Thermoelectric generators (TEGs) convert temperature gradient into electrical power. The shape (or topology) of thermoelectric (TE) leg has a significant impact which can directly affect TEG performance. The conventional uniform, rectangular TE leg configurations were employed widely in TEGs to evaluate the performance of the TE devices. Different leg geometries have been proposed in the past by researchers to enhance thermoelectric efficiency. However, there is no consensus, nor a systematic study exists to find out the ideal leg geometry and maximize the energy conversion efficiency in thermoelectric systems. The current study investigates various configurations of TE legs such as trapezoidal leg, zig-zag leg, cross-shaped leg, X-leg, Y-leg, I-leg based on their individual shape construction. 3-dimensional finite element simulations are conducted to investigate the thermoelectric output power and conversion efficiency of these configurations and compared to (conventional) rectangular TE leg shape geometries. The reliability and accuracy of the used finite element based numerical model are validated with analytical and numerical results. Bismuth telluride (*Bi~2~ Te~3~*) was selected as TE material for all configurations. The dimensions of TE leg such as thickness (*t*), length (*L*) and top (hot) surface area of TE legs were kept similar for all TE leg configurations. The hot and cold surfaces of all models are maintained at constant temperature value of 327 °C and 27 °C, respectively. From the study, results indicate that the conventional, rectangular TE leg can still generate more TE output power compared to all other configurations. The rectangular TE leg generates around 1.46 Watts which is around 28% TE power higher than cross-shaped TE leg configuration. On other hand, the zig-zag leg generates the lowest TE power compared to other TE leg configurations.

After optimizing and evaluating the TE leg structure, the comparison between unicouple and unileg TE configurations is explored. In unileg TEG, single (*n*- or *p*-) thermoelectric material is used in both legs of a thermoelectric system instead of dual material (*n*- and *p*-) which reduces the material cost and the thermal mismatch between the multiple TE materials. To investigate the effect of leg configuration (unileg or unicouple), the rectangular TE leg was used since it gives the optimal energy output. TE output power of unileg TE system was quantified and compared to (conventional) unicouple TE system. Intermetallic connector of copper and constantan were employed as metal conductor which transfers the electrons between TE legs for both unicouple and unileg TE system. When copper is used, the unileg TE system generates output power of 1.24 Watts which is 15 % lower than unicouple TE system. By using constantan, however, unileg TE produces 1.52 Watts which is around 3.94 % higher than unicouple TE system. This study introduces optimization of various TE leg configurations to investigate and quantify the possibility to enhance thermoelectric output power and conversion efficiency. Both unicouple and unileg TE systems are considered which can benefit the future applications of thermoelectric generators.


Effect of Leg Topology on the Energy Conversion Performance of Thermoelectric Generators Systems

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Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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