Heat transfer of swirling impinging jets with TiO2-water nanofluids

An experimental work has been carried out to study the heat transfer of swirling impinging jets (SIJs) with TiO2-water nanofluids using thermochromic liquid crystal technique. Experiments were carried out at constant jet-to-target spacing ratio (L/D) of 1.0, 2.0, 3.0 and 4.0 for Reynolds numbers from 5000 to 20,000 by using nanofluids with TiO2 concentrations of 0.5%, 1.0%, 1.5%, 2.0% and 2.5% by volume, twisted tapes with twist ratios (y/W) of 4.0, 5.0, 6.0 and 7.0. Conventional impinging jets (CIJs) and swirling impinging jets (SIJs) with pure water were also tested, for comparison. At similar operation conditions, swirling impinging jets (SIJs) offer superior heat transfer to conventional impinging jets. It is also found that the nanofluids with concentrations of 0.5%, 1.0%, 1.5% and 2.0% by volume give higher Nusselt numbers than the base fluid (water) while the one with concentration of 2.5% shows opposite result. Over the studied range, the optimum condition where the maximum Nusselt number is achieved at TiO2-water nanofluids with concentration of 2.0% by volume and y/W = 6.0. (C) 2017 Elsevier B.V. All rights reserved.