Thermal-hydraulic performance in a tube with punched delta winglets inserts in turbulent flow

A punched delta winglet (PDW) was proposed and investigated numerically and experimentally in a turbulent flow. The effect of delta winglets with different punching holes on heat transfer performance was studied. The experimental results showed that the fluid in the core flow region and the near-wall region was fully mixed due to the blocking effect of the delta winglets on the fluid. Due to the guidance of the PDWs, the recirculation region in the near-wall region was diminished because of the impaction of the fluid from the core flow region, which enriched the local heat transfer rate in this area. However, the jet flow from the punched holes restrained the longitudinal vortices behind the vortex generators. As a result, the heat transfer coefficient was reduced slightly in this area and the pressure loss of the channel was decreased. Moreover, the heat transfer coefficient and friction factor were lower with the largest area of the hole. When the area of the punched holes was the same, the thermal enhanced factor (TEF) was the largest at the large width and low height of the hole. In addition, the heat transfer coefficient and friction factor increased with the decrease of pitch ratio (PR). The maximum TEF was 1.49 for PR = 1.0, w = 6 mm, h = 2 mm at Re = 9090, which provided a basis for practical application.