Modeling and Analysis of Advanced Thermoelectric Modules Considering Thermal Losses

Abstract

A mathematical model for a thermoelectric generator (TEG) based on constitutive equations has been developed to analyze temperature-dependent performance in terms of output power and efficiency. Effective material properties were invoked for understanding the influence of temperature dependence of material parameters and related adverse effects on the model TEG. It is shown that analytical equations with effective properties can capture the contribution from thermal losses and interfacial resistance. Finite element simulation and multi-physics analysis were utilized in conjunction with an analytical model to examine the effects of different operating conditions and geometry on thermal losses within the TEG. A comprehensive method for assessing the performance of a segmented TEG using effective properties was developed and provides understanding of the influence of detrimental effects inside the device. Using the experimental results on the half-Heusler, skutterudites, and lead telluride materials, segmented TEG�s have been analyzed for their performance in terms of power and efficiency. Non-linear and temperature-dependent material properties and thermal losses were considered in the numerical model. Contact resistance is also taken into account and incorporated into the effective coefficients. The design of the segmented TEG enables efficient operation over a wide temperature range depending upon the constituent materials. Calculated results demonstrate that efficiency up to 14.3% can be achieved at a temperature difference of �"T=770K, using a segmented module. This results in a high output power of 48W from a 49 couple module, which is significantly higher compared to the single-material traditional modules at the same temperature difference. Furthermore, a two-stage cascade device is modeled and is compared with the segmented device. The devices consist of skutterudite-based materials on the cold side and half-Heusler alloys on the hot side. Temperature-dependent material properties and thermal losses, which occur as conductive and radiative heat transfer, were considered in the finite element model. It is proven that the modeling with effective properties can provide an excellent estimation of the performance of a TEG over a broad operating range. Moreover, the effective properties provide a precise description of the transport properties inside the TEG and quantification of the actual figure of merit with thermal losses is performed.