Influence Of Transverse Magnetic Field Research Articles

Study on the influence of transverse magnetic field on the arc and reignition characteristics of HVDC relays

Abstract It is of great significance to clarify the influence of transverse magnetic field (TMF) on arc control in high-voltage direct current (HVDC) relays. In this paper, the influence of TMF in a wide range of 0-140 mT on the arc characteristics of HVDC relays is studied, the experimental observations of arc reignition are carried out, and the effect of arc reignition on contact erosion, the criterion of arc reignition and the mechanism of TMF enhancement on arc reignition are further analyzed. The results show that the TMF enhancement is beneficial for shortening the arc voltage stagnation duration and accelerating the speed of arc elongation, arc dispersion, and dispersed arc motion, thereby improving the arc extinguishing performance. However, higher TMF leads to more severe and earlier arc reignition, as also shown in the experimental observations. The arc reignition further causes a sudden drop in arc voltage, prolonged arc duration, and uneven contact erosion. To evaluate the occurrence of arc reignition caused by TMF enhancement, a simplified breakdown criterion is proposed through the defined characteristic variable C(t). Based on this, the mechanism by which the TMF enhancement more easily causes arc reignition is explained, that is the higher TMF leads to an earlier and faster increase in C(t) and slightly reduces the breakdown threshold. Further, measures to suppress the arc reignition are proposed.

Analysis of Newtonian heating in fractional hybrid nanofluid with the influence of transverse magnetic field

This article deals with the effects of Newtonian heating in second grade Hybrid nanofluid. For memory effects the problem is modeled with the help of generalized Fourier law along with generalized boundary conditions. A hybrid nanofluid model is used with nano particles of the form Magnetic Iron Oxide (Fe3O4) and Silver (Ag) nano particles with engine oil (EO) as based fluid. A uniform magnetic field perpendicular to the plate is also taken. General solutions of the problems are obtained with the help of Laplace Transform Technique. Influence of related physical parameters on the fluid flow are discussed with the help of graphical display of the solutions. It is also observed that generalized boundary conditions provides more effective and new solutions for the oscillating flow of hybrid nanofluid which produces a better way of understanding of hybrid nanofluid.

MAGNATIC FIELD INFLUENCE ON RADIATIVE CASSON FLUID FLOW OVER AN EXPONETIAL STRETCHING SURFACE

The flow and heat transfer properties of a Casson liquid past an exponential stretching sheet under the influence of transverse magnetic-field are investigated in this work. The numerical simulations were solved by using Keller Box method. The impact of various flow quantities such as the Casson fluid parameter, magnetic-field parameter, Prandtl number, and suction parameters on velocity and temperature fields are analysed through graphs. Moreover, the current method is compared with the existing methods, and the results are found to be similar.

4D synchrotron X-ray tomographic study of the influence of transverse magnetic field on iron intermetallic compounds precipitation behavior during solidification of Al–Si–Fe alloy

Hard and brittle iron intermetallic compounds (IMCs) will be formed during solidification due to the existence of iron element in Aluminum alloy. These IMCs will cause cracks or fractures in the material, which can deteriorate the mechanical properties. Synchrotron X-ray tomography were used to study the real time formation and growth dynamics of IMCs in Al-10 wt.%Si-1 wt.%Fe alloy during solidification under transverse magnetic field (TMF). The results indicated that the precipitation behavior of IMCs was significantly affected by 0.07 T TMF. The IMCs were observed to form only on the periphery of the sample under TMF, comparing with random distribution without TMF. In addition, the growth dynamics of IMCs were also affected by TMF. When solidified without TMF, an explosive nucleation and growth of IMCs was presented at the intermediate solidification stage, where a large number of fine IMCs precipitated at the entire regions of the sample. In contrast, the IMCs located at the periphery areas were observed to grow steadily under TMF. The growth rate and formation mechanism of IMCs were also quantified and revealed, showing difference with and without TMF. The tip growth rate was relatively stable when solidified with TMF, while an accelerating growth stage was presented when TMF is absent. The discrepancy in precipitation behavior of IMCs could be best explained as the convection of the melt resulted from the applied TMF. The TMF was demonstrated to generate a directional flow with a velocity of ∼3.3 mm/s. The flow was supposed to drive the Fe solute from the center to the edge of the sample, providing enough Fe solute for IMCs to nucleate and grow on the surface of the sample. In addition, due to the influence of TMF induced flow on the distribution of Fe solute and temperature, the morphology and tip growth rate of IMCs were also affected. The result presented in current study provides the possibility to regulate the precipitation behavior of Fe-rich IMCs in Al alloys. The imposed TMF also shows the potential application in Fe removal by driving the Fe solute to the surface of sample in Al alloys.

The Influence of TMF and AMF Components on Arc Movement Characteristics in Spiral-Slot Contacts

Spiral-slot contacts produce an axial magnetic field (AMF) and the transverse magnetic field (TMF). The magnetic field between TMF contacts will affect the breaking performance of vacuum interrupters. In order to study the effect of TMF and AMF on arcing process and movement characteristics, five contacts with different TMF and AMF, but the same ratio of TMF to AMF, were designed and experimentally investigated in a demountable vacuum chamber. The arc movement phenomenon under different TMF and AMF was obtained. It was found that increasing TMF and AMF could reduce the arc jets to the outer electrode, and arc stagnation was more likely to occur in the later stage of the movement. The influence of TMF and AMF on arc movement characteristics and the utilization of contact surfaces was investigated. With the increase in TMF and AMF, the number of arc rotations increased, and the range of arc movement and the utilization of contact surface increased first and then decreased. Simulations were performed to analyze that the influence mechanism of TMF and AMF on arc movement characteristics was investigated. With the increase in TMF and AMF, the tangential force of the concentrated arc was increased, and the radial force was reduced.

Natural Convective Effects on MHD Boundary Layer Nanofluid Flow over an Exponentially Accelerating Vertical Plate

The problem of unsteady natural convective nanofluid flow along with an exponentially accelerating vertical plate under the influence of transverse magnetic field is discussed in two important cases when the magnetic lines of force are fixed relative to the fluid or the moving plate. The governing equations are transformed into dimensionless form and tackled with the usual time-frequency Laplace transform technique. The impacts of various parameters on the heat transfer characteristics and nanofluid flow transport with thermal radiation, heat generation/absorption, and nanoparticle volume concentration have been studied through graphs.

Entropy Analysis of the Nonlinear Convective Flow of a Jeffrey Fluid over an Inclined Sheet with Variable Electrical Conductivity and Thermal Conductivity

A steady two-dimensional nonlinear convective flow of a viscous, incompressible, electrically conducting, and non-Newtonian Jeffrey fluid over an inclined stretching sheet with convective boundary conditions and entropy generation is studied under the influence of transverse magnetic field, electrical conductivity and thermal conductivity. The thermal conductivity and electrical conductivity are temperature dependent functions. The governing continuity, momentum and energy equations are transformed to ordinary differential equations (ODEs) using appropriate similarity variables. The resulting coupled ODEs and the corresponding boundary conditions, are solved numerically using Runge-Kutta fourth order method and shooting technique. The velocity, entropy generation rate, temperature and Bejan distributions are presented graphically and discussed. The numerical values of the skin-friction and Nusselt number are obtained and also discussed for various thermophysical parameters through a Table. Furthermore, a comparison with earlier work done with limiting case was carried out and found to be in excellent agreement.

Influence of transverse magnetic field on the properties of laser ablation produced nickel oxide nanoparticles

Influence of transverse magnetic field on the nickel produced plasma plume and structural and optical properties of nickel oxide nanoparticles produced by pulsed laser ablation (PLA) method have been investigated experimentally. Ablation container was placed between the poles of permanent magnets. Strength of external magnetic field was controlled by the distance between magnets. The direction of the magnetic field was perpendicular to the direction of laser pulse propagation. 5 samples were synthesized in the presence of magnetic fields with different strengths in distilled water. Ablation was carried out by 1064 nm wavelength beam of pulsed Nd:YAG laser of 7 ns pulse width. Effects of external magnetic field on the properties of nickel oxide nanoparticles were characterized by X-ray diffraction patterns, field emission scanning electron microscope images, transmission electron microscope microimages, UV–Vis-NIR absorption spectra, dynamic light scattering patterns, FTIR and photoluminescence spectra. Furthermore, magnetic properties of synthesized nanoparticles were studied using their hysteresis curve which were recorded by vibrating sample magnetometer. Results show that with increasing the strength of external magnetic field, the intensity of XRD peaks of synthesized nanoparticles was increased while their size was decreased. Applying the external magnetic field caused the cyclotron motion of the charged particles in the plasma plume on the surface of target which increased their energy, and decreased their agglomeration.

Influence of transverse magnetic field on dynamics of Sn plasma produced by CO2 laser

In the present work we report the effect of magnetic field on the emission intensity of the neutral and singly ionized transition line of the Tin plasma in vacuum produced by the CO2 laser. We have investigated time of flight measurement and the expansion velocity of the excited neutral and ions of the tin plasma in the absence and in the presence of the magnetic field of 0.64T in vacuum at a distance of 1 mm and 3 mm from the sample surface. The estimated values of the expansion velocities of Sn+ at the distance of 1 mm and 3 mm from the surface is 0.23 × 106 cm/s and 0.32 × 106 cm/s respectively in the field-free case, whereas in the case of the magnetic field of 0.64 T these values were found to be 0.19 × 106 cm/s and 0.27 × 106 cm/s respectively. It is observed in our estimated experimental result of the TOF the expansion velocity in the presence of field is considerably lower as compare to field free region.We have also estimated the electron number density and electron temperature of the tin plasma using Stark broadened profiles of Sn+ transition line and Boltzmann plot method respectively. In the temporal variations, the electron temperature and the electron number density with and without magnetic field of 0.64T is estimated as (1.48–0.63) eV and (1.04–0.58) eV and (2.06 × 1016–6.7 × 1015) cm−3 and (1.5 × 1016–4.42 × 1015) cm−3 respectively at the delay of (200–1100) ns.

2-D Particle Simulation on the Influence of Transverse Magnetic Field on the Plasma Decay in Postarc Stage of Vacuum Circuit Breakers

In this article, the plasma decay in the postarc stage of vacuum circuit breakers and the influence of the transverse magnetic field (TMF) on this process are investigated with a 2-D particle-in-cell model. In this model, distributions of electric field and plasma are solved by Poisson's equation and Newton's law, respectively, in 2-D Cartesian coordinate system. The distributions of charged particles and the velocity of the sheath development in the simulation without magnetic field in this article agree well with those in the simulation solved in cylindrical coordinate system in the published work. The TMF in the postarc phase leads to asymmetric distributions of charged particles, which slows down the plasma decay process in the postarc phase. In addition, the TMF results density fluctuations in the plasma and makes the plasma discontinuous and cluster, which can disturb the ion sheath near the postarc anode and result the local electric fields in the plasma. Electrons can be accelerated and gain high velocities in these local fields. These effects of TMF will slow down the dielectric recovery in the postarc stage of vacuum circuit breakers and may increase the risk of rebreakdown in the postarc stage when the vacuum circuit breaker interrupts large fault currents.

Effect of TMF and AMF Components on Expansion Process in Different Ignition Modes of Vacuum Arc Between Spiral-Type TMF Contacts

The drawn vacuum arc begins with a bridge column formed from the explosion of a liquid metal bridge after separating the contacts. The expansion process of the initial arc has an effect on arc motion or diffusion. In order to deeply study the influence of transverse magnetic field (TMF) and axial magnetic field (AMF) on the drawn arc characteristics in the initial expansion stage, in this article, arc ignition mode and appearance under two groups of contacts with different AMF and TMF components were experimentally studied. It was found that simultaneously reducing TMF and AMF components would end the expansion stage earlier, and the fluctuation of the arc column pressure during the expansion was larger. When TMF and AMF components were further reduced, the arc needs to take a longer time to extend across the slot gap due to insufficient Ampere force. When TMF was basically unchanged and AMF was reduced, the arc burned more intense, the diameter of the arc column was smaller, and the arc would merge earlier in multipoint ignition mode. The characteristics of arc voltage, pressure, and duration of expansion stage were analyzed, founding that the arc with a moderate TMF and AMF components had a smaller rising slope of arc voltage, a faster reducing speed of arc pressure, and a smaller range of the duration of expansion stage. In addition, the variation of magnetic field strength in different ignition modes and contact structures during the arc expansion stage was simulated to explain the mechanism of arc behavior.

Modelling of Thin CNTs Nanoliquid Film Flow Over a Bi-directional Stretching Surface

Unsteady flow of water and ethylene-glycol based carbon nanotubes (CNTs) nanoliquid film is examined on a bi-directional stretching surface under influence of transverse magnetic field and thermal radiation. Single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) are considered within the base liquid for investigation. Guiding full Navier–Stokes and energy equations were simplified using the thin film approximations and solved using the method of the asymptotic expansion. The result shows that nanoliquid thinning rate diminishes with rising values of CNTs volume fraction, Hartmann number and Biot number. The result also indicates that the thinning rate is more for MWCNTs with reference to the SWCNTs. It is seen that film thinning rate enhances for water-MWCNTs nanoliquid but reverse scenario is found for ethylene-glycol MWCNTs nanoliquid. The effect of various physical parameters on temperature profile has been discussed.

Thermal convection studies in liquid metal flow inside a horizontal duct under the influence of transverse magnetic field

An experiment is conducted to study the effect of magnetic field on heat transfer in a magnetohydrodynamic flow of molten lead–lithium, in a stainless steel thin-wall duct, with a uniform surface heat flux at its bottom wall. A novel technique of measuring fluid temperature inside the duct is applied to map the temperature profile in a flow cross section, at both ends of the heated section, using a 4 × 4 array of 16 equidistantly placed thermocouples. Surface temperature, as well as electric potential, is measured at seven different locations along the heated section. Based on the temperature profiles obtained at the outlet of the heated section, various flow regimes have been identified over the experimentally investigated flow parameters. Distinctively, three flow regimes have been recognized depending on the dominance of buoyancy force, electromagnetic force, and inertial force. In order to better understand the experimental data, numerical simulations are performed using COMSOL. In the buoyancy force dominated flow regime, a quasi-two-dimensional turbulence flow is predominant, determining the overall heat transfer mechanism. In the electromagnetic force dominated regime, the perturbation due to buoyancy force is suppressed by the magnetic field. Finally, in the inertial force dominated regime, the electromagnetic force and buoyancy force do not play a significant role in determining the heat transfer mechanism. The transition between observed flow regimes has been identified in terms of Grashof, Reynolds, and Hartmann numbers, and the Nusselt number has been calculated for quantitative comparison of heat transfer in these flow regimes.

Influence of transverse magnetic field on plume dynamics and optical emission of nanosecond laser produced tungsten plasma in vacuum

The particles transport and optical emission of tungsten plasma in magnetic field are two of the prime aspects for the diagnosis of plasma wall interaction process in nuclear devices such as EAST tokamak. In this work, the effect of the magnetic field (1.1 T) on the laser produced tungsten plasma plume dynamics and its optical emission produced by laser in vacuum (~4 × 10−3 Pa) were investigated. Fast imaging results presented that magnetic field confined the plasma and affected the plasma geometry. Temporal evolution of the optical emission showed that the continuum radiation at early stage (>100 ns) was not affected by the magnetic field while the tungsten ionic and atomic lines were significantly enhanced at later delay times (>200 ns, >400 ns, respectively). The negligible influence on the early continuum radiation was due to the laser-plasma pressure was far higher than the magnetic pressure as the plasma was hot and dense at early times. The higher electron temperature (Te) and electron density (ne) at later delay times were also observed in the magnetic field. The time-dependent plume dynamics in the magnetic field was correlated to the temporal variation of the plasma parameter β (the ratio of plasma pressure to magnetic pressure) and the electron collision frequency (ve), and electron cyclotron frequency (ωce) were also discussed. Moreover, the information including plasma evolution, plasma velocity, electron temperature electron density, ionic and atomic velocities with and without magnetic field were obtained.

Effect of Magnetic Field on the Unsteady Boundary Layer Flows Induced by an Impulsive Motion of a Plane Surface

Abstract The unsteady laminar boundary layer flow of an electrically conducting viscous fluid near an impulsively started flat plate of infinite extent is considered, with a view to examine the influence of transverse magnetic field fixed to the fluid. A new type of similarity transformation is proposed, which renews the governing partial differential equation into a linear ordinary differential equation with four physical parameters, viz. unsteadiness parameter β, magnetic parameter M, and the velocity indices (p, q). The analytic solution of this equation has been found in terms of a first kind confluent hypergeometric function for some specific parameter regimes. This solution shows the structure of a new type of boundary layer flow that includes the solution of the first Stokes problem as a special case. For non-zero values of (p, q), there is a definite range of p (either −∞ < p < 2q or 2q < p < ∞ according to β < or > 0) for which this flow problem will be valid. This analysis reveals an important relation ( p β + M 2 = q β ) $(p\beta+{M^{2}}=q\beta)$ at which separation appears inside the layer and has been detected as the separation threshold of the problem. Indeed, this relation gives us the critical value of one when the others are known. Flow separation inside the layer is delayed with an increasing value of q but cannot be completely removed whatever is the value of q (>0). The present analysis ensures that the reverse flow can be suppressed by the use of a proper amount of magnetic field M depending upon the values of p, q, and β. The obtained result provides insight into the stability of the boundary layer flows.

Influence of magnetic field on a curved circular plate and flat plate lubricated with non-Newtonian fluid

This paper presents a Analytical study of the effect of magnetic field on the performance of flat and curved circular plate with Non-Newtonian fluids. From the Stokes theory a Modified Reynolds equation is derived. The solution for pressure, load capacity and squeeze time is obtained to study the influence of transverse magnetic field and couple stress parameter on these characteristics. The non-dimensional pressure, load and squeeze film time is computed numerically and presented graphically. The results predicts that, the effect of Hartmann number M 0 and Non-Newtonian fluid l * is improved in pressure, load carrying capacity significantly whereas delay in squeezing time as compared to the non-magnetic(NMC) and Newtonian(NC) cases.

Heat transfer and buoyancy‐driven convective MHD flow of nanofluids impinging over a thin needle moving in a parallel stream influenced by Prandtl number

AbstractThe current study focuses on investigating the influence of transverse magnetic field, variable viscosity, buoyancy, variable Prandtl number, viscous dissipation, Joulian dissipation, and heat generation on the flow of nanofluids over thin needle moving in parallel stream. The theory of nanofluids that includes the Buongiorno model featured by slip mechanism, such as Brownian motion and thermophoresis, has been implemented. Further, convective boundary condition and zero mass flux condition are considered. The nondimensionally developed boundary layer equations have been solved by Runge–Kutta–Fehlberg method with shooting technique for different values of parameters. The most relevant outcomes of the present study are that the augmented magnetic field strength, viscosity parameter, buoyancy ratio parameter, and the size of the needle undermine the flow velocity, establishing thicker velocity boundary layer while Richardson number and Brownian motion show opposite trend. Another most important outcome is that increase in the size of the needle, viscous dissipation, convective heating, and heat generation upsurges the fluid temperature, leading to improvement in thermal boundary layer. The effects of different natural parameters on wall shear stress and heat and mass transfer rates have been discussed.

MHD natural convection boundary-layer flow over a semi-infinite heated plate with arbitrary inclination

The aim of this article is to study the natural convection boundary-layer flow over a semi-infinite heated plate with arbitrary inclination. Existing solutions of similar models can be recovered as the limiting cases of horizontal and vertical plates from our generalized problem. Moreover, porous effects and the influence of transverse magnetic field; fixed to the fluid or the plate are accounted. The dimensionless velocity, in conjunction with the corresponding skin friction, have been presented as the sum of mechanical, thermal and concentration components. Furthermore, the contribution of the system parameters to the fluid motion in question has been depicted graphically. The novelty of the present study is to analyze the effect of angle of inclination of the plate and the case when the magnetic field is fixed relative to the fluid or to the plate on the fluid motion.

Study of liquid metal surface wave damping in the presence of magnetic fields and electrical currents

Abstract Experiments and predictions of surface wave damping in liquid metal due to a surface aligned magnetic field and externally regulated j × B force are presented. Fast-flowing, liquid-metal plasma facing components (LM-PFCs) are a proposed alternative to solid PFCs that are unable to handle the high heat flux, thermal stresses, and radiation damage in a tokamak. The significant technical challenges associated with LM-PFCs compared to solid PFCs are justified by greater heat flux management, self-healing properties, and reduced particle recycling. However, undesirable engineering challenges such as evaporation and splashing of the liquid metal introduce excessive impurities into the plasma and degrade plasma performance. Evaporation may be avoided through high-speed flow that limits temperature rise of the liquid metal by reducing heat flux exposure time, but as flow speed increases the surface may become more turbulent and prone to splashing and uneven surfaces. Wave damping is one mechanism that reduces surface disturbance and thus the chances of liquid metal impurity introduction into the plasma. Experiments on the Liquid Metal eXperiment Upgrade (LMX-U) examined damping under the influence of transverse magnetic fields and vertically directed Lorentz force.

MHD Convection Fluid and Heat Transfer in an Inclined Micro-Porous-Channel

Abstract This study is devoted to investigate the influence of transverse magnetic field as well as suction/injection on MHD natural convection flow of conducting fluid in an inclined micro-porous-channel. The analytical solutions for velocity profile and temperature profile have been obtained considering the velocity slip and temperature jump conditions at the micro-porous-channel walls. The solution obtained for the velocity has been used to compute the skin friction, while the temperature has been used to compute the Nusselt number. The effect of various flow parameters entering into the problem are discussed with the aid of line graphs. Results reveal that the impact of inclination angle on fluid velocity is dependent on the value of the wall ambient temperature difference ratio, hence increase in inclination angle yields an enhancement in fluid velocity within the micro-porous-channel for some selected values of the wall ambient temperature difference ratio whereas it displays a dual character for other values. Also, injecting through the micro-porous channel thickens the thermal boundary layer, resulting to weakening the convective current and consequently decreasing the fluid velocity whereas suction weakens the thermal boundary layer yielding an increase in fluid velocity.