Performance evaluation of a hybrid alkali metal thermal electric converter-two stage thermoelectric generator system

Abstract

• A two-stage thermoelectric generator is proposed to recover waste heat from AMTEC. • Feasibility and effectiveness of TTEG as bottoming cycle are justified. • Power density, energetic and exergetic efficiency gain obvious improvements. • Effects of some key parameters on the system performance are revealed. A great part of high-quality heat is wasted, which significantly lowers the performance of alkali metal thermal electric converters. To achieve gradual and efficient utilization of the waste heat, a new cogeneration system model composed of an alkali metal thermal electric converter and a two-stage thermoelectric generator is established, in which the high-quality waste heat of alkali metal thermal electric converter is further reused by two-stage thermoelectric generator for additional power generation. Based on the theories of electrochemistry and non-equilibrium thermodynamics, mathematical expressions of power outputs and efficiencies of alkali metal thermal electric converter, two-stage thermoelectric generator and hybrid system are derived by taking the main irreversible losses into account. Calculations show that the maximum attainable power output density and its efficiency of hybrid system are, respectively, 5152.7 W/m 2 and 30.0%, which are approximately 54.1% and 27.7% greater than that of the sole alkali metal thermal electric converter system in previous studies. Two-stage thermoelectric generators are efficient to utilize the waste heat from alkali metal thermal electric converters. Comprehensive parametric studies show that operating conditions and designing parameters can be tuned to optimize the hybrid system performance. The results may offer some theoretical guidance for designing and running such a hybrid system.