Thermionic refrigeration with planar and nonplanar electrodes - chances and limits

In this paper for the first time a precise theoretical analysis of efficiencies and power densities for nano-scaled therm-ionic vacuum gap devices is presented. Plane electrodes with nano-gaps will be treated first. With nonplanar elec-trodes (nanotips) enhanced electron field emission occurs, giving rise to new design options. The theories of field and thermionic emission are combined by calculating the transmission coefficient for the surface potential barrier ex-actly numerically for thermionic and tunnelling energies. This then is used for current and energy transport determi-nation and derivation of cooling and generator efficiencies. Because of the high work function of metals, efficient thermionic electron emission takes place only at high tem-peratures. At low temperatures also efficiencies near Carnot are possible but with very low power densities. The energy exchange processes in the cathode during emission are re-viewed and an improved model is presented