NUMERICAL STUDY OF THE ELECTRODYNAMICS BEHAVIOR OF THE CDIF MHD GENERATOR

The electrical characteristics of the diagonally connected MHD generat or are studied analytically using a two-dimensional, time dependent nu merical modeling technique which is based on a finite element mathemat ical formulation for electrodynamics. The analysis is directed at stud y of the near electrode electrical behavior as influenced by slag cove rage. The Component Development Integration Facility (CDIF) 1A(4) gene rator is analyzed, and experimental results from CDIF testing are used as boundary values of the electrical model. Simulation results agree well with CDIF experimental results, i.e. the electrical measurement f or the electric field and current density based upon Faraday voltage a nd inter-electrode voltage. By the influence of the Hail electrical fi eld, the current patterns are slightly complex in the boundary layer. Because of the thermal insulation effect of the slag coverage, the cur rent transport is maintained by diffuse discharge through the boundary layers. Through elevated electrical conductivity of the slag and the strong influence of the Hall effect in the boundary layer, the equipot ential lines bend into complex patterns near the electrodes. The numer ical simulation was also performed considering the effect of slag pola rization. The leakage current in the slag layer had some effect on the behavior of the slag. Slag polarization causes a reversed current phe nomenon by which a cathode exhibits operation of an anode within the s lag layer. The high electrical conductivity of the slag is a main fact or to support leakage currents and are currents in the slag layer. A l ocal blowout of the slag can be supported by the ''Fuse Theory'', wher e the slag leakage current is locally broken by leakage and are curren ts, much like a fuse. The damage of electrode and insulator walls :Is caused by local concentrations of the current density and the large el ectric field near the electrodes. (C) 1998 Elsevier Science Ltd. All r ights reserved.