Thermo-Hydraulic Performance and Entropy Generation Analysis of Serpentine and Straight Tubes with Twisted Tape Inserts Using SST k-ω Turbulence Modeling

Serpentine heat exchangers are extensively used in energy and chemical engineering owing to their compact geometry and high thermal performance. To improve their efficiency, three-dimensional numerical simulations are conducted using the SST k-ω turbulence model for both serpentine and straight tubes fitted with twisted tape inserts. Three twist ratios (y = 5.77, 8.57, 12.48) are examined across a Reynolds number range of 10,000 to 22,000. Results show that the average Nusselt number increases with Reynolds number, while the friction factor decreases. In particular, due to curvature-driven secondary motions, serpentine configurations consistently outperform straight tubes in thermal performance. The addition of twisted tapes intensifies fluid mixing through strong swirl generation, disrupting the thermal boundary layer and significantly enhancing heat transfer, albeit with increased flow resistance. Among all cases, the lowest twist ratio (y = 5.77) generates the strongest swirl intensity and highest turbulent kinetic energy, yielding maximum thermal augmentation but also the greatest pressure drop. Performance Evaluation Criterion analysis indicates PEC > 1 for all twisted tape configurations under equal pumping power, confirming an overall beneficial trade-off between enhancement and hydraulic penalty. Entropy generation results further demonstrate that improved thermal performance is accompanied by higher irreversibility. Overall, the combination of serpentine geometry with low to moderate twist ratios offers the most favorable thermo-hydraulic balance for compact heat exchanger optimization.