Anisotropic Flux Research Articles

Computational study of the segmental catalysis of steam-methanol reforming in heat integrated microchannel reactors for hydrogen production

The present study focuses upon segmentally catalyzed steam-methanol reforming processes for producing hydrogen in heat integrated microchannel reactors. Computational simulations are carried out to understand the causes of the fundamental phenomena involved in segmental catalysis and the autothermal operation. The benefits of segmental catalysis are discussed, and some aspects of heat phenomena are explained. The effects of wall thermal conductivity, flow velocity, and catalyst segment thickness are evaluated to determine how to design heat integrated reactors for specific operations by tailoring segmental catalysis approaches. To understand the importance of thermal management, the phenomena of heat in the catalyst structure are discussed in terms of anisotropic thermal conductivity and reaction heat flux. The results indicate that the benefits of segmental catalysis are surprisingly great. Segmental catalysis can be applied to greatly extend the operation regime, and the segmented oxidation design offers distinct advantages. The segmented design may offer improvements in heat and mass transport but presents thermal management challenges caused by the rapidly varying concentrations and temperatures. The wall thermal conductivity is vital in achieving heat balance and high process efficiency. Transverse wall heat conduction is of especially critical importance in thermal management. The flow velocity and catalyst segment thickness are of great importance to the improvement of conversion and productivity. An optimum flow velocity for highest overall performance exists.

Magnetic equivalent circuit and finite element modelling of anisotropic rotor axial flux permanent magnet synchronous motors with fractional slot distributed winding

AbstractAxial flux motors have been in the focus of many research work due to their promising properties when compared to conventional radial flux machines. Axial flux permanent magnet synchronous motors (AFPMSM) studied in the literature were mostly limited to surface‐mounted permanent magnet machines (SPMSM), excluding only a few studies about axial flux internal permanent magnet (AFIPM) or permanent magnet‐assisted synchronous reluctance (AFPMaSynRM) machines. Since numerous rotor topologies have been proposed and investigated in case of radial flux motors, analogous design methodologies can be developed in case of axial flux motors with rotor saliency. The parametrisation and modelling of a magnetically anisotropic rotor axial flux motor are presented. This approach is described generally and the method is applied to an example motor geometry. The results were validated by FEA (Finite Element Analysis), using the 2D multi‐slice and 3D modelling approaches. The modelling error was calculated and the analytical and numerical methods were compared. It was found that the proposed model was suitable for calculating important parameters of the anisotropic rotor axial flux permanent magnet synchronous motor (AnR‐AFPMSM) during the design process.

Effects of surface vacancy-adatom pair formation on PFC tungsten surface morphological response

We report a simulation study of the effect of He-irradiation-induced surface vacancy-adatom pair formation on the surface morphological evolution of plasma-facing component (PFC) tungsten and examine a number of factors that impact such evolution. Our analysis is based on self-consistent dynamical simulations according to an atomistically-informed, continuum-scale surface evolution model that has been developed following a hierarchical multiscale modeling strategy and can access the spatiotemporal scales of relevance to fuzz formation. The model accounts for the flux of surface adatoms generated as a result of the surface vacancy-adatom pair formation effect upon He implantation, which contributes to the anisotropic growth of surface nanostructural features due to the different rates of adatom diffusion along and across step edges of islands on the tungsten surface. We have carried out atomic-scale computations of optimal diffusion pathways along and across island step edges on the W(110) surface and calculated Ehrlich–Schwoebel (ES) barriers in adatom diffusion along and across such step edges. This aspect of surface adatom diffusion contributes to anisotropic surface atomic fluxes, terrace and step diffusive currents, and has been incorporated into our PFC surface evolution model, which predicts the formation of preferentially aligned nanoridge stripe patterns on the PFC surface. We establish that these anisotropic diffusive currents accelerate nanotendril growth on the PFC surface and the onset of surface nanostructure pattern formation. We also explore systematically the dependence of the PFC surface morphological response on the surface temperature and He ion incident flux, characterize in detail the resulting surface topographies and growth kinetics, and compare the predicted surface morphologies with experimental observations. Our simulation predictions for the emerging surface nanostructure patterns under certain plasma exposure conditions are consistent with experimental findings in the literature.

Transverse Momentum Dependence on Fourier Elliptic and Triangular Flow Harmonics in Mid-Central Pbpb Collisions at

We have collected particle collision data from the experiment using CMS apparatus, where we studied charged ions in the nucleus-to-nucleus collision’s PbPb branch in Pb at the 2.76 TeV energy scale. So far for the present work, we report the anisotropy of the thermal observational flux in lead-lead nucleon collisions at sqrt = 2.76 TeV. We observed that the collisions produced a large ion azimuth angle ranging from −π to π radian and a pseudo-conductance ranging from -2.6 to 2.6. In this work, we report the correlation function of transverse momentum, Pt , Δη, and ΔΦ over a wide range of centroids. When the transverse momentum is about 1-2 GeV/c and Δη is in range -1 to 1, we observe a jet peak in the η and Φ correlation plot as the centrality increases. In the case of ν 2, which is an elliptic current signal, we measured it with a 4-part correlation method in the 40-50% centrality class. Asymptotic angular correlations in the far range have been studied by Fourier decomposition on the product of anisotropies when the cross-correlation is equal to 3-3.5 GeV/c. The obtained Fourier coefficients are factorized into the singular product of -ion Φ anisotropies. The assumptions of the hydrodynamic model with the shear viscosity correlation increase accordingly.

First measurements of periodicities and anisotropies of cosmic ray flux observed with a water-Cherenkov detector at the Marambio Antarctic base

A new water-Cherenkov radiation detector, located at the Argentine Marambio Antarctic Base (64.24S-56.62 W), has been monitoring the variability of galactic cosmic ray (GCR) flux since 2019. One of the main aims is to provide experimental data necessary to study interplanetary transport of GCRs during transient events at different space/time scales. In this paper we present the detector and analyze observations made during one full year. After the analysis and correction of the GCR flux variability due to the atmospheric conditions (pressure and temperature), a study of the periodicities is performed in order to analyze modulations due to heliospheric phenomena. We can observe two periods: (a) 1 day, associated with the Earth’s rotation combined with the spatial anisotropy of the GCR flux; and (b) ∼ 30 days due to solar impact of stable solar structures combined with the rotation of the Sun. From a superposed epoch analysis, and considering the geomagnetic effects, the mean diurnal amplitude is ∼ 0.08% and the maximum flux is observed in ∼ 15 h local time (LT) direction in the interplanetary space. In such a way, we determine the capability of Neurus to observe anisotropies and other interplanetary modulations on the GCR flux arriving at the Earth.

Anisotropic cosmic optical background bound for decaying dark matter in light of the LORRI anomaly

Recently anomalous flux in the cosmic optical background (COB) is reported by the New Horizon observations. The COB flux is $16.37\pm1.47\, \rm nW m^{-2} sr^{-1}$, at the LORRI pivot wavelength of $0.608\,\rm \mu m$, which is $\sim 4\sigma$ level above the expected flux from the Hubble Space Telescope (HST) galaxy count. It would be great if this were a hint for the eV scale dark matter decaying into photons. In this paper, we point out that such a decaying dark matter model predicts a substantial amount of anisotropy in the COB flux, which is accurately measured by the HST. The data of the HST excludes the decay rate of the dominant cold dark matter larger than $10^{-24}$-$10^{-23}\,{\rm s}^{-1}$ in the mass range of $5$-$20\,$eV. As a result, the decaying cold dark matter explaining the COB excess is excluded by the anisotropy bound. We discuss some loopholes: e.g. warm/hot dark matter or two-step decay of the dark matter to explain the COB excess.

Verification of the Discrete Ordinates Goal-Oriented Multi-Collision Source Algorithm with Neutron Streaming Problems

The shielding calculation of neutron streaming problems with ducts is characterized by the strong anisotropy of angular flux, which poses a challenge for the analysis of nuclear installations. The discrete ordinate method is one of the most commonly deterministic techniques to solve the neutron transport equation, in which the accuracy and efficiency neutron are crucial to ensure the reliability of the streaming shielding simulation. We implemented the goal-oriented multi-collision source algorithm in the 3D transport code ARES. This algorithm can determine the importance factor based on the adjoint transport calculation, obtain the response function to enable problem-dependent, goal-oriented spatial decomposition, and provide the error estimation as a driving force behind the dynamic quadrature to optimize the source iteration. This study focuses on verifying the goal-oriented multi-collision source algorithm under the neutron streaming problems, and the capabilities of the algorithm have been tested on IRI-TUB benchmark of SINBAD database. The numerical results show that the algorithm can effectively control the angular discretization error for the neutron streaming problems, which is more economical than the traditional discrete ordinate calculation.

Large-eddy simulation of turbulent heat transfer in negative buoyant fountain

This paper presents the results of large-eddy simulation (LES) of a downward wall jet that encounters an upward flow in a vertical rectangular channel, named negative buoyant fountain (NBF). The downward jet fluid has higher temperature than the opposing upward stream so that the influence of the buoyancy force on the physics of the mixing process can be investigated. Two subgrid-scale models available in the OpenFOAM platform, i.e. the dynamic k-equation model (DKM) and the wall-adapting local eddy-viscosity (WALE) model, are used for cross-comparison. The numerical results of the time-averaged and fluctuating velocity fields agree satisfactorily with the experimental data. The LES results form an accurate, high-resolution, three-dimensional database of buoyant turbulent mixing, which has expanded the sparse flow field measurements provided by the experiment, hence the numerical database could be used to validate the Reynolds-averaged Navier–Stokes (RANS) simulation method and to contribute to the turbulence modeling. In particular, the statistics of turbulent heat flux have been analyzed and various turbulent heat flux models have been a priori tested based on the LES numerical database. Such information could be useful for RANS simulation guidelines or for deriving anisotropic turbulent heat flux models applicable for turbulent buoyant flows sharing the similar principal flow structures in complex geometries.

Impact of inflow turbulence on large‐eddy simulation of film cooling flows

The paper investigates the impact of industrially appropriate inflow turbulence on the turbulent state, mixing capability and surface coolant distribution of film cooling flow using LES. Near-wall and freestream turbulence, corresponding to turbulent boundary layers and stochastic turbulent fluctuations away from the wall, have been investigated. In our study, we set up three main test scenarios: no inflow turbulence, near-wall boundary layer turbulence and freestream turbulence. Our work shows that surface adiabatic cooling effectiveness differs significantly with and without inflow turbulence. It is also evident that freestream turbulence enhances the mixing ability of a cooling flow, providing an initial enhancement of surface cooling close to the hole but with reduced cooling effectiveness downstream. Turbulent length scales, turbulent heat flux and turbulent anisotropy are compared and illustrate the changes in cooling effectiveness as a result of the upstream turbulent behaviour. As a result, despite inflow turbulence being a complex subject and problem-dependent, the importance of introducing realistic turbulent inflow in LES of cooling flows is demonstrated.

Study on dynamic behaviors from non-circular dense granular jet impact

Dynamic behaviors of non-circular dense granular jets impacting a sufficiently large target are studied by experiment and DEM simulation. Effects of the granular jet velocity, particle diameter, and aspect ratio on the anisotropic pattern were investigated. Results show that the anisotropy of particle concentration of the granular sheet is enhanced with increasing aspect ratio. Interestingly, despite the significant differences in flux, the particle velocities are approximately consistent along the long and short axes. Unlike liquid, a dead zone is present in the impact zone, and the axial-to-radial transformation of the velocity is achieved by similar circular motion along the dead zone. Because the dead zone is adaptively adjusted with the cross section, the particle fluxes are anisotropic. Frequent collisions and frictions contribute to the homogenization of velocity in azimuths. Increasing particle diameter causes the enhancement of velocity fluctuations, the circular motion cannot be maintained and particles become scattered and isotropic. • The anisotropy in velocity and flux of particles from non-circular dense particle jet impact is characterized. • The effects of the velocity, aspect ratio, and particle diameter on anisotropy are assessed. • The mechanism of the anisotropy of the granular sheet is simulated by DEM.

A New Method for Determining Fluid Flux at High Pressures Applied to the Dehydration of Serpentinites

AbstractA new method to determine fluid flux at high pressures and temperatures has been developed and used to study serpentinites at subduction zone conditions. Drill cores of a natural antigorite‐serpentinite with a strong foliation were used in multi‐anvil experiments in the range of 2–5 GPa and 450–800°C. Fluids released upon dehydration are fixed by the formation of brucite in an adjacent fluid sink. The amount and distribution of brucite serves as a proxy for fluid flow. In our specific setup the sample reacted with the surrounding fluid sink to form an additional layer of olivine, which has the potential to limit fluid flux within our experiments. For conditions prior to serpentine dehydration we used Al(OH)3 as fluid source. Fluid in this experiment did not migrate through the serpentinite, indicating that serpentine has a low diffusivity. The experiments also show that small deviatoric stresses have an influence on the fluid flux and can cause an anisotropic fluid flux. Comparison between the time scales of the determined fluid flux with fluid production rates indicates fluid pressure buildup during dehydration reactions. Adjacent less permeable layers can inhibit fluid flux and cause fluid pressure buildup even at conditions when an interconnected pore space formed.

Realizability conditions for relativistic gases with a non-zero heat flux

This work introduces a limitation on the minimum value that can be assumed by the energy of a relativistic gas in the presence of a non-zero heat flux. Such a limitation arises from the non-negativity of the particle distribution function and is found by solving the Hamburger moment problem. The resulting limitation is seen to recover the Taub inequality in the case of a zero heat flux but is more strict if a non-zero heat flux is considered. These results imply that, in order for the distribution function to be non-negative, (i) the energy of a gas must be larger than a minimum threshold; (ii) the heat flux, on the other hand, has a maximum value determined by the energy and the pressure tensor; and (iii) there exists an upper limit for the adiabatic index Γ of the relativistic equation of state and that limit decreases in the presence of a heat flux and pressure anisotropy, asymptoting to a value Γ = 1. The latter point implies that the Synge equation of state is formally incompatible with a relativistic gas showing a heat flux, except in certain gas states.

Achieving Sustainable and Stable Potassium-Ion Batteries by Leaf-Bioinspired Nanofluidic Flow.

In nature, living systems have evolved integrated structures, matching optimized nanofluidics to adapt to external conditions. In rechargeable batteries, high-capacity electrodes are often plagued by the crucial and universal bottleneck of dissolution and shuttle of active substance into electrolyte, posing obstacles of inevitable capacity degradation. Introducing the concept of intelligent nanofluidics to electrodes, a leaf-bioinspired electrode configuration with hierarchical architecture to tackle this problem is proposed. This integrated structure with fine-tuned surface pores and unobstructed interior porous media, can spatially control the anisotropic nanofluidic flux, in an efficient and self-protectable way: tailoring the outflow across the electrode's surface and free transport in interior, to ensure speedy and stable energy conversion. As proofs of concept, applications of sustainable electrodes rejuvenated from fallen leaf and spent commercial batteries, are designed with leaf-bioinspired architecture. Both KCoS2 and KS battery systems show advanced steady cycling with effectively mitigated shuttle issues in this smart architecture (0.15% and 0.21% capacity decay per cycle), even at high areal mass loading, when compared with open porous structure (0.60% and 0.39%). This work may pave a new way from a biomimetic view to integrated electrode engineering with regulated surface shielding to conquer the universal dissolution-shuttle problems facing high-capacity materials.

Complexity analysis of charged dynamical dissipative cylindrical structure in modified gravity

This article focuses on the formulation of some scalar factors which are uniquely expressed in terms of matter variables for dynamical charged dissipative cylindrical geometry in a standard gravity model \(\mathcal {R}+\Phi \mathcal {Q}\) (\(\Phi \) is the coupling parameter, \(\mathcal {Q}=\mathcal {R}_{\varphi \vartheta }\mathcal {T}^{\varphi \vartheta }\)) and calculates four scalars by orthogonally decomposing the Riemann tensor. We find that only \(\mathcal {Y}_{TF}\) involves inhomogeneous energy density, heat flux, charge and pressure anisotropy coupled with modified corrections, and thus call it as complexity factor for the considered distribution. Two evolutionary modes are discussed to study the dynamics of cylinder. We then take the homologous condition with \(\mathcal {Y}_{TF}=0\) to calculate unknown metric potentials in the absence as well as presence of heat dissipation. The stability criterion of the later condition is also checked throughout the evolution by applying some constraints. We conclude that the effects of charge and modified theory yield more complex system.

Pitch Angle Distribution of MeV Electrons in the Magnetosphere of Jupiter

AbstractThe magnetosphere of Jupiter harbors the most extreme fluxes of MeV electrons in the solar system and therefore provides a testbed of choice to understand the origin, transport, acceleration, and loss of energetic electrons in planetary magnetospheres. Along this objective, the Pitch Angle Distribution (PAD) of energetic electrons may reveal signatures of the dominant physical processes. Here, we analyze for the first time the PAD of MeV electrons observed by the Galileo‐Energetic Particle Detector (EPD) experiment in orbit around Jupiter from 1995 to 2003. We find that the MeV electron PADs observed by the integral channels of EPD appear relatively isotropic with a flux anisotropy lower than a factor of 3. Due to the relatively large angular apertures of the EPD telescopes, the actual anisotropy may be larger than the observed one. The fine anisotropy observed by Galileo‐EPD reveals persistent pancake distributions at the M‐shell of M = 9. Outward of this distance, at M = 15 and M = 20–60, MeV electron distributions have pancake, isotropic, and scattered beam field‐aligned distributions. The scattered beam distributions can either be evidence of outward adiabatic transport or may suggest that high‐latitude auroral acceleration can transiently supply as much trapped MeV electrons to the middle magnetosphere as the inward adiabatic transport of electrons from an outer equatorial reservoir.

Assessment of turbulent heat flux models for URANS simulations of turbulent buoyant flows in ROCOM tests

Turbulent mixing in buoyant flows is an essential mechanism involved in many scenarios related to nuclear safety in nuclear power plants. Comprehensive understanding and accurate predictions of turbulent buoyant flows in the reactor are of crucial importance, due to the function of mitigating the potential detrimental consequences during postulated accidents. The present study uses URANS methodology to investigate the buoyancy-influenced flows in the reactor pressure vessel under the main steam line break accident scenarios. With a particular focus on the influence of turbulent heat flux closure models, various combinations of two turbulence models and three turbulent heat flux models are utilized for the numerical simulations of three ROCOM tests which have different characteristic features in terms of the flow rate and fluid density difference between loops. The simulation results are compared with experimental measurements of the so-called mixing scalar in the downcomer and at the core inlet. The study shows that the anisotropic turbulent heat flux models are able to improve the accuracy of the predictions under conditions of strong buoyancy whilst in the weak buoyancy case, a major role is played by the selected turbulence models with essentially a negligible influence of the turbulent heat flux closure models.

Isotropic and Anisotropic Flux Pinning Induced by Heavy-Ion Irradiation

Ion irradiation of REBCO films and coated conductors, in which the ions pass completely through the REBCO film, produces damage tracks which form near-ideal flux-pinning defects. The radius and aspect ratio of the tracks depends on the mass and energy of the incident ions. We have investigated the effect of Ag ion irradiation, at different incident energies and incidence angles, on REBCO production-quality coated conductors from American Superconductor Corp. Transmission electron microscopy and in-field transport critical current anisotropy analysis indicates that the ion-energy threshold for the formation of elongated tracks is around 50 MeV. At this energy tracks are not readily identifiable in low-resolution TEM, and enhancement of critical current is nearly isotropic. For a higher ion energy of 100 MeV, on the other hand, clear elongated (but still not fully continuous) tracks are visible in TEM, and the critical current is anisotropic with strong enhancement occurring when the applied field is parallel to the ion incidence angle. We particularly analyze the case of 60° inclined irradiation. This produces a clear peak in the field-angle dependence of critical current for 100 MeV irradiation, but only an incipient peak for 50 MeV irradiation. The incipient peak can be identified by curve fitting using a minimal number of maximum-entropy functional components.

Modelling general-relativistic plasmas with collisionless moments and dissipative two-fluid magnetohydrodynamics

ABSTRACT Relativistic plasmas are central to the study of black hole accretion, jet physics, neutron star mergers, and compact object magnetospheres. Despite the need to accurately capture the dynamics of these plasmas and the implications for relativistic transients, their fluid modelling is typically done using a number of (overly) simplifying assumptions, which do not hold in general. This is especially true when the mean free path in the plasma is large compared to the system size, and kinetic effects start to become important. Going beyond common approaches used in the literature, we describe a fully relativistic covariant 14-moment based two-fluid system appropriate for the study of electron–ion or electron–positron plasmas. This generalized Israel-Stewart-like system of equations of motion is obtained directly from the relativistic Boltzmann–Vlasov equation. This new formulation can account for non-ideal effects, such as anisotropic pressures and heat fluxes, not present in previous formulations of two-fluid magnetohydrodynamics. We show that a relativistic two-fluid plasma can be recast as a single fluid coupled to electromagnetic fields with (potentially large) out-of-equilibrium corrections. We keep all electron degrees of freedom, which provide self-consistent evolution equations for electron temperature and momentum. The out-of-equilibrium corrections take the form of a collisional 14-moment closure previously described in the context of viscous single fluids. The equations outlined in this paper are able to capture the full two-fluid character of collisionless plasmas found in black hole accretion and flaring processes around compact objects, as well Braginskii-like two-fluid magnetohydrodynamics applicable to weakly collisional plasmas inside accretion discs.

Complexity of a dynamical dissipative cylindrical system in non-minimally coupled theory

This paper aims to formulate certain scalar factors associated with the matter variables for a self-gravitating non-static cylindrical geometry by considering a standard model R+ζQ of f(R,T,Q) gravity, where Q=RφϑTφϑ and ζ is the arbitrary coupling parameter. We split the Riemann tensor orthogonally to calculate four scalars and deduce YTF as a complexity factor for the fluid configuration. This scalar incorporates the influence of the inhomogeneous energy density, heat flux and pressure anisotropy along with correction terms for the modified gravity. We discuss the dynamics of the cylinder by considering the two simplest modes of structural evolution. We then take YTF=0 with a homologous condition to determine the solution for the dissipative as well as non-dissipative scenarios. Finally, we discuss the criterion under which the complexity-free condition shows stable behavior throughout the evolution. It is concluded that the complex functional of this theory results in a more complex structure.

Accurate Solutions to Non-Linear PDEs Underlying a Propulsion of Catalytic Microswimmers

Catalytic swimmers self-propel in electrolyte solutions thanks to an inhomogeneous ion release from their surface. Here, we consider the experimentally relevant limit of thin electrostatic diffuse layers, where the method of matched asymptotic expansions can be employed. While the analytical solution for ion concentration and electric potential in the inner region is known, the electrostatic problem in the outer region was previously solved but only for a linear case. Additionally, only main geometries such as a sphere or cylinder have been favoured. Here, we derive a non-linear outer solution for the electric field and concentrations for swimmers of any shape with given ion surface fluxes that then allow us to find the velocity of particle self-propulsion. The power of our formalism is to include the complicated effects of the anisotropy and inhomogeneity of surface ion fluxes under relevant boundary conditions. This is demonstrated by exact solutions for electric potential profiles in some particular cases with the consequent calculations of self-propulsion velocities.