The Effect of Combined Circular and Hexagonal Perforation on Multi-Blade Twisted Tape on Thermal-Hydraulic Performance

Twisted tape is a passive method to enhance the thermal hydraulic performance of heat exchangers, but increasing the number of blades in a multi-blade twisted tape (MBTT) can lead to flow blockage and reduce performance at high blade counts. This study evaluates alternating circular-hexagonal perforations on multi-blade twisted tape (MBTT) with 2, 4, 6, and 8 blades at Reynolds numbers of 6,000–22,000 using Computational Fluid Dynamics (CFD). Performance is evaluated based on the Nusselt number, friction factor, pressure drop, and Performance Evaluation Criterion (PEC). The results show a maximum Nusselt number increase of 82.0% on MBTT 6-H at Re=22,000, while a maximum PEC of 1.136 is obtained on MBTT 2-C-H. In the MBTT 8-C-H configuration, the pressure drop reaches 12,246.76 Pa and the PEC decreases to 0.851. The results indicate that circular–hexagonal perforation can maintain an increase in heat transfer at a high number of blades, but the hydraulic penalty becomes more dominant in the eight-blade configuration.