Graphene thermionic energy converter combined with an absorption heat transformer for electricity generation and thermal upgrading

Abstract

To improve energy utilization by recycling waste heat, a novel hybrid system composed of a graphene-based thermionic energy converter (GTEC) and an absorption heat transformer (AHT) is presented, where the GTEC anode waste heat is absorbed by the AHT for thermal upgrading. Considering major irreversible losses, the mathematical expressions for the equivalent power density, energy efficiency and exergy efficiency of the hybrid system are derived using thermionic emission and nonequilibrium thermodynamic theory. The hybrid system's general performance characteristics are also discussed in detail. Additionally, according to numerical calculation, the hybrid system's maximum energy efficiency (MEE), maximum power density (MPOD), and maximum exergy efficiency are 54.53 %, 7.73 W/cm2 and 68.16 % respectively, at the high-temperature heat source temperature of 1500 K. The hybrid system MPOD and MEE have risen by 17.97 % and 17.96 %, respectively, and maximum exergy efficiency has increased by 17.97 % as compared to a single GTEC. Furthermore, the impacts of the high-temperature heat source temperature, the Fermi energy level of graphene, cathode work function, ambient temperature, heat transfer coefficients of AHT, and the temperature of heated space on the hybrid system are investigated in depth. This study provides a new avenue for waste heat utilization in GTEC.