Magnetohydrodynamic Generators

Magnetohydrodynamic (MHD) generators may be regarded as an attempt to find practical applications of magnetic forces on ionized gases at the lowest possible temperatures. A sketch of one elementary MHD generator configuration is shown in Fig. 1. Heated gas flows through the channel across magnetic field lines which are perpendicular to the plane of the drawing. A vertical EMF is induced which causes current to flow between the electrodes and through the load. Thus, as the gas expands through the channel, it does work on the magnetic field and produces electric power. The primary energy source for heating the gas may be either ordinary combustion or fission. For central power station using combustion the efficiency of a conventional steam cycle is limited by the upper temperature at which rotating machinery can operate. MHD offers the advantage that energy can be extracted from the gas at temperatures above those which can be withstood by solids. The chamber walls may always be cooled below the gas temperature, as is done in a conventional rocket. Suggested designs use an MHD generator for the upper part of the temperature range, i.e. from the combustion temperature down to the temperature at which the conductivity becomes too low for effective interaction with the magnetic field. At this temperature there is still significant heat energy in the gas so that a steam cycle is used to extract the remaining energy