On the efficient topology of the exhaust heat exchangers equipped with thermoelectric generators for an internal combustion engine

Abstract

The increasing energy demand and simultaneously growing concerns about pollution and climate change can clarify the importance of energy recovery, especially in the transportation section where a huge amount of fossil fuels is still consumed. Thermoelectric modules (TEMs) are one of the most stable means to extract energy from flue gases. However, the heat recovery by TEMs require a precise thermo-hydrodynamic design for heat exchangers to transfer more energy, owing to the low efficiency of the modules. Therefore, the current numerical study follows the ideas that can increase the efficiency of electrical power generation in vehicles. Three various simple or dimpled geometries, called Dual Flat, C-shaped, and U-shaped models, are introduced involving the ideas of chaotic flows, extending heat transferring surfaces, and intensifying turbulence levels. The number of TEMs is kept constant for all geometries and a trial procedure is performed to specify the thermo-physical properties of TEMs, directly connected to their hot and cold side temperature. The results are compared to the traditional Flat geometry, in terms of power generation, efficiency, and thermo-hydrodynamic evaluations. Dual Flat and Flat geometry are respectively labeled as the most and least power generating models by 45% relative difference. Despite the highest pressure drop, the chaotic flow in a C-shaped geometry provides the most efficient case if the pressure drop is freely provided by the engine exhaust inertia, while dimpled Dual Flat geometry is ranked the first for best efficiency when pressure drop compensation needs additional cost. The latter geometry can produce nearly 700 W power, as the maximum value.