Electrode processes in MHD generators

Electrode processes strongly influence the performance and durability of an MHD generator. In this paper a theoretical analysis of these processes is made based on a model suggested by experimental work. According to these observations current transfer at the cathode usually occurs by means of small arc spots, while at the anode the discharge covers the electrode. The basic relations resulting from an energy balance within these discharges, Poisson´s equation for space charge, and the electrical and thermal boundary conditions are derived in terms of the properties of the ambient gas. The calculation of these properties for MHD duct gases is then described and special attention given to the perturbation of the ionization equilibrium resulting from charge transport within the discharge. Preliminary results of computer programs designed to carry out the calculation for open and closed cycle duct conditions are presented, and it is shown that under certain conditions the discharge part of the calculation can be presented as a unique set of curves, from which the running conditions and erosion can be calculated for any electrode material.