Experimental and numerical studies of air flow and heat transfer due to insertion of novel delta-winglet tapes in a heated channel

Abstract

The use of vortex-generators is one of the most effective ways to enhance the thermal performance of heat exchangers. The vortex-generators are commonly designed and made in two forms: wings and winglets. In this work, an investigation is carried out on a heated channel equipped with the novel delta-winglet tapes (DWTs). Eight non-uniform arrangements of the delta-winglets with variable pitches and heights along the axial direction are proposed and compared with the original model as the uniform case. All cases are studied experimentally, and also numerical simulations are used to analyze the corresponding mechanisms. The thermal and hydrodynamic characteristics are reported using the dimensionless parameters of Nusselt number, friction factor, and overall performance index for the Reynolds number range between 1643 and 8215. The results show that equipping the channel with the non-uniform DWTs affects the performance of the channel, and in some cases, it leads to better thermal performance compared to the uniform tape. The range of the variations is between 0.88 and 1.14 times for the Nusselt number and between 0.95 and 1.49 times for the friction factor. In general, placing the delta-winglets with longer height or shorter pitches at the upstream of DWTs improves the channel's thermal performance. The maximum Nusselt number ratio of 1.62 is recorded for the DWT in which the height of delta-winglets is from High to Low with the uniform arrangement of pitches. On the other hand, the DWT with the uniform heights of delta-winglets and Low to High arrangement of pitches possess the best overall performance among the studied cases. The performance index for this model is in the range of 1.44 to 1.07.