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. A prototype TEG was fitted to a test engine and evaluated across a range of engine operating conditions. A CFD model of the TEG was then validated against these results. As expected, the results show that the power generation of the TEG increases with increasing the exhaust inlet temperature and the flow rate, and also with reducing coolant inlet temperature of the TEG heat exchanger. Further, the pressure drop across the TEG was measured on a gasoline test engine and found to be very small, varying from 10-30 Pa depending on the exhaust gas flow rate. It was found that the heat transfer across the TEG heat exchanger can be enhanced by increasing the fin length, fin thickness, number of fins, length of the heat exchanger, inner wall thickness, installing a turbulent device in the hot heat exchanger and making counter flow arrangement of the heat exchanger. All of these methods increase the pressure drop across the TEG while enhancing the heat transfer across the device. Thus, the heat transfer augmented method has to be carefully selected to optimise the heat transfer and pressure drop through the device. GT-Power engine simulation results showed that the backpressure generated by the TEG is insignificant and has a negligible effect on the overall engine efficiency and the BMEP. This result provides a strong indication that implementation of the TEG in engine exhaust system does not significantly reduce the overall engine performance and hence, TEG continues to present itself as a promising heat recovery method in automobile applications.


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    Titel :

    Exhaust system heat exchanger design for thermal energy recovery in passenger vehicle applications


    Beteiligte:
    Stobart, R. (Autor:in) / Wijewardane, A. (Autor:in)


    Erscheinungsdatum :

    2011


    Format / Umfang :

    14 Seiten, 9 Bilder, 5 Tabellen, 11 Quellen




    Medientyp :

    Aufsatz (Konferenz)


    Format :

    Print


    Sprache :

    Englisch




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