Multiscale modeling of thermoelectric generators for the optimized conversion performance

An attractive option for constructing thermoelectric generators (TEGs) is to incorporate a water-fed heat exchanger with commercially available thermoelectric modules. In this paper, two different thermoelectric models are applied to predict the energy conversion performance of the TEGs. The first model employs a derivation of the Carnot efficiency. The second model presents a rigorous interfacial energy balance by capturing Joule heating, Seebeck, Peltier and Thomson effects, yielding better predictions of the conversion capability. This model is then used to perform a computational examination of the TEGs embedded in 30 different configurations, which allows the identification and quantification of key design parameters including flow types, hot stream inlet temperatures (T_in-hot), pressure drops (ΔP), cross-sectional area (A_C), channel length (L_ch) and number of channels. The positive effects of T_in-hot and ΔP can be easily captured and parallel flows of the hot and cold streams are found to provide greater overall TEG efficiency as compared to counter flows. In general, micro-sized A_C reduces temperature gradients across the channels, providing a greater ΔT across the thermoelectric material. However, enhancements of the conversion capability are eventually limited by the reduced convective heat transport due to increased flow resistance. Finally, further improvements in the power generation are achieved by reducing L_ch while increasing the number of channels. The resulting reduction in flow resistance is found to facilitate increases in convective heat transfer, as well as in ΔT, and thus a great increase in conversion efficiency (η).