Abstract: This paper presents the comprehensive performance analysis of thermionic power generation when the interelectrode vacuum gap shrinks to the submicron range. Although reducing the vacuum gap has been suggested as an effective approach to mitigate space-charge accumulation in thermionic-energy conversion (TEC) devices, previous theoretical works have predicted the optimal gap distance in the single-digit micrometer range. However, we demonstrate that nanoscale charge and thermal interactions between thermionic electrodes, such as Schottky barrier lowering due to image charge perturbation and near-field enhanced radiative heat transfer, significantly affects the TEC performance within the submicron vacuum gap. Carefully conducted energy-balance analysis reveals that submicron-gap TEC at d ≈ 700 nm can produce an approximately fourfold increase in power output with a higher energy conversion efficiency than micron-gap TEC under the same operating condition. In addition, significant thermionic and nearfield radiative heating of the collector in the submicron-gap TEC system can be beneficially used to further enhance the power output and efficiency by combining with a bottom-cycle heat engine. We believe that the present work provides a theoretical framework for submicron-gap thermionic power generation as a promising energy recycling scheme for high-quality heat sources.
Our work on sub-micron gap thermionic devices has been published in the physical review applied. The paper title is “Submicrometer-Gap Thermionic Power Generation Based on Comprehensive Modeling of Charge and Thermal Transport”