Susumu Shioda

Comparative studies of the performance of closed cycle disk MHD generators using argon, helium and an argon-helium mixture

Abstract Comparative studies of the performance of closed cycle disk MHD generators using argon, helium and an argon-helium mixture are performed under the concept of fully ionized seed. Calculations show that either pure argon or pure helium is desirable as an inert gas in closed cycle MHD generators compared to the mixture of argon and helium and that a typical MHD channel for helium becomes compact. In typical disk generators, it is found that partial load operation with high efficiency can be established, and that fluctuations of the seed fraction are permitted within the limits of about ±3% and ±6% for the disk generator using argon and helium as inert gases, respectively. Furthermore, it is shown that a stable plasma can be maintained for a wide range of gas temperature by adjusting the seed fraction.

Magnetohydrodynamic power generation experiments with Fuji-1 blowdown facility

Experimental results of nonequilibrium plasma magnetohydrodynamic (MHD) power generation from the Fuji-1 blowdown facility are presented. The Fuji-1 experiments have been conducted since 1983, and the disk-shaped MHD generators called Disk-F3a, F3r, and F4 have been tested during the last decade. In the experiment with the newest Disk-F4 generator, which was designed based on the results of previous experiments with the Disk-F3a and F3r generators, an output power of 506 kW and an enthalpy extraction ratio of 18.4% for thermal input of 2.75 MW were simultaneously obtained. During the experiment, however, the deposition of seed material on the electrodes and the insulator walls was revealed, and large amount of impurity (water vapor) contamination in the working gas was detected. In the last experiment the stainless-steel-coated anodes were used instead of copper anodes to prevent the seed material from depositing on the generator walls, and the impurity contamination was reduced by increasing the bottom temperature of the heat exchanger. Consequently, an output power of 544 kW for thermal input of 3.38 MW and an enthalpy extraction ratio of 18.9% for thermal input of 2.17 MW were successfully demonstrated. Each value is the highest among those achieved with the Fuji-1 facility.

Measurements of properties concerning isentropic efficiency in a nonequilibrium MHD disk generator

The isentropic efficiency and the effective Hall parameter in a nonequilibrium disk MHD generator have been successfully evaluated on the basis of the experiments under high enthalpy extraction conditions. Special attention is devoted to measuring the exit total pressure and the Faraday current. The maximum isentropic efficiency achieved in the present experiments was 46% with the enthalpy extraction ratio of 31.6%. The experimentally obtained values of the effective Hall parameter covered a range of 2-3.

Improvement of enthalpy extraction over 30% using a disk MHD generator with inlet swirl

Abstract Performance of a disk-type CCMHD generator has been investigated. In the present power generation experiments, special attention has been devoted to the effect of inlet swirl on generator performance. In order to clarify this effect, one-dimensional numerical simulation has also been performed. The results showed that the enthalpy extraction ratio was successfully improved up to 32.5% by employing inlet swirl with the swirl ratio S(= U 0 U r ) of 1. Static pressure and Hall potential distributions were measured and showed that the inlet swirl reduced the steep increase in static pressure owing to the strong Lorentz force at the inlet of the disk channel. Hence, relatively low static pressure and, thus, high Hall parameter were kept throughout the channel, and therefore, the remarkable increase in output performance was achieved. Numerical simulation can qualitatively confirm these experimental results well. Realization of high Hall parameter and high enthalpy extraction with smaller pressure ratio of inlet to exit for the case with inlet swirl led to improvement of the isentropic efficiency.

Experimental studies of closed cycle MHD power generation with FUJI-1 blow-down facility

Abstract Recent results of power generation experiments with an improved heat exchanger system in the FUJI-1 facility were described. One of the main purposes was to study the effect of working gas temperature on generator performance. The results with argon working gas showed that the gas temperature of 1850 K is enough to eliminate the effect of inlet relaxation under the present experimental conditions and that gas temperature does not greatly affect the output performance so long as the inlet relaxation is not significant. The radial component of velocity was successfully measured with high time resolution by means of the cross-correlation method. The effect of seed fraction on the measured velocity was discussed. For the case of helium working gas, the voltage drop owing to an inlet relaxation was remarkably decreased, and improvement in both output power and enthalpy extraction can be observed by the increase of gas temperature. The voltage drop still existed at the inlet of the channel, and therefore, higher gas temperature and higher seed fraction are required in order to achieve higher generator performance.

High enthalpy extraction experiments with Fuji-1 MHD blow-down facility

Abstract Recent experimental results of closed cycle MHD electrical power generation with the “Fuji-1” blow-down facility are presented. In the experiment with Disk-F4 MHD generator, which was conducted with a modified seed injection system in 1997, an enthalpy extraction ratio of 18.4% was successfully demonstrated with a large output power of 506 kW. This enthalpy extraction ratio is the highest among those achieved with the Fuji-1 facility. The experimental results also revealed the electrical characteristics of the generator installed in the blow-down facility. The decline in the output power and its recovery were observed at the early stage of the power generation run. This fact could be attributed to the attachment of seed material to the generator walls and to its detachment, related to the relatively slow rise in temperature on the wall surface. It was verified for the first time in the Fuji-1 experiment that the reduction of impurity contamination resulted in improvement in the generator performance.

High enthalpy extraction from a helium-driven disk magnetohydrodynamic generator

A power-generation experiment with a disk MHD generator driven by potassium-seeded helium was made. High values of the output power density and of the enthalpy extraction have been obtained. For helium temperatures between 2200 and 2400 K, an output power density of 120 MW/cu m and an enthalpy extraction of 20.4 percent have been measured. The measured static pressure distribution has shown that strong gasdynamical shock has not been observed in the MHD channel under this high enthalpy extraction. It has been suggested that the disk generator performances can be predicted by one-dimensional calculations with ideal plasma parameters for the case of no negative potential region at the channel inlet and no shock formation in the disk generator. 11 refs.

Unsteady Discharge and Fluid Flow in a Closed-Cycle Disk MHD Generator

Unsteady electrical discharges in a nonequilibrium disk MHD generator and its effects on the flowfield are studied theoretically. Numerical results obtained from time-dependent and one-dimensional MHD equations have shown a periodic motion of the discharge, which induces fluctuations of Hall current and flowfield. Repetitional frequency of the discharge becomes higher with increasing seed fraction and external load resistance. When Joule heating is large, the unsteady discharge becomes limited only near the anode, and a steady discharge dominates over the disk generator. 17 references.

Boundary layer effects in He and Ar driven disk MHD generators

Abstract A two-dimensional compressible turbulent boundary layer model is adopted to predict the boundary layer characteristics of the 100 MW thermal input supersonic disk MHD generator walls for helium and argon under various enthalpy extraction conditions. The results show that the boundary layer thickness increases downstream in the channel for both argon and helium, and for helium, there occurs a boundary layer separation under high enthalpy extraction conditions. A slow variation of the Faraday current is observed through the boundary layer, while the Hall current decreases sharply, and the direction of the Hall current gets reversed in the vicinity of the insulator wall at the channel downstream end. This effect is observed to be more prominent for helium than for argon. The percentage of pressure loss through friction is found to be more for argon than for helium, while the heat loss is observed to be more for helium than for argon.

Dynamic properties of nonequilibrium plasma in disk MHD generator

The realization of the stable plasma due to the fully ionized seed has been dynamically confirmed in a channel of the closed cycle disk generator by solving time-dependent MHD equations. The relaxation process is examined near the inlet of the disk generator. In the stable state, as the load resistance increases, the width of the relaxation region becomes narrower and, as a result, the uniformity of the plasma in a whole channel becomes better. The influences of the inlet conditions on changes of the relaxation region are also examined.