Interplay Between Near-Field Radiative Coupling and Space Charge Effects in a Micro gap Thermionic Energy Converter under Fixed Heat Input

TL;DR

This paper analyzes how near-field radiative heat transfer and space charge effects influence the performance of a micro gap thermionic energy converter, revealing optimal interelectrode distances for maximum efficiency.

Contribution

It introduces a comprehensive model considering both space charge and near-field radiative effects, providing new insights into optimal device design parameters.

Findings

Optimal interelectrode distance is higher than previously reported.

Maximum efficiency achieved by tuning operating voltage and distance.

Electrode temperatures are determined through iterative energy balance calculations.

Abstract

We investigate the performance of a micro gap vacuum thermionic energy converter considering the loss mechanisms due to the space charge effect and interelectrode radiative heat transfer. The dependencies of the space charge effect and near-field radiative heat exchange on the interelectrode distance are derived based on established theories. The electrode temperatures are determined by solving the steady-state energy balance equations in a numerical, iterative process and considering a constant energy flux input to the emitter. The resultant behaviour of the different mechanisms of energy flow from the electrodes is studied for a wide range of interelectrode distances, which provides new insights into the device operation. The maximum efficiency of the converter is obtained by optimizing the operating voltage and interelectrode distance. Considering the interplay between space charge and near-field radiative heat transfer, an optimal range is determined for the interelectrode distance. The optimal value of the distance and the lower limit of this range are found to be significantly higher than previously reported, where constant electrode temperatures had been assumed.