Exhaust Heat Recovery Unit Equipped With Nanofluid and Helical Tapes, a Solution for Cleaner Energy Production

In internal combustion engines (ICE), a major part of the generated energy via burning the fuel is wasted. The cooling fluid controlling the temperature, the reclaimed hot gases for reducing the environmental impacts, and the hot combustion productions leaving the engine from the exhaust are the main origins of energy waste in such a machine. Waste heat recovery and flue gas condensation are the methods by which the overall efficiency of a thermal engine is enhanced, and its environmental impacts are mitigated. In this paper, the utilization of the exhaust waste energy of ICE by using a heat exchanger with nanofluid and helical tape, in order to augment the thermal performance of the engine and reduce its environmental impact, is investigated numerically. In this heat exchanger, the flue gas of the engine at high temperature and H2O-CuO nanofluid are considered as the primary and secondary working fluids, and the twisted tape makes the flow further disturbed so that a larger overall heat transfer coefficient is obtained. The finite volume method has been applied to scrutinize the impacts of Reynolds number as well as the twisting-tape turns number on the operation and performance of the tube. As such, suitable correlations for the prediction of some of the thermos-physical parameters of the problem (such as Nusselt number and Darcy factor) are extracted regarding the obtained data. The results of the study reveal that Nusselt number is higher for larger numbers of the tape turn and higher Reynolds numbers, while a lower friction factor is achieved as the number of the turns is reduced.