Effects of Collector Temperature on the Performance of Grooved Electrode Thermionic Converters

摘要

Experiments are conducted to compare the performance of the smooth electrodes, grooved emitter, and grooved collector converters at the same emitter and collector temperatures. The focus of the experiments is to investigate the effects of collector temperature on the performance of grooved electrode converters. The converters with various electrode configurations and a 0.5 mm gap are tested at emitter temperatures, T_E = 1473 - 1673 K, collector temperatures, T_C = 773 - 1023 K, and cesium pressures, P_(Cs) = 10 - 500 Pa. All electrodes are planar and fabricated with polycrystalline Molybdenum. The grooved electrodes have concentric macro-grooves 0.5 mm wide, 0.5 mm deep, and 1.0 mm apart. The output electrical power density and the conversion efficiency are calculated from the measured I-V curves and the maximum power density and conversion efficiency are determined from the calculated P_D-V and η-V envelopes. At T_E = 1473 K, the electrical power density for the smooth electrodes converter at the optimum collector temperature (873 K) is 2.25 W/cm~2 at η = 13.8%, decreasing to 1.46 W/cm~2 at η = 12.4% as T_C increases by only 75 K to 948 K. However, the corresponding decrease in the electrical power density for the grooved collector converter is only 0.04 W/cm~2 (from 1.24 W/cm~2 at η = 11.4% and T_C = 873 K to 1.20 W/cm~2 at η = 10.7% and T_C = 948 K) and that for the grooved emitter converter is 0.12 W/cm~2 (from 0.82 W/cm~2 at η = 8.1% and T_C = 873 K to 0.70 W/cm~2 at η = 6.8% and T_C = 948 K). At the higher emitter temperatures of 1573 K and 1673 K, similar results are obtained. In all experimental conditions, however, the grooved emitter converter shows the lowest power density and conversion efficiency, followed by the grooved collector converter, and the smooth electrodes converter, except for T_E = 1673 K and T_C = 1023 K at which the converter with a grooved collector operates at the highest power density (2.38 W/cm~2) and conversion efficiency (14.0%).