Heat transfer enhancement in circular tubes using helical swirl generator insert at the entrance

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 degrees, 45 degrees and 60 degrees 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 (alpha) 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. (C) 2007 Elsevier Masson SAS. All rights reserved.