Experimental thermal–hydraulic evaluation and correlation development of geometrically modified wire-matrix turbulators in the tube side of double-pipe heat exchangers

Passive tube inserts, such as wire-matrix (WM) turbulators, are widely used to enhance convective heat transfer in tubular heat exchangers by increasing flow disturbance and promoting mixing. However, the role of WM geometric parameters under turbulent single-phase flow has not been systematically quantified. This study experimentally examines the effects of ring height, ring width, and pitch on the tube-side thermo-hydraulic performance of a counter-flow double-pipe heat exchanger using water, covering Reynolds numbers (Re) from 4400 to 9000. Seven WM configurations are fabricated, and the Nusselt number (Nu), friction factor (f), and performance evaluation criterion (PEC, based on constant pumping power) are compared with a plain tube. Increasing the ring height and width, and decreasing the pitch, intensify disturbance and mixing, enhancing both Nu and f. Results show that Nu improves by 1.37–3.66 times relative to the plain tube, while PEC ranges from 0.52 to 1.56, indicating that only certain geometries provide net thermo-hydraulic benefits under equal pumping power. The best performance occurs with the largest ring height and width and the smallest pitch, achieving a PEC of up to 1.56 and remaining near or above unity at low-to-moderate Re values. Empirical correlations for Nu and f are developed and validated to support the practical design of tubular heat exchangers where pumping power is limited and enhanced heat-transfer duty is required.