Development of Compliant Thermoelectric Generators (TEGs) in Aerospace Applications Using Topology Optimization

Abstract

Abstract Thermoelectric generator (TEG) elements typically made of Bismuth Telluride (Bi2Te3) have good thermoelectric properties but are very brittle. In practice, however, TEG elements often are subject to both mechanical and thermal loading. Although clamping is the main source for mechanical loading in TEGs, other loadings such as from vibrations can occur and inducing stresses which can lead to failure. If the allowable stress is exceeded, then device failure will result. Axial stress is predominantly found in vertically oriented elements. Elements oriented in other positions experience both axial and bending stresses. However, when shear and bending occur, failure is far more likely. Therefore, TEG shape and orientation relative to the thermal and structural loading are critical. In this context, a topology optimization approach is posed to develop a compliant TEG, capable of maintaining thermoelectric functioning and sustaining mechanical loadings. This approach builds on previous research on topology optimization for multifunctional materials, but uniquely deals with multifunctional design of a composite TEG. First a tool is developed and validated to study the unique compliant structure and second a composite 3-D unit cell comprised of structural and thermoelectric materials is created. The volume fractions and orientation of the two materials are optimized to support applied structural shear, bending, and axial structural loads and thermal loads. A optimal structural model was shown to have equal shear and adjoint loads that resulted to a an increase of 9.61 % displacement while using 8.5 % less material. The integrated model (structural and thermal) used 8.5 % less material and had a 9.64 % increase in displacement. The implication of this research is that it could help to inform 3-D printing of more compliant TEGs optimized for a particular application.