Numerical Study of Turbulent Nanofluid Flow in Double-Tube Heat Exchanger: The Role of Second Law Analysis

In this paper flow features and heat transfer characteristics of finned and finless double-tube counter flow heat exchanger at wide range of Reynolds numbers were numerically analyzed. Various fins configurations combined with use of water-based TiO2 nanofluid at different nanoparticles volume concentrations were employed in this study to show their effects on nanofluid Nusselt number, friction factor and thermal performance index. Furthermore, the thermal perfection and the overall assessment of heat exchanger were also taken into account in the light of thermodynamics second law efficiency which is defined as a ratio of recovered to expended exergy. The results showed that thermo-hydrodynamical performance of heat exchanger was intensively dependent to the thickness of embedded fins. Employed sensitivity analysis revealed that fins with large thicknesses equal or larger than 10 mm provide better thermal performance than fins with small thicknesses (i.e. t = 1 mm). Furthermore, the use of circular fin with thickness as large as 10 mm at the highest Reynolds number up to about 87,500 led to pronounce both Nusselt number and flow resistance up to 15% and 4.64 folds, respectively. On the other hand, using smooth heat exchanger operating at the lowest Reynolds number (i.e. Re = 3400) filled with 1% TiO2 water-based nanofluid led to obtain the highest recovered exergy and thermodynamic second law efficiency up to 0.46 W and 10.33%, respectively.