Experimental investigations of heat transfer enhancement by plane and curved winglet type vortex generators with punched holes

• Plane and curved winglet VGs with and without holes experimentally investigated.
• Curved delta winglet has best thermohydraulic performance among 6 VGs without hole.
• The hole on VG improves thermohydraulic performance and decreases flow resistance.
• Smaller hole diameter presents better performance for VG with small face area.
• The hole at lower position and at centerline in lateral has better performance.

Experiments were carried out to investigate the performance of plane and curved winglet (rectangular, trapezoidal and delta) vortex generators (VGs) with and without punched holes. Effects of hole diameter and positions on the performance of VGs were evaluated using dimensionless numbers – j/j0, f/f0 and R = (j/j0)/(f/f0). The results showed that curved winglet type VGs (CRWP, CTWP and CDWP) have better heat transfer enhancement and lower flow resistance than corresponding plane winglet VGs in both laminar and turbulent flow regions. CDWP presents the best thermohydraulic performance followed by CTWP (α = 20°) covering all flow regions. The punched holes really improve the thermohydraulic performance of VGs and decrease the flow resistance for all cases; but the optimal diameter of the holes needs to be matched with the VG face area, i.e. the smaller the VG face area, the relatively smaller hole diameter is better. The hole punched at lower position in vertical direction and at the centerline of lateral direction presents better heat transfer enhancement and thermohydraulic performance; but hole positions have slight influence on the flow resistance of VGs. The results indicate the advantages of using curved winglet VGs with punched holes in the surface for heat transfer enhancement.