Modelling and simulation study of a converging thermoelectric generator for engine waste heat recovery

Recently, thermoelectric generators (TEGs) used to recover waste heat from engines have been widely studied due to their promising advantages, such as free heat sources, no pollution, and silent operation. In this study, a converging TEG has been proposed based on typical plate-type TEGs, where the hot-side wall of the heat exchanger was designed with an inward incline. To investigate the influence of the tilt angle, a mathematical model was developed. Combining the numerical simulation results, analyses of the TEG performance and model accuracy were carried out under 5 cases of boundary conditions. The results show that (i) the design of the tilt angle can apparently improve the Reynold's number and the convective heat transfer coefficient of the exhaust gas. (ii) The hot-side temperature of the thermoelectric module also increases, and the larger the tilt angle is, the greater the hot-side temperature becomes. (iii) Through a comparison of the results between the mathematical model and simulation, the model presents good agreement, and the maximum error of the hot-side temperature is 4.24%. (iv) Although the TEG power is apparently improved, the pressure drop has a substantial influence on the TEG net power. It seems that the optimum angle is alpha = 2 degrees when the mass flow rate of the exhaust gas is greater than 37.25 g/s, which increases the TEG net power by 5.96% in case 1. The findings of this work may provide a guide to the design, theoretical analysis, and optimization of thermoelectric generators.