Enhanced heat transfer characteristics and performance of composite thermoelectric devices

Abstract

Thermoelectric elements made of semiconductor slices layered onto highly conducting inter-connector materials are termed as Composite Thermoelectric Device (CTED). An integrated TED (iTED) is a CTED with flow channels drilled through an inter-connector, it acts as a heat exchanger, directing the heat transfer between the fluid stream and element legs. In this work, thermoelectric performance of such elements in terms of power output P 0 , heat input Q h , conversion efficiency η, electric current and Ohmic and Seebeck voltages for various hot surface temperatures T h , load resistances R L and semiconductor slice sizes d has been investigated using both analytical and numerical methods. The thermoelectric performance of CTED has been compared with a geometrically equivalent conventional TED element. For an optimum load resistance R optmL , an increase in T h showed a substantial increase in P 0 and a minor increase in Q h . At T h = 550K and 350 K, the optimum η for CTED, 11% and 9% respectively lesser and nearly four-fold increase in P 0 as compared to the conventional TED is observed. The semiconductor slice size d has a significant effect on the CTED performance: an observed increase in both P 0 and Q h and decrease in η is a result of decreasing d. At fixed d = 5 mm and hot stream inlet temperature (450 K) values, the single-stage iTED showed five-times in P 0 and two-fold in η for a flow rate Re = 500 compared to the values at Re = 100. These novel TEDs help extract larger amounts of waste heat, reduce thermal stresses and minimize semiconductor material usage as compared to conventional TEDs.