The heat transfer enhancement (HTE) in tubular heat exchangers fitted with vortex-generator (VG) inserts is experimentally investigated. The studied four parameters and ranges are:winglets-pitch ratio (1.33

2.67

and 4)

winglets-length ratio (0.33

0.67

and 1)

winglets-width ratio (0.2

0.4

and 0.6)

and Reynolds number (5200 to 12200). The testing fluids are the water and Cu-water nanofluid at the volumetric fraction of 0.2%. The results obtained on HTE

pressure drop

and performance evaluation criterion (PEC) are compared with those for water in a smooth tube. It is found that the VG inserts with lower winglets-pitch ratio and higher winglets-length/width ratios present higher values of HTE and pressure drop. Over the range studied

the maximum PEC of 1.83 is detected with the Cu-water nanofluid inside the tube equipped with a VG insert at the winglets-width ratio of 0.6 for the maximum Reynolds number

when the heat transfer rate and pressure drop are 1.24 times and 2.03 times of those in the smooth tube. Generalized regression equations of the Nusselt number

friction factor

and PEC are presented for the tubular heat exchangers with the VG inserts for both water and Cu-water nanofluid. It is concluded that the main advantage of the VG inserts is their simple fabrication and considerable performance

particularly at higher Reynolds number.