Thermo-hydraulic enhancement of turbulent tube heat exchangers using novel perforated helical twisted tape inserts

Abstract

This article presents an experimental investigation of the thermo-hydraulic performance of a single-pass forced convection tube heat exchanger equipped with perforated helical twisted tape (PHTT) inserts. Building upon the baseline helical twisted tape (HTT), the present work introduces three novel parameters: (i) a perforation diameter ratio p/D (0.10, 0.15, 0.20) carved into the tape body in a staggered inline pattern; (ii) an extended Reynolds number range from 3,000 to 30,000 (a 43% extension beyond the baseline 21,000 ceiling); and (iii) empirical Nu and f correlations covering the full three-parameter (DR, TR, p/D) design space. Air is the working fluid under a uniform heat flux of 1,000 W/m². Measurements are validated against the Dittus– Boelter and Blasius correlations within 4.73% and 7.11% respectively. Perforated tapes at p/D = 0.15 generate additional radial fluid jets that disrupt the thermal boundary layer while partially relieving flow blockage, producing a peak Nusselt number ratio of 5.3× over the plain tube (DR = 0.5, TR = 2) — a 32% gain over the solid HTT baseline. The optimal thermal performance factor of η = 1.48 is achieved at DR = 0.8, TR = 4, p/D = 0.15 at Re ≈ 5,000, representing a 21% improvement over the best solid-tape result. Empirical power-law correlations (R² = 0.978 and 0.963 for Nu and f) provide a practical design tool. Results are benchmarked against 10 published studies, confirming the PHTT at p/D = 0.15 as superior across the full turbulent Re range.