Abstract:

Water was used as a working medium to investigate the internal heat transfer and flow resistance properties of the twisted tube with large twist ratio in the conditions of variable short-long diameter ratio （ B/A = 0. 27- 0.47） and twist ratio （the lead-to-diameter ratio, S/de = 17.19 - 50.62）. Experimental results indicate that the B/A value greatly affects the internal Nusselt number and friction factor of the twisted tube because the parameters decrease with the increase of B/A and S/de values, more rapidly with the former, and that the Nusseh number and friction factor of the twisted oblate tube increase respectively by 30% - 150% and 20% - 50% , as compared with those of the smooth tube at the same Reynolds number and Prandtl number. Moreover, the formulae of Nusselt number and friction factor of the twisted oblate tube with large twist ratio are both deduced based on the multiple linear regression of experimental data, the maximum errors of which being respectively 12% and 6%. The proposed formulae lay a foundation for the design of heat exchanger with twisted oblate tubes.

Key words: twisted oblate tube, heat transfer enhancement, flow resistance, twist ratio