Kazumi Tsunoda

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.

Study of a Disk MHD Generator for Nonequilibrium Plasma Generator (NPG) System

Abstract Design and performance prediction studies of a disk type magnetohydrodynamic (MHD) generator which is applied to the non equilibrium plasma generator (NPG) system have been performed. The main objective of the present study was to find out whether a sufficiently high output performance demonstration is possible with the disk generator which is planned to be used for the NPG-MHD disk pulse power demonstration. A present numerical simulation showed that the original constant height channel could provide not more than 20% of enthalpy extraction because its channel shape could not sustain the working plasma in the stable regime against ionization instability throughout the channel. We concluded that, in order to obtain much higher generator performance, a detailed design of the channel shape was necessary. Design work has also been performed based on the concept that the local electron temperature must be kept at 5000K, i.e. the plasma must be controlled to locate at the center of the stable regime. With the designed channel, enthalpy extraction of up to 40% and output power of 7.2 MW can be successfully expected under the thermal input of 18 MW. In addition, the designed channel requires no major modification of the supersonic nozzle, the inlet swirl vanes and the configuration of the magnet system.

High-enthalpy extraction demonstration with closed-cycle disk MHD generators

Recent results of high-enthalpy extraction experiments with closed-cycle MHD disk generators are described. Power generation experiments were carried out with two types of facility: the shock tube facility with the Disk-IV generator and the FUJI-1-blow-down facility. In the shock tube experiments, the effect of channel shape on generator performance was studied using helium seeded with cesium as working fluid. A more divergent channel shape was effective in sustaining a high Hall field throughout the channel and achieving high generator performance even under the strong MHD interaction. High-enthalpy extraction of 27.3% was achieved. Furthermore, these experimental results agree well with the result of one-dimensional calculations. In the FUJI-1 blow-down experiments, the effect of stagnation gas pressure on performance was studied with a working gas of seeded argon. The highest enthalpy extraction ratio of 15.7% was achieved with the lower stagnation pressure of 0.46 MPa, whereas the largest output power of 516.7 kW and power density of 70 MW/m{sup 3} were extracted with the nominal stagnation pressure of 0.6 MPa. This suggested the possibility of a part-load operation without significant degradation of generator performance by reducing stagnation pressure.

Turbulent near-wakes of periodic array of square blocks on a plate

Abstract This paper describes the experimental study of the flow structure past square blocks located on a ground plate with various spacings. The experiment was carried out in a circuit type wind tunnel of a 200 × 200 mm working section and 2000 mm in length at a Reynolds number of 990, which is based on the free-stream velocity and the height of block. The test blocks, side length D = 23 mm and height H = 5 mm, were aligned at a regular spacing S in a square array on the lower wall of the test section, and the spacing was systematically varied to provide S H = 2, 3, 5, 7, 10, and 13 . The mean velocity and turbulence intensities were measured by a laser Doppler velocimeter (LDV). It was found that the spacing ratio S H = 7 is optimum to augment the turbulence intensity near the ground plate when the repeated blocks are aligned in a square array.

Numerical simulation studies on FUJI-1 experiments

Abstract Experimental results of the FUJI-1 disk generator have been discussed from the calculated results based on the quasi-one-dimensional model. The calculations have been performed for generators with different channel shape to investigate the effects of the area ratio on power generation performance. The increase of output power at the high load resistance regime with increase of area ratio has been qualitatively shown by calculations, however absolute values of the plasma properties in an MHD channel obtained from the calculations have not been in agreement with experiment values. To clarify the pressure loss mechanism, the influences of the plasma properties on the changes of stagnation pressure have been investigated analytically. It has been found that the strong Lorentz force takes a significant role in the pressure loss processes as compared with wall friction under a strong MHD interaction conditions. Furthermore, it has been suggested that a 100 MW class thermal input generator is required to reduce the stagnation pressure loss by wall friction with high gas velocity and high output power.

Improvement of the Performance of a Supersonic Nozzle by Riblets

We describe an experimental study of supersonic internal flow over a riblet surface mounted on a channel wall to reduce pressure loss and improve the performance of a supersonic nozzle. The magnitude of the static pressure in the pressure-rise region observed in channels with riblet surface became lower than that for a smooth surface, and the significance of its difference was indicated by uncertainty analysis estimated at 95 percent coverage

Effects of swirl on velocity-field uniformity in disk shape SOFC channel flow

Swirling flow behavior between two parallel disk shape plates was experimentally investigated with the aid of a particle image velocimetry (PIV). The experiment was performed at low Reynolds numbers (Re < 100) to simulate the practical operation in a disk shape planar-type solid oxide fuel cell (SOFC). To improve flow uniformity, we designed a new channel with circle involute shape current collectors. In the new channel, a swirling flow was generated and its velocity in a core region was kept at nearly constant value toward the channel exit. This trend was observed regardless of flow rates, and hence flow uniformity was achieved over the wide range of Reynolds numbers. This is because a flow passage consisting of two adjacent involute shape current collectors functions as a constat-area channel due to the geometrical property of the circle involute. In order to understand the above mentioned flow behavior, a swirling fluid motion in the channel with the circle involute shape current collector was investigated by using steady state Euler’s equation of motion. We confirmed that the velocity component in the flow direction was dominant compared with that in the other direction and played primary role to maintain a swirling motion through the centripetal acceleration term.Copyright

Effect of spacing ratio on flow over repeated two-dimensional square ribs on ground plane

This paper describes a detailed study of the flow structure over repeated two-dimensional square ribs on a ground plane for various values of S/D, and the optimum value of S/D to augment the turbulence intensity near the ground plane. The pitch between the centers of two adjoining square ribs was varied at S/D=2, 3, 5, 7, 9, 11, 13 and 17. The time-mean velocity and turbulence intensity were measured by Laser Doppler Velocimeter. The static pressure was measured by Pitot static tubes. As a result, it is concluded that the pitch ratio S/D=9 is optimum to augment the turbulence intensity in the groove between two adjoining square ribs, when the two-dimensional square ribs are aligned on the wall as a heat transfer promoter.