Numerical and thermodynamic analysis of external flow over tube banks for waste heat recovery
This study will involve numerical energy and exergy analyses for unsteady cross flow over heated circular cylinders. Several simulations were conducted using Ansys FLUENT 18.2 with different values of Reynolds number, inlet temperatures, number of in-line cylinders, pitch ratios, as well as the heat transfer coefficient of artificial heat leakages. Heat leakages were considered as the source terms for the concerned domain. The comparison of the numerical results with published data was favorable with regard to values of Nusselt number and pressure drop. It was found that the energy efficiency varies from 72%–99% for all cases, while viscous dissipation had a highly limited effect on the energy efficiency of cases with low Reynolds number values. The exergy efficiency ranged from 26%–70%, while the entropy generation due to heat transfer was found to have a significant effect on exergy efficiency. Furthermore, while heat leakage had a considerable effect on energy efficiency, its effect was more prominent in the exergy analysis, especially for low Reynolds number and high pitch ratio cases. It was observed that while energy efficiency increases with increasing inlet temperature, exergy efficiency demonstrates a decreasing trend. Therefore, inlet temperature was determined as the most influential parameter in this analysis. The results suggest that energy and exergy efficiencies can be maximized through the selection of specific pitch ratios for various Reynolds number values. The results of this study could be useful in designing more efficient heat recovery systems, especially for low, medium, and high-temperature applications.