Effects of cathode slag polarization on MHD generator performance

A series of experiments was conducted on a slagging MHD generator to investigate the loss in channel performance brought about by slag polarization phenomena in which large reductions in slag resistivity are observed on the cathode wall. However, tests in which the seed was discontinued resulted in relatively no change in generated Hall voltage (about 500 volts) while power levels dropped to less than 1 kW, demonstrating minimal leakage in the slag layer. It is concluded that the cathode slag layer is not continuous but is periodically ''broken''. Shorting of Faraday currents in the presence of a Hall field results in increasing current concentrations at the downstream edge of the shorted group until sufficient joule heating is produced to locally remove or thin the slag layer and create an open insulator gap capable of sustaining the Hall voltage. The net effect was a resegmentation of the cathode wall from a design pitch of 1.5 cm to a pitch of between 4 and 10 cm depending on the iron oxide concentration in the ash.