Numerical simulation of plasma and fluid behavior in the ISTEC-2 nonequilibrium disk MHD generator with multiple loads

Plasma and fluid behavior in a nonequilibrium disk magnetohydrodynamics generator with multiple loading has been investigated with a time-dependent three-dimensional numerical simulation. Particular attention is paid to the effects of the downstream load resistance and the influences of the middle electrode on the plasma and fluid flow. The possibility to improve generator performance by multiple-loading operation is also examined. It is shown that increase in the downstream load resistance raises the static pressure and decelerates the working gas in the upstream region. This is because the static pressure increase and the boundary layer development near the middle electrode have the same effects as the change of the outlet boundary conditions for the upstream region. It is found that the ionization degree of seed atoms is kept high on the middle electrode, whereas, the electron temperature is decreased rapidly. This results from the longer relaxation time of ion number density compared to that of the electron temperature. The multiple-loading operation leads to an improvement of the enthalpy extraction ratio. Isentropic efficiency, however, becomes somewhat lower under the multiple-loading condition. This is caused by the high static pressure and the low electrical efficiency under the high enthalpy extraction condition for the multiple loading.