Heat transfer enhancement of wavy finned flat tube by punched longitudinal vortex generators

Punched longitudinal vortex generators (LVGs) were employed to enhance air-side heat transfer on the wavy fin surface of flat tube used in direct air-cooled condenser. The heat transfer enhancement of four types of the longitudinal vortex generators with different attack angles were compared by numerical simulations. It was found that the delta winglet pair with attack angle 25° could reach the greatest performance evaluation criteria (PEC) under the conditions of the inlet air flow velocity varied from 1 m/s to 5 m/s. The influences of locations on the wavy fin surface and the row number of the longitudinal vortex generators were also discussed. One delta winglet pairs at the middle of the wavy fin surface and the minimum row number, n = 1, with the average PEC is 1.23, has the best heat transfer performance of all conditions, which can be recommended for practical applications. Experimental study in wind tunnel with flow field visualization by Particle Image Velocimetry (PIV), as well as the numerical simulations verified that the delta winglet pairs can generate obvious longitudinal vortex pairs at the down-sweep zone, which can enhance the heat transfer between the cooling air flow and heated wall surface with acceptable pressure loss.