Three-dimensional structures of MHD flow in a disk generator

Three-dimensional nonuniform plasmas and boundary layers have been studied numerically under an MHD interaction. The nonuniform plasma of “streamer” owing to weak ionization of seed material has a spiral structure in the r-&thetas; plane, and the plasma becomes almost uniform between the walls in the r-z plane. This structure is almost the same as that in our previous paper (1997), where the gas (heavy particle) properties are assumed to be invariant and steady. In addition to the streamer, the nonuniform plasma of “domain” owing to weak ionization of noble gas is revealed. The domain has the structure perpendicular to the streamer. In a strong MHD interaction case, the static pressure considerably increases in the upstream region of a generation channel, and the pseudo-shock waves appear in the generator, but the plasma is almost uniform along the &thetas; direction. The boundary layer in the strong MHD interaction is considerably thick, and in the broad region near the wall the Hall current flows reversely. In the weak MHD interaction case, the plasma forms a nonuniform structure along the &thetas; direction, and the Hall current does not always flow in the opposite direction even on the insulator wall since the azimuthal electric field is not zero     

Numerical study on performance of disk MHD generator using frozen inert gas plasma

In an magnetohydrodynamic (MHD) generator using a frozen inert gas plasma (FIP), the availability of a frozen argon plasma, the influence of plasma uniformity at the generator inlet on the performance, and the feasibility of a large-scale generator are numerically examined by /spl gamma/-/spl theta/ two-dimensional simulation. The FIP is produced by pre-ionizing inert gas without an alkali metal seed at the generator inlet, then the ionization degree of the plasma is kept almost constant in the whole of the channel because of considerable slow recombination of the inert gas just like frozen reaction plasma. It is found that not only helium, but also argon frozen plasma MHD generation is realized, although highly accurate control of inlet ionization degree is necessary for argon. It is important to reduce the nonuniformity of plasma properties at the generator inlet in order to raise the maximum enthalpy extraction ratio. Even for the large-scale generator with 1000-MW thermal input, the ionization degree is kept almost constant in the whole of the channel and the high performance is obtainable. This result is extremely attractive for the FIP MHD generator.     

Optical spectrum of a closed cycle MHD generator plasma

The spectra of argon-cesium plasmas, used as working fluids of closed-cycle MHD generators, were investigated in the visible and near-i.r. regions by using a Hilger-Watts medium quartz spectrograph. A number of argon and cesium lines was observed, as well as some lines originating from the impurities present in the cesium capsule. The molecular bands of aluminum monoxide have also been detected. The population temperatures estimated from relative intensities of cesium lines lie below those obtained by using either the line-reversal method or recombination-radiation measurements. The intensities of some neutral cesium lines follow the Boltzmann population relation at the population temperature. The Zeeman effect and reversed profiles of cesium resonance lines were not observed because of low resolution of the spectrograph used and because of light scattering on the film.     

Numerical simulation of nonlinear ionization nonuniformities innonequilibrium disk MHD generator

The formation and evolution of the ionization nonuniformities from initial disturbances of finite amplitude in the nonequilibrium Ar-Cs plasma in a disk magnetohydrodynamic (MHD) generator is studied by the numerical simulation, The simulations are carried out in the wide interval of electron temperatures corresponding to the region at which the seed partially ionizes, the region of the linear plasma stability at the fully ionized seed, and the region of the instability corresponding to the partial ionization of Ar at high electron temperatures. Initial disturbances of finite amplitude in electron temperature and density are introduced at the time t=0 into the homogeneous plasma distribution, and the critical amplitudes determining the development of the instability are calculated. The initial disturbances are constructed using random functions with different spatial scales, The results are compared with the calculation of the critical amplitudes from the nonlinear theory of the plane ionization waves, It is found that at electron temperatures lower than 5500 K, the temperature dependence of the critical amplitudes and the structure of the nonlinear waves agree well with the nonlinear theory, In the electron temperature region corresponding to the partial ionization of the noble gas (T_e>5500 K), the finite ionization rate of argon atoms is essential for analysis of the instability, In this region the margin of the plasma stability is wider than it is predicted by the nonlinear theory, The nonuniformity in the argon ion number density plays the dominating role in the instability development at high electron temperatures (T_e>5500 K) in comparison with the nonuniformity in T_e in the initial disturbances,     

Numerical simulation of plasma and fluid behavior in the ISTEC-2 nonequilibrium disk MHD generator with multiple loads

Plasma and fluid behavior in a nonequilibrium disk magnetohydrodynamics generator with multiple loading has been investigated with a time-dependent three-dimensional numerical simulation. Particular attention is paid to the effects of the downstream load resistance and the influences of the middle electrode on the plasma and fluid flow. The possibility to improve generator performance by multiple-loading operation is also examined. It is shown that increase in the downstream load resistance raises the static pressure and decelerates the working gas in the upstream region. This is because the static pressure increase and the boundary layer development near the middle electrode have the same effects as the change of the outlet boundary conditions for the upstream region. It is found that the ionization degree of seed atoms is kept high on the middle electrode, whereas, the electron temperature is decreased rapidly. This results from the longer relaxation time of ion number density compared to that of the electron temperature. The multiple-loading operation leads to an improvement of the enthalpy extraction ratio. Isentropic efficiency, however, becomes somewhat lower under the multiple-loading condition. This is caused by the high static pressure and the low electrical efficiency under the high enthalpy extraction condition for the multiple loading.     

MHD flow and heat transfer over a radially stretching/shrinking disk

A steady magnetohydrodynamic (MHD) flow past a radially stretching or shrinking disk is investigated. The governing partial differential equations are transformed into a set of ordinary (similarity) differential equations by a similarity transformation. These equations along with the corresponding boundary conditions are solved numerically using the boundary value problem solver (bvp4c) in Matlab. The effects of magnetic field and suction on the shear stress and the heat transfer are analyzed and discussed. It is found that both parameters affect more in the shrinking region. The increase in the magnetic parameter results in the increase of the skin friction coefficient but decrease in the local Nusselt number.The skin friction coefficient and the local Nusselt number increase as suction increases.     

Characterization of the three-dimensional supersonic flow for the MHD generator

A numerical procedure based on a five-wave MHD model associated with non-ideal, low magnetic Reynolds number MHD flows was developed in the present study for analyzing the flow fields in the MHD generator of a MHD bypass scramjet. The numerical procedure is composed of an entropy conditioned scheme for solving the non-homogeneous Navier-Stokes equations, in conjunction with an SOR method for solving the elliptic equation governing the electrical potential. It was found that a separation would take place near the downstream edge of the second electrode, where the local adverse pressure gradient is large, and the core of the flow field is characterized as a 2-D flow due to the Hartmann effects along the direction of the magnetic field. The electric current lines would be increasingly distorted as the magnetic interactive parameter increases, and even induce an eddy current. Induced eddy current was also found in the different cross-sections along the axial direction, all of these would definitely deteriorate the performance of the MHD generator. The cross-sectional M-shape velocity profile found along the axial direction between the insulating walls is responsible for the formation of the vortex flow at the corner of the insulator cross-section, which, in turn, induces the corner eddy current at the corner. A numerical parametric study was also performed, and the computed performance parameters for the MHD generator suggest that, in order to enhance the performance of MHD generator, the magnetic interaction parameter should be elevated.     

Entropy analysis on unsteady MHD biviscosity nanofluid flow with convective heat transfer in a permeable radiative stretchable rotating disk

We examine the entropy analysis in three-dimensional hydromagnetic flow and convective heat transport of a biviscosity nanofluid over a rotating porous disk with a time-dependent stretching rate in the direction of the radius of the circular disk. We also examine the influence of thermal radiation and viscous dissipation due to nanoparticles and applied magnetic field. We invoked suitable self-similar transformations to covert the modeled coupled nonlinear PDEs into a set of nonlinear ODEs. The transformed system of equations is then worked out numerically by a well-known shooting technique and the fourth-order Runge–Kutta–Fehlberge method. The rotating phenomenon yields an additional parameter known as a rotation parameter, which controls the disk’s rotation. The study shows that the fluid motion is accelerated along the radial and cross-radial directions with an increase in the rotation of the disk. The skin-friction and the heat transfer rate at the disk strongly depend on the rotation of the disk, permeability of the porous medium, thermal radiation, and nanoparticle size. The Bejan number quantifies the entropy production of the system. It has a considerable impact on the magnetic field, rotation of the disk, thermal radiation, and Biot number. The efficient performance of the system is possible by a suitable choice of the physical parameters discussed in this article.     

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利用朗缪尔探针和发射光谱两种诊断手段,测量了某固体工质等离子体发生器的喷流流场参数。结果表明,在输入功率为2kW时,发生器可持续稳定工作300s;发生器燃烧室内最高温度为800K。稳定工作时,发生器壳体结构正常,没有发现损毁现象;等离子体喷流的电子密度为1011～1012cm–3量级,电子温度为1.5～3.5eV。     

Role of equilibrium plasma flow on damping of slow MHD waves

In the solar corona waves and oscillatory activities are observed with modern imaging and spectral instruments. These oscillations are interpreted as slow magneto-acoustic waves excited impulsively in coronal loops. This study explores the effect of steady plasma flow on the dissipation of slow magneto-acoustic waves in the solar coronal loops permeated by uniform magnetic field. We have investigated the damping of slow waves in the coronal plasma taking into account viscosity and thermal conductivity as dissipative processes. On solving the dispersion relation it is found that the presence of plasma flow influences the characteristics of wave propagation and dissipation. We have shown that the time damping of slow waves exhibits varying behavior depending upon the physical parameters of the loop. The wave energy flux associated with slow magnetoacoustic waves turns out to be of the order of 10⁶ erg cm⁻² s⁻¹ which is high enough to replace the energy lost through optically thin coronal emission and the thermal conduction below to the transition region.     

MHD Stokes flow in a corrugated curved channel

Magnetohydrodynamic (MHD) flow through a corrugated curved channel is modelled. The flow is perpendicular to the corrugations and applied magnetic field. A boundary perturbation analysis for small corrugation amplitude is used to find the expressions for the stream function and the flow rate. It is found that the flow is inevitably decreased by the corrugations. For a given Hartmann number, the flow reduction varies with the channel radius of curvature. The effect of the phase difference between the corrugated walls is distinct, with minimum and maximum effects when the corrugated curved walls are in-phase and out-of-phase, respectively, for small corrugation wavenumber. However, when the corrugation wavenumber is large enough, the flow is independent of the phase difference. Generally, the study shows that the Hartmann number decreases the effect of the corrugations on the flow rate.     

Hall MHD model of a microsecond plasma opening switch and its application to experiments on a pulsed current generator installation

The necessity of considering the motion of electrons and ions in the plasma of a microsecond switch in the conduction and cutoff stages (Hall MHD model) is substantiated experimentally. We give the Hall MHD model relations that describe the main parameters of the plasma opening switch as an element of the electrical circuit of a pulsed current generator. Comparison of the deductions of the theory with the experimental results obtained in pulsed current generator (PCG) installations indicates that the theory and experiment at least are not in contradiction with each other. An improvement of the POS design from the standpoint of the Hall MHD model is proposed. Institute of High-Current Electronics, Siberian Branch of the Russian Academy of Sciences. Laboratory of the Physics of Ionized Media. école Polytechnique, France. Translated from Izvestiya Uchebnykh Zavedenii, Fizika, No. 12, pp. 56–66, December, 1997.     

Design of Closed-Cycle MHD Generator with Nonequilibrium Ionization and System

A closed-cycle MHD generator topping a steam bottoming plant is analyzed. The combined power plant involves three working fluids in three loops. The MHD loop is investigated more thoroughly since it is the least conventional of the three. Equations are developed to determine the geometric and thermodynamic variables throughout the MHD channel for inlet conditions of mass flow, temperature, pressure, and velocity. Limiting design parameters are output power, channel length, channel aspect ratio, Hall parameter, and interaction parameter. The basic closed-cycle MHD loop working fluid can consist of either argon or helium seeded with cesium. Both non-equilibrium ionization produced by the elevation of the electron temperature from joule heating of the plasma and thermal ionization are considered. Equations used to calculate the electrical conductivity and the elevation of electron temperatures are derived. These equations are coupled with the one-dimentional differential equations applicable to an MHD generator. The chief interest is in determining those MHD channel conditions which result in the most thermodynamically efficient MHD-steam plantcombination. Thus an overall heat balance forthe system is required. Equations are developed to calculate the gas properties at the various stations of the closed loop and to determine the overall efficiency of the cycle. A rather flexible computer program written in Fortran is used to solve the MHD generator equations and to make the overall heat balance. Some typical results presented demonstrate the feasibility and adaptability of the analysis for optimizing the thermal efficiency and the sensitivity of thermal efficiency to various parameters.     

Heat transfer in MHD flow in a rotating channel

An exact solution of the temperature profile in the MHD flow in a rotating straight channel is derived. It is found that the rate of heat transfer decreases with increasing the Hartmann numberM whenK is small, but at large values ofK it increases with increasingM.     

Nonequilibrium volume plasma chemical processing

A review is presented of plasma chemical processes occurring in the volume part of electrical nonequilibrium discharges. The role of energetic electrons as initiators of chemical reactions in a cold background gas is discussed. Different discharge types of (glow, corona, silent, RF, and microwave discharges) are investigated with respect to their suitability for plasma processing. Emphasis is placed on the requirements of initiating and maintaining the discharge and, at the same time, optimizing plasma parameters for the desired chemical process. Using large-scale industrial ozone production as an example, the detailed process of discharge optimization is described. Other applications of volume plasma processing include other plasma chemical syntheses as well as decomposition processes such as flue gas treatment and hazardous waste disposal. The author only deals with plasmas which are not in equilibrium     

Nonequilibrium thermodynamics SAW-induced acoustic flow

Acoustic flow excited in a planar gap by a surface acoustic wave (SAW) during free-molecular flow along the length of the SAW is investigated by nonequilibrium thermodynamics methods. The entropy production is calculated and the cross effect and the kinetic coefficient for the cross effect are determined. Zh. Tekh. Fiz. 67, 134–136 (October 1997)     

Experimental studies on isentropic efficiency of a nonequilibriumMHD disk generator

Isentropic efficiency of the nonequilibrium MHD power generator was studied by a shock tube driven disk generator. Cesium seeded helium was used as a working gas. From the measurements of Faraday current density distribution, it was possible to estimate the general tendency of Joule dissipation in the generator. The Joule dissipation did not decrease due to the occurrence of nonuniformity of the plasma when external load resistance was low, although it decreased with the decrease in the load resistance when the load resistance was high. The electrical efficiency increased with the increase in applied magnetic flux density. This fact is thought to be caused by high Hall parameter and the stabilization of the plasma due to high degree of seed ionization     

MHD stagnation point flow towards a stretching sheet

The steady two-dimensional MHD stagnation point flow towards a stretching sheet with variable surface temperature is investigated. The governing system of partial differential equations are transformed into ordinary differential equations, which are then solved numerically using a finite-difference scheme known as the Keller-box method. The effects of the governing parameters on the flow field and heat transfer characteristics are obtained and discussed. It is found that the heat transfer rate at the surface increases with the magnetic parameter when the free stream velocity exceeds the stretching velocity, i.e. ε>1, and the opposite is observed when ε<1.     

MHD laminar thin-film flow along a vertcal wall

An accelerating magnetohydrodynamic laminar flow of an electrically conducting fluid under the influence of gravity and in presence of transverse magnetic field is investigated in the paper. Using a cubic polynomial for the velocity profile inside the boundary layer, the momentum integral equation is solved numerically by Runge-Kutta method to determine the boundary layer thickness and the corresponding film thickness is then calculated for the entrance region. The effect of magnetic field on these solutions is shown in graphical form.List of symbols u, v local velocity components - p pressure - density - kinematic viscosity - viscosity= - electrical conductivity - g acceleration due to gravity - U _s (x) inviscid core velocity - h(x) film thicknes - (x) boundary layer thickness - M Hartmann number - B ₀ external magnetic field The authors remain thankful to the referee for some helpful criticisms.