LAUSR

Abstract The effect of perforated twisted tapes with alternate axis (PATT), perforated twisted tapes (PTT) and regular twisted tapes (TT) with twist ratios (TR) of 3,4 and 5 are compared by experimental investigation in a circular tube under constant heat flux condition. Using water as the testing fluid, experiments are conducted within the Reynolds number range of 3000–16000. The heat transfer rates in the tube fitted with PATT, PTT and TT are respectively improved up to 48.12%, 44.3% and 33% of that in the plain tube. Similarly, the increase in friction factor for PATT, PTT and TT is 19.1%, 17.6% and 15.85% respectively, compared to that of the plain tube. For all inserts, the empirical correlations were established for Nusselt number and friction factor along with plain tube and the obtained correlations are fitted with the experimental data. At constant pumping power, the maximum thermal performance factor obtained is 1.433, 1.396 and 1.24 respectively for PATT, PTT and TT. Hence, the passive element which gives better energy efficiency along with lower operating cost is suggested for practical heat transfer applications.