Flow and thermodynamic behavior of viscoelastic fluids in twisted oval tubes

The flow and heat transfer behavior of viscoelastic fluids in twisted oval tubes (TOT) under various Reynolds (Re) and Weissenberg (Wi) numbers are investigated numerically using a finite volume method based on the FENE-P model. Results show that the viscoelasticity increases the flow resistance and reduces the heat transfer efficiency, leading to a performance evaluation criterion (PEC) reduction of up to 20%. As the Wi number increases, even though TOT exhibits greater heat transfer degradation due to stronger coupling between helical streamline deformation and elastic stresses, TOT still maintains a 15% thermal-hydraulic advantage at Re = 500 compared with a circular pipe. Further analysis reveals that the field synergy angle (FSA) only partially describes viscoelastic flow behavior in TOT, particularly at Re = 500. While the vorticity field synergy angle (VFSA) better captures the Nu-Wi trend, suggesting that the field synergy principle is useful for optimizing heat transfer but not for precise performance prediction. These findings provide insights into the complex interactions of viscoelastic fluids in TOT and offer guidance for heat exchanger design.