Magnetic Hydrodynamic Research Articles

Electron-acoustic solitary potential in nonextensive streaming plasma

The linear/nonlinear propagation characteristics of electron-acoustic (EA) solitons are examined in an electron-ion (EI) plasma that contains negative superthermal (dynamical) electrons as well as positively charged ions. By employing the magnetic hydrodynamic (MHD) equations and with the aid of the reductive perturbation technique, a Korteweg-de-Vries (KdV) equation is deduced. The latter admits soliton solution suffering from the superthermal electrons and the streaming flow. The utility of the modified double Laplace decomposition method (MDLDM) leads to approximate wave solutions associated with higher-order perturbation. By imposing finite perturbation on the stationary solution, and with the aid of MDLDM, we have deduced series solution for the electron-acoustic excitations. The latter admits instability and subsequent deformation of the wave profile and can’t be noticed in the KdV theory. Numerical analysis reveals that thermal correction due to superthermal electrons reduces the dimensionless phase speed (bar{U}_{ph}) for EA wave. Moreover, a random motion spread out the dynamical electron fluid and therefore, gives rise to bar{U}_{ph}. A degree enhancement in temperature of superthermal (dynamical) electrons tappers of (increase) the wave steeping and the wave dispersion, enhancing (reducing) the pulse amplitude and the spatial extension of the EA solitons. Interestingly, the approximate wave solution suffers oscillation that grows in time. Our results are important for understanding the coherent EA excitation, associated with the streaming effect of electrons in the EI plasma being relevant to the earth’s magnetosphere, the ionosphere, the laboratory facilities, etc.

Stochastic Magnetic Hydrodynamic Hierarchy in a Strong External Magnetic Field

Based on a stochastic microscopic collisional model of the motion of charged particles in a strong external magnetic field, a hierarchy of equations of magnetic hydrodynamics is constructed. The transition to increasingly rough approximations occurs in accordance with a decrease in the dimensioning parameter, similar to the Knudsen number in gas dynamics. The result is stochastic and nonrandom macroscopic equations that differ from the magnetic analog of the Navier–Stokes system of equations, as well as from the systems of magnetic quasi-hydrodynamics. The main feature of this derivation is more accurate velocity averaging due to the analytical solution of stochastic differential equations with respect to the Wiener measure, in the form of which the intermediate meso model is presented in the phase space. This approach differs significantly from the traditional one, which uses not the random process itself but its distribution function. Emphasis is placed on the clarity of assumptions when moving from one level of detail to another, and not on numerical experiments that contain additional approximation errors.

Progress in Application of Energy-Saving Measures in Aluminum Reduction Cells

The Hall–Herault process is the only methodology applied in the industrial production of aluminum. Energy saving has long been the focus of the aluminum industry since its invention. Nowadays, the pursuit of high productivity, low DC energy consumption and large-scale cell adds new urgency to energy saving, among which the improvement of magnetic-hydro-dynamic (MHD) stability in aluminum electrolysis cells plays a very important role. This article reviewed the developments and applications of the measures in improving MHD stability in terms of structure, effectiveness, simulation, pilot and industrial results. Also some studies were conducted on a TiB2 wettable cathode. At the end, some suggestions on further reduction of energy consumption in the future are proposed.

ABNORMAL CHANGES OF THE NON-TIDAL VARIATIONS OF GRAVITY

Non-tidal variations of gravity are the residual part of the monitoring of the variations after subtraction from them the lunar-solar gravity variations and the drift of the zero point of the gravimeter. Non-tidal variations are sometimes of complex morphology and structure. The sources of the non-tidal variations are the intracrustal processes and flows of the charged particles in space. The streams of the charged particles can affect the sensor of the gravimeter. The streams of the charged particles can create a powerful magnetic hydrodynamic (MHD) shocks that cause abnormal changes of gravity. It is necessary to consider the non-tidal variations when carrying out high-precision gravimetric measurements.

Analysis of Fault Arc in High-Speed Switch Applied in Hybrid Circuit Breaker**supported by National Key Basic Research Program of China (973 Program) (No. 2015CB251001), National Natural Science Foundation of China (Nos. 51221005, 51177124, 51377128, 51323012), the Science and Technology Project Funds of the Grid State Corporation SGSNKYOOKJJS1501564 and Shaanxi Province Natural Science Foundation of China (No. 2013JM-7010)

The behavior of fault arc in a high-speed switch (HSS) has been studied theoretically and experimentally. A simplified HSS setup is designed to support this work. A two-dimensional arc model is developed to analyze the characteristics of fault arc based on magnetic-hydrodynamic (MHD) theory. The advantage of such a model is that the thermal transfer coefficient can be determined by depending on the numerical method alone. The influence of net emission coefficients (NEC) radiation model and P1 model on fault arc is analyzed in detail. Results show that NEC model predicts more radiation energy and less pressure rise without the re-absorption effect considered. As a consequence, P1 model is more suitable to calculate the pressure rise caused by fault arc. Finally, the pressure rise during longer arcing time for different arc currents is predicted.

Application of Analytical Model of the Electric Potential Distribution for Calculation of Charged Particle Dynamics in a Near-Wall Layer and Sputtering of the Plasma Facing Surfaces

Simple analytical formulas are derived for calculation of the electric field potential distribution in the magnetic pre-layer and the Debye layer near the plasma facing surfaces. It is shown that the calculated potential profiles are in good agreement with the dependences of the potential distribution on the magnetic field inclination obtained by solving the magnetic hydrodynamic (MHD) equations and modeling using the PIC code SPICE2. Dependences of the angular distribution of ions incident on the surface of plasma facing elements on the magnetic field inclination are obtained. Results of calculations demonstrate that the surface areas, on which the magnetic field is incident at sliding angles, are critical from the viewpoint of the increase of sputtering.

Multimedia physical feature for unsteady MHD mixed convection viscoelastic fluid over a vertical stretching sheet with viscous dissipation

A multimedia feature for unsteady magnetic hydrodynamic (MHD) flow of two-dimensional mixed convection flow of an incompressible viscoelastic fluid over a vertical stretching sheet with viscous dissipation was studied. Similar transformation and an implicit finite-difference method were used to analyze the present problem. The numerical solutions of the flow velocity distributions, temperature profiles, the wall unknown values of f''(0) and -for calculating the heat transfer of the similar boundary-layer flow were carried out as functions of the unsteadiness parameter (S), the Eckert number (Ec), the Prandtl number (Pr), the magnetic parameter (M), the buoyancy parameter (G), the viscoelastic parameter (α), the space-dependent parameter (A) and temperature-dependent parameter (B) for heat source/sink. The effects of these parameters were also discussed. The results showed that greater heat transfer effect was produced with a larger S and α. On the other hand, parameters G, Pr, Ec, A and B reduced the heat transfer effect at some specific conditions. Key words: Mixed convection, viscous dissipation, MHD, multimedia feature, viscoelastic, heat transfer, unsteady flow, vertical stretching sheet.

Investigation on a low-melting-point gallium alloy MHD power generator

A magnetic hydrodynamic (MHD) power generator using an electro-conductive low-melting-point gallium alloy is introduced. An experimental setup is designed and established to investigate its performance with aids of numerical simulations. Theoretical derivations based on Faraday Law are also presented as a theoretical foundation of the present study. It is found that the electric output increases with flow velocity, magnetic strength and electric conductivity, and the theoretical predictions and numerical results are in good agreement with the experimentally measured data. It is understood that in order to obtain a practical power generation, priority should be put on increasing fluid flow velocity and magnetic field strength. The present MHD power generation system has shown to be operated reliably in a long time at room temperature and could be used as a micro-distributed energy supply system for domestic use in the future. Copyright © 2010 John Wiley & Sons, Ltd.

MHD stagnation point viscoelastic fluid flow and heat transfer on a thermal forming stretching sheet with viscous dissipation

AbstractAn incompressible steady two‐dimensional forced convection with magnetic hydrodynamic (MHD) second‐grade non‐Newtonian (Viscoelastic) fluid flow on a stagnation point of a thermal forming stretching sheet has been studied. A parameter M which is used to represent the dominance of the magnetic effect has been presented in governing equations. The similar transformation, the perturbation expansion and an implicit finite‐difference method have been used to analyse the present problem. The numerical solutions of the flow velocity distributions, temperature profiles, the wall unknown values of f″(0) and θ'(0) for calculating the heat transfer of the similar boundary‐layer flow are carried out as functions of the viscoelastic number k, the Prandtl number Pr, the dissipation parameter E and the magnetic parameter M. The effects of these parameters have also discussed. The value of k is an important factor in this study. It will produce greater heat transfer effect with a larger k or Pr and parameters M or E will reduce heat transfer effect. The non‐Newtonian flow heat transfer effect is better than a Newtonian flow heat transfer effect.

Modeling of axis-symmetric steam plasma flow in a non-transferred torch

This paper discusses the numerical modeling of steam plasma in a DC non-transferred torch equipped with well-type cathode, where the non-trivial azimuthal velocity component and turbulent effect are both taken into account. In order to investigate the complicated flow characteristics of thermal plasma due to the interaction between steam and electric arc, the flow filed inside the plasma torch is modeled by the magnetic–hydrodynamic (MHD) equations. The governing equations are then solved numerically using a non-staggered finite volume discretization based on Cartesian grid system. The anode location and maximum current density at cathode are fixed by the corresponding experimental measurement at a given flow rate. The predicted result suggests that the steam plasma can be accelerated to a mean velocity of 1500 m/s at torch outlet with the mass flow rate of 5 g/s and the system current of 180 A. A strong vortex flow structure is found inside the torch due to the introduction of azimuthal velocity at the gas inlet, which should help to stabilize the rotating arc during the torch operation.

MHD mixed convection for viscoelastic fluid past a porous wedge

A magnetic hydrodynamic (MHD) mixed convective heat transfer problem of a second-grade viscoelastic fluid past a wedge with porous suction or injection has been studied. Governing equations include continuity equation, momentum equation and energy equation of the fluid. It has been analyzed by a combination of a series expansion method, the similarity transformation and a second-order accurate finite-difference method. Solutions of wedge flow on the wedge surface have been obtained by a generalized Falkner–Skan flow derivation. Some important parameters have been discussed by this study, which include the Prandtl number (Pr), the elastic number (E), the free convection parameter (G) and the magnetic parameter (M), the porous suction and injection parameter (C) and the wedge shape factor (β). Results indicated that elastic effect (E) in the flow could increase the local heat transfer coefficient and enhance the heat transfer of a wedge. In addition, similar to the results from Newtonian fluid flow and conduction analysis of a wedge, better heat transfer is obtained with a larger G and Pr.

Viscoelastic Fluid over a Stretching Sheet with Electromagnetic Effects and Nonuniform Heat Source/Sink

A magnetic hydrodynamic (MHD) of an incompressible viscoelastic fluid over a stretching sheet with electric and magnetic dissipation and nonuniform heat source/sink has been studied. The buoyant effect and the electric numberE1couple with magnetic parameterMto represent the dominance of the electric and magnetic effects, and adding the specific item of nonuniform heat source/sink is presented in governing equations which are the main contribution of this study. The similarity transformation, the finite-difference method, Newton method, and Gauss elimination method have been used to analyze the present problem. The numerical solutions of the flow velocity distributions, temperature profiles, and the important wall unknown values off''(0)andθ'(0)have been carried out. The parameter Pr,E1, orEccan increase the heat transfer effects, but the parameterMorA*may decrease the heat transfer effects.

MHD Mixed Convection of Viscoelastic Fluid Over a Stretching Sheet with Ohmic Dissipation

AbstractA magnetic hydrodynamic (MHD) mixed convection of an incompressible viscoelastic fluid over a stretching sheet with ohmic dissipation is studied. The buoyant effect and the electric number E1 couple with magnetic parameter M to represent the dominance of the ohmic effect are presented in governing equations which is the main contribution by this study. The similarity transformation, the finitedifference method have been used to analyze the present problem. The numerical solutions of the flow velocity distributions, temperature profiles and the important wall unknown values of f″(0) and θ′(0) are carried out.

MHD simulation of high-current subsonic vacuum arc under different distributed axial magnetic fields

Based on two-temperature magnetic hydrodynamic (MHD) model, the influence of saddle-shaped distributed axial magnetic field (AMF, linearly increases along radial position) and bell-shaped distributed AMF (linearly decreases along radial position) on plasma loss and heat flux density to anode in subsonic high-current vacuum arc (HCVA) is simulated and analyzed. According to the simulation results, the saddle-shaped AMF can more effectively inhibit plasma loss from arc column than that of bell-shaped AMF. Comparisons between simulation results and experimental results further verify the correctness of model and simulation.

Modeling and experimental validation of a 1.2 MW DC transferred well-type plasma torch

This paper discusses the numerical modeling and experimental validation of a 1.2 MW DC transferred plasma torch, which is equipped with a well-type cathode (WTC). In order to investigate the complicated thermal and flow characteristics due to the interaction between the working gas and electric arc, the flow filed inside the plasma torch is modeled by the magnetic–hydrodynamic (MHD) equations. The governing equations are solved numerically using a finite volume discretization for both cold and hot flow simulations. The numerical simulations are then validated by experimental measurements at a specific operation condition. The predicted results successfully reflect some important features of the studied transferred WTC plasma torch.

MHD evolutionary processes in the Earth’s model magnetic resonator

Specific features of the spatial-temporal dynamics of LF disturbances of the Earth’s magnetosphere have been analyzed by the method of numerical simulation of magnetic hydrodynamic equations taking into account plasma temperature variations. The effects related to the appearance of long-living magnetospheric jumps of density and temperature, MHD wave scattering on such inhomogeneities, Alfven wave reflection from the near-Earth region, and magnetospheric plasma heating as a result of dissipative processes at a repeated propagation of MHD waves between magnetically conjugate regions have been considered. The problems of conformity of the discrete mathematical model with continuous equations of magnetic hydrodynamics are discussed.

Completely two-dimensional model for examining the characteristics of a linear cylindrical induction pump

A completely two-dimensional mathematical model for calculating the characteristics of induction magnetichydrodynamic (MHD) machines with a cylindrical channel is proposed. The flow pattern of a liquid metal in an electromagnetic pump under MHD instability is obtained by numeric analysis. This pattern is characterized by the formation of large-scale vortices traveling longitudinally and azimuthally. The calculated basic characteristics of the pump are in good qualitative and in satisfactory quantitative agreement with the experiment.