Optimally Distributed Transport Properties Can Produce Highest Performance Thermoelectric Systems

Optimum cooling of conventional thermoelectric (TE) devices is limited to about ⅙ Carnot efficiency for TE materials with figure of merit, ZT ≈ 1. This is ¼ to ½ the efficiency of typical two‐phase refrigeration systems and limits the use of TE materials to specialized applications where a combination of small size, solid‐state operation, and simplicity outweighs device performance limitations. Similarly, TE heating and power generation systems exhibit low efficiency in comparison with most current energy conversion systems. Herein, it is shown that performance efficiencies of TE couples with suitable distributed transport properties (DTP) exceed those of all other TE systems. TE material fabrication methods, including spark plasma sintering, additive manufacturing, and nanoscale material production processes, are evolving, making TE materials with controlled spatially dependent properties more practical to fabricate. Therefore, it is important to determine the performance advantages achievable through the fabrication of such TE couples. Governing equations for the optimum performance of DTP TE systems are derived and solved in a closed analytical form for the spatially dependent Seebeck coefficient, thermal conductivity, and electrical resistivity. Results are presented as analytical solutions for optimum efficiency, optimum spatial distribution of DTP properties, and other operating conditions of interest. Thermoelectric (TE) fabrication methods are evolving, making TE materials with controlled spatially dependent properties more practical to fabricate on a commercial scale. This analysis shows that performance characteristics including maximum efficiency, coefficient of performance (COP), and ΔT of TE couples with suitable distributed transport properties (DTP) exceed those of all other TE systems.