Performance evaluation of a thermionic converter with a macro-grooved emitter and a smooth collector

Abstract

The performance of a thermionic converter with a planar, macro-grooved, Molybdenum emitter and a smooth Molybdenum collector was investigated experimentally. The emitter’s concentric macro-grooves were 0.5 mm deep, 0.5 mm wide, and 1.0 mm apart and the inter-electrode gap was 0.5 mm wide. The emitter temperature was varied from 1573 to 1773 K, the collector temperature was 1073 and 1173 K, and the cesium pressure, PCs, in the inter-electrode gap was varied from 50–500 Pa. A peak electric power density of 1.2 W/cm2 and a peak conversion efficiency of ∼8.3%, were achieved at a relatively low emitter temperature of 1773 K and a high collector temperature of 1173 K. When the emitter and collector temperatures were 1673 and 1073 K, the maximum peak conversion efficiency at PCs=300 Pa was 8.1%, and the peak electric power density was ∼1.0 W/cm2. At emitter and collector temperatures of 1573 and 1073 K, respectively, the maximum peak power density (0.46 W/cm2) and the maximum peak conversion efficiency (5.4%) were ∼20% higher and 2% lower, respectively, than for a larger gap of 1.5 mm (0.4 W/cm2 and 5.5%, respectively).