scholarly journals Analysis of the Magnetohydrodynamic Behavior of the Fully Developed Flow of Conducting Fluid

Energies ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2463
Author(s):  
Wellington da Silva Fonseca ◽  
Ramon C. F. Araújo ◽  
Marcelo de Oliveira e Silva ◽  
Daniel Onofre de A. Cruz
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Flow Velocity ◽  
Numerical Study ◽  
Mhd Flow ◽  
Initial Section ◽  
Industrial Applications ◽  
Conducting Fluid ◽  
Field Orientation ◽  
Circular Duct

Important industrial applications are based on magnetohydrodynamics (MHD), which concerns the flow of electrically conducting fluids immersed in external magnetic fields. Using the Finite Volume Method, we performed a 3D numerical study of the MHD flow of a conducting fluid in a circular duct. The flow considered was laminar and fully developed. Along the initial section of the duct, there were magnets placed around the duct producing magnetic fields in the radial direction. Two arrangements of magnetic field orientation were considered: fields pointing toward and away from the duct’s center alternately, and all fields pointing toward the duct’s center. For each arrangement of magnets, various intensities of magnetic fields were considered to evaluate two effects: the influence of the magnetic field on the flow velocity, and the influence of the flow velocity on magnetic field induction. It was found that for the second arrangement of magnets and Hartmann numbers larger than 10, the flow velocity was reduced by as much as 35%, and the axial magnetic induction was as high as the field intensity applied by each magnet. Those effects were negligible for the first arrangement and low fields because of the distribution of field lines inside the duct for these situations.

Numerical Study of the Effect of Magnetic Fields on Melt-Crystal Interface-Deflection in Czochralski Crystal Growth

2003 ◽  
Author(s):  
Lijun Liu ◽  
Koichi Kakimoto
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Numerical Study ◽  
Silicon Crystal ◽  
Czochralski Growth ◽  
Thermal Flow ◽  
Interface Shape ◽  
Convective Thermal ◽  
And Control ◽  
Crystal Interface

In order to control the impurity distribution and remove defects in a crystal grown in Czochralski growth for high quality crystals of silicon, it is necessary to study and control the melt-crystal interface shape, which plays an important role in control of the crystal quality. The melt-crystal interface interacts with and is determined by the convective thermal flow of the melt in the crucible. Application of magnetic field in the Czochralski system is an effective tool to control the convective thermal flow in the crucible. Therefore, the shape of the melt-crystal interface can be modified accordingly. Numerical study is performed in this paper to understand the effect of magnetic field on the interface deflection in Czochralski system. Comparisons have been carried out by computations for four arrangements of the magnetic field: without magnetic field, a vertical magnetic field and two types of cusp-shaped magnetic field. The velocity, pressure, thermal and electromagnetic fields are solved with adaptation of the mesh to the iteratively modified interface shape. The multi-block technique is applied to discretize the melt field in the crucible and the solid field of silicon crystal. The unknown shape of the melt-crystal interface is achieved by an iterative procedure. The computation results show that the magnetic fields have obvious effects on both the pattern and strength of the convective flow and the interface shape. Applying magnetic field in the Czochralski system, therefore, is an effective tool to control the quality of bulk crystal in Czochralski growth process.

scholarly journals Magnetic clouds' structure in the magnetosheath as observed by Cluster and Geotail: four case studies

2014 ◽  
Vol 32 (10) ◽  
pp. 1247-1261 ◽  
Author(s):  
L. Turc ◽  
D. Fontaine ◽  
P. Savoini ◽  
E. K. J. Kilpua
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Magnetic Fields ◽  
Bow Shock ◽  
Field Direction ◽  
Magnetic Clouds ◽  
Magnetic Field Direction ◽  
Field Orientation ◽  
The Impact ◽  
The Magnetic Field

Abstract. Magnetic clouds (MCs) are large-scale magnetic flux ropes ejected from the Sun into the interplanetary space. They play a central role in solar–terrestrial relations as they can efficiently drive magnetic activity in the near-Earth environment. Their impact on the Earth's magnetosphere is often attributed to the presence of southward magnetic fields inside the MC, as observed in the upstream solar wind. However, when they arrive in the vicinity of the Earth, MCs first encounter the bow shock, which is expected to modify their properties, including their magnetic field strength and direction. If these changes are significant, they can in turn affect the interaction of the MC with the magnetosphere. In this paper, we use data from the Cluster and Geotail spacecraft inside the magnetosheath and from the Advanced Composition Explorer (ACE) upstream of the Earth's environment to investigate the impact of the bow shock's crossing on the magnetic structure of MCs. Through four example MCs, we show that the evolution of the MC's structure from the solar wind to the magnetosheath differs largely from one event to another. The smooth rotation of the MC can either be preserved inside the magnetosheath, be modified, i.e. the magnetic field still rotates slowly but at different angles, or even disappear. The alteration of the magnetic field orientation across the bow shock can vary with time during the MC's passage and with the location inside the magnetosheath. We examine the conditions encountered at the bow shock from direct observations, when Cluster or Geotail cross it, or indirectly by applying a magnetosheath model. We obtain a good agreement between the observed and modelled magnetic field direction and shock configuration, which varies from quasi-perpendicular to quasi-parallel in our study. We find that the variations in the angle between the magnetic fields in the solar wind and in the magnetosheath are anti-correlated with the variations in the shock obliquity. When the shock is in a quasi-parallel regime, the magnetic field direction varies significantly from the solar wind to the magnetosheath. In such cases, the magnetic field reaching the magnetopause cannot be approximated by the upstream magnetic field. Therefore, it is important to take into account the conditions at the bow shock when estimating the impact of an MC with the Earth's environment because these conditions are crucial in determining the magnetosheath magnetic field, which then interacts with the magnetosphere.

MHD flow and heat transfer of a magnetite–water nanofluid in porous medium under the effects of chemical reaction

2017 ◽  
Vol 14 (3) ◽  
pp. 193-199 ◽  
Author(s):  
Meysam Amini ◽  
Esmaeil GhasemiKafrudi ◽  
Mohammad Reza Habibi ◽  
Azin Ahmadi ◽  
Akram HosseinNia
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Chemical Reaction ◽  
Fluid Velocity ◽  
Mhd Flow ◽  
Industrial Applications ◽  
Temperature Fields ◽  
Stagnation Flow ◽  
Content Type ◽  
Flow And Heat Transfer

Purpose Due to the extensive industrial applications of stagnation flow problems, the present work aims to investigate the magnetohydrodynamics (MHD) flow and heat transfer of a magnetite nanofluid (here Fe3O4–water nanofluid) impinging a flat porous plate under the effects of a non-uniform magnetic field and chemical reaction with variable reaction rate. Design/methodology/approach Similarity transformations are applied to reduce the governing partial differential equations with boundary conditions into a system of ordinary differential equations over a semi-infinite domain. The modified fourth-order Runge–Kutta method with the shooting technique which is developed for unbounded domains is conducted to give approximate solutions of the problem, which are then verified by results of other researchers, showing very good agreements. Findings The effects of the volume fraction of nanoparticles, permeability, magnetic field, chemical reaction and Schmidt number on velocity, temperature and concentration fields are examined and graphically illustrated. It was found that fluid velocity and temperature fields are affected strongly by the types of nanoparticles. Moreover, magnetic field and radiation have strong effects on velocity and temperature fields, fluid velocity increases and thickness of the velocity boundary layer decreases as magnetic parameter M increases. The results also showed that the thickness of the concentration boundary layer decreases with an increase in the Schmidt number, as well as an increase in the chemical reaction coefficient. Research limitations/implications The thermophysical properties of the magnetite nanofluid (Fe3O4–water nanofluid) in different conditions should be checked. Practical implications Stagnation flow of viscous fluid is important due to its vast industrial applications, such as the flows over the tips of rockets, aircrafts, submarines and oil ships. Moreover, nanofluid, a liquid containing a dispersion of sub-micronic solid particles (nanoparticles) with typical length of the order of 1-50 nm, showed abnormal convective heat transfer enhancement, which is remarkable. Originality/value The major novelty of the present work corresponds to utilization of a magnetite nanofluid (Fe3O4–water nanofluid) in a stagnation flow influenced by chemical reaction and magnetic field. It should be noted that in addition to a variable chemical reaction, the permeability is non-uniform, while the imposed magnetic field also varies along the sheet. These, all, make the present work rather original.

scholarly journals On a limitation of Zeeman polarimetry and imperfect instrumentation in representing solar magnetic fields with weaker polarization signal

2021 ◽  
Vol 11 ◽  
pp. 14
Author(s):  
A.A. Pevtsov ◽  
Y. Liu ◽  
I. Virtanen ◽  
L. Bertello ◽  
K. Mursula ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Transverse Field ◽  
Vector Magnetic Field ◽  
Field Orientation ◽  
Fill Fraction ◽  
Structure Morphology ◽  
Full Disk

Full disk vector magnetic fields are used widely for developing better understanding of large-scale structure, morphology, and patterns of the solar magnetic field. The data are also important for modeling various solar phenomena. However, observations of vector magnetic fields have one important limitation that may affect the determination of the true magnetic field orientation. This limitation stems from our ability to interpret the differing character of the Zeeman polarization signals which arise from the photospheric line-of-sight vs. the transverse components of the solar vector magnetic field, and is likely exacerbated by unresolved structure (non-unity fill fraction) as well as the disambiguation of the 180° degeneracy in the transverse-field azimuth. Here we provide a description of this phenomenon, and discuss issues, which require additional investigation.

A numerical study of a bubble pair rising side by side in external magnetic fields

2021 ◽  
Vol 926 ◽  
Author(s):  
Jie Zhang ◽  
Ming-Jiu Ni
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Lorentz Force ◽  
Stokes Equations ◽  
Numerical Study ◽  
Three Dimensional ◽  
Transverse Field ◽  
Asymmetric Distribution ◽  
Streamwise Vortices ◽  
Horizontal Magnetic Field

The motion of a pair of bubbles rising side by side under the influence of external magnetic fields is numerically examined. Through solving the fully three-dimensional Navier–Stokes equations, the results reveal that the bubble interactions are rather sensitive to the field direction and strength. At first, we identify that, in a hydrodynamic flow, whether the two bubbles will bounce or coalesce depends on the developments of the counter-rotating streamwise vortices during the collision. In particular, for an originally bouncing bubble pair, a streamwise magnetic field tends to promote their coalescence by weakening the strengths of the standing streamwise vortices, and such a weakening effect is caused by the asymmetric distribution of the Lorentz force in the presence of another bubble such that a torque is induced to offset the original streamwise vortices. Under a horizontal magnetic field, on the other hand, the influences are highly dependent on the angle between the bubble centroid line and the field: a transverse field or a moderate spanwise field always leads the bubble pair to coalescence while a strong spanwise field has the opposite effect. This anisotropic effect comes from the Lorentz force induced flow diffusion along the magnetic field, which not only produces two pairs of streamwise vortices at the bubble rear, but also homogenizes the pressure along the magnetic lines. As the competition between the two mechanisms varies with the magnetic direction and strength, the interaction between the bubble pair also changes. We show that the external magnetic fields control the bubble interaction through reconstructing the vortex structures, and hence the core mechanisms are identified.

Possible Use of Magnetic Fields in Determining Pore Geometry of Porous Media

1971 ◽  
Vol 11 (03) ◽  
pp. 223-228 ◽  
Author(s):  
C.I. Pierce ◽  
L.C. Headley ◽  
W.K. Sawyer
Keyword(s):  
Magnetic Field ◽  
Porous Media ◽  
Magnetic Fields ◽  
Transverse Magnetic Field ◽  
Field Intensity ◽  
Flow Rate ◽  
Transverse Magnetic ◽  
Conducting Fluid ◽  
Petroleum Reservoir ◽  
The Magnetic Field

Abstract Simplified models, consisting of single, circular channels and channels of different length and diameter in series and parallel combinations, are used in conjunction with the equations of Poiseuille and Hartmann to demonstrate the dependence of the rate of flow of mercury in the models on channel dimensions when the models are subjected to transverse magnetic fields. Experimental tests conducted on mercury-saturated, glass-bead packs and a natural rock sample show that a magnetic field applied transversely to the direction of flow retards flow rate. The magnitude of the magnetic effect increased with increasing bead size and field intensity. Results of this work suggest that magnetic fields have potential in the study of the internal geometry of flow channels in porous media. Introduction The purpose of this work is to determine qualitatively by theoretical and experimental considerations whether or not a magnetic method has potential in the study of the basic properties of rock. The nature of the solid surface and the geometry of the pore network in petroleum-bearing rock plays an important role in the flow behavior of fluids in a petroleum reservoir. Hence, any technique of study that would provide new and additional information on the rock matrix would contribute to a better understanding of petroleum reservoir performance. One such technique appearing to offer performance. One such technique appearing to offer promise is in the area of magnetohydrodynamics. promise is in the area of magnetohydrodynamics. While much research, both theoretical and experimental, has been devoted to the problems concerned with the flow of conducting fluids in transverse magnetic fields in single channels, very little information has been published regarding the behavior of conducting liquids in porous media under the influence of a transverse magnetic field. Perhaps this dearth of information can be attributed Perhaps this dearth of information can be attributed to two main causes:the pores and pore connections are generally so small that intense magnetic fields are required to produce Hartmann numbers of sufficient magnitude to exert appreciable influence on flow rate, andthe extreme complexity of the channel systems in porous media render them intractable to theoretical analysis unless numerous assumptions are made to simplify network geometry. When a conducting fluid moves in a channel in a transverse magnetic field, a force is exerted on the fluid which retards its flow. The magnitude of flow-rate retardation increases with increasing field intensity, channel dimensions and channel-wall conductivity. These magnetohydrodynamic phenomena and theory have been described and developed by various investigators. Since a petroleum reservoir rock is an interconnected network of pores and channels within a rock framework, one would anticipate that the geometry of the network would exert some influence on the magnitude of the effect of a transverse magnetic field on the rate of flow of a conducting fluid therein. The purpose of this work is to demonstrate through the use of simple models and experimental data that the magnetic field effect on flow rate has potential for use in determining size and size potential for use in determining size and size distribution of pores in porous materials. THEORY Electromagnetic induction in liquids is not completely defined, and the complexities involved in many cases appear to defy true analytical expression. However, by applying some simplifying assumptions, these cases may be made tractable to solution to provide qualitative indication of system behavior. The following analysis was conducted in conjunction with laboratory tests to determine if magnet ohydrodynamics has possible potential as a tool for studying the internal geometry of porous systems. When a conducting liquid moves in a channel in a transverse magnetic field, an emf is developed in the channel normal to both the channel axis and the magnetic field. This emf causes circulating currents to flow in the liquid as shown in Fig. 1. SPEJ P. 223

scholarly journals Rotation induced by uniform and non-uniform magnetic fields in a conducting fluid carrying an electric current

RSC Advances ◽  
2016 ◽  
Vol 6 (113) ◽  
pp. 112641-112645 ◽  
Author(s):  
R. Shirsavar ◽  
M. Nasiri ◽  
A. Amjadi ◽  
A. Nejati ◽  
S. O. Sobhani ◽  
...  
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Magnetic Fields ◽  
Electric Current ◽  
Conducting Fluid

External magnetic field induces controllable rotation in a conducting fluid carrying an electric current.

Monte Carlo investigation of electron fluence perturbation in MRI-guided radiotherapy beams using six commercial radiation detectors

2022 ◽  
Author(s):  
Yunuen Cervantes ◽  
Simon Duane ◽  
Hugo Bouchard
Keyword(s):  
Magnetic Field ◽  
Monte Carlo ◽  
Solid State ◽  
Magnetic Fields ◽  
Radiation Detectors ◽  
Detector Response ◽  
Field Orientation ◽  
Solid State Detector ◽  
Parallel Orientation ◽  
The Magnetic Field

Abstract With the integration of MRI-linacs to the clinical workflow, the understanding and characterization of detector response in reference dosimetry in magnetic fields are required. The magnetic field perturbs the electron fluence (Fe), and the degree of perturbation depends on the irradiation conditions and the detector type. This work evaluates the magnetic field impact on the electron fluence spectra in several detectors to provide a deeper understanding of detector response in these conditions. Monte Carlo calculations of Fe are performed in six detectors (solid-state: PTW60012 and PTW60019, ionization chambers: PTW30013, PTW31010, PTW31021, and PTW31022) placed in water and irradiated by an Elekta Unity 7 MV FFF photon beam with small and reference fields, at 0 T and 1.5 T. Three chamber-axis orientations are investigated: parallel or perpendicular (two possibilities: FL towards the stem or the tip) to the magnetic field and perpendicular to the beam. One orientation for the solid-state detector is studied: parallel to the beam and perpendicular to the magnetic field. Additionally, Fe spectra are calculated in modified detector geometries to identify the underlying physical mechanisms behind the fluence perturbations. The total Fe is reduced up to 1.24% in the farmer chamber, at 1.5 T, in the parallel orientation. The interplay between the gyration radius and the farmer chamber cavity length significantly affects Fe in the perpendicular orientation; the total fluence varies up to 5.12% in magnetic fields. For the small-cavity chambers, the maximal variation in total Fe is 0.19%, for the reference field, in the parallel orientation. . In contrast, significant small-field effects occur; the total Fe is reduced between 9.86% to 14.50% at 1.5T (with respect to 0T) depending on the orientation. The magnetic field strongly impacted the solid-state detectors in both field sizes, probably due to the high-density extracameral components. The maximal reductions of total Fe are 15.06±0.09% (silicon) and 16.00±0.07% (microDiamond). This work provides insights into detector response in magnetic fields by illustrating the interplay between several factors causing dosimetric perturbation effects: 1) chamber and magnetic field orientation, 2) cavity size and shape, 3) extracameral components, 4) air gaps and their asymmetry, 5) electron energy. Low-energy electron trajectories are more susceptible to change in magnetic fields, and generally, they are associated with detector response perturbation.

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