Abstract
Despite its great potential, thermionics has a low Carnot efficiency because a considerable percentage of cathode thermionic energy is wasted to heat the anode. This paper introduces a novel concept of anode-thermoradiative enhanced thermionic (A-TET) conversion, where a metal-n-p junction serves as thermionic anode to induce a cascading effect of thermionic-thermoradiative emission. An elaborated model based on first and second law of thermodynamics is established to evaluate energy transfer and irreversibility of A-TET converter. The simulation results show that the A-TET converter achieves a higher energy efficiency of 36.0 %, up by 56.2 % compared to pure thermionics and outperforms the thermionics & thermoradiatives combined system, with an absolute exergy efficiency improvement of 10.47 % at cathode temperature of 1400 K. A-TET conversion exhibits an extremely minimal exergy loss ratio of thermionic emission of 0.66 %, attributing to the inhibiting effect of thermoradiative on the thermionic emission. A temperature-entropy diagram is further established to pinpoint the irreversibility of A-TET conversion, with the entropy change of thermionic emission of 0.0311 W/(K·m2) and thermoradiative emission of 0.7666 W/(K·m2). This concept of A-TET conversion paves a way for the development of efficient thermionic converter for power-to-heat-to-power system.
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