Thermoelectric Performance of Novel Composite and Integrated Devices Applied to Waste Heat Recovery

摘要

Thermoelectric elements, made of semiconductor slices laminated onto highly conductive interconnector materials, are termed composite thermoelectric device (TED). An integrated TED is a composite TED with the interconnector designed as an internal heat exchanger with flow channels directing the working fluid between the source and element legs. In this work, novel composite and integrated TEDs are proposed as an alternative to conventional TEDs, and their performance in terms of power output P_o, heat input Q_h, conversion efficiency η, and the produced electrical current I is studied using analytical solutions. The top and bottom surfaces of the TED are subjected to a temperature differential while the side surfaces are exposed to either ambient or adiabatic conditions. An increment in temperature differential results in enhanced device performance. For a fixed temperature differential, the integrated TED shows nearly an eight-fold increase in both P_o and Q_h and a four-fold increase in I, whereas the composite TED shows approximately a two-fold increase in P_o, Q_h, and I when compared to the conventional TED values. Both novel TED designs have a minimal impact on efficiency predictions. However, an increase in semiconductor slice thickness resulted in an exponential decrease in P_o, Q_h, and I, and an exponential increase in η values and reaches a limit of conventional TED values. The effect of semiconductor slice thickness on η in the novel TEDs is remarkable when it is less than I mm. The change in ambient conditions via convective heat transfer coefficient has negligible effects on P_o; however, a substantial change in n occurs when it is less than 100 Wm~(-2)K~(-1).