This study addresses a critical gap in the literature: the lack of standardized, comparative evaluation of geometrically modified twisted tapes under identical operating conditions, which has hindered objective performance assessment. To resolve this, the work presents a comparative analysis of three passive heat transfer enhancement techniques in a circular pipe using modified twisted tape inserts: Rectangular Cut Twisted Tape (RCT), Central Rectangular Cut Twisted Tape (CRCT), and Crosscut Twisted Tape with Alternate Axis (CCTA). The investigation focuses on the thermofluidic performance of these designs to determine how geometric modifications influence heat transfer efficiency. Important design parameters, such as length, width, pitch ratio, and twist angle (for CCTA), were investigated systematically and optimized using the Taguchi method for maximum thermal performance factor (TPF). Taguchi results indicate that for both RCT and CRCT, the length of the cut made the highest contribution to TPF. For CCTA, the width of the cut had the highest contribution, at 34%, among all design parameters across the inserts, followed by the twist angle with a 33.6% contribution. For CCTA, the lateral dimension of the cut and the degree of axial twisting were crucial in promoting heat transfer efficiency compared to RCT and CRCT designs, giving the highest TPF of 1.29. From flow analysis, CCTA's highest thermal performance was attributed to its ability to generate stronger swirl intensity, multiple recirculation zones, thermal homogeneity, and enhanced secondary flows, resulting in more effective fluid mixing.
Voddepalli et al. (Thu,) studied this question.