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 Δp. Among the studied models, the 0° turbulators give the highest values, followed by the 90° and 180° turbulators come in the second and third, respectively. The use of 0° 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° and 180° turbulators are 133.2 %–102.7 % and 54.6 %–42.1 %, respectively. The numerical results display that the 0° 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° 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° turbulators at the Reynolds number of 1643.