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

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Document pages: 32 pages

Abstract: We investigate the performance of a micro gap vacuum thermionic energyconverter considering the loss mechanisms due to the space charge effect andinterelectrode radiative heat transfer. The dependencies of the space chargeeffect and near-field radiative heat exchange on the interelectrode distanceare derived based on established theories. The electrode temperatures aredetermined 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 theelectrodes is studied for a wide range of interelectrode distances, whichprovides new insights into the device operation. The maximum efficiency of theconverter is obtained by optimizing the operating voltage and interelectrodedistance. Considering the interplay between space charge and near-fieldradiative heat transfer, an optimal range is determined for the interelectrodedistance. The optimal value of the distance and the lower limit of this rangeare found to be significantly higher than previously reported, where constantelectrode temperatures had been assumed.

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