Heat transfer and friction characteristics of turbulent flow through plain tube inserted with rotor-assembled strands

The paper reported thermohydraulic characteristics of turbulent flow in the circular smooth tubes equipped with rotor-assembled strands of different diameters and leads with Reynolds number ranging from 20,000 to 75,000. An experiment using a smooth tube was done to calibrate the experimental system and data reduction method. The effects of the rotor diameter and lead on the heat transfer augmentation, friction factor and PEC value have been presented respectively. The obtained results of inserted tube revealed that rotor-assembled strand significantly improved heat transfer with the Nusselt number increased by 91.4–178.7% and friction factor increased by 158.5–295.9% within the experimental Reynolds number range. The comparisons of different rotor-assembled strands inserted tubes and plain tube showed that the heat transfer benefited from the growing diameter and decreasing lead of rotor-assembled strands, the friction factor increased with the increasing diameter and the decreasing lead of rotor-assembled strands, and PEC value increased with an increase of rotor diameter and lead. Based on thorough multivariate linear normal regression method, the correlations of average Nusselt number, friction factor and PEC value are presented.