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     

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     

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     

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     

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.     

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     

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     

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     

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 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     

Plasma Fluid Flow Behavior and Power Generation Characteristics in a High‐Temperature Inert Gas Plasma Faraday MHD Generator

The plasma fluid flow behavior and power generation characteristics in a Faraday magnetohydrodynamic (MHD) generator using a high‐temperature inert gas (argon) plasma have been examined in a time‐dependent two‐dimensional numerical simulation. The inhomogeneous and unstable plasma at an inlet total temperature of 7000 K results in reductions and fluctuations in the output power. The plasma becomes homogeneous and stable as the inlet total temperature increases to 9000 K. One of the reasons for the suppression of ionization instability may be weakness of the dependency of the electrical conductivity on the electron number density, because the Coulomb collision of electrons becomes dominant during deviation from Saha equilibrium.     

发电机组高中压缸通流部分的节能改造

国产引进型300 MW机组高中压缸效率低是一个普遍性问题。对机组高中压缸通流部分实施节能技术改造,包括更换喷嘴组、减少单齿汽封径向间隙、增设阻汽片等。随着300 MW汽轮机组通流部分改造技术日趋成熟,机组性能大大提高。改造后的热力试验表明,高压缸效率及热耗值均超过设计值,机组发电煤耗明显下降,取得了较好的经济效益和环保效益。