Enhancement of system conversion energy from I.C. engine exhaust using heat exchanger and thermoelectric generators

After an extensive review of previous research, it was evident that the heat exchanger design governs the harvesting of electricity from the I.C. engine exhaust gases, which is then included, and not the cooler, which is then excluded. This was determined by the range of temperature differences between the inlet and outlet of the heat exchangers, which were significant larger than those of the coolers. Therefore, the cold-side temperature of the thermoelectric generator was considered to be constant. However, this limitation reduces the CPU time and costs. In this study, the authors developed and solved differential equations that describe turbulent flow within heat exchangers. A modified k-ɛ turbulent model with a finite volume method was used along with an automatic adaptive mesh generation technique to achieve a precise numerical simulation and convergent criterion. Additionally, the authors proposed five interior designs for the heat exchangers, including empty, hybrid girders, zigzag girders, punched zigzag girders, and waffles, while preserving the same number of thermoelectric generators (60 units) in each design and keeping the external dimensions of the heat exchanger unchanged at 400 × 305 × 25 mm3. The boundary conditions were kept the same for all five designs for suitable comparison. An acceptable level of convergence was achieved when the results were confirmed in the existing literature. The comparison among the five distinct designs was based on the results obtained regarding the conversion of energy to electrical power (i.e., energy harvesting) and the pressure drop caused by the interior design of the heat exchanger. The findings indicated that the heat exchanger with the highest surface temperature uniformity and a reasonable pressure drop could produce an acceptable output power. Therefore, the hybrid girder heat exchanger was the most efficient, generating approximately 731.2 W of energy, which was excellent when compared to a recent study [48] where the amount of energy produced was approximately doubled three and a half times. In addition, it achieved the best balance between the accepted harvested energy and a reasonable pressure drop of 170.7 mm H2O. This was followed by the zigzag girders at 537 W. Conversely, the empty design was found to be the least effective, generating only 210.5 W.