Turbulent Heat Transfer and Pressure Drop in Tube Fitted with Square-cut Twisted Tape

Heat transfer, friction factor and thermal enhancement factor characteristics of a double pipe heat exchanger fitted with square-cut twisted tapes (STT) and plain twisted tapes (PTT) are investigated experimentally using the water as working fluid. The tapes (STT and PTT) have three twist ratios (y = 2.0, 4.4 and 6.0) and the Reynolds number ranges from 2000 to 12000. The experimental results reveal that heat transfer rate, friction factor and thermal enhancement factor in the tube equipped with STT are significantly higher than those fitted with PTT. The additional disturbance and secondary flow in the vicinity of the tube wall generated by STT are higher compared to that induced by the PTT is referred as the reason for better performance. Over the range considered, the Nusselt number, friction factor and thermal enhancement factor in a tube with STT are respectively, 1.03 to 1.14, 1.05 to 1.25 and 1.02 to 1.06 times of those in tube with PTT. An empirical correlation is also formulated to match with experimental data of Nusselt number and friction factor for STT and PTT.