Power generation and thermal stress characterization of thermoelectric modules with different unileg couples by recovering vehicle waste heat

Unileg thermoelectric generators (TEGs) possess a simple structure, high mechanical strength, and lower thermal stress and cost than conventional TEGs. So it is a promising clean and green energy device that directly converts waste heat into power. This study focuses on the performance and thermal stress of unileg thermoelectric modules (TEM) with different leg heights and numbers of legs by harvesting the vehicle's waste heat. This work also combines TEM and computational fluid dynamics (CFD) to analyze the influence of fluid flow. When the hot-side and cold-side temperatures are fixed, the results reveal that the shorter the leg height, the higher the output power, as a consequence of smaller internal resistance. Alternatively, the maximum efficiency is merely reduced by 1.45% when the height decreases from 12 mm to 8 mm. The output power linearly increases with the number of legs, showing no interaction between the unilegs. Compared to the CFD predictions, the results without considering the fluid flows overestimate the maximum output power and efficiency by 80% and 32%, respectively. Because the thermal expansion coefficients of different materials in the TEM are not matched, thermal stress is generated. The thermal stress increases from the center of the TEM outward along the x- and y-axes, yielding maximum thermal stress of 219.48 MPa. Compared with conventional TEM thermal stress (348 MPa) at moderate and high-temperature applications, the maximum thermal stress is reduced by 36.9% from the unileg TEG.