Experiments on the performance of a nonequilibrium disk MHD generator with helium

Power generation experiments have been conducted with a shock-tube driven disk-shape Hall-type MHD generator using cesium seeded helium gas. The generator performance relies heavily on a seed fraction rather than channel load resistance; suggesting that a plasma condition in a supersonic nozzle is quite responsible for the performance. It is inferred from characterizing the fluid-dynamical behavior by static pressure increase that keeping a higher total pressure ratio under the condition of the relatively lower seed fraction enable us to achieve the higher isentropic efficiency as long as appropriate electrical conductivity is obtained. Attempts to clarify the time- and spatial-variations of electron temperature and electron number density are indicative that the plasma behavior in an MHD channel has considerable effects on the generator performance as well as an inlet plasma condition does. One of the most revealing finding is the fact that the excessive nozzle resistance has been one of the performance-limiting parameters. The employment of the high seed fraction under the high nozzle loading condition results in large pressure loss and deterioration of the performance.