Thermionic Diode as a Heat-to-Electrical-Power Transducer

Abstract

The high‐vacuum thermionic diode is shown to be capable of converting heat to electric power. For this purpose, a low work‐function collector, a small spacing, and sufficient temperature difference between the emitter and the collector are necessary. A detailed understanding of both thermionic emission and space‐charge phenomena are needed for evaluating the effectiveness of this transducer. With V_R defined as the critical bias potential that gives zero potential gradient at the collector, the maximum available power is given by the relation 3.7×10⁻⁶ V_T^½(V_R²/w²) watts/m². Here, V_T is the voltage equivalent of the temperature T/11 600. In the range of emitter temperature from 1200°K to 1700°K, the most optimistic conversion efficiency lies between 3 and 4% for a diode of 0.001‐inch spacing. With a suitable choice of emitter inhomogeneity, the introduction of cesium vapor should improve the efficiency of this device.