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This paper presents an experimental study of heat transfer and friction characteristics in decaying turbulent swirl flow generated by a short helical tape placed at the entrance of the test section. In the experiments, total mass flux was varied from 160 kg m−2 s−1 to 1628 kg m−2 s−1 and the momentum ratio ( M h / M T ) was varied from 0 to 8.6. The experiments were conducted for water flow rates in the range of 5000 ⩽ Re ⩽ 30 000 . Three different helical tapes with helical angels of 30°, 45° and 60° were used. Experimental results confirm that, the use of a helical tape inserted to the tube leads to a higher heat transfer rate than the non-swirling flow. The local heat transfer coefficients were found to be increasing to very high values along the downstream of the helical tape, and then decreasing with the distance ( x / L ). The augmentation of heat transfer was found to be the function of the momentum ratio, M h / M T and Reynolds number. No pronounced effect of the number of the helical channels ( N h ), and helical angle (α) on heat transfer was observed. It is found that using the helical tape can help to increase the heat transfer rate up to 20% depending on M h / M T and Re at constant pumping power. Enhancement efficiency increases with increasing momentum ratio and decreases with increasing Reynolds number. |
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