Study On Convective Heat Transfer Enhancement Of Longitudinal Swirl Flow In Tube

With the development of economy,the energy problems have become increasingly prominent,and the energy conservation and emission reduction has become one of the major development strategies of the country.Heat exchanger is a general heat and mass exchange device and is widely used in industry.Heat transfer enhancement technology can improve the heat transfer performance of heat exchangers,but often causes additional power consumption,which weakens the effect of energy saving.Based on the longitudinal swirl flow structure obtained by the optimization principle and the design experience of passive heat transfer enhancement technology,the tube insert is developed under different working conditions,and the relevant flow and heat transfer performance is studied through numerical simulation and experiment.The drainage vortex generator structure is designed for the heat transfer characteristics of laminar flow conditions.The numerical simulation result and PIV experiment show that the drainage vortex generator can effectively generate multiple pairs of longitudinal vortex structures and guide the fluid to wash the wall surface,which is a better kind of tube insert.Meanwhile,the effects of spacing,central angle and height of vortex generator on flow and heat transfer performance were studied.The results show that both the heat transfer and flow resistance decrease with the increase of the spacing,and increase with the increase of the central angle and the height of the vortex generator.Moreover,the empirical formulas related to the flow and heat transfer parameters of the vortex generator were fitted,and the enthalpy efficiency analysis was carried out.Finally,the performance factor R3 was applied under the same pump power as the evaluation index.It is found that the R3 value is higher in the equivalent laminar flow region and moderate in the transitional flow region.The winglet vortex generator structure is designed for the heat transfer characteristics of turbulent conditions.Simulation results show that the winglet vortex generator can also generate multiple pairs of longitudinal vortex structures.Meanwhile,the effect on the flow and heat transfer performance were studied of the attack angle and the spacing of the rectangular winglet vortex generator.The results show that the heat transfer ratio decreases with the increase of Reynolds number and the pitch,and the heat transfer capacity of the angle of attack ?=45° is the best.The resistance ratio increases with the increase of the Reynolds number and the attack angle,and decreases with the increase of the pitch.Moreover,the effect of perforation was investigated on the performance of the winglets.The resistance is reduced by the perforated structure,but the overall heat transfer performance is also reduced accordingly.Based on the rectangular winglets,the effects of the shape,number,attack angle and circumferential arrangement of the winglets on flow and heat transfer performance were further studied.Finally,the PEC value of various vortex generators was investigated under the same working conditions.The winglet vortex generator structure is found to have a moderate performance.