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.     

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.     

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     

Plasma behavior and characteristics of a pulsed‐laser‐driven MHD electrical power generation

The fundamental electrical power generation experiment of a pulsed‐laser‐driven magnet hydrodynamics generator with a divergent channel and segmented electrodes has been conducted with a rough estimate of gas heating efficiency of laser energy. The output energy is increased with the decrease in the initial filling gas pressure because of the increase in the gas velocity and the electrical conductivity with the gas temperature. The output power is surely improved in comparison with the previously examined generator with constant height channel and continuous electrode. About 70% of the incident laser energy is absorbed and less than 20% is transferred to the blast wave energy at low initial filling gas pressure in the present experimental setup.     

Performance analysis of experimental‐scale scramjet engine driven DCW‐MHD generator

Numerical analyses of the experimental‐scale scramjet engine driven magnetohydrodynamics generator implemented in the Hypersonic Vehicle Electric Power System project have been carried out to clarify plasma behaviors and power generation characteristics. Three‐dimensional numerical analyses have been performed under the two inlet conditions: one is the uniform inlet temperature condition, and the other is the nonuniform inlet temperature condition. Under the nonuniform inlet temperature condition, the generator performance approximately agrees with the experimental result. The tendency of the voltage loss is also reconstructed near the power takeoff electrodes though the voltage loss is smaller than that observed in the experimental result. The electric power output under the nonuniform inlet temperature condition is 40% smaller than that under the uniform inlet temperature condition. This is because the ratio of the Joule dissipation to the work by the Lorentz force increases owing to the decrease of active generator region as the current concentrates in the high‐temperature region when the inlet temperature nonuniformity is considered. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Numerical Study on Periodic Structure Evolution of Output Power in MHD Generator by Using Pulse‐Assisted Ionization Discharge

A pulse‐assisted ionization discharge applied to a magnetohydrodynamic (MHD) generator is proposed as a technique to increase an electrical conductivity of working fluid. In this study, a periodic structure of output power in the MHD generator by using pulse‐assisted ionization discharge was evaluated. As a result, the discharge electrode length and the velocity of working fluid affect the discharge current distribution. The periodic structure of output power was observed in the several conditions. When the velocity of working fluid is roughly same as the sound speed, the periodic structure of output power was not observed.     

Fundamental experiments of radio‐frequency preionized inert gas plasma MHD electrical power generation

A seed‐free radio‐frequency (RF) preionized inert gas plasma MHD electrical power generation has been first demonstrated in fundamental experiments with a shock‐tunnel facility. An enthalpy extraction ratio of 2.6% was successfully obtained even under an inlet total temperature of 2200 K at which the power generation can be operated continuously. Since the RF input power required for the preionization tends to be increased for lower inlet total temperature, the reduction of the RF input power is needed for further improvement in the total performance.     

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     

Fundamental experiment and numerical simulation of pre-ionized inert gas plasma MHD electrical power generation

The experiments of pre-ionized inert gas plasma MHD electrical power generation are conducted, and the performance and plasma behavior in the experimental generator are examined through time-dependent r-_ two-dimensional numerical simulation. In the experiment, an enthalpy extraction ratio of 4.01% has been obtained with a disk-shaped MHD generator with radio-frequency pre-ionization. In the numerical simulation, at an assumed inlet electron temperature around 5600 K (inlet ionization degree 0:10 × 10⁻⁴)_6600 K (1:36 × 10⁻⁴), the plasma structure is similar to the non-uniform structure observed in the experiment. An enthalpy extraction ratio around 2_5% matches well with that in the experiment. At a suitable inlet electron temperature of 7000 K (3:15 × 10⁻⁴)_8000 K (1:79 × 10⁻³), although non-uniform plasma structure still occurs, a high enthalpy extraction ratio over 10% is expected.     

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.     

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     

Transient response of closed‐loop MHD experimental facility

Transient responses of a closed‐loop MHD experimental facility from nonpower generation to power generation have been investigated by means of time‐dependent quasi‐one‐dimensional numerical simulations. For the long‐time continuous power generation experiment, the time required to obtain the steady state for the power generation is estimated to be approximately 20 hours. By increasing the electrical input power to the heater as an exponential function of time, the temperature increment of ceramics can be moderated. When the duration of the experiment is around 10 minutes, argon gas temperature at the exit of the heater hardly changes because of the large heat capacity of structure materials. It is found that the fluid disturbances are induced at the instant of the power generation and they propagate as they repeatedly reflect at the sudden change of duct shape. Since all of the induced disturbances attenuate approximately 0.4 second after the power generation, the time scale that the disturbances exist in the facility is estimated to be 1 second at most. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(1): 46–52, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20237     

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     

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     

大功率风力发电机转子温度场数值仿真

本文以一台1.5MW双馈风力发电机为例,研究发电机转子内流体流动与传热问题。根据发电机通风结构与传热的特点,建立转子1/8区域的三维求解模型,并采用CFD技术对求解域进行耦合求解,得出发电机转子内流体流动特点和温升分布规律。     

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     

Voltage‐current characteristics of subsonic disk CCMHD generator

Voltage–current characteristics of a subsonic disk CCMHD generator are examined by time‐dependent quasi‐one‐dimensional numerical simulations. The output voltage is found to be almost constant for load resistances higher than the designed value, whereas the output current is kept almost constant for lower load resistances. It is confirmed that at high load resistances the subsonic flow is maintained in the whole generator, and a steady and uniform nonequilibrium plasma is realized. The connection of the low load resistances causes flow choking at the generator inlet, leading to the supersonic flow. Then shock waves and ionization instability occur in the generator. © 2000 Scripta Technica, Electr Eng Jpn, 130(4): 58–65, 2000     

Internally Self‐Sustaining Electric Power Generation

The electrical double layer capacitor‐electrostatic induction electric power generation system (EDLC‐ESIG) undergoes an electric cycle consisting of three steps: energy storage by electrostatic induction, power generation, and initialization by electromechanical coupling. An internally self‐sustaining electric power can be generated by repetition of cycles with periods of the order of seconds. The objective of this paper is to show the design of EDLC‐cell configuration for practical use to produce constant power output. On the basis of energy densities of the conventional EDLCs for energy storage, the volumetric power density has been estimated to be 450 W/L for the discharge time of 10 s. Possibilities of commercial applications of the EDLC‐ESIG system to vehicles and high power generations in central station have been considered with respect to the power densities of the EDLC‐cells consolidated into a generation system.     

A High‐Efficiency Single‐Phase Utility Interactive Inverter with an Active Power Decoupling Function and its Control Method

The present paper introduces a single‐phase utility interactive inverter with a power decoupling function. In a conventional single‐phase inverter, power pulsation at twice the grid frequency appears in the input power. Hence, electrolytic capacitors having large capacitances have been connected to the DC input terminal to stabilize the input DC‐bus voltage. Because the lifetime of the electrolytic capacitor is relatively shorter than that of another component, the lifetime of the inverter is affected by the capacitor. In order to prevent such a problem, a novel single‐phase inverter circuit with an active power decoupling function is introduced. The pulsating power on the input DC‐bus line and the pulsated energy on the input DC capacitor is transferred to the energy in a small film capacitor. Hence, the extension of the inverter lifetime can be expected by substituting a small film capacitor for the large electrolytic capacitors. In addition, the loss in the power decoupling circuit is very small; hence, the reduction in the overall conversion efficiency of the inverter can be minimized. The effectiveness of the proposed method is verified using a 300 W experimental setup.