Transient modeling and analysis of a stepped-configuration thermoelectric generator considering non-uniform temperature distribution

Aiming at the low output power(P) and conversion efficiency(η) of a conventional thermoelectric generator(TEG), a stepped-configuration TEG integrating half-Heusler-based(HH) and bismuth-telluride-based(BT) thermoelectric modules(TEM) is proposed in this paper. A transient model considering the temperature drop along the gas flow direction is developed to predict the performance of the TEG and proved to be reliable. The effects of time, spatial location, input temperature(Ta,0) and flow rate(ṁa) on the thermoelectric performance of the stepped-configuration TEG are investigated. The results show that the stabilization time of the thermoelectric properties of the high-temperature TEG with HH is shorter than that of the low-temperature TEG with BT, and there is inertia in the transfer of key thermal properties. The thermoelectric properties of the TEM decrease gradually along the gas flow direction and the spatial variation is related to the ratio of the area of the high and low temperature TEG (RHL). P and η of the stepped-configuration TEG increase with RHL by 8.6% and 15.5%, respectively. P increases with Ta,0 and ṁa and η varies with Ta,0 and ṁa in relation to RHL. The maximum P and η of the stepped-configuration TEG are 276.6 W and 5.90%, respectively, and the corresponding Ta,0 and ṁa are 1573 K and 8 g/s, respectively, which are 32.3% higher than that of the conventional TEG. ṁa is a decisive factor affecting the distribution of energy flow in the stepped-configuration TEG, which is more important than Ta,0 and RHL. This scheme can effectively improve η of TEG and provide useful guidance for the study of TEG.