Optimal Design of Thermionic Generator for High Power and High Efficiency Applications

The Thermionic Generator (TIG) works on the principle of thermionic emission effect to convert thermal energy into electricity directly. It is a clean source of energy like solar and wind power generation sources. The conventional resources are getting depleted and their polluting nature urges for the development of alternative resources. In this paper, the thermionic generator has been explored as an alternative direct energy conversion device. It has two electrodes which are the cathode and the anode. The cathode is kept at a higher temperature than that of the anode. Electrons evaporate from the surface of the heated cathode and flow through the vacuum gap and reach the anode. The circuit for thermionic current is completed with the load resistance. The TIG has comparatively very low power output and efficiency owing to the barriers such as the space charge effect and high work function of known materials. The heat transfer equations of the TIG as obtained from Newton's law of cooling and Stefan-Boltzmann's law and from energy balance equations and the first law of thermodynamics for cathode and anode are equated respectively. The two equations thus obtained are solved simultaneously to determine the operating temperatures of the two electrodes. The metaheuristic algorithms such as Particle Swarm Optimization (PSO) and Genetic Algorithm (GA) are used to determine the operating voltage and work functions of the two electrodes at maximum output power and maximum efficiency operating conditions of the irreversible model of a vacuum TIG under different conditions i.e., without and with fixing the value of work function of the anode. The multi-objective function for optimizing the operation of TIG for maximizing both power and efficiency simultaneously is also evaluated. The obtained model has high power and efficiency as compared to earlier work.