Local heat transfer augmentation in a square channel with delta wing vortex generators

The influence of delta wing vortex generators (DWVGs) on local heat transfer characteristics in a square channel was investigated experimentally. The influence of pitch-to-vortex generator height ratio (P/e = 4, 8, 12 and 16), Reynolds number (Re = 8000, 12000, 16000, 20,000 and 24,000) and vortex generator height-to-hydraulic diameter ratio (e/Dh = 0.2, 0.3, 0.4 and 0.5) on Nu and Nu‾ were studied. The Nu distribution was obtained using thin-foil heating and infrared thermal imaging. The Nu characteristics of delta wing vortex generators of different configurations were compared with those of a smooth duct. As the Reynolds number (Re) increased from 8000 to 24,000, the Nusselt number (Nu) increased for both the smooth and DWVG-equipped ducts owing to improved turbulent mixing and a thinner thermal boundary layer. The DWVGs increased the heat transfer, with the maximum Nu increasing from 6.33 in the smooth duct to 304.1 at Re = 24000. The findings show that a smaller P/e ratio and higher e/Dh ratio lead to better heat transfer performance. This is because closely spaced and larger DWVGs resulted stronger vortices, enhanced secondary flow mixing and consistently disrupted the thermal boundary layer of the channel. When P/e was increased from 4 to 16 at Re = 8000 and e/Dh = 0.4, Nu decreased from 178.7 to 117.1, resulting in a 34.5% reduction. Conversely, increasing e/Dh from 0.2 to 0.5 at P/e = 4 increased Nu from 54.37 to 72.65, which is a 33.6% improvement. A correlation of Nu‾ was developed based on Re, P/e and e/Dh with a maximum deviation of ±11% to predict and optimize the Nu distribution in a square channel with delta wing vortex generators.