Effects of transversely twisted-turbulators on heat transfer and pressure drop of a channel with uniform wall heat flux

Air flow and heat transfer through a rectangular channel equipped with transversely twisted-turbulators are studied experimentally. Three twist-angles and two pitch-ratios are considered to explore the effects of design factors. To create a better understanding of possible mechanisms, a numerical simulation is also carried. The experimental data show that decreasing twist-angle and pitch-ratio increases both h and Ap. Among the studied models, the 0 degrees turbulators give the highest values, followed by the 90 degrees and 180 degrees turbulators come in the second and third, respectively. The use of 0 degrees turbulators enhances h by about 141.2 % at pitch-ratio of 1.875 and 109.4 at pitch-ratio of 3.75, but these enhancements for the models with 90 degrees and 180 degrees turbulators are 133.2 %-102.7 0/0 and 54.6 %-42.1 %, respectively. The numerical results display that the 0 degrees turbulators are more effective in fluid dispersion towards hot walls and generate stronger swirl flows. However, the best overall performance is seen for the 90 degrees turbulators. It is also found that at min. Re, the models with lower pitch-ratio show a better overall performance, while at the max. Re, an inverse outcome is found. The highest performance index of 1.62 is recorded for the 90 degrees turbulators at the Reynolds number of 1643.