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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 [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

The article discusses the effects of electric arc behavior and electrode temperature on the current distribution and the location of arc spots in the boundary layer of magnetohydrodynamic generator. Based on numerical analysis, the potential distribution between electrodes drop dramatically across the boundary layer. If the wall temperature in the arc is high, the heat flux is concentrated on the laminar layer due to the presence of high effective thermal conductivity. The arc spots move in three-dimensional space.

The article discusses the operational characteristics of a power consolidation circuit for Faraday-type magnetohydrodynamic generator. The fundamental characteristics of Christmas tree type and Master/Slave type consolidation circuits are discussed, as well as the electrical nonuniformities caused by slag polarization. A schematic diagram of Christmas tree type power consolidation circuit with electrodes is presented.

The high-temperature ceramic electrode for an open-cycle MHD generator is now under intensive study but it can not be used in practice today. Presently available electrodes are of low-temperature type and made of copper. Currents of such low-temperature electrodes are carried in an arc discharge mode if natural gas or heavy oil is used as fuel. The current and voltage distributions around the electrodes often become very non- linear due to the effect of negative voltages current characteristics of the arc current.

This article discusses a study related to diagonal-type MHD generator interconnected to the transmission line through an inverter. Since an MHD generator produces a dc output power, it aust be connected to an ac system through an inverter. The inverter is classified into two types, line and forced commutation types, depending upon its commutation scheme. The forced-commutated inverter has been used little so far in the power application field. The progress of semiconducting power switches in capacity, switching speed and computer-based control techniques will help develop inexpensive reliable forced-commutated inverters.