The experimental study on the heat transfer and friction factor characteristics in tube with a new kind of twisted tape insert

In this paper, an experimental research was carried out to study the heat transfer and friction factor characteristics in a tube with a new kind of twisted tape insert. Four twisted tapes with different lengths (2400, 1800, 1200 and 600 mm) were used in the experimental study. The experimental data revealed that Nusselt number caused by these four twisted tapes were 1.45-1.90, 1.23-1.55, 1.18-1.45 and 1.15-1.37 times of that for the plain tube, while the values for friction factor were 3.69-5.75, 2.30-4.48, 2.15-2.75 and 1.21-1.31. The performance evaluation criteria (PEC) for length ratio of 1.0, 0.75, 0.50 and 0.25 is 0.94-1.06, 0.82-0.94, 0.89-1.04 and 0.89-1.06, respectively. What's more, correlations for Nusselt number and friction factor were established in the paper. The predicted values calculated by correlations were in good agreement with experimental data, within 7% for Nusselt number and within 10% for friction factor.