Convection Heat Transfer, Entropy Generation Analysis and Thermodynamic Optimization of Nanofluid Flow in Spiral Coil Tube

In this study, heat transfer, flow characteristics, and entropy generation of turbulent TiO₂/water nanofluid flow in the spiral coil tube were analytically investigated considering the nanoparticle volume fraction, curvature ratio, flow rate and inlet temperature between 0.01–0.05 percent, 0.03–0.06, 1.3–3.3 l/min, and 15–27 °C, respectively. Results showed that the augmentation of the nanoparticle volume fraction increased the Nusselt number and friction factor up to 11.9% and 1.1%, respectively, while it reduced the entropy generation number up to 10.9%. Reducing the curvature ratio led to a maximum of 11.1% increase in the Nusselt number, while it resulted in a 5.6% increase in the entropy generation number. A decline in the inlet temperature from 21 °C to 15 °C proceeded a 28.4% and 7.1% increase in the heat transfer and pressure drop, respectively. The total entropy generation reduced with increasing nanoparticle volume fraction. For a low Reynolds number, a decrease in the curvature ratio led to a reduction in the total entropy generation, while reducing the curvature ratio was detrimental for a high Reynolds number. Analytical relations for optimum curvature ratio and optimum Reynolds number were derived. For the range of parameters studied in this paper, a range of optimum Reynolds number from 9000 to 12,000 was proposed.