A Comparative study on thermo-hydraulic performance in a tube with different punched winglets

In this work, heat removal and flow behaviors of rectangular winglet vortex generators (VGs) in a heated tube are analyzed experimentally and numerically. The object of present work is to quantify the heat removal perfor-mance of VGs with five different holes (circular, regular triangle, square, rectangular, and rhombus). The winglet parameters include three different pitch ratios (PR = 1.63, 3.27, 4.89) at a fixed attack angle (alpha = 45). Com-parisons of thermal performances between planar VGs and drilled VGs are made. It is found that jet flow from holes boosts local heat removal but weakens heat removal of the entire tube. Visualization of the temperature fields and local turbulent kinetic energy fields show that the holes with circular shapes are beneficial for fluid to pass through the hole with rotation. This kind of flow pattern results in a relatively intense flow mixing in the recirculation region, which boosts local heat removal. However, the holes with sharp corners are not helpful to heat removal enrichment. Thermal enhancement factor (TEF), the ratio of the boosted heat removal and cost in energy, is used to scale the comprehensive performance. The maximum TEF is 1.14 for Case A (circular hole) at Re = 9090.