The overall efficiency of internal combustion (IC) engines can be significantly improved by recovering the waste heat in exhaust gas. Use of thermoelectric (TE) waste heat recovery systems, has proved to be an attractive proposition when compared with other methods proposed in the literature. Recent investigations in TE waste heat recovery systems have highlighted the need for advanced heat exchanger (HE) designs to enhance the heat transfer rates across the thermo-electric generator (TEG). The objectives of this paper are (1) to present the results of an investigation into boundary layer development and heat transfer characteristics in such heat exchangers and (2) the analysis of the effect of back pressure development on both the heat exchanger behaviour and the overall engine performance.
A theoretical heat exchanger integrated with 16 thermo-electric modules (TEM), was modeled and simulated using the computational fluid dynamics (CFD) software, Fluent. The model was validated against experimental results taken from a diesel and a gasoline automotive test engines equipped with a TEG. The investigation is extended to analyze the efficiency of the TEG by increasing the level of turbulence and the back pressure within the exhaust heat exchanger. The results have shown that the heat exchanger model remarkably agrees with the experimental results. It has further revealed that the increased back pressure created by the TEG is insignificant and has only a little effect on the overall engine performance.