Heat transfer enhancement of internal flow by inserting punched delta winglet vortex generators with various attack angles

Effects of punched delta winglet vortex generator inserts (PDWVGs) on single-phase forced convection heat transfer and friction loss of internal flow were experimentally investigated. The PDWVGs were manufactured by punching directly on aluminum strips with different attack angles (α) of 30°, 50° and 70°. Winglet-pitch ratio (Rp) and a winglet-width ratio (Rb) of PDWVGs were 1.05 and 0.42, respectively. Longitudinal strip and plain tube were also tested for comparison. The experiments were carried out under the conditions of Reynolds number from 5500 to 14500. Experimental results reveal that the PDWVG insert in a tube provided considerably higher heat transfer coefficient than the tube without the insert through pressure loss was also increased. The Nusselt number and friction factor increased with the increasing of α. The heat transfer enhancement by the PDWVGs with α of 30°, 50° and 70° provided higher than the plain tube in the range of 110-131%, 157-188% and 218-264%, respectively. The average friction factors in the inner tube generated by the PDWVGs with α of 30°, 50° and 70° were about 8.80, 10.21 and 11.87 times above the plain tube, respectively. The thermal enhancement factor was in the range of 0.91-1.22 for PDWVGs and 0.88-0.99 for L-S. In addition, the empirical correlations of Nusselt number, friction factor and thermal performance factor for PDWVGs were developed from the experimental results.