Numerical investigation of heat transfer and flow characteristics in eccentrically twisted oval tubes

• The innovative ETOT is designed by introducing the asymmetric geometric disturbance. • Nu increases by 38.12%, and the PEC value reaches 1.21. • The eccentricity of ETOT induces wall-attached vortices and stronger secondary flows. • The enhanced heat transfer mechanism of ETOTs is explored through field synergy theory. • Empirical correlations for Nu and f are established for ETOTs, with average errors below 5%. To overcome the performance limitations of traditional twisted oval tubes, the innovative design of eccentrically twisted oval tubes is proposed by introducing the asymmetric geometric disturbances through offsetting the twisted axis. This asymmetric structure can enhance the intensity of the secondary flow and expand the influence area of the secondary flow, thus effectively enhancing heat transfer in the eccentrically twisted oval tube. Based on the k-ω turbulence model, the influences of eccentric parameters on the thermal–hydraulic performance are numerically investigated through the analysis of temperature, pressure, and velocity fields as well as their synergistic interactions. In addition, correlations for the Nusselt number and friction factor are established. The results indicate that the performance evaluation criteria increase with both the eccentric angle and eccentric distance, reaching their maximum values in the direction of the minor axis. Specifically, when the eccentric distance is 7 mm, the Nusselt number increases by 38.12 %, and the performance evaluation criteria value reaches 1.21. This improvement can be attributed to the wall-attached vortex structures induced by the eccentricity of the twisted axis. Simultaneously, strong lateral secondary flows are generated in the eccentric direction, resulting in a 50 % increase in flow intensity compared to that in standard twisted oval tubes. These secondary flows decrease the synergy angle of velocity field and temperature gradient, thereby further contributing to the heat transfer enhancement of the eccentrically twisted oval tubes.