Heat transfer investigation in a rotating U-turn smooth channel with irregular cross-section

In the current study, heat transfer performance in a rotating U-turn smooth channel with engine-similar irregular cross-section was investigated experimentally. The channel consists of an inlet pass with irregular cross section (d1 = 24.5 mm), a sharp 180-degree turn, and an outlet pass with nearly rectangular cross section (d2 = 19.6 mm). In the experiments, the Reynolds number ranges from 25,000 to 50,000 for the inlet pass and 31,000 to 62,000 for the outlet pass, respectively. In addition, the highest rotation number is 0.72 for the inlet pass and 0.37 for the outlet pass. The mean density ratio maintains around 0.138 in all working conditions. The results indicate that the cross-section affects the heat transfer in both stationary and rotating conditions; but the strengths of effect are different. In the stationary case, the Nu/Nu0 ratio on the trailing side is up to 1.5 times of that on the leading side in the inlet pass. In the rotating case, the Nu/Nu0 ratio is up to 4.3 on the trailing side in the inlet pass, but not changing remarkable on the leading side and all sides in the outlet pass. Due to the shrinking hydraulic diameter of the outlet pass, the Nu/Nu0 ratio in the outlet pass is approximately 1.5 times of that in the inlet pass. In the outlet pass, the Nu/Nus ratio shows different trendency with Ro at different Reynolds numbers, which means that the Nu/Nus-Ro graph cannot eliminate the influence of Re for the current work.