Enhanced heat transfer characteristics and performance of composite thermoelectric devices

摘要

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 Po, heat input Q_h, conversion efficiency n, 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 n, 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.