Experimental problems in magnetohydrodynamic power coversion

Part A of this thesis is concerned with the study of the mechanism of discharges in shock heated Argon between cold electrodes, in a configuration similar to that of a MHD generator. A model which describes the total voltage between the electrodes as a function of the current density J is proposed. This model takes into consideration boundary layer conditions and electrode processes. Experiments were carried out with different electrode cross sections to check the theory and its range of application. The current was found to vary smoothly with the voltage and reached higher values than the saturation ionic current density through the cathode sheath, so that field emission in the cathode is a conduction mechanism present in the high current regime. A determination of the profile of ne(electronic density) behind the shock front was also carried out using interferometric techniques. These results have been used in Part B of the thesis which is concerned with MHD Power Generation using the same facility and very similar geometry to that in Part A . The performance of the generator was studied with the help of a model which takes account of the finite dimensions of the electrodes This model was extended to a case when voltage electrode losses appear, and variations of the flow parameters and B due to the strong interaction were considered. Faraday and Hall configurations were used with different electrode/insulator ratios and external loads. The Faraday generator performance showed good agreement with the theory if electrode voltage losses were taken into account, and the power output was high. When the ratio insulator/electrode was small, power output dropped sharply due to leakage currents; a explanation is given and a parallel to the ease with high Hall coefficient is drawn. The influence of electrode losses on the performance is also studied. The Hall generator performance does not agree with the theory and the power output is very low. This is tentatively explained in terms of electrode voltage losses and shorting between adjacent electrodes.