Heat transfer study in rotating smooth square U-duct at high rotation numbers

Rotation effects on heat transfer in a rotating smooth square U-duct at high rotation numbers have been experimentally investigated via classical copper plate technique. In order to obtain convincing correlations, an extensive heat transfer data are measured. The Reynolds number ranges from 10,000 to 70,000, and the highest rotation number reaches to 2.08. Besides, the mean density ratio maintains around 0.14 in all working conditions. Due to these experimental data, two interesting phenomena are observed in current work. Firstly, in consistent with the previous study, the critical rotation number phenomenon on leading wall (heat transfer on a specific location is weakened by rotation at first, then after a critical Ro, the descending trend is reversed) in radial outward channel is observed. Moreover, we found that the critical Ro varies with dimensionless location parameter XID. Interestingly, the product of critical Ro and MD is a constant. Secondly, in radial inward passage, the heat transfer enhancement on leading wall is lower than trailing wall at high rotation numbers, which differs from low Ro scenario. Possible explanations for these two phenomena are proposed. It seems that centrifugal buoyancy force plays an important role in influencing the flow and heat transfer in this channel at high rotation numbers. The interactions of buoyancy and Coriolis force act in different ways in radial outward and inward passages, and are responsible to these phenomena mentioned above. Finally, comprehensive correlations on leading and trailing surfaces in both legs are fitted. The effects of Ro and XID are included in these correlations simultaneously. (C) 2013 Elsevier Ltd. All rights reserved.