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Prediction of thermoelectric performance parameters by numerical methods is an inherent part of thermoelectric generator (TEG) development and allows for time-and cost-saving assessment of material combinations and variations of crucial design parameters (e.g., shape, pellet length, and thermal coupling). Considering the complexity of a TEG system and its numerous affecting factors, the clarity and the flexibility of a mathematical treatment comes to the fore. Comfortable tools are provided by commercial finite element modeling (FEM) software offering powerful geometry interfaces, mesh generators, solvers, and postprocessing options. We describe the level of development and the simulation results of a three dimensional (3D) TEG FEM. Using ANSYS 11.0, we implemented and simulated a TEG module geometry under various conditions. Comparative analytical one dimensional (1D) results and a direct comparison with inhouse-developed TEG simulation software show the consistency of results. Several pellet aspect ratios and contact property configurations (thermal/electrical interface resistance) were evaluated for their impact on the TEG performance as well as parasitic effects such as convection, radiation, and conductive heat bypass. The scenarios considered revealed the highest efficiency decay for convectionally loaded setups (up to 4.8%pts), followed by the impacts of contact resistances (up to 4.8%pts), by radiation (up to 0.56%pts), and by thermal conduction of a solid filling material within the voids of the module construction (up to 0.14%pts).
Thermal durability of CoSb 3 in vacuum, helium and air was investigated over the temperature range of 20-850°C. A scanning electron microscope (SEM) and X-ray powder diffraction technique were used to investigate the microstructure and to carry out the phase analysis of the degradation products. The analysis of a non-isothermal and isothermal decomposition and oxidation of the CoSb 3 powders and polycrystalline samples were performed using simultaneous TG/DTA technique. More detailed studies were carried out on the oxidation in the temperature range 400-600°C. It was established that the decomposition products are CoSb 2 and a volatile antimony. In case of oxidation a complex three-layered scale is formed, consisting of CoSb 2 O 4 , CoSb 2 O 6 and Sb 2 O 4 layers. Both the decomposition and the oxidation kinetics are determined by a diffusion through the growing layers of products. The electrical resistivity and Seebeck coefficient measurements have been also performed on pure and oxidized samples, which showed a large influence of the oxidation on the electrical properties.
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