Nonequilibrium MHD generator losses due to wall and insulator boundary-layer leakages

The current leakages through the channel walls, ground-loop paths, and insulator-wall boundary layers are examined, and simplified analytical models are developed for nonequilibrium Faraday MHD generators. The results indicate that high insulator wall resistance and high insulator boundary-layer resistance are considerably more important for supersonic generators employing nonequilibrium ionization than for those employing equilibrium or frozen ionization. The high electrical resistance for these current leakage paths is required to keep the attainable nonequilibrium electron density high and the electron-density relaxation length short. The analytical models should prove useful to experimentalists, both as a guide in designing MHD generator test sections and in the analysis and interpretation of experimental results. In particular, the models can be used to estimate the minimum acceptable channel dimensions, wall resistances, wall temperatures, and pre-ionizer performance required for good test results.