Performance Of MHD Generator Research Articles

Performance of a Faraday Rare Gas Alkali MHD Generator

The performance of the IPP rare gas alkali MHD generator was theoretically and experimentally investigated. The open-circuit Faraday voltage, the short-circuit Hall voltage, and the load characteristic were measured at different segmentation ratios s/h and various magnetic field strengths. Furthermore, the current streamline pattern in the generator duct was determined from the equipotential lines measured by means of a movable probe. From these measurements it could be concluded that the generator is practically free of any leakage currents and internal plasma short-circuits. This conclusion was further supported by the reasonably good agreement between theory and experiment regarding the current voltage characteristic of the generator. In the calculation allowance was made for the influence of instabilities, segmentation effects, and voltage drops at the electrode, but mechanisms producing leakage currents or internal plasma short-circuits were not considered. N rare gas alkali MHD generators the electron density and hence the electrical conductivity attain equilibrium in accordance with the electron temperature elevation. This nonequilibrium ionization in conjunction with the fact that the electron temperature elevation in the generator may show strong local variations and occurs in a medium flowing at high velocity through the generator duct gives rise to a number of complications which are not so pronounced in the case of an equilibrium generator or not even present there. The most important ones are: elongation of the current paths due to relaxation and convection effects particularly pronounced at the generator entrance, inhomogeneities in the current density distribution produced by the electrode configuration, axial leakage currents and instabilities. All of these phenomena impair the performance of the generator. It is therefore necessary to investigate them, and if possible, lessen their influence. The performance of nonequilibri um MHD generators has already been investigated in a variety of test rigs. It was possible to achieve high power densities and electron temperature elevations in short-time MHD generator systems1'2 with operating times of up to a few milliseconds. The test rigs working in continuous operation3'4 involved technical problems which prevented the theoretically predicted power output from being attained. Better, but still not quite the ideal values of the power density and electron temperature elevation were obtained in the blow-down facilities.57 Whereas this deviation is accounted for in Ref. 5 by assuming external leakages strictly associated with the duct technology, it is ascribed in Refs. 6 and 7 to the presence of highly conducting layers along the electrode walls which impair the generator performance. This paper reports investigations on a generator working in continuous operation. These were concerned not only with the measurement of the Faraday voltage across the duct, the Hall voltage between the electrodes, and the current flowing through one electrode pair, but also with the local distributions of the various plasma parameters, viz., the potential and current density distributions, the velocity profile, and the electron and gas

Calculation of the Performance of Large Scale Diagonal MHD Generator

Calculation of the Performance of Large Scale Diagonal MHD Generator

The steady state performance, magneto-acoustical response, and stability of flow in a hall MHD generator

The steady state performance, magneto-acoustical response, and temporal stability of a ring electrode Hall MHD generator of constant cross-sectional area and zero electrode ring slant angle are investigated numerically by means of a digital computer. The generator is shown to be stable under “stiff load” terminal conditions. The magneto-acoustical response is found to be relatively insensitive to changes in the steady state terminal current near open circuit conditions.

A study of influence of non-uniformity of flow parameters and imperfect wall insulation on MHD-generator performance in presence of Hall effect

A study of influence of non-uniformity of flow parameters and imperfect wall insulation on MHD-generator performance in presence of Hall effect

The effect of swirl on MHD generator performance

The effect of swirl on MHD generator performance

The effect of swirl on MHD generator performance : John B. Heywood, Central Electricity Research Laboratories, Leatherhead, Surrey, England. Energy Conversion8, 181–183 (1968)

The effect of swirl on MHD generator performance : John B. Heywood, Central Electricity Research Laboratories, Leatherhead, Surrey, England. Energy Conversion8, 181–183 (1968)

Effects of electrode and boundary-layer temperatures on MHD-generator performance.

Effects of electrode and boundary-layer temperatures on MHD-generator performance.

The electrodynamic effects of non-uniformity of magnetic field and fluid parameters in mhd generators

The two-dimensional effects of axial non-uniformity of the electrical conductivity, gas velocity, magnetic field, Hall parameter, duct cross-sectional area and electrical loading upon the performance of MHD generators are considered. Various methods of calculation of the duct performance are examined. These include the standard one-dimensional theory and also an approximate equation, which is derived in order to take account of the non-uniformities. Comparisons are then made with results given by a two-dimensional relaxation process. It is shown that for most purposes, the one-dimensional theory is a good approximation.

Effects of electrode and boundary-layer temperatures on MHD generator performance

Experiments were performed in a combustion-driven MHD generator to determine the effects of electrode temperature and boundary-layer temperature on its performance. The generator was a single electrode pair guarded to avoid end effects by two electrode pairs both upstream and downstream. However, end effects were found to be small, so the tests can be interpreted in terms of a five-electrode-pair generator. The electrodes were held at three temperature levels--775°, 1475°, and 1685°K--by controlling individual cooling circuits. Two electrode boundary-layer temperature profiles were investigated: one resulting from a hot (2400°K) upstream wall, and the other resulting from a cold (750°K) water-cooled plate that replaced the normal upstream electrode wall. Probes were installed in the insulator side wall between the center pair of electrodes to measure the voltage profile in the gas. Visual and photographic observations of the electrodes were made. It was found that the generator with hot electrodes downstream of the hot walls produced about seven times the power of the generator with cold dectrodes downstream of cold walls. Electrode voltage drops, obtained from the side wall probe data, were found to vary with load current, electrode temperature, and upstream wall temperature. Cathode voltage drops were higher than anode voltage drops, but the difference decreased with increasing electrode temperature and upstream wall temperature. An analytical model was postulated to interpret the data. The ohmic resistance of the boundary layer was calculated by integrating an equilibrium conductivity profile through the boundary layer to a point one Debye length from the electrode surface. The calculated values agree with resistance of the anode boundary layer obtained from probe data. The difference between resistances of cathode and anode boundary layers was attributed to surface and/or sheath effects at the cathode.

Status report on MHD electrical power generation–IAEA/ENEA International Liaison Group on MHD Electrical power generation

The present status of commercial large-scale MHD electrical power generation is reviewed in the light of information presented at the Third International Symposium on MHD Electrical Power Generation (Salzburg, 1966) and of subsequent developments. Research and development activities, and the state of evaluation of engineering and economic factors are assessed in respect of open-cycle MHD power plant, closed-cycle MHD power plant, and the associated electromagnet.The MHD power generator is attractive in that energy is extracted directly from that of the flow of working fluid. The generator itself is of simple static construction, thus permitting high maximum cycle temperature, high specific power output and potentially much larger unit size than may ultimately be achievable with turbomachinety. In principle, these features should offer increased thermal efficiency and reduced capital cost compared with conventional plant.In the ‘open-cycle’ MHD system electrical energy is extracted directly from the flow of a plasma formed by the seeded products of combustion of a hydrocarbon fuel. The ‘closed-cycle’ MHD system similarly employs a working fluid which may be a seeded inert gas (helium, neon, argon) or a pure alkali metal. Operation may be based on the gas turbine or Brayton cycle, or incorporate steam plant (for the lower range of temperature) based on the condensing or Rankine cycle. In the case of the open-cycle MHD system, installations are being constructed or already operating successfully with hundreds of MW thermal input and tens of MW electrical output, and substantial effort has been devoted to other aspects of the plant. It is concluded that a pilot-scale power station is technically feasible but that the economics of MHD steam plant are not fully established.Research and development towards the closed-cycle MHD system is at an earlier stage, and there are fundamental aspects of plasma behaviour relating to instabilities and the feasibility of utilizing magnetically-induced non-equilibrium ionization which have to be resolved. Engineering and economic evaluation of system concepts requires attention. Closed-cycle systems operated on a condensing or Rankine cycle with liquid-metal MHD generators are also at an early stage of development. There is as yet insufficient information on the performance of various liquid acceleration schemes and MHD generators to allow assessment for commercial plant, although for special applications (e.g. space vehicle power systems) the concept is attractive.Superconducting electromagnets are technically and economically necessary for MHD power systems which, in almost all respects, derive benefit from operation at higher magnetic fields. Field levels of 5 – 7 T are attainable at present, and there are good prospects for further development to large size and higher fields.

Performance of a segmented electrode MHD generator for various electrode-insulator length ratios

Performance of a segmented electrode MHD generator for various electrode-insulator length ratios

Performance of a segmented electrode mhd generator for various electrode-insulator length ratios

The increase of internal resistance caused by finite electrode size effects is calculated by means of conformal mapping in a fashion similar to that used by Hurwitz et al. but also taking into account the effect of varying the relative size electrodes and insulators. It is shown that the relation insulator length/electrode length = Hall angle/ninety degrees leads to a minimum of the generator internal resistance and a minimum of ohmic dissipation in the vicinity of the electrodes. The relation also gives the largest size which the electrode can attain before current starts to flow between adjacent electrodes.

Theoretical performance of MHD generators with various electrode geometries

The performance of various electrode geometries has been analysed for MHD generators, assuming scalar electrical conductivity and steady inviscid incompressible flow, with the following results: (a) For electrodes whose height is less than the channel height, the electrode current is reduced, but the open circuit voltage and efficiency are unchanged, as compared to the ideal case. (b) However, “wrapped around” electrodes cause internal shorting with a resulting decrease in voltage and efficiency. (c) Finned electrodes cause less internal shorting and loss of efficiency than “wrapped around” electrodes, and may be of importance in reducing the apparent impedance of segmented electrodes for the case of tensor conductivity.

The magnetohydrodynamic power generator-basic principles, state of the art, and areas of application

The paper opens with a review and discussion of the basic principles of MHD power generation. It is seen that the MHD generator operates in a manner similar to that of a conventional generator in that the "armature" of the MHD is a hot, high-speed electrically-conducting gas, while the force or torque-required to move a metallic conductor through a field is replaced by a pressure gradient in the gaseous armature. Thus the functions of turbine and generator are combined in a single machine. Because this machine has no moving parts, it can, in principle, accept a working fluid at very high temperature. After a derivation of the basic MHD-generator flow equations a brief synopsis of losses in an MHD generator is given. The nature of these losses is such that the MHD generator is applicable where large amounts of power are involved. In gases, the Hall effect can be very pronounced, and its influence on MHD generator design and performance is pointed out. There follows a brief statement of the state of the art in MHD-generator development at the Avco-Everett Research Laboratory. It is shown that gases produced by conventional heat sources can be made adequate conductors of electricity for use in an MHD if a small amount of easily ionizable impurity called seed is added to the gas. Recent developments in superconducting materials, plus detailed studies of MHD-generator fluid mechanics in a large combustion-driven generator point to early realization of the potential of MHD.