A numerical study of near electrode phenomena in the coal-fired MHD generator

Electrical characteristics of the diagonally connected MHD generator are studied analytically using a two-dimensional time-dependent numerical modeling technique developed at Yatsushiro National College of Technology. The modeling method is based on a Finite Element mathematical formulation for the generator electrodynamics. The analysis is directed at study of near electrode electrical behavior as influenced by slag coverage. Physical characteristics of the 1A4 MHD generator are used to fix the geometry of the generator analyzed and experimental results from CDIF testing to impose boundary values to the electrical model. In this fashion, a model to data type comparison can be inferred from the results. This simulations achieved agreed well CDIF experimental results based upon link current and inter-electrode voltage data obtained from the CDIF generator test. The following observations are drawn from the analyses. Slag plays the role by thermally insulating the electrode walls and influencing the electrode current transport. With slag coverage, the current becomes the diffuse discharge through the boundary layers. Through the influence of the Hall effect, the leakage current and are discharge near the electrodes, a current eddy is predicted driven by the Hall effect and Lorentz force. The electrode walls and insulators are subject to local concentrationsmore » of the current and large voltage differentials which should be reviewed in terms of observed damage to surfaces by these electric stresses.« less