Presence Of Non-uniform Magnetic Field Research Articles

A simplified lattice Boltzmann implementation of the quasi-static approximation in pipe flows under the presence of non-uniform magnetic fields

A simplified lattice Boltzmann implementation of the quasi-static approximation in pipe flows under the presence of non-uniform magnetic fields

Computational study of heat transfers and hydrodynamic of nanofluid flow inside double pipe heat exchanger in presence of non-uniform magnetic field

The improvement of heat exchangers is important for energy savings and environmental protection. In this work, the application of the non-uniform magnetic source for the enhancement of the hydrodynamic in double-pipe heat exchangers is comprehensively studied. The hydrodynamics of nanofluid flow is also investigated in our research by performing computational modeling. In addition, the thermal efficiency of a selected system in different conditions of magnetic field and nanofluid velocity are studied. In addition, role of wall profile of inner tube on hydrodynamic is also disclosed in this work. The simulation of the nanofluid flow is done by computational fluid dynamics and solving Navier-stokes equations. The usage of non-uniform magnetic field would raise average skin friction about 230 %, 400 % and 500 % on sinusoidal, triangular and rectangular profiles, respectively.

Magneto-Acousto-Electrical Tomography With Nonuniform Static Magnetic Field

Magneto-acousto-electrical tomography (MAET) is a powerful tool for numerous applications, including medical imaging and process tomography. In these applications, and to enable precise reconstruction of images of a given process using MAET, high-quality measurements must be obtained from the target of interest. It is thus obvious that the magnetic field excitation used in these measurements plays an important role in this task. However, the existing reports in the literature to date have usually assumed that the static magnetic field is a uniform field, which is challenging to achieve in practice. In this article, we circumvent this challenge and present a comprehensive mathematical model for MAET in the presence of nonuniform magnetic fields. In the proposed model, a relationship is established between the measurement signal and the reciprocal current density. The conductivity distribution is obtained via a simulation model and compared with the second norm error of the images and the various uniformities of the nonuniform magnetic fields obtained from the imaging results. The model is then validated for different test cases, which range from a simple phantom with three layers to a phantom with a cylindrical geometry. It is concluded that the use of a nonuniform magnetic field can lead to significant changes and improvements in the reconstruction of the conductivity, thus making it possible to use this technique in bedside detection applications.

Evaluation of separation point in a divergent channel in the presence of non-uniform magnetic field

Due to the pressure gradient increasing downstream, the boundary layer separation phenomena may occur on the divergent channel flow wall. Still, several methods have been applied to control or postponed the separation. Exerting a magnetic field on the fluid flow is one solution. In the present research, we aim to investigate the impact of magnetic fields on the separation location in a divergent channel numerically. Hence, the finite volume method using the OpenFOAM CFD toolbox is employed, and a code for 2-D divergent channel flow under a non-uniform magnetic field is developed. The obtained results have been validated in comparison with previous studies. The results are presented for a test case of the channel with divergence half-angle equals 2.5°, 30 cm length, and 2 cm inlet height. It is demonstrated when Ha increases from 0 to 2, the separation points for liquid lithium fluid flow with Re = 208.33 are postponed from 12.93 cm to 23.18 cm. Moreover, it is shown that the separation phenomena disappear entirely for the Ha value of more than 3.

MHD mixed convective slip flow of Casson fluid over a porous inclined plate with Joule heating, viscous dissipation and thermal radiation

The present study examines numerically heat and mass transfer on mixed convective Casson fluid flow over an inclined plate in presence of non-uniform magnetic field. The impact of Joule heating, viscous dissipation and thermal radiation are taken into consideration. The resulting ordinary differential equations obtained from the governing partial differential equations of the flow are solved by using MATLAB bvp4c method. The effects of relevant parameters on velocity, temperature and concentration are discussed graphically, while skin-friction coefficient, rate of heat transfer and mass transfer are presented in tabular structure.

FERROFLUID FLOW IN MAGNETIC FIELD ABOVE STRETCHING SHEET WITH SUCTION AND INJECTION

The aim of this paper is to investigate the boundary layer of ferrofluid flow induced by a permeable stretching sheet. Fluid is electrically non-conducting in the presence of non-uniform magnetic field. The governing non-linear partial differential equations are reduced to non-linear ordinary differential equations by applying a similarity transformation. Numerical solutions are obtained by using Maple. The effects of the magnetic field, the Reynolds number and the porosity on the velocity and thermal fields are investigated. The impact of the parameters on the skin friction and the local Nusselt number is numerically examined. The skin friction and heat transfer coefficients are decreasing with enhancing the stretching, the values of porosity and the ferromagnetic parameter.

Hall conductivity as topological invariant in phase space

It is well known that the quantum Hall conductivity in the presence of constant magnetic field is expressed through the topological TKNN invariant. The same invariant is responsible for the intrinsic anomalous quantum Hall effect (AQHE), which, in addition, may be represented as one in momentum space composed of the two point Green’s functions. We propose the generalization of this expression to the QHE in the presence of non-uniform magnetic field. The proposed expression is the topological invariant in phase space composed of the Weyl symbols of the two-point Green’s function. It is applicable to a wide range of non-uniform tight-binding models, including the interacting ones.

Heat transfer and thermal efficiency of a lab-fabricated ferrofluid-based single-ended tube solar collector under the effect of magnetic field: An experimental study

Heat transfer and thermal efficiency of a single-ended all-glass evacuated tube solar collector (SEETSC), as a special type of heat exchanger in the solar thermal systems, can be improved using ferrofluids, as working fluid, under the effect of the magnetic field. The present experimental study investigates the natural convection, and thermal efficiency of a lab-fabricated ferrofluid (Mn–Zn Fe2O4/water) based single-ended tube solar collector, as a simplified model of the SEETSCs, in the presence of non-uniform magnetic field. Effect of the nanoparticles volume fraction (0.0–0.5%), input heat flux (qin′′=50–350 W/m2) and the magnetic field generated by several identical permanent magnets (remanent magnetization (Br) = 0.02–1.0 T) on the heat transfer and thermal efficiency of the collector is investigated. The results show that applying a magnetic field causes not only compensation of the heat transfer reduction due to the high viscosity values but also improvement of it. The maximum enhancements in the obtained average Nusselt number and thermal efficiency are respectively about 73.0% and 47.0% for the 0.5 vol% ferrofluid at qin′′ = 350 W/m2 and Br = 1.0 T. According to this study, it can be feasible to enhance the thermal efficiency of the SEETSCs-based solar thermal systems using the ferrofluid under the effect of magnetic field.

Ferrofluid Flow and Heat Transfer From a Sphere in the Presence of Nonuniform Magnetic Fields

Abstract In this article, the effects of nonuniform magnetic fields on the hydrodynamics and heat transfer from a heated sphere to its surrounding ferrofluid flow have been investigated. Kelvin body forces originate from the nonuniformity of the applied magnetic field and can generate the vortices behind the sphere leading to a considerable change in the velocity and temperature fields. The applied magnetic field disturbs the thermal boundary layer and decreases heat-transfer resistance, leading to a significant enhancement in the heat-transfer coefficient. Variations of the local and average Nusselt number value (Nu), separation angle, recirculation length, and drag coefficient were considered to investigate the effects of magnetic field intensity, Reynolds number, and the relative magnetic permeability of the sphere. In addition, the arrangement of the coils was optimized to provide the highest heat-transfer rate. Moreover, the obtained results indicate that enhancement in Nuavg is much larger than the drag resistance penalty.

Heat transfer enhancement inside semi-insulated horizontal pipe by controlling the secondary flow of oil-based ferro-fluid in the presence of non-uniform magnetic field: A general correlation for the Nusselt number

In the present study, hydrodynamic and hydrothermal behavior of the laminar nano-fluid actuated by the non-uniform magnetic field in a horizontal semi-insulated tube was numerically investigated. Firstly, the impact of key parameters such as Reynolds number (Re), magnetic field intensity (Mn), wall heat flux (q) as well as the wire location (as a source of magnetic field producer) was examined on the flow and heat transfer characteristics and compared with the non-magnetic case. Numerical results showed that the heat transfer and pressure drop in the presence of the magnetic field were about 3.7 and 1.8 times higher than the non-magnetic case (Re = 500, Mn = 5.7e8), respectively. As a result, to gain a more general conclusion, the effectiveness parameter (ε) was evaluated in different vital situations, in which both heat transfer and pressure drop were involved. Accordingly, using the magnetic field is affordable to increase heat transfer in the practical works. Finally, a general correlation for the Nusselt as a function of non-dimensional length (x*), magnetic number (Mn) and non-dimensional heat flux (Q*mag) is presented with an average error of 3.43%.

Laminar ferrofluid heat transfer in presence of non-uniform magnetic field in a channel with sinusoidal wall: A numerical study

This research is allocated to numerical study of two dimensional laminar forced convective heat transfer of ferrofluid (water and Fe3O4) in the presence of a non-uniform magnetic field in a channel with a sinusoidal corrugated wall. The hydrodynamic and thermal behavior of the ferrofluid is examined using the mixture model and the finite volume method. The effects of an increase in wavy channel amplitude, volume fraction, Reynolds number, and negative magnetic field gradient on the hydrodynamic and thermal behaviors are investigated and discussed. Nusselt number is found to increase as wave amplitude, volume fraction of nanoparticles, Reynolds number, or negative magnetic field gradient increase. The negative magnetic field gradient increases the pump work with a greater effect at lower Reynolds numbers. The results of this research can be utilized to enhance heat transfer in heat exchangers and to increase their efficiency.

Application of nonuniform magnetic fields in a Brownian dynamics model of ferrofluids with an iterative constraint scheme to fulfill Maxwell’s equations

Ferrofluids are steadily rising in applications across many fields, preferred for their ability to be remotely positioned and controlled via external magnetic fields. In magnetic separation operations, nonuniform magnetic fields elicit a phenomenon known as magnetophoresis so that the ferroparticles will undergo migration toward areas of higher magnetism. To comprehend this behavior, the authors developed a Brownian dynamics simulation of particles in ferromagnetic clusters under the influences of a simple shear flow and an applied magnetic field gradient. An iterative constraint mechanism was implemented to satisfy Maxwell’s equations throughout the dense colloidal suspension, ensuring that essential laws of magnetostatics are rigorously fulfilled at all times over small, finite sub-volumes of the system. Because of the presence of nonuniform magnetic fields, magnetophoresis and magnetic separation behavior were analyzed to assess the effectiveness of the model. Results showed that, when compared to “unconstrained” models, separation caused by magnetic field gradients occurred at a decreased rate under the constraint scheme due to relatively weaker non-Newtonian aggregation property trends. Through application of a dimensionless number analysis to observe varied levels of particle-particle interactions, thermal fluctuations, and viscous shearing, it was confirmed that the aggregation and magnetic separation modeling of ferrofluid colloidal suspensions without acceptable adherence to Maxwell’s equations produces an unreliable representation of current ferrofluids.

Melt ejection from copper target in air in the presence of magnetic field using nanosecond pulsed laser ablation

The authors report on the study of the crater generated using a nanosecond laser on a copper target in air in the presence of uniform and nonuniform magnetic fields. The analysis of particles deposited inside and around the crater revealed that the generation of large particles (≥0.68 μm) is due to the melt ejection and instability in the liquid layer. The presence of a nonuniform magnetic field causes an additional drift to molten liquid which in turn increases the Kelvin–Helmholtz instability. The percentage of large particles increased due to the enhancement in the Kelvin–Helmholtz instability and mass ejection. The intensity of copper atomic transitions was enhanced in the presence of a uniform magnetic field compared to a nonuniform magnetic field. This is more likely due to an increase in melt ejected mass in the plasma in the presence of a nonuniform magnetic field which may scatter or absorb laser light which in turn decreases laser–matter interaction. The energy-dispersive x-ray spectroscopy and Raman spectroscopy showed the deposited particles are Cu2O. In the presence of a nonuniform magnetic field, the intensity of Raman Cu2O was enhanced, which is attributed to an increase in the number of Cu2O particles.

Effect of non-uniform magnetic field on heat transfer of swirling ferrofluid flow inside tube with twisted tapes

In this article, a three-dimensional numerical simulation is performed to investigate the effect of magnetic field on the heat transfer of ferrofluid inside a tube which is equipped with twisted tape. This work comprehensively focused on the flow feature and temperature distribution of ferrofluid in presence of non-uniform magnetic field while ferrofluid swirled inside a tube with twisted tape. In this study, it is assumed that the ferrofluid is single phase and laminar and constant heat flux is applied on the outside of the tube. The magnetic field is established by wire in parallel direction with the axis of the tube. The base fluid is water with 0.86Vol% Nano particles (Fe3O4). The finite volume approach with the SIMPLEC algorithm is used for calculating the flow feature and heat transfer inside the tube. The numerical simulations are validated with experimental data with reasonable discrepancy. Parametric studies are performed to reveal the influence of various factors such as concentration of nanoparticle, intensity of magnetic field, geometric shape of twisted tape and Reynolds number on the heat transfer is investigated. According to obtained results, average Nusselt number of ferrofluid increases more than 200% as it flows inside tube with twisted tapes. Furthermore, our finding shows that magnetic field induced by parallel wire enhances the average heat transfer of the swirling ferrofluid (about 30%). The results also show that the Nusselt number also rises as the concentration of the nanoparticle is increased. In addition, heat transfer augments in high Reynolds number.

Magnetization of disclinated graphene in nonuniform magnetic field

Two-dimensional disclinated atomic graphene layer in curved space–time is exactly discussed, and the explicit dependence of Landau levels on the topological defect and external magnetic field are obtained in the presence of nonuniform magnetic field. It is worth mentioning that the presence of topological defect reduces the degeneracy of energy levels. The persistent current, magnetization, susceptibility and the magnetoresistance of structure are investigated. It can be shown that the curvature of the conical surface affects the pattern of oscillations of persistent current and, of course, corresponding magnetoresistance. The behavior of the above physical quantities as a function of magnetic flux is explicitly found for various defects. We observe that increasing magnetic field leads to a aperiodic oscillation. The large Aharonov–Bohm flux gives rise to vanish the magnetization oscillations.

Computational modeling of geometry effects on the IDL surface concentration in the presence of non-uniform magnetic field – links to atherosclerosis

Effect of geometry on the atherosclerosis is a significant issue, so the 3D s-shape and 2D axisymmetric stenosis tube as a blood vessel have been analyzed in this work. This paper has focused on the most important parameters in the LSC uptake, inlet Re number and infiltration velocity in the presence of non-uniform magnetic field. The magnetic field is arising from the thin wire with electric current placed vertically to the arterial blood vessel. According to the results of this study, applying magnetic field can be a treatment for atherosclerosis by reducing LSC along the vessel wall. It is observed that, application of magnetic field leads to production of a vortex in the flow, high strain rate, increment of WSS, and also reduction in LSC. For solving the mass transport equation, Lumen-wall model has been used. Blood flow has been considered laminar and incompressible containing Ferro fluid (blood and 4vol% Fe3O4) under steady state conditions. Numerical solution of governing equations was obtained by using the single-phase model and control volume technique for flow field.

Effect of non-uniform magnetic field on forced convection heat transfer ofFe3O4–water nanofluid

In this paper force convection heat transfer in a lid driven semi annulus enclosure is studied in presence of non-uniform magnetic field. The enclosure is filled with Fe3O4–water nanofluid. It is assumed that the magnetization of the fluid is varying linearly with temperature and magnetic field intensity. Control volume based finite element method is used to solve the governing equations in the form of vorticity–stream function formulation. The calculations were performed for different governing parameters namely, the Reynolds number, nanoparticle volume fraction and Hartmann number. Results show that Nusselt number has direct relationship with Reynolds number, nanoparticle volume fraction while it has reverse relationship with Hartmann number.

Direct numerical simulation of electromagnetically forced flows using OpenFOAM

We present direct numerical simulation results of a conducting fluid subject to the Lorentz force resulting from an external static magnetic field normal to the electric current direction. This research discipline, generally known as electromagnetic forcing flows, is motivated by many engineering and physical applications such as plasma physics, geophysics, weather prediction and solid melting processes. In this paper, a computational fluid dynamics (CFD) code is developed using the open source C++ library OpenFOAM. The solver is based on the electric potential method coupled to the Navier–Stokes equations. The code is then benchmarked to other well-known solvers using different numerical techniques and to the experiment. Excellent agreement is obtained for the forced toroidal channel flow, with three-dimensional dynamics, as well as for the confined vortex-pair in a cylindrical container, with quasi-two-dimensional dynamics. Quasi-two-dimensional forced flow in the presence of non-uniform magnetic field at low Hartmann number is also used for comparison. Furthermore, qualitative comparison with the experiment is made where we are able to successfully simulate the vortex pairs generated by the Lorentz force and the effect of the magnetic field gradient leading to the so-called gradB jets in accordance with the experiment.

Numerical Investigation of the Transient Hydrothermal Behavior of a Ferrofluid Flowing Through a Helical Duct in the Presence of Nonuniform Magnetic Field

This paper investigates numerically the time dependent hydrothermal behavior of a ferrofluid (water and 4 vol. % Fe3O4) flowing in a helical channel, which is exposed to a nonuniform transverse magnetic field and its walls are subjected to uniform heat flux. The two phase mixture model and control volume technique have been used to study the flow. The results show that applying the nonuniform transverse magnetic field considerably increases the velocity and flow rate in the vicinity of the channel walls while it significantly decreases the velocity at the center of the channel. Applying magnetic field also decreases considerably the temperature of the inner wall of the helical channel. Furthermore, the average Nusselt number is increased by applying the nonuniform transverse magnetic field and it is more enhanced by increasing the magnetic field intensity.

Concentration polarization effects on the macromolecular transport in the presence of non-uniform magnetic field: A numerical study using a lumen-wall model

In this paper, the concentration polarization phenomena in a two dimensional tube under steady state conditions containing ferrofluid (blood and 4vol% Fe3O4) is reported in the presence of non-uniform magnetic field. Lumen-wall model has been used for solving the mass transport equation. Hemodynamics parameters such as flow rate, viscosity, wall shear stress (WSS) and the macromolecules surface concentration which accumulate on the blood vessel wall, influenced the formation and progression of atherosclerosis disease. Effective parameters on the low density lipoprotein (LDL) surface concentration (LSC) such as: the wall filtration velocity, inlet Reynolds number and WSS under applied non-uniform magnetic field have been examined.Numerical solution of governing equations of the flow field have been obtained by using the single-phase model and the control volume technique. Magnetic field is generated by an electric current going through a thin and straight wire oriented perpendicular to the tube. Results show WSS in the vicinity of magnetic field source increased and LSC decreased along the wall.