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EFFECTS OF ELECTRODE SIZE ON THE PERFORMANCE OF A COMBUSTION-DRIVEN MHD GENERATOR.
Technical rept. Jul 66-Jul 69,
STANFORD UNIV CALIF INST FOR PLASMA RESEARCH
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A single molybdenum electrode pair, shielded from end effects by two additional electrode pairs, was located at the downstream end of an MHD channel. Two types of experiments were performed. First, the effects of electrode size on performance was examined at electrode temperatures between 530K and 1600K for a fixed channel geometry, combustion gas mass flow rate, magnetic field strength, and upstream wall temperature 2200K. Three electrode sizes were used length-to-pitch ratios of 0.2, 0.5, and 0.8, and performance was evaluated directly from electrode voltage drops determined as a function of current. The second type of experiment investigated electrode size effects in the presence of dissimilar boundary layer conductivities, reflecting coupling between electrode and gas boundary layer temperatures in a cold-electrode generator. A hot wall was used upstream of small electrodes and a cold 750K wall upstream of large electrodes. For similar conditions of surface and gas boundary layer temperature, larger electrodes were found to yield lower voltage losses at a given load current. However, for dissimilar boundary layers, total voltage losses for a large electrode pair were equal to or greater than those of a small electrode pair at the same surface temperature. Author
APPROVED FOR PUBLIC RELEASE