Feasibility improvement in performance of a disk CCMHD generator by means of an electromagnetic diffuser

The feasibility of improving the performance of a disk CCMHD generator by means of an electromagnetic diffuser is investigated by a two‐dimensional numerical simulation which provides information on the development of the boundary layer. The Mach number at the exit of the electromagnetic diffuser can be controlled by a load resistance between electrodes provided in the diffuser. The total enthalpy extraction ratio and the adiabatic efficiency can be improved by optimizing the load resistance, because an additional power output can be obtained in the electromagnetic diffuser without a change in the total pressure at the exit. © 2000 Scripta Technica, Electr Eng Jpn, 133(3): 26–34, 2000     

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     

Characteristics of flow and plasma under high MHD interaction in nonequilibrium disk MHD generator using argon

Results of experimental studies on behavior of a supersonic flow and of a nonequilibrium plasma in a disk MHD generator are presented. The experiments with cesium seeded argon were carried out under high MHD interaction conditions. Effects of seed fractions on static pressure distributions, flow Mach numbers, electron temperatures and uniformity of discharge in the disk MHD channel were investigated. The results have shown that the flow is kept supersonic throughout the disk MHD channel when a sufficient Joule heating exists in a supersonic nozzle and the seed is fully ionized. It was found that there was an optimum seed fraction at which the power output became maximum and, at the same time, the seed was fully ionized. Furthermore, an almost uniform discharge due to the full ionization of seed was observed. It is noted that enthalpy extractions and adiabatic efficiencies were increased remarkably, and the highest enthalpy extraction of 26.5 percent was achieved for cesium seeded argon. However, adiabatic efficiencies remained still low due to large pressure losses.     

Measurement of Faraday current in a disk MHD generator

The Faraday current flowing in a circumferential direction in a disk MHD generator was successfully measured using the Rogowski coil method. This fact allowed us to estimate the radial distributions of fluid and electrical properties, such as the gas flow velocity, Hall parameter, and electrical conductivity, from the experimental data. In this paper, a system for measuring the Faraday current measuring system and its calibration method are described in detail. As an example of the experimentally estimated properties, factors governing total pressure reduction along the radial direction are described. © 1998 Scripta Technica, Electr Eng Jpn, 125(4): 19–25, 1998     

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     

Experiments of the improvement in the performance of a disk CCMHD generator

The present experiment has aimed at the improvement in the performance of a shock‐tube‐driven disk CCMHD generator. For that purpose, an experimental setup was arranged as follows: (1) An inlet swirl was introduced. (2) The area ratio of the disk generator was small. (3) A cesium‐seeded helium gas was used as a working medium. Not only these factors but also the production of a homogeneous plasma contributed to outstanding performance characterized by an isentropic efficiency of 63% and an enthalpy extraction ratio of 30.8% at a stagnation temperature of 2250 K and stagnation pressure of 0.14 MPa. Furthermore, a maximum electrical power output of 1.23 MW and a maximum power density of 297 MW/m³ were obtained. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(2): 24–31, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20024     

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.     

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     

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     

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     

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     

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     

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     

Plasma behavior in a non‐equilibrium disk MHD generator with a spatially non‐uniform seed fraction

The influence of azimuthal non‐uniformity of the seed fraction on plasma structure and performance in a non‐equilibrium disk MHD generator is investigated with a two dimensional r–θ numerical simulation. It is found that a locally high seed fraction causes mainly non‐uniformity of gas‐dynamical properties, whereas a locally low seed fraction develops a non‐uniform plasma. Both locally high and low seed fractions reduce generator performance considerably. These results suggest a spatially uniform seed fraction should be required for high power generation. ©1999 Scripta Technica, Electr Eng Jpn, 126(4): 48–54, 1999     

Operation and control of coupled nonequilibrium disk MHD generator and inverter system under power line fault condition

Numerical simulations of detailed time‐dependent behavior are performed on a simulation model in which a coupled system of nonequilibrium disk MHD generator and line‐commutated inverter is connected to an infinite bus through the transmission line, showing that continuous operation of the system is usually possible even when a power line fault occurs near the system. Then, time‐dependent swing simulations are carried out on another simulation model in which the MHD/inverter system and a synchronous generator are connected in parallel to an infinite bus through the common transmission line, revealing that the rotor angle swing of the synchronous generator caused by the power line fault can be effectively suppressed by the fast output power control of the MHD/inverter system. © 1999 Scripta Technica, Electr Eng Jpn, 127(3): 13–24, 1999     

Performance and conceptual design of superconducting magnet for disk MHD generator

This paper describes superconducting magnets coupled with two kinds of disk-type MHD generators. One is coupled with a disk generator in the closed-cycle MHD experimental facility FUJI-1. The other is for a full-scale disk MHD generator. These are split-pair magnets. In the magnet for the FUJI-1 facility, a unique structure which supports the coils against the electromagnetic force has been fabricated and the magnet has been operating stably. During MHD power generation experiments, an induced voltage across the terminals of the coil was measured. A magnitude of the Faraday current in the generator was calculated from this induced voltage. A possible construction of magnetics for a full-scale disk MHD generator is indicated. It is suggested that a high performance of the generator (output power density of 0.3-1 GW/m³) can be obtained with high magnetic field up to 10 T.     

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     

Analysis of performance characteristics of pulsed MHD generator with gas–liquid two‐phase flow

A preliminary analysis of two‐phase flow in the pulsed MHD generator Pamir‐3U is carried out. The two‐fluid model for dusty gas flow is applied to treat the two‐phase working body which consists of combustion gas and liquid particles of Al₂O₃. One‐dimensional time‐dependent calculations show that the velocity lag and the thermal lag between the two phases are large when the particle diameter is 15 μm. The lags become small when the diameter is small because the decrease of the diameter increases the momentum transfer and the heat transfer between the two phases. When the large Lorentz force develops a shock wave, the interaction between the two phases relaxes the shock wave. The increase of the particle diameter decreases the channel current and the power output because the increased diameter decreases the energy conversion from the liquid phase. © 1999 Scripta Technica, Electr Eng Jpn, 127(2): 15–23, 1999     

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