Modeling of the structure and characteristics of thermoelectric generators based on magnesium compounds

In the context of global climate change, the imperative for decarbonization and improvement in efficiency of processes and equipment within the energy sector has become increasingly urgent. One promising approach to improving energy efficiency involves the recovery of low-grade waste heat through the implementation of thermoelectric generators (TEG). Silicide-based materials are considered promising for such devices. However, their utilization is constrained by insufficient thermal stability at elevated temperatures. Specifically, the efficient material Mg₂Si_0.4Sn_0.6 undergoes degradation above 400 °C, whereas the more thermally stable Mg₂Si has lower thermoelectric performance. To address this limitation, a segmented design of the n-type leg in TEG is proposed, integrating both materials. The objective of this study is to model and optimize a TEG with a segmented n-type leg, thereby extending the operational temperature range while maintaining high energy conversion efficiency. The simulation was performed with COMSOL Multiphysics software. A three-dimensional stationary model of a TEG consisting of 127 leg pairs has been developed. The p-type leg was composed of the higher manganese silicide MnSi_1.75. The segmented n-type leg consisted of Mg₂Si on the hot side and Mg₂Si_0.4Sn_0.6 on the cold side. The model employed modules to describe the processes of thermal transport and electrical transport, taking into account the thermoelectric effect. Thermal contact between different parts of the generator was taken into account. To analyze the influence of geometry, the height ratio of the segments varied (with Mg₂Si_0.4Sn_0.6 ranging from 30 % to 80 % of the total leg height). According to the simulation results, the efficiency of the module with a segmented n-type leg increases to 5.3 % compared to 2.9 % for a TEG with n-type legs consisting only of Mg₂Si, at a hot-side temperature of 500 °C. With an optimized segmented-leg configuration, this temperature regime becomes acceptable, and the simulated performance is comparable to commercially available generators. The simulation results demonstrate that the proposed segmented silicide-based TEG effectively addresses the thermal stability problem of Mg₂Si_0.4Sn_0.6. This TEG configuration substantially extends the generator operating temperature range while maintaining an acceptable level of efficiency.