Most researches and developments presently dealing with thermoelectric materials and devices focus on high performances and/or low cost materials. However, for practical applications, thermoelectric modules based on these materials are needed. The main challenge in the design of thermoelectric modules is the development of efficient electrical and thermal contacts. Even though studies deal with electrical contacts [1], former work showed that thermal contacts present a stronger effect on the module performances [2], mostly in the base of commercial modules [3]. The present study deals with the design of thermal contacts for thermoelectric modules based on the low-cost Fe2VAl Heusler compound [4]. With low-cost thermoelectric materials, the cost of modules tends to be dominated by the ceramic insulators. Therefore, new low-cost substrates need to be developed. Innovative substrates for low and medium temperature modules have been investigated. Experimental results will be presented and unravelled by FEM simulations. Results show that the optimized thermal contacts significantly enhance the performances of the thermoelectric modules. References: Liu, W., et al. Current progress and future challenges in thermoelectric power generation: From materials to devices. Acta Materialia 87 (2015): 357-376. Rowe, D. M., et al. Design theory of thermoelectric modules for electrical power generation. IEE Proceedings-Science, Measurement and Technology 143.6 (1996): 351-356. Wang, S., et al. Experimental study of the effects of the thermal contact resistance on the performance of thermoelectric generator. Applied Thermal Engineering 130 (2018): 847-853. M. Mikami, et al. Evaluation of the thermoelectric module consisting of W-doped Heusler Fe2VAl alloy. Journal of Electronic Materials. 43 (2014) 1922-1926.
It was recently discovered that inclusions, fatigue damage and other types of material imperfections and defects in metals can be nondestructively detected by noncontacting magnetic measurements that sense the thermoelectric currents produced by directional heating and cooling. Since detection of small defects in thermoelectric materials is ultimately limited by intrinsic thermoelectric anisotropy and inhomogeneity of the material to be inspected, a thorough study is required on their impact on the nondestructive capability. Therefore, in this investigation the induced electric current densities and thermal fluxes are first derived for a steady line heat source in an inhomogeneous and anisotropic thermoelectric material. The exact closed-form solutions are obtained by converting the original problem into two inhomogeneous Helmholtz equations via eigenvalue/ eigenvector separation. The material properties are assumed to vary exponentially in the same manner in an arbitrary direction. For the corresponding homogeneous but anisotropic material case, we also present an elegant formulation based on the complex variable method. It is shown that the induced magnetic fields can be expressed in a concise and exact closed form for a line heat source in an infinite homogeneous anisotropic material and in one of the two bonded anisotropic half-planes. Our numerical results demonstrate clearly that both property anisotropy and gradient in thermoelectric materials can significantly influence the induced thermoelectric currents and magnetic fields.
Engineering of an enhanced Multi-Mission Radioisotope Thermoelectric Generator (eMMRTG) began 3 years ago with agreement between the U.S. National Aeronautics and Space Administration (NASA) and the U.S. Department of Energy (DOE). The Jet Propulsion Laboratory is leading the transfer of skutterudite thermoelectric couple technology to industry and leading the systems engineering of the proposed eMMRTG. Should NASA fund the flight development of an eMMRTG, the DOE would lead the flight system development. The analytical models and design of the MMRTG have been enhanced to use skutterudite couples developed at Jet Propulsion Laboratory over the last two decades. This required a thorough evaluation of the MMRTG design, and concurrent engineering of an enhanced MMRTG to shed light on potential design issues or risks. At the end of the U.S. fiscal year (FY) 2015, a complete catalog of risks was produced. Tests, hardware development, and analyses have now been put in place to mitigate those risks to acceptable levels. Few risks can ever be truly eliminated unless a design is modified to eliminate specific risks and not introduce more severe risks. The design imperative for the eMMRTG is to change only a few MMRTG features; therefore, risks can largely only be mitigated, not eliminated, through design changes. However, many risks can be effectively - though not totally - eliminated without design changes. This paper briefly describes some of the documented risks and mitigations or reduction approaches to be applied in the coming 3 years, on the way to completing the eMMRTG concept.
Antimony-doped bismuth telluride (Sb-doped Bi 2 Te 3 ) is one of the best and most-used p-type thermoelectric materials for near-room-temperature application [1, 2, 3]. It has a stacked two-dimensional (2D) layered crystal structure, and exhibits the anisotropic thermoelectric properties [4]. In this work, we investigated the correlations between spark plasma sintering (SPS) conditions and the thermoelectric properties of Sb-doped Bi 2 Te 3 samples. Af-ter sintered using SPS, the Sb-doped Bi 2 Te 3 samples showed distinctive density, microstruc-ture, and crystalline preferential orientation as the sintering conditions (temperature, pres-sure, and ramping rates) changed. Accordingly, different thermoelectric properties were also observed by these samples. An optimized sintering condition was found and an in-plane fig-ure of merit ZT up to 1.3 at 298 K was achieved. Such high ZT was supported by the excellent in-plane electrical transport properties, which was mainly resulted from a high degree of c-plane orientation. A high in-plane power factor of 4.79 ×10 -3 W m -1 K -2 was shown compared with the out-of-plane value of only 2.76 ×10 -3 W m -1 K -2 . On the other hand, the micron-scaled
Current studies in design of thermoelectric generators (TEGs) are mostly disconnected to the parametric optimization of the TEG, and realistic mechanical and thermal boundary conditions. In this study, a three dimensional (3D) model is used to design, optimize and study potential TEGs intended for satellite applications. This model takes into account the real boundary conditions of space application such as spatial constraints, maximum allowable internal resistance and temperatures on the cold and hot junctions. The temperature de-pendent thermoelectric properties of Bi 2 Te 3 -based materials are used as input parameters. The numerical model used to solve the system is based on the finite element commercial software, COMSOL. The optimal geometrical dimensions, including the dimensions of the thermoelectric legs, the number of unicouples and module fill factor (effective cross-section area of thermoelectric materials) are calculated through an optimization process. The 3D model also considers the influence of contact resistance on power generation by inclusion of experimentally obtained contact resistance data. Furthermore, this study investigates thermal stress and displacement of the thermoelements under practical thermal and mechanical boundary conditions. The simulations are based on optimal load resistance that provides the maximum power in the TEGs. The results of this study show detailed 3D infor-mation of TEG optimal geometry, temperature distribution, voltage generation, electric voltage generation, total current density, effect of actual contact resistance
