A Constant Properties Model for the Performance Estimation in Segmented Thermoelectric Generator Elements and Its Experimental Validation Using an n-Type Mg₂Si_0.3Sn_0.7–Bi₂Te_2.7Se_0.3 Segmented Leg

Abstract

Segmenting multiple compatible thermoelectric (TE) materials can improve the conversion efficiency in thermoelectric generators (TEGs) compared to single-material TEGs. A model to accurately estimate the performance in segmented TEGs is essential for optimizing the geometric parameters. Constant properties models (CPMs) help in the quick estimation of the performance of TEGs working under large temperature differences using averaged material properties. This work discusses a CPM to predict the performance of single and segmented TEG elements using a combination of temperature-averaged and spatially-averaged TE properties. Spatial averaging requires the knowledge of the temperature profile across the TEG element length, which was obtained by solving the heat balance equation with a numerical integration approach as suggested by Ponnusamy et al. In this work, we develop the CPM for the segmented TEG elements (CPMS). The model predictions were validated experimentally from the performance evaluation of single Mg 2 (Si 0.3 Sn 0.7 ) 0.98 Bi 0.02 and segmented Mg 2 (Si 0.3 Sn 0.7 ) 0.98 Bi 0.02 − Bi 2 (Te 2.7 Se 0.3 ) 0.98 (CuI) 0.02 TEG elements. Single and segmented TEG elements with Cu contacts were prepared by a hot-pressing technique. Both Mg 2 (Si 0.3 Sn 0.7 ) 0.98 Bi 0.02 and Bi 2 (Te 2.7 Se 0.3 ) 0.98 (CuI) 0.02 TE materials show peak zT > 1 in their measurement range. The experimental results show a maximum efficiency (η max ) of ∼8.25% with 18% improvement for the segmented structure at ΔT ≈ 302 K. The improvement mainly originated from lower heat input (Q in ) even though the maximum power output (P max ) became lower by ∼30%. The performance prediction using the CPM matches well with <10% error for P max and η max for the single TEG element, and using the CPMS, the predictions were <10% error for P max and <25% error for η max for the segmented TEG element experimental results. This work demonstrates how CPMS can be used to predict device performance characteristics in segmented TEGs.

Realizing 10% Conversion Efficiency by Contact Engineering of Mg3Sb1.5Bi0.5 for Medium Temperature Thermoelectric Power Generation

“…In Figure , the obtained η max as a function of Δ T is shown, along with the reported data ,,− for state-of-the-art TE materials. The reported data include measurements on both single legs and TE modules.…”

“…A comparison of the measured η max values with those of other reported materials in the literature. ,,− (Reproduced with permission from ref . Copyright 2023 AIP.…”

“…The maximum studied Δ T value was 330 K, for which the obtained peak power output and efficiency (η max ) were 80 mW and ∼10%, respectively. A cross-check of the accuracy of the measured data was carried out by performing theoretical calculations of these values using the CPM model. , A numerical integration technique , was used for the calculation of the spatial dependence of the electrical and thermal resistivities as well as the temperature-averaged Seebeck coefficient, which were then used to calculate the TEG properties. The contact resistance that was obtained from the measurements was used as input to the model.…”

“…Sequential measurements of S and σ were done in a custom-built setup, while the thermal conductivity values were calculated using the measured thermal diffusivity data (NETZSCH LFA 467 HT HyperFlash), specific heat (Dulong–Petit value), and density (Archimedes’ method). The measured S , σ, and κ values were utilized to calculate the theoretical TEG properties using the CPM model. , …”

“…(ii) The outer layer in the ML technique can be kept as Cu, as has been demonstrated in the literature. , (iii) Tin has a low melting point (232 °C), and the reactants (Cu 6 Sn 5 and Cu 3 Sn) melt beyond 400 °C, which is lower than the maximum operating temperature of most TE materials. − Mg 3 Sb 1.5 Bi 0.5 was chosen as the TE material due to its high figure of merit zT − and superior device performance. − Contacted legs were prepared, and the TEG performance was measured as a function of the temperature gradient. The obtained results were further confirmed by theoretical calculations using a constant property model (CPM) numerical integration technique. , The data highlight the efficacy of the proposed technique and the possibility of using it for other TE material systems.…”