Takayasu Fujino

Experimental studies on performance of a nonequilibrium disk MHD generator with radio-frequency preionization

The possibility of the improvement in performance of a nonequilibrium disk magnetohydrodynamics (MHD) generator by externally applying a radio frequency (RF) electromagnetic field (RF preionization) was examined experimentally. The MHD power generation experiments were carried out using a shock-tube driven disk MHD generator with the RF induction coils for the two inlet stagnation temperatures of 2275(/spl plusmn/75) K and 2650(/spl plusmn/50) K. As a result, under the conditions of both high and low stagnation temperatures, the output power was increased by the RF preionization. The increase was markedly observed for the low inlet stagnation temperature, where the plasma could not be produced only by the Joule heating attributed to a self-excited electromotive force. For the high inlet stagnation temperature, the plasma state in the MHD channel was improved by the RF preionization, leading to the increase in the output power. For the low inlet stagnation temperature, the marked increase in the output power by the preionization was not only because applying the RF electromagnetic field triggered the plasma production by the Joule heating attributed to a self-excited electromotive force but also because the plasma with the high electrical conductivity was produced in the more upstream region of MHD channel by the Joule heating attributed to the RF electromagnetic field.

Numerical Study of Thermal Protection Utilizing Magnetohydrodynamic Technology in Super-Orbital Reentry Flight

The present study investigates the influence of the MHD flow control on the convective and radiative wall heat fluxes under the condition of super-orbital reentry flight. Plasma flows around a capsule body are computed by a 2-D computational MHD code. The radiative wall heat flux is calculated by “SPRADIAN” in a non-coupled manner with a computation of plasma flows. Applying the magnetic field leads to a decrease in convective wall heat flux, and leads to an increase in radiative wall heat flux. The increase in radiative wall heat flux is attributed to the expansion of shock layer, the rise of plasma temperatures and the increase in ion species by applying the magnetic field. Under the strong MHD interaction, the total wall heat flux, which is the summation of convective and radiative wall heat fluxes, increases by applying the magnetic field due to the increase in radiative wall heat flux.

Optimization of Seed Fraction and Performance Analysis for Commercial-Scale Faraday-Type MHD Generator

In this study, the seed fraction is optimized for the Faraday type MHD generator by means of the quasi-one-dimensional analysis to design the generator which is suitable for the regenerative and circulation type coal combustion power generating system, and the designed generator is examined in detail by the two-dimensional analysis. The following results have been obtained: (1) the enthalpy extraction ratio increases with the channel length, but the increase shows the tendency of saturation, (2) the seed fraction has an optimal value between 3 wt% and 4 wt% for a 12 m MHD channel with 24.0 % of the enthalpy extraction ratio, (3) the output power in quasi-one- and two-dimensional analyses is almost the same in the first 6 m region, and (4) the electrodes voltage drop (about 200 V) in the two-dimensional analysis is close to the value assumed in the quasi-one-dimensional analysis.

Numerical Simulation of Unsteady Behavior of Rotary Arc Plasma under Magnetic Field

We are currently developing a time-dependent, three-dimensional computational magneto-plasma-dynamics (MPD) code for simulating a rotary gas circuit breaker utilizing an external applied magnetic field. In order to test the computational code under development, we have conducted the numerical simulation of arc plasma in a cylindricalshaped chamber filled with SF6 gas in the presence of externally applied magnetic field. The present paper describes details of the MPD model in the computational code, and also shows numerical simulation results.

Three-Dimensional Analysis of Generator Performance of Large-Scale DCW-MHD Generators with Circular and Square Cross-Section

The purpose of this study is to examine the influence of shape of cross-section of scramjet driven DCW-MHD generator on generator characteristics under several load conditions by three-dimensional numerical analyses. Under the optimum load conditions, the electric power output becomes over 10 MW for both generators with circular and square crosssection. The generator performance of both generators is almost equal. Under the open and short circuit condition, the Lorentz force pushes the flow against the upper or lower wall, and results the growing of the boundary layer on the opposite wall. The fluid pushed by the Lorentz force flows along the side wall. Especially, under the open circuit condition, the eddy-like secondary flow is induced in the boundary layer. The appearance of the boundary layer becomes different from each cross-sectional shape by the eddy-like secondary flow.

Effect of Inlet Swirl on Performance of Commercial Scale Disk Magnetohydrodynamic Generator

Two-dimensional (r-z) numerical simulation has been carried out to investigate the effects of inlet swirl and applying radio frequency (RF) electromagnetic field on the generator performance of a commercial scale disk magnetohydrodynamic (MHD) generator. With inlet swirl, the fluid work against circumferential Lorenz force is enhanced and the stagnation pressure loss due to joule dissipation is reduced. The enthalpy extraction ratio and the isentropic efficiency are, therefore, improved by inlet swirl. The excessive selfexcited joule heating in the case with inlet swirl is suppressed by applying the RF electromagnetic field, which results in the improvement in the isentropic efficiency. In total, the net enthalpy extraction ratio and the isentropic efficiency are, respectively, improved up to around 29 % and 70 % by inlet swirl and applying the RF electromagnetic field.

Three-dimensional Numerical Simulation of Cylindrical Shaped Magnetohydrodynamic Generator under Strong Magnetohydrodynamic Interaction

The present study carries out three-dimensional numerical simulations of fluid dynamics and electrodynamics in a cylindrical and a rectangular shaped Faraday-type MHD generator with continuous electrodes under strong MHD interaction. An analytical condition is based on the experimentally operating condition of the pulsed MHD generator “Pamir-3U” with rectangular cross section. Numerical results show that the electric power output of cylindrical shaped MHD generator is almost the same as that of rectangular shaped MHD generator under low voltage condition. Under high voltage condition, the electric power output of cylindrical shaped MHD generator is larger than that of rectangular shaped MHD generator. The eddy current appears near insulating wall on cross section of cylindrical shaped MHD generator. Under the high voltage condition, the eddy current is caused by the difference of the electric field between the side of electrode edge and the others. Under the low voltage condition, the eddy current is due to the electromotive force directed opposite to the core current flow in the boundary-layer separation region.

Performance Characteristics of Commercial Scale Disk MHD Generator with Plasma Production Technique

§R-z two-dimensional numerical simulations have been carried out to explore the usefulness of the rf preionization and the influences of asymmetric configurations of anode electrode and rf coil on the generator performance for a commercial scale, large disk-shaped MHD generator with the thermal input of 1000 MW. The numerical results have clearly demonstrated that the rf preionization is useful for improving the plasma state and the generator performance, and also that the asymmetric configurations of anode electrode and rf coil have little negative influence on the generator performance.