the support of usual similarity transformations. Consequently, the highly nonlinear ODEs are solved numerically through Runge-Kutta and Shooting method. The computational results for Non-dimensional temperature and velocity profiles are offered through graphs ( ϕ = 0 and ϕ = 0.05 ) cases. Additionally, the numerical values of friction factor and heat transfer rate are tabulated numerically for various physical parameters obtained. We also validated the current outcomes with previously available study and found to be extremely acceptable. From this study we conclude that in the presence of nanofluid heat transfer rate and temperature distribution is higher compared to micro fluid.

55 citations


Journal ArticleDOI
15 May 2018-Energy
TL;DR: In this article, a numerical model was developed to analyze the conduction, convection and radiative heat transfer with the chemical reaction kinetics in a volumetric solar reactor.

53 citations


Journal ArticleDOI
TL;DR: In this article, an analytical study of the advective-diffusive transport phenomena in a microreactor filled with porous media and with catalytic surfaces is presented, where the thermal diffusion of mass, viscous dissipation of the flow momentum and local thermal non-equilibrium in the porous medium are considered.

46 citations


Journal ArticleDOI
TL;DR: In this article, a three-dimensional, non-isothermal, two-phase flow mathematical model is developed and applied to investigate the effect of the GDL deformation on transport phenomena and performance of proton exchange membrane (PEM) fuel cells with interdigitated flow fields.

45 citations


Journal ArticleDOI
15 Oct 2018-Energy
TL;DR: In this article, the authors developed a numerical approach to predict the current density, oxygen mass transport, water concentration and pressure distribution in a proton exchange membrane fuel cell and compared the results with the conventional single serpentine flow field pattern.

44 citations


Journal ArticleDOI
TL;DR: An analytical model for electro-hydrodynamic flow that describes the relationship between the corona voltage, electric field, and ion charge density is presented, shedding new insights into mass, charge, and momentum transport phenomena.
Abstract: We present an analytical model for electro-hydrodynamic flow that describes the relationship between the corona voltage, electric field, and ion charge density. The interaction between the accelerated ions and the neutral gas molecules is modeled as an external body force in the Navier-Stokes equation. The gas flow characteristics are solved from conservation principles with spectral methods. This multiphysics model is shown to match experimental data for a point-to-ring corona configuration, shedding new insights into mass, charge, and momentum transport phenomena, and can be readily implemented in any numerical simulation.

38 citations


Posted Content
TL;DR: In this article, a magnetic gauge field for phonon transport in a scalable, on-chip optomechanical system is demonstrated, which can be used to explore topological acoustic phases in manymode systems resilient to realistic disorder.
Abstract: Gauge fields play important roles in condensed matter, explaining for example nonreciprocal and topological transport phenomena. Establishing gauge potentials for phonon transport in nanomechanical systems would bring quantum Hall physics to a new domain, which offers broad applications in sensing and signal processing, and is naturally associated with strong nonlinearities and thermodynamics. In this work, we demonstrate a magnetic gauge field for nanomechanical vibrations in a scalable, on-chip optomechanical system. We exploit multimode optomechanical interactions, which provide a useful resource for the necessary breaking of time-reversal symmetry. In a dynamically modulated nanophotonic system, we observe how radiation pressure forces mediate phonon transport between resonators of different frequencies, with a high rate and a characteristic nonreciprocal phase mimicking the Aharonov-Bohm effect. We show that the introduced scheme does not require high-quality cavities, such that it can be straightforwardly extended to explore topological acoustic phases in many-mode systems resilient to realistic disorder.

38 citations


Journal ArticleDOI
TL;DR: This Letter shows that the steady-state profiles, the cold-pulse rise time, and disappearance at higher density as measured in these experiments are successfully captured by a recent local quasilinear turbulent transport model, demonstrating that the existence of nonlocal transport phenomena is not necessary for explaining the behavior and time scales of cold-Pulse experiments in tokamak plasmas.
Abstract: A long-standing enigma in plasma transport has been resolved by modeling of cold-pulse experiments conducted on the Alcator C-Mod tokamak. Controlled edge cooling of fusion plasmas triggers core electron heating on time scales faster than an energy confinement time, which has long been interpreted as strong evidence of nonlocal transport. This Letter shows that the steady-state profiles, the cold-pulse rise time, and disappearance at higher density as measured in these experiments are successfully captured by a recent local quasilinear turbulent transport model, demonstrating that the existence of nonlocal transport phenomena is not necessary for explaining the behavior and time scales of cold-pulse experiments in tokamak plasmas.

Journal ArticleDOI
TL;DR: In this paper, a simple 1D heat conduction model as well as a fully 3D thermo-fluid dynamics model were developed for Li||Bi LMBs. And the latter was implemented in the CFD library OpenFOAM, extending the volume of fluid solver, and validated against a pseudo-spectral code.

Journal ArticleDOI
TL;DR: In this article, a fully three dimensional, multiphase, micro-scale solid oxide fuel cell anode transport phenomena numerical model is proposed and verified using FIB-SEM tomography of a commercial SOFC stack anode.

Journal ArticleDOI
TL;DR: In this paper, a physical model is developed to resolve temporally and spatially reactions and transport phenomena taking place inside planar, anode-supported solid oxide fuel cell (SOFC) stacks, which can be used for optimizing cell microstructure and developing a reliable SOFC stack design.

Journal ArticleDOI
TL;DR: In this paper, Wang et al. analyzed the squeezing flow of water-based carbon nanotubes as a Darcy-Forchheimer porous medium with thermal radiation, and the Xue model was used for nanoliquid transport phenomena.

Journal ArticleDOI
TL;DR: In this paper, a multi-phase model was proposed to track the motion of the free surface with high resolution while ensuring that mass conservation was not violated, and the mass addition from the preheated filler wire was modeled as the source terms in the continuity and energy equations.

Journal ArticleDOI
TL;DR: An analytical study of pressure-driven flow of micropolar non-Newtonian physiological fluids through a channel comprising two parallel oscillating walls, relevant to hemodynamics in narrow capillaries and also bio-inspired micro-fluidic devices.
Abstract: In this paper, we present an analytical study of pressure-driven flow of micropolar non-Newtonian physiological fluids through a channel comprising two parallel oscillating walls. The cilia are arranged at equal intervals and protrude normally from both walls of the infinitely long channel. A metachronal wave is generated due to natural beating of cilia and the direction of wave propagation is parallel to the direction of fluid flow. Appropriate expressions are presented for deformation via longitudinal and transverse velocity components induced by the ciliary beating phenomenon with cilia assumed to follow elliptic trajectories. The conservation equations for mass, longitudinal and transverse (linear) momentum and angular momentum are reduced in accordance with the long wavelength and creeping Stokesian flow approximations and then normalized with appropriate transformations. The resulting non-linear moving boundary value problem is solved analytically for constant micro-inertia density, subject to physically realistic boundary conditions. Closed-form expressions are derived for axial velocity, angular velocity, volumetric flow rate and pressure rise. The transport phenomena are shown to be dictated by several non-Newtonian parameters, including micropolar material parameter and Eringen coupling parameter, and also several geometric parameters, viz eccentricity parameter, wave number and cilia length. The influence of these parameters on streamline profiles (with a view to addressing trapping features via bolus formation and evolution), pressure gradient and other characteristics are evaluated graphically. Both axial and angular velocities are observed to be substantially modified with both micropolar rheological parameters and furthermore are significantly altered with increasing volumetric flow rate. Free pumping is also examined. An inverse relationship between pressure rise and flow rate is computed which is similar to that observed in Newtonian fluids. The study is relevant to hemodynamics in narrow capillaries and also bio-inspired micro-fluidic devices.

Journal ArticleDOI
TL;DR: In this article, the local conditions in the through-thickness of the electrodes are modeled by rigidly integrating classical electrochemistry into a three dimensional multiphysics model of an electrochemical cell.

Journal ArticleDOI
TL;DR: This paper builds a coarse-scale solver based on Generalized Multiscale Finite Element Method (GMsFEM) for a coupled flow and transport in perforated domains and presents an algorithm for adaptively adding online multiscale basis functions, which are computed using the residual information.

Journal ArticleDOI
TL;DR: In this article, the authors focus on a numerical analysis of a heat and mass transfer process in a novel type of methane/steam reforming reactor, where a reformer is divided into segments of various lengths and reactivity.

Journal ArticleDOI
TL;DR: In this paper, the authors considered a multi-site nearest neighbor interaction model with pure dephasing environmental noise with spatio-temporal correlation and showed how an accelerated rate for the energy transfer results especially under negative spatial correlation (anti-correlation).
Abstract: Transport phenomena are ubiquitous throughout the science, engineering, and technology disciplines as it concerns energy, mass, charge, and information exchange between systems. In particular, energy transport in the nanoscale regime has attracted significant attention within the physical science community due to its potential to explain complex phenomena like the electronic energy transfer in molecular crystals or the Fenna-Matthews-Olson (FMO)/light harvesting complexes in photosynthetic bacteria with long time coherences. Energy transport in these systems is highly affected by environmental noise but surprisingly not always in a detrimental way. It was recently found that situations exist where noise actually enhances the transport phenomena. Such noise can take many forms, but can be characterised in three basic behaviors: quantum, correlation in time, or space. All have been shown potential to offer an energy transport enhancement. The focus of this work is on quantum transport caused by stochastic environment with spatio-temporal correlation. We consider a multi-site nearest neighbor interaction model with pure dephasing environmental noise with spatio-temporal correlation and show how an accelerated rate for the energy transfer results especially under negative spatial correlation (anti-correlation). Spatial anti-correlation provides another control parameter to help one establish the most efficient transfer of energy and may provide new insights into the working of exciton transport in photosynthetic complexes. Further the usage of spatio-temporal correlated noise may be a beneficial resource for efficient transport in large scale quantum networks. Propagation of energy through microscopic noisy systems is more efficient when the noise shows site-to-site anticorrelation. Chikako Uchiyama and collaborators from Japan modeled the transport of energy in two-sites and three-sites chains when the environmental noise is not completely random, but rather can show some level of spatial correlation (meaning that the fluctuation is the same for different sites) or anticorrelation (the fluctuation is opposite in two neighbor sites). What they found is that spatial anticorrelation gives a clear advantage for energy transport. They also explored the role played by the time scale at which these correlations are present, finding an optimal coherence time which maximizes energy transport. These studies could help understanding processes such as photosynthesis, both at a fundamental level and for applications.

Journal ArticleDOI
TL;DR: It is shown that electron transfer between molecular sites with different local temperatures can also generate a thermal rectification effect and that electron hopping through molecular bridges connecting metal leads at different temperatures gives rise to asymmetric Seebeck effects, that is, thermoelectric rectification, in molecular junctions.
Abstract: Controlling the direction and magnitude of both heat and electronic currents using rectifiers has significant implications for the advancement of molecular circuit design. In order to facilitate the implementation of new transport phenomena in such molecular structures, we examine thermal and thermoelectric rectification effects that are induced by an electron transfer process that occurs across a temperature gradient between molecules. Historically, the only known heat conduction mechanism able to generate thermal rectification in purely molecular environments is phononic heat transport. Here, we show that electron transfer between molecular sites with different local temperatures can also generate a thermal rectification effect and that electron hopping through molecular bridges connecting metal leads at different temperatures gives rise to asymmetric Seebeck effects, that is, thermoelectric rectification, in molecular junctions.

Journal ArticleDOI
TL;DR: Insight is discussed into the underlying physics that can be gained from studying the emergence of non-Fermi liquid behavior as a function of the heterostructure parameters and the role of lattice symmetry and disorder in phenomena such as metal-insulator transitions in strongly correlated heterostructures.
Abstract: Understanding the anomalous transport properties of strongly correlated materials is one of the most formidable challenges in condensed matter physics. For example, one encounters metal-insulator transitions, deviations from Landau Fermi liquid behavior, longitudinal and Hall scattering rate separation, a pseudogap phase, and bad metal behavior. These properties have been studied extensively in bulk materials, such as the unconventional superconductors and heavy fermion systems. Oxide heterostructures have recently emerged as new platforms to probe, control, and understand strong correlation phenomena. This article focuses on unconventional transport phenomena in oxide thin film systems. We use specific systems as examples, namely charge carriers in SrTiO3 layers and interfaces with SrTiO3, and strained rare earth nickelate thin films. While doped SrTiO3 layers appear to be a well behaved, though complex, electron gas or Fermi liquid, the rare earth nickelates are a highly correlated electron system that may be classified as a non-Fermi liquid. We discuss insights into the underlying physics that can be gained from studying the emergence of non-Fermi liquid behavior as a function of the heterostructure parameters. We also discuss the role of lattice symmetry and disorder in phenomena such as metal-insulator transitions in strongly correlated heterostructures.

Journal ArticleDOI
03 Sep 2018
TL;DR: In this article, a theoretical and numerical study is described for unsteady pulsatile flow, heat and mass transport through a tapered stenosed artery in the presence of nanoparticles.
Abstract: Nanofluids are becoming increasingly popular in novel hematological treatments and also advanced nanoscale biomedical devices. Motivated by recent developments in this area, a theoretical and numerical study is described for unsteady pulsatile flow, heat and mass transport through a tapered stenosed artery in the presence of nanoparticles. An appropriate geometric expression is employed to simulate the overlapping stenosed arterial segment. The Sisko non-Newtonian model is employed for hemodynamic rheology. Buongiorno’s formulation is employed to model nanoscale effects. The two-dimensional non-linear, coupled equations are simplified for the case of mild stenosis. An explicit forward time central space (FTCS) finite difference scheme is employed to obtain a numerical solution of these equations. Validation of the computations is achieved with another numerical method, namely the variational finite element method (FEM). The effects of various emerging rheological, nanoscale and thermofluid parameters on flow and heat/mass characteristics of blood are shown via several plots and discussed in detail. The circulating regions inside the flow field are also investigated through instantaneous patterns of streamlines. The work is relevant to nanopharmacological transport phenomena, a new and exciting area of modern medical fluid dynamics which integrates coupled diffusion, viscous flow and nanoscale drug delivery mechanisms.

Posted Content
TL;DR: In this paper, the effects of packing structure on heat transfer in granular media are evaluated at macro-and grain-scales at the grain-scale, a gas-solid coupling heat transfer model is adapted into a discrete-element method to simulate this transport phenomenon.
Abstract: Structural characteristics are considered to be the dominant factors in determining the effective properties of granular media, particularly in the scope of transport phenomena Towards improved heat management, thermal transport in granular media requires an improved fundamental understanding In this study, the effects of packing structure on heat transfer in granular media are evaluated at macro- and grain-scales At the grain-scale, a gas-solid coupling heat transfer model is adapted into a discrete-element-method to simulate this transport phenomenon The numerical framework is validated by experimental data obtained using a plane source technique, and the Smoluschowski effect of the gas phase is found to be captured by this extension By considering packings of spherical SiO2 grains with an interstitial helium phase, vibration induced ordering in granular media is studied, using the simulation methods developed here, to investigate how disorder-to-order transitions of packing structure enhance effective thermal conductivity Grain-scale thermal transport is shown to be influenced by the local neighbourhood configuration of individual grains The formation of an ordered packing structure enhances both global and local thermal transport This study provides a structure approach to explain transport phenomena, which can be applied in properties modification for granular media

Journal ArticleDOI
TL;DR: In this paper, a finite element computational solution is presented for magnetohydrodynamic, incompressible, dissipative, radiative and chemically-reacting micropolar fluid flow, heat and mass transfer adjacent to an inclined porous plate embedded in a saturated homogenous porous medium.
Abstract: Non-Newtonian flows arise in numerous industrial transport processes including materials fabrication systems. Micropolar theory offers an excellent mechanism for exploring the fluid dynamics of new non-Newtonian materials which possess internal microstructure. Magnetic fields may also be used for controlling electrically-conducting polymeric flows. To explore numerical simulation of transport in rheological materials processing, in the current paper, a finite element computational solution is presented for magnetohydrodynamic, incompressible, dissipative, radiative and chemically-reacting micropolar fluid flow, heat and mass transfer adjacent to an inclined porous plate embedded in a saturated homogenous porous medium. Heat generation/absorption effects are included. Rosseland’s diffusion approximation is used to describe the radiative heat flux in the energy equation. A Darcy model is employed to simulate drag effects in the porous medium. The governing transport equations are rendered into non-dimensional form under the assumption of low Reynolds number and also low magnetic Reynolds number. Using a Galerkin formulation with a weighted residual scheme, finite element solutions are presented to the boundary value problem. The influence of plate inclination, Eringen coupling number, radiation-conduction number, heat absorption/generation parameter, chemical reaction parameter, plate moving velocity parameter, magnetic parameter, thermal Grashof number, species (solutal) Grashof number, permeability parameter, Eckert number on linear velocity, micro-rotation, temperature and concentration profiles. Furthermore, the influence of selected thermo-physical parameters on friction factor, surface heat transfer and mass transfer rate is also tabulated. The finite element solutions are verified with solutions from several limiting cases in the literature. Interesting features in the flow are identified and interpreted.

Journal ArticleDOI
TL;DR: In this paper, a non-Fourier Cattaneo-Christov model is employed to simulate thermal relaxation effects which cannot be simulated with the classical Fourier heat conduction approach.
Abstract: Reactive magnetohydrodynamic flows arise in many areas of nuclear reactor transport. Working fluids in such systems may be either Newtonian or non-Newtonian. Motivated by these applications, in the current study, a mathematical model is developed for electrically conducting viscoelastic oblique flow impinging on stretching wall under transverse magnetic field. A non-Fourier Cattaneo–Christov model is employed to simulate thermal relaxation effects which cannot be simulated with the classical Fourier heat conduction approach. The Oldroyd-B non-Newtonian model is employed which allows relaxation and retardation effects to be included. A convective boundary condition is imposed at the wall invoking Biot number effects. The fluid is assumed to be chemically reactive and both homogeneous–heterogeneous reactions are studied. The conservation equations for mass, momentum, energy and species (concentration) are altered with applicable similarity variables and the emerging strongly coupled, nonlinear non-dimensional boundary value problem is solved with robust well-tested Runge–Kutta–Fehlberg numerical quadrature and a shooting technique with tolerance level of 10−4. Validation with the Adomian decomposition method is included. The influence of selected thermal (Biot number, Prandtl number), viscoelastic hydrodynamic (Deborah relaxation number), Schmidt number, magnetic parameter and chemical reaction parameters, on velocity, temperature and concentration distributions are plotted for fixed values of geometric (stretching rate, obliqueness) and thermal relaxation parameter. Wall heat transfer rate (local heat flux) and wall species transfer rate (local mass flux) are also computed and it is observed that local mass flux increases with strength of heterogeneous reactions whereas it decreases with strength of homogeneous reactions. The results provide interesting insights into certain nuclear reactor transport phenomena and furthermore a benchmark for more general CFD simulations.

Journal ArticleDOI
TL;DR: In this paper, the authors review the historical developments that led to the unified physical concept of fluxes for transport phenomena and then use MD simulations to show that these popular flux formulas conserve neither momentum nor energy, nor do they produce fluxes that are consistent with their physical definitions.
Abstract: Irving and Kirkwood [J. Irving and J. G. Kirkwood, The statistical mechanical theory of transport processes. IV. The equations of hydrodynamics, J. Chem. Phys. 18, 817 (1950)] derived the transport equations from the principles of classical statistical mechanics using the Dirac delta to define local densities. Thereby, formulas for fluxes were obtained in terms of molecular variables. The Irving and Kirkwood formalism has inspired numerous formulations. Many of the later developments, however, considered it more rigorous to replace the Dirac delta with a continuous volume-weighted averaging function and subsequently defined fluxes as a volume density. Although these volume-averaged flux formulas have dominated the literature for decades and are widely implemented in popular molecular dynamics (MD) software, they are a departure from the well-established physical concept of fluxes. In this paper, we review the historical developments that led to the unified physical concept of fluxes for transport phenomena. We then use MD simulations to show that these popular flux formulas conserve neither momentum nor energy, nor do they produce fluxes that are consistent with their physical definitions. We also use two different approaches to derive fluxes for general many-body potentials. The results of the formulation show that atomistic formulas for fluxes can be fully consistent with the physical definitions of fluxes and conservation laws.

Journal ArticleDOI
TL;DR: In this paper, the effect of the inclination angle on convective heat transfer and entropy generation in an inclined lid driven square enclosure with a circular porous cylinder positioned at the center has been investigated numerically.

Journal ArticleDOI
TL;DR: In this paper, a three-dimensional lattice Boltzmann model based on the quasi-random nanostructural model is proposed to evaluate the mass transport properties and catalyst utilization of fuel cell catalyst layers in pursuance of catalyst performance improvement.