Numerical study on heat transfer and flow characteristics of a tube fitted with double spiral spring

Heat transfer and friction loss characteristics of a plain tube fitted with double spiral spring (DSS) are investigated by a three dimensional numerical simulation. The outer diameters of the DSS are 9 mm, 12 mm, 15 mm, and 18 mm, respectively. The simulation results indicate that the fluid in the tube inserted with DSS shows three-dimensional helical flow, and that the circumferential and the radial velocity of fluid near the tube wall are improved. At the same Reynolds number, the average radial and tangential velocities of the DSS tube are significantly higher than those of the plain tube. The Nusselt number increases and the friction factor decreases in tube with DSS insert as the Reynolds number increases. With the increase of the ds/D of DSS, the friction factor becomes higher. The field synergy principle (FSP) and entransy dissipation extremum principle (EDEP) analysis provide a reliable criterion for exploring the mechanism of heat transfer enhancement. The field synergy number of the tube inserted with DSS is much higher than that of plain tube, which indicates effective improvement of flow and heat transfer by inserted DSS. Meanwhile, the value of performance evaluation criterion (PEC) could be up to 1.5.