Improvement of performance of disk MHD generator with argon by introduction of swirl

An experimental study of performance of the disk MHD generator with argon was carried out using a shock‐tube driven facility. An inlet swirl was introduced in the MHD channel in order to improve the enthalpy extraction and the isentropic efficiency. The experimental results were compared with those of the disk MHD generator without the inlet swirl. A high enthalpy extraction of 25.7% was obtained and the highest isentropic efficiency for argon was achieved at the same time in the present experiment. The measured static pressure in the MHD channel was kept lower than that without the inlet swirl. This has suggested that the introduction of the inlet swirl reduces the retarding force for the flow and that the increase of the enthalpy extraction is ascribed to the increase of the flow velocity and of the electrical efficiency. Furthermore, the flow without shock wave was observed at low seed fractions and low load resistances. At the same time, it was found for the first time that when there was no shock wave, the isentropic efficiency became higher than that with the shock wave. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(1): 18–25, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10045     

Adiabatic efficiency and Joule dissipation in supersonic Faraday MHD generator

The adiabatic efficiency of a supersonic Faraday MHD (magnetohydrodynamic) generator and its relation to Joule dissipation in the MHD channel were studied in a shock tube experiment. An adiabatic efficiency of 39.7% was obtained at enthalpy extraction of 8.3%. A dissipation process, which reduces the adiabatic efficiency, is examined by evaluating loading parameters and entropy production caused by Joule dissipation. At low load resistance, large Faraday currents in the channel upstream cause extremely large Joule dissipation in both the main flow and the region near the electrodes. It is confirmed experimentally that a high loading parameter yields a high adiabatic efficiency because Joule dissipation is small throughout the MHD channel. © 1999 Scripta Technica, Electr Eng Jpn, 128(4): 47–54, 1999     

Production of nonequilibrium plasma and MHD interaction in disk MHD channel

The production of nonequilibrium plasma and the fluid flow with the MHD interaction are examined experimentally with a shock‐tube driven disk channel with no loading electrodes. For low magnetic flux density and low seed fraction, where nonuniform and unsteady plasma is generated, the static pressure decreases monotonically in the radial direction, although the pressure increases in the entire region of the channel in comparison with the value under no MHD interaction. For magnetic flux density and seed fraction above some critical values, a fairly uniform plasma is produced. The static pressure, however, is found to increase abruptly in the channel and the total pressure is considerably reduced at the location, where the abrupt pressure increase occurs. These facts imply that steady and uniform plasma should be produced without locally constricted strong Lorentz force to improve the adiabatic efficiency of a disk MHD generator. © 2002 Scripta Technica, Electr Eng Jpn, 138(4): 42–49, 2002; DOI 10.1002/eej.1137     

Electron temperature measurement and performance of a nonequilibrium disk MHD generator

Electron temperatures of nonequilibrium cesium seeded argon plasmas in a disk MHD generator installed in a blow-down facility are measured spectroscopically, and the generator performance is discussed in relation to the electron temperature. The temperature is decreased from ∼9000 K to ∼3000 K when the seed fraction is increased from 1 × 10⁻⁴ to 3 × 10⁻⁴. For the seed fraction of about 2 × 10⁻⁴ corresponding to the maximum power output, the temperature is found to be 4000–5000 K and the temperature fluctuation becomes minimal. For the seed fraction around 2 × 10⁻⁴, the electrical conductivity evaluated from the temperature is almost independent of the temperature. These facts suggest that the plasma is almost in the full seed ionization regime. Partially ionized argon and cesium plasmas are dominant at seed fractions below 1.3 × 10⁻⁴ and over 2.3 × 10⁻⁴, respectively, which degrades generator performance. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 120(1): 16–22, 1997     

Effects of diffuser shape and back pressure on the performance of disk MHD generators

The effects of diffuser shape and back pressure on the performance of closed‐cycle disk MHD generators are investigated with two‐dimensional numerical simulations taking account of the boundary layer. The enthalpy extraction ratio decreases and fluctuates periodically with increase in the back pressure. The amplitude of power output fluctuation and the period depend on the volume of the inverse flow region. For the reduced height diffuser, the inverse flow region is suppressed and the fluctuation becomes smaller than that for the constant height diffuser. When operated with a back pressure lower than an optimum value, the diffuser does not work because of reacceleration in the diffuser. For the higher back pressure, on the contrary, the inverse flow region propagates into the MHD channel, then the enthalpy extraction ratio is reduced and the Mach number at the exit of the MHD channel becomes lower than unity. For the optimum back pressure, high enthalpy extraction ratio is achieved and the adiabatic efficiency at the diffuser exit is decreased by several percent from that evaluated at the MHD channel exit. © 2000 Scripta Technica, Electr Eng Jpn, 133(2): 11–19, 2000     

Study of a coal-fired transonic disk MHD generator for a power system with CO2 recovery

A conceptual design of a transonic disk MHD channel is carried out for a power generation system with liquefaction recovery of CO₂. A previous study has shown that the subsonic disk MHD channel has rather poor performance and the supersonic disk channel yields sufficiently high power output, although its stability should be improved. The present paper proposes a transonic disk channel which can be stably operated with high power output. It is assumed that the transition between supersonic flow and subsonic flow is accompanied by a cylindrical shock wave in the channel. The transonic channel yields enthalpy extraction ratios of 20.2 and 22.9%, respectively, for thermal inputs of 1100 and 2000 MW, and is nearly equal to the performance of the supersonic channel. The stability of the transonic disk channel is examined by r-0 two-dimensional time-dependent calculations. The two-dimensional analysis shows that the transonic disk channel works stably with fewer load sections than the supersonic channel even when inlet perturbations are added. © 1998 Scripta Technica. Electr Eng Jpn, 122(2): 21–29, 1998     

Stability analysis of MHD disk generators designed for a coal-fired power system with CO2 recovery

Design and stability analyses of MHD disk-type generators are carried out, which are applied for coal-fired electrical power generation system with CO₂ recovery. Channels designed with subsonic flow show rather poor performance compared with supersonic flow channels. Inflow channels show better performance than outflow channels. The inflow channel gives enthalpy extraction ratios of 20.21% and 21.12% for thermal inputs of 1100 MW and 2000 MW, respectively, while the outflow channel operated with supersonic flow yields enthalpy extraction ratios of 17.92% and 18.12% when the magnetic flux density is 8 T. The open-cycle disk channels tend to become unstable at the exit region. It seems possible to stabilize the disk channels when operated with 8 T but seems difficult to stabilize them when operated with 10 T. © 1997 Scripta Technica, Inc. Electr Eng Jpn 119(1): 9–16, 1997     

Numerical Simulation of Power Generation Characteristics of a Disk MHD Generator with High‐Temperature Inert Gas Plasma

The power generation characteristics of a disk magnetohydrodynamics (MHD) generator with high‐temperature inert gas (argon) plasma have been examined by a time‐dependent two‐dimensional numerical simulation. The numerical simulation results based on the experimental conditions show that the enthalpy extraction ratio (= electrical output power/thermal input) can reach above 10%, which surely supports the reasonability of the experimental results. Proper selection of working conditions, especially the inlet total gas temperature, is necessary, since the gas temperature dominantly determines the electrical conductivity in the generator, unlike the conventional seeded plasma MHD generator. It is also found that the plasma is not in the recombination process but in the ionization process, where the ionization degree moderately increases along the flow. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(3): 23–30, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21237     

Configuration optimization for a coupled 200-MWe MHD channel and magnet coil system

This paper reports on the results of the optimization of the cross-sectional shape of a magnet coil system including an MHD channel. This optimization was carried out for a 200-MWe supersonic Faraday-type MHD generator. It was shown that the channel length can be shortened more than 30 percent, without the decrease of the enthalpy extraction by the optimization of the coil shape from the crescent shape coil producing a uniform magnetic field. It was estimated also that the capital cost for a commercial MHD/steam combined plant can be decreased more than 6 percent by this coil shape optimization.     

Behavior of magneto‐acoustic waves in a nonequilibrium subsonic disk MHD generator

The behavior of magneto‐acoustic waves in a nonequilibrium subsonic disk MHD generator was examined. The solution of the sixth‐order dispersion relation obtained by linearizing the set of MHD equations suggested that a magneto‐acoustic wave which propagates at a velocity of u_r ? a(u_r: radial fluid velocity, a: sound velocity) should be damped in subsonic flow. From time‐dependent quasi‐one‐dimensional simulations, it was verified that the pressure disturbance in the subsonic generator was damped at approximately the same rate as the value predicted by the linear theory. From a simplified analytical model, the mechanism of magneto‐acoustic instability with fully ionized seed was discussed, and the damping criterion for the magneto‐acoustic wave was clarified. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 142(4): 20–26, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10108     

Performance analysis of closed loop in a CCMHD single power generation system

Results of numerical study on performance of closed loop in the CCMHD single power generation system are presented. The small closed loop with thermal input of 2.3 MW was designed. The fluid‐dynamical and thermal performance of the closed loop was calculated for the first time by one‐dimensional numerical simulation. The result indicates that pressure loss and heat loss are large in the designed small closed loop. The large pressure loss was due to the wall friction or the pebble bed and it occurred at the supersonic nozzle, the MHD channel, and the regenerative heat exchanger used for argon cooling. The enthalpy extraction remained low (= 17.6%) owing to the large pressure loss and as a result, the thermal efficiency of the closed loop remained only 21.6%. The enthalpy extraction and the thermal efficiency became maximal at the optimal inlet total pressure of 0.60 MPa. At inlet total pressure lower than the optimal one, the electric conductivity, the flow velocity, and the electric efficiency became higher. However, the total pressure ratio (= exit/inlet) in the MHD channel became larger particularly at low inlet total pressure because of the increase in the pressure loss due to pebble bed and wall friction. These led to the existence of the optimal inlet total pressure. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 143(1): 27–38, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10118     

Effects of fluid flow on the performance of a subsonic nonequilibrium disk MHD generator

The fluid flow and performance of a nonequilibrium disk MHD generator with subsonic flow are examined by time‐dependent two‐dimensional r–z numerical simulations. It is found that the development of the boundary layer is enhanced with increasing load resistance, as is the case in supersonic generators. The development of the boundary layer affects not only the performance of the generator but the thermal input to it, in contrast to supersonic generators. These facts lead to considerable departures from the performance predicted by a quasi‐one‐dimensional simulation and suggest that two‐dimensional design of the generator channel, taking account of boundary layer development, is necessary in order to assure high performance of a subsonic generator. © 2000 Scripta Technica, Electr Eng Jpn, 133(3): 18–25, 2000     

An analytical study of the plasma conditions and performance of an MHD generator

In order to investigate the effects of plasma conditions on fluid‐dynamical prediction of the performance of an MHD generator, local steady‐state calculations are employed. The effective Hall parameter and effective electrical conductivity are estimated by taking the linear theory of ionization instability into account. The results of analytical calculations are compared with experimental ones. Although a fully ionized seed condition, which suppresses instability, provides the highest power generation performance, the condition could be realized only at a high seed fraction in the experiments. It is suggested by the analysis that the fully ionized seed plasma produced at a low seed fraction is desirable in order to achieve high performance. The analysis implies that instability due to insufficient or excessive electron temperatures is a performance‐limiting factor. The effects of plasma conditions on performance are clearly explained by the present simple analysis. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 144(2): 9–15, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10196     

Power control of coupled nonequilibrium disk MHD generator and line-commutated inverter system

A new power control method is proposed which is suitable for the MHD power generation system which consists of nonequilibrium disk generator and line-commutated inverter. The thermal input of the generator is controlled by changing the inlet stagnation pressure, whereas the seed mass flow rate instead of the inlet stagnation pressure is utilized as a manipulated variable of power control system. It is possible that the proposed method can realize both high performance for part load operation and fast output power control of which the time constant is much shorter than the response time of thermal input. Numerical simulations are carried out for the MHD power generation system connected to infinite bus and then it is confirmed that the system is stable and shows excellent power control performance.     

Power Generation Experiments with a High Temperature Inert Gas Plasma Faraday Type MHD Generator

MHD power generation experiments have been conducted by using a single‐pulsed shock‐tunnel facility, where a high‐temperature inert gas (pure argon) at a fixed total temperature of 9000 K is introduced into a linear Faraday generator without seeding. The fluctuations in the output power and light emission from the plasma are found to be small, and the pure inert gas plasma seems to be rather consistently free of ionization instability. The output power is improved by increasing the magnetic flux density in near‐quadric fashion and the enthalpy extraction ratio does not depend on the inlet total pressure (11.2% to 12.9% for 0.063 MPa to 0.105 MPa). The generator performance obtained is competitive with or superior to that of existing seed plasma MHD generators.     

The effect of an externally applied radio‐frequency electromagnetic field on the performance of a disk MHD generator

The effects of an externally applied radio‐frequency (rf) electromagnetic field on the nonequilibrium performance of a disk MHD generator were examined experimentally. As a preliminary experiment, plasma production by the applied rf electromagnetic field was attempted in the disk generator (Disk‐PIA), in which rf induction coils were embedded in the one‐side disk wall, under the conditions of no seeding, no flow, and no magnetic field. From the results of the preliminary experiment, it was confirmed that the argon plasma (～110 Torr) was produced uniformly in the azimuthal direction by the rf electromagnetic field even in the presence of exposed anodes in the faced disk wall and metallic support at the disk center. In MHD power generation experiments with the Disk‐PIA installed in the shock‐tube facility, the increase in the electrical output and more indiscrete discharge attributed to the rf electromagnetic field were verified with good reproducibility for the first time. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(4): 46–53, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10009     

Numerical performance simulation of frozen helium plasma disk MHD generator

MHD electrical power generation with frozen helium plasma (FHP) is examined numerically. The FHP can be initiated by preionized helium without the alkali metal seed at the generator inlet. Since the three‐body recombination coefficient of helium ions is low at electron temperatures above 5000 K, the ionization degree can be kept almost constant in the entire region of the generator channel. The r?θ two‐dimensional numerical results show that the performance of the FHP MHD generator is comparable to that of the seeded plasma MHD generator, if the additional power consumed to preionization is ignored. In the FHP MHD generator, the ionization degree at the inlet should be controlled precisely, as well as the seed fraction in the seeded plasma MHD generator. Under an adequate inlet ionization degree for sustaining the FHP plasma, the plasma maintains the uniform structure. On the other hand, a slightly excess ionization degree causes a strong Lorentz force in the upstream region of the generator, deteriorating the generator performance. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(3): 26–33, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10030     

Two-dimensional stability of an open-cycle disk MHD generator: Effects of electrical boundary conditions

Two-dimensional stability analyses for open-cycle supersonic disk MHD generators are carried out which take into account electrical boundary conditions. A method of r-θ two-dimensional linear stability analysis for supersonic disk MHD generators is proposed which examines the time growth rate of perturbations. The growth rate is determined by the characteristic equation which is derived from the electrical boundary conditions. Whether the perturbations grow or decay is judged diagrammatically in a way similar to the Nyquist method. A coal-fired outflow supersonic disk MHD generator of commercial scale is analyzed under several types of boundary conditions. The stability is much affected by the electrical boundary conditions and also by the azimuthal wavenumber of disturbances. Two-dimensional analysis has revealed an azimuthally nonuniform instability in one of the load sections of the generator, where no instability is found in the one-dimensional analysis. The analysis also shows that the instability can be suppressed by subdividing the load section with control electrodes. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 120(4): 23–30, 1997     

Transient phenomena of disk MHD generator due to change of load resistance

The results of an experimental study on transient phenomena in a closed cycle disk MHD generator are described in this paper. The transient phenomena were caused by a steplike change of load resistance during testing of the shock‐tube driven disk MHD generator. The load resistance was varied by using an IGBT (insulated gate bipolar transistor) installed in the load circuit. When the load resistance was changed from 0.096 Ω to 2.5 Ω, overshoot of the Hall output voltage and of the Hall electric field was observed, and a large fluctuation of static pressure was also observed. At the same time, a spikelike increase of the cesium recombination continuum and line spectrum appeared just after the load change. The results of quasi‐one‐ dimensional numerical simulation indicate that the observed overshoot was caused by the following phenomena: (1) a steep reduction of the Hall current and a steep increase in both the Faraday current and the electrical conductivity and (2) a slow reduction of the gas velocity due to the enhanced retarding force. Furthermore, the measured spikelike increase of the radiation intensity was ascribed to an increase of electron temperature and electron number density due to a steep increase of Joule heating. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 175(4): 34–42, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21004     

Numerical simulation of blow‐down closed‐cycle disk MHD generator

Numerical simulations of the closed‐cycle disk MHD generation experiment with Tokyo Institute of Technology's Fuji‐1 blow‐down facility are performed. In the calculations, the r–z two‐dimensional time‐dependent simulation code developed by the authors that can take the effect of water contamination into account is used, and the experimental conditions of Run A4109 operated by Disk‐F4 generator are selected as the numerical conditions. When the water contamination is the lowest level realized in the experiments, the simulation results coincide with the experimental results reasonably well, though there exist some discrepancies caused by inaccuracy of used basic plasma parameters, limitations of the two‐dimensional approximation, and so on. The voltage–current curve is almost linear, indicating that the MHD interaction is relatively weak and the flow field is mainly determined by the back‐pressure. The increase of the water contamination level results in decreased seed ionization rate at the generator channel inlet, leading to the steep deterioration of the generator performance. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(2): 46–54, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10335