Analysis On the Inception of the Magnetohydrodynamic Flow Instability in the Annular Linear Induction Pump Channel

2021 ◽  
Author(s):  
Ruijie Zhao ◽  
Xiaohui Dou ◽  
Qiang Pan ◽  
ZHANG Desheng ◽  
Bart van Esch
Keyword(s):  
Magnetic Field ◽  
Pressure Gradient ◽  
Lorentz Force ◽  
Flow Rate ◽  
Flow Instability ◽  
Fluid Velocity ◽  
Magnetic Reynolds Number ◽  
Wave Number ◽  
Magnetic Flux Density ◽  
Linear Induction

Abstract Flow instability is the intricate phenomenon in the Annular Linear Induction Pump when the pump runs at off-design working condition. A 3D numerical model is built to simulate the flow in the pump channel. The pump heads at different flow rates are accurately predicted by comparing with experiment. The simulation results show the fluid velocity is circumferentially non-uniform in the pump channel even at the nominal flow rate. The flow in the middle sector continuously decelerates to nearly zero with the reducing flow rate. Reversed flow occurs in the azimuthal plane, followed by vortex flow. The reason for the heterogeneous velocity field is attributed to the mismatch between non-uniform Lorentz force and relatively even pressure gradient. It is seen that the flow in the region of small Lorentz force has to sacrifice its velocity to match with the pressure gradient. An analytic expression of the axial Lorentz force is then developed and it is clearly demonstrated the Lorentz force could be influenced by the profiles of velocity and radial magnetic flux density. The coupling between velocity and magnetic field is studied by analyzing the magnitudes of different terms in the dimensionless magnetic induction equation. It is found the dissipation term is determined not only by the magnetic Reynolds number but the square of wave number of the disturbance in each direction. The smaller disturbing wave number weakens the dissipating effect, resulting in the larger non-uniform magnetic field and axial Lorentz force.

Effects of External Transverse Alternating Magnetic Field on the Oscillating Amplitude of Atmospheric Pressure Plasma Arc

2010 ◽  
Vol 129-131 ◽  
pp. 692-696
Author(s):  
Jian Bing Meng ◽  
Xiao Juan Dong ◽  
Chang Ning Ma
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Flux Density ◽  
Flow Rate ◽  
Gas Flow ◽  
Atmospheric Pressure Plasma ◽  
Alternating Magnetic Field ◽  
Magnetic Flux Density ◽  
Plasma Arc ◽  
Arc Current

A mathematical model was developed to describe the oscillating amplitude of the plasma arc injected transverse to an external transverse alternating magnetic field. The characteristic of plasma arc under the external transverse alternating magnetic field imposed perpendicular to the plasma current was discussed. The effect of processing parameters, such as flow rate of working gas, arc current, magnetic flux density and the standoff from the nozzle to the workpiece, on the oscillation of plasma arc were also analyzed. The results show that it is feasible to adjust the shape of the plasma arc by the transverse alternating magnetic field, which expands the region of plasma arc thermal treatment upon the workpiece. Furthermore, the oscillating amplitude of plasma arc decreases with decrease of the magnetic flux density. Under the same magnetic flux density, more gas flow rate, more arc current, and less standoff cause the oscillating amplitude to decrease. The researches have provided a deeper understanding of adjusting of plasma arc characteristics.

scholarly journals Ablation in Externally Applied Electric and Magnetic Fields

Nanomaterials ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 182
Author(s):  
Jovan Maksimovic ◽  
Soon-Hock Ng ◽  
Tomas Katkus ◽  
Nguyen Hoai An Le ◽  
James W.M. Chon ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Laser Ablation ◽  
Lorentz Force ◽  
Negative Electrode ◽  
Magnetic Flux Density ◽  
Ripple Formation ◽  
Electric And Magnetic Fields ◽  
Potential Applications ◽  
Application Potential ◽  
X Ray Absorption

To harness light-matter interactions at the nano-/micro-scale, better tools for control must be developed. Here, it is shown that by applying an external electric and/or magnetic field, ablation of Si and glass under ultra-short (sub-1 ps) laser pulse irradiation can be controlled via the Lorentz force F = e E + e [ v × B ] , where v is velocity of charge e, E is the applied electrical bias and B is the magnetic flux density. The external electric E-field was applied during laser ablation using suspended micro-electrodes above a glass substrate with an air gap for the incident laser beam. The counter-facing Al-electrodes on Si surface were used to study debris formation patterns on Si. Debris was deposited preferentially towards the negative electrode in the case of glass and Si ablation. Also, an external magnetic field was applied during laser ablation of Si in different geometries and is shown to affect ripple formation. Chemical analysis of ablated areas with and without a magnetic field showed strong chemical differences, revealed by synchrotron near-edge X-ray absorption fine structure (NEXAFS) measurements. Harnessing the vectorial nature of the Lorentz force widens application potential of surface modifications and debris formation in external E-/B-fields, with potential applications in mass and charge spectroscopes.

PDMS Membrane Microactuator for Focal Tunable Microlens

2006 ◽  
Author(s):  
Seok Woo Lee ◽  
Seung S. Lee
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Flux Density ◽  
Lorentz Force ◽  
Spin Coating ◽  
Large Displacement ◽  
Pdms Membrane ◽  
Magnetic Flux Density ◽  
Optical Performance ◽  
Electrical Components

In this paper, PDMS membrane for a large displacement is fabricated by new fabrication process which can be integrated with electrical components on substrates fabricated by conventional microfabrication processes and the performance of the membrane using electromagnetism was evaluated. Rectangular PDMS membranes are designed as 2mm and 3mm in width, respectively and are actuated by Lorentz force induced by current paths spread on the membrane. The PDMS membrane is fabricated by reducing a viscosity of uncured PDMS with dilution and spin coating on the substrate on which electric components generating Lorentz force. Finally, PDMS membrane including electric components is opened by a bulk micromachining. The device is tested in magnetic field induced by Nd-Fe-B magnet whose magnetic flux density is 90G. When applied currents are 20, 25, and 30mA, the maximum deflections of membranes are 1.21, 3.07, and 20.2μm for 1.5mm width membrane and 3.34, 31.0, and 50.9μm for width 3mm membrane, respectively. The large displacement PDMS membrane actuator has potentially various applications such as fluidics, optics, acoustics, and electronics. Currently, we are planning to measure the optical performance of the actuator as a focal tunable liquid lens.

Addressing the siphoning effect in new shunt designs by decoupling the activation pressure and the pressure gradient across the valve

2013 ◽  
Vol 11 (2) ◽  
pp. 181-187 ◽  
Author(s):  
Tobias A. Mattei ◽  
Martin Morris ◽  
Kathleen Nowak ◽  
Daniel Smith ◽  
Jeremy Yee ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Flow Rate ◽  
Fluid Velocity ◽  
Component System ◽  
The Past ◽  
Benchmark Tests ◽  
Final Design ◽  
Actual Flow Rate ◽  
Actual Flow ◽  
Labview Program

Object Although several improvements have been observed in the past few years in shunt technology, currently available systems still present several associated problems. Among these, overdrainage along with its complications remains one of the great challenges for new shunt designs. To address the so-called siphoning effect, the authors provide a practical example of how it is possible to decouple the activation pressure and the pressure gradient across the valve through a 3–key component system. In this new shunt design, the flow is expected to depend only on the intracranial pressure and not on the pressure gradient across the valve, thus avoiding the so-called siphoning effect. Methods The authors used computer models to theoretically evaluate the mechanical variables involved in the operation of the newly designed valve, such as the fluid's Reynolds number, proximal pressure, distal pressure, pressure gradient, actual flow rate, and expected flow rate. After fabrication of the first superscaled model, the authors performed benchmark tests to analyze the performance of the new shunt prototype, and the obtained data were compared with the results predicted by the previous mathematical models. Results The final design of the new paddle wheel valve with the 3–key component antisiphoning system was tested in the hydrodynamics laboratory to prove that the siphoning effect did not occur. According to the calculations obtained using the LabVIEW program during the experiments, each time the distal pressure decreased without an increase in the proximal pressure (despite the range of the pressure gradient), the pin blocked the spinning of the paddle wheels, and the calculated fluid velocity through the system tended to zero. Such a situation was significantly different from the expected flow rate for such a pressure gradient in a siphoning situation without the new antisiphon system. Conclusions The design of this new prototype with a 3–key component antisiphoning system demonstrated that it is possible to decouple the activation pressure and the pressure gradient across the valve, avoiding the siphoning effect. Although further developments are necessary to provide a model compatible to clinical use, the authors believe that this new prototype illustrates the possibility of successfully addressing the siphoning effect by using a simple 3–key component system that is able to decouple the activation pressure and the pressure gradient across the valve by using a separate pressure chamber. It is expected that such proof of concept may significantly contribute to future shunt designs attempting to address the problem of overdrainage due to the siphoning effect.

Pulsatile flow in rigid tubes

1965 ◽  
Vol 20 (5) ◽  
pp. 1078-1082 ◽  
Author(s):  
Robert G. Linford ◽  
Norman W. Ryan
Keyword(s):  
Fluid Flow ◽  
Pressure Gradient ◽  
Flow Rate ◽  
Pulsatile Flow ◽  
Fluid Velocity ◽  
Fluid Flow Rate ◽  
Tube Radius ◽  
Low Frequencies ◽  
Time Relationship ◽  
Fluid Properties

The purpose of this study was to examine critically the theoretical equations derived for pulsatile laminar flow in rigid straight tubes. These equations, presented in their most useful form by J. R. Womersley in 1955, give the fluid flow rate as a function of the pressure gradient-time relationship, pulse frequency, fluid properties, and tube radius, and they give the fluid velocity as a function of the above quantities and the radial position in the tube. A pulsatile flow apparatus was constructed which would allow measurement of all the variables mentioned above, and a computer program based on Womersley's equations was used to calculate the fluid flow rate and velocity profile from the pressure gradient-time relationship, fluid properties, and tube radius. Thus a comparison between measured and calculated values of flow and velocity could be made. Calculations and data agree within the estimated experimental error, thus providing evidence of the applicability of the theoretical equations to actual flow with large pulse amplitudes. The analog computer “pressure gradient technique” of D. Fry and associates was compared with the exact solution for straight rigid tubes and found to deviate less than 20% in amplitude and phase except at very low frequencies. hydrodynamics, pulsatile flow; blood flow, arterial; hemodynamics, pulse characteristics Submitted on April 6, 1964

Spherical shell rotating convection in the presence of a toroidal magnetic field

1995 ◽  
Vol 448 (1933) ◽  
pp. 245-268 ◽  
Keyword(s):  
Magnetic Field ◽  
Prandtl Number ◽  
Spherical Shell ◽  
Lorentz Force ◽  
Thermal Convection ◽  
Toroidal Magnetic Field ◽  
Wave Number ◽  
Convective Motions ◽  
Magnetic Convection ◽  
Convection Rolls

Convective instabilities of a self-gravitating, rapidly rotating fluid spherical shell are investigated in the presence of an imposed azimuthal axisymmetric magnetic field in the form of the toroidal decay mode that satisfies electrically insulating boundary conditions and has dipole symmetry. Concentration is on two major questions: how purely thermal convection of the different forms (Zhang 1992, 1994) is affected by the Lorentz force, the strength of which is measured by the Elsasser number ∧, and in what manner purely magnetic instabilities in a spherical shell (Zhang & Fearn 1993, 1994) are associated with magnetic convection. It is found that the two-dimensionality of purely thermal convection (Busse 1970) survives under the influence of a strong Lorentz force. Convective motions always attempt to satisfy the Proudman–Taylor constraint and remain predominantly two-dimensional in the whole range of ∧, 0 ≤ ∧ ≤ ∧ c , where ∧ c ═ O (10) is the critical Elsasser number for purely magnetic instabilities. Though the optimum azimuthal wave number m of convection rolls decreases drastically, from m ~ O ( T 1/6 ) at ∧ ═ 0 to m ═ O (5) at ∧ ═ O (1). We show that there exist no optimum values of ∧ that can give rise to an overall minimum of the (modified) Rayleigh number R *; the optimum value of R * is a monotonically, smoothly decreasing function of ∧, from R * ═ O ( T 1/6 ) at ∧ < O ( T -1/6 ) to R * ═ O (–10) at ∧ ═ 20. We also show that the influence of the magnetic field on thermal convection is crucially dependent on the size of the Prandtl number. At sufficiently small Prandtl number, the Poincaré convection mode (Zhang 1994) is preferred in the region 0 ≤ ∧ < ∧ c , and is only slightly affected by the presence of the toroidal magnetic field. Analytical solutions of the magnetic convection problem are then obtained based on a perturbation analysis, showing a good agreement with the numerical solution.

Dimensionality of Anisotropic Homogeneous Turbulence With Distortions: Compared Effects Between the Coriolis Force and the Lorentz Force

2014 ◽  
Author(s):  
Fabien Godeferd ◽  
Claude Cambon ◽  
Alexandre Delache
Keyword(s):  
Magnetic Field ◽  
Lorentz Force ◽  
Coriolis Force ◽  
Magnetic Reynolds Number ◽  
Homogeneous Turbulence ◽  
Spectral Space ◽  
Structure And Dynamics ◽  
Induction Equation ◽  
The Magnetic Field

We consider initially isotropic homogeneous turbulence which is submitted to an external force, in statistically axisymmetric configurations. First, we study hydrodynamical turbulence in a rotating frame, in which case the Coriolis force modifies the structure and dynamics of the flow, thus creating elongated structures along the axis of rotation, corresponding to an accumulation of energy in the neighbourhood of the equatorial spectral plane. Secondly, a very similar configuration is that of magnetohydrodynamics (MHD) of a conducting fluid within an externally applied space uniform magnetic field, in which case the Lorentz force also concentrates energy to the same spectral equatorial manifold, but creates axially extending current sheets, along the magnetic field. We more specifically consider the quasi-static limit at small magnetic Reynolds number, in which the induction equation is analytically solved. We study the anisotropy of each turbulent flow using progressively refined statistics applied to results of direct numerical simulations, and we show that an accurate characterization of the flow structure requires advanced two-point statistics, which are available easily only in spectral space.

Galvanomagnetic and thermomagnetic phenomena

2004 ◽  
Author(s):  
Robert E. Newnham
Keyword(s):  
Magnetic Field ◽  
Heat Flow ◽  
Magnetic Fields ◽  
Hall Effect ◽  
Electric Current ◽  
Lorentz Force ◽  
Electrical Resistance ◽  
Magnetic Flux Density ◽  
Wide Range ◽  
The Magnetic Field

The Lorentz force that a magnetic field exerts on a moving charge carrier is perpendicular to the direction of motion and to the magnetic field. Since both electric and thermal currents are carried by mobile electrons and ions, a wide range of galvanomagnetic and thermomagnetic effects result. The effects that occur in an isotropic polycrystalline metal are illustrated in Fig. 20.1. As to be expected, many more cross-coupled effects occur in less symmetric solids. The galvanomagnetic experiments involve electric field, electric current, and magnetic field as variables. The Hall Effect, transverse magnetoresistance, and longitudinal magnetoresistance all describe the effects of magnetic fields on electrical resistance. Analogous experiments on thermal conductivity are referred to as thermomagnetic effects. In this case the variables are heat flow, temperature gradient, and magnetic field. The Righi–Leduc Effect is the thermal Hall Effect in which magnetic fields deflect heat flow rather than electric current. The transverse thermal magnetoresistance (the Maggi–Righi–Leduc Effect) and the longitudinal thermal magnetoresistance are analogous to the two galvanomagnetic magnetoresistance effects. Additional interaction phenomena related to the thermoelectric and piezoresistance effects will be discussed in the next two chapters. In tensor form Ohm’s Law is . . .Ei = ρijJj , . . . where Ei is electrical field, Jj electric current density, and ρij the electrical resistivity in Ωm. In describing the effect of magnetic field on electrical resistance, we expand the resistivity in a power series in magnetic flux density B. B is used rather than the magnetic field H because the Lorentz force acting on the charge carriers depends on B not H.

Instability of a surface of discontinuity of velocity in a parallel uniform magnetic field

1963 ◽  
Vol 16 (2) ◽  
pp. 187-196 ◽  
Author(s):  
D. D. Mallick
Keyword(s):  
Magnetic Field ◽  
Secular Equation ◽  
Magnetic Reynolds Number ◽  
Wave Number ◽  
Inviscid Fluid ◽  
Dimensionless Wave Number ◽  
Electrically Conducting ◽  
Two Parameters ◽  
Two Sides ◽  
The Magnetic Field

The problem described by the title is investigated when the magnetic field is uniform and parallel to the velocity on the two sides of a surface of discontinuity of velocity in an electrically conducting inviscid fluid. The secular equation depends on two parameters β and N, where β is the ratio of magnetic Reynolds number to dimensionless wave number and N is the ratio of the magnetic to the kinetic energy of the fluid. It is found that the flow is unstable for all values of β and N.

scholarly journals Gravitation modulation impact on MHD free convection flow of micropolar fluid

2020 ◽  
Vol 17 (2) ◽  
pp. 199-218
Author(s):  
Sanjib Sengupta ◽  
Reshmi Deb
Keyword(s):  
Magnetic Field ◽  
Skin Friction ◽  
Micropolar Fluid ◽  
Perturbation Technique ◽  
Rotational Velocity ◽  
Fluid Velocity ◽  
Magnetic Reynolds Number ◽  
Convection Flow ◽  
Induced Magnetic Field ◽  
Modulation Parameter

In this paper, a theoretical study is carried out on unsteady three dimensional, laminar, free convective flow of micropolar fluid with Hall effect, Joule heating and heat sink under gravitation modulation. A uniform transverse magnetic field is applied normal to the plate along the fluid region. The magnetic Reynolds number is considered to be small due to incomparability of applied and induced magnetic field, as such the influence of induced magnetic field can be neglected. The multi parameter perturbation technique is used to solve the governed dimensionless equations. The fluid velocity profile, temperature profile and the concentration profiles are discussed with the aid of graphs and tables. The coefficient of skin friction and couple stresses are numerically computed in addition to Nusselt number and Sherwood number. The result reveals that the linear velocity increases due to escalation in gravitation modulation parameter values but for intensification in values of gravitation modulation parameter, a reverse effect is observed for the rotational velocity. A comparative analysis shows that the skin friction coefficient is less in micropolar fluid than the corresponding Newtonian fluids.

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