Heat Transfer and Friction Factor in a Tube Equipped with U-cut Twisted Tape Insert

Experimental investigation of heat transfer and friction factor characteristics of circular tube fitted with plain twisted tapes (PTT) and U–cut twisted tapes (UTT) with twist ratios y = 2.0, 4. 4 and 6.0 were studied. The experimental data obtained from plain tube and PTT were verified with the standard correlation to ensure the validation of experimental results. The experimental results reveal that heat transfer rate, friction factor and thermal enhancement factor in the tube equipped with UTT significantly higher than those in the tube fitted with PTT and plain tube. The additional disturbance and secondary flow in the vicinity of the tube wall generated by the UTT compared to that induced by the PTT is referred as the reason for the enhancement. Subsequently an empirical correlation is also formulated to match with experimental results with ± 6% and ± 5%, variation respectively for Nusselt number and friction factor.