Numerical and SPIV experimental investigation of a novel arc bifurcation insert for synergistic heat transfer enhancement in tubes

The application of longitudinal swirl generators (LSGs) has received considerable attention in recent years as an effective approach for heat transfer enhancement with low consumption. This study proposes a novel insert—bifurcated arc semi-pipes (BASPs)—by introducing a curved bifurcation structure into conventional LSGs, designed to achieve synergistic heat transfer enhancement. The primary semi-pipes generate multiple longitudinal swirling flows to improve temperature uniformity of core flow region, while the curved bifurcations generate local disturbances near wall hotspots, thus improving wall temperature uniformity, with minimal mutual interference between these two mechanisms. The heat transfer enhancement mechanisms of BASPs under laminar conditions are explored via computational fluid dynamics (CFD) simulations and stereoscopic particle image velocimetry (SPIV) experiments. The complex effects of five geometric parameters (slant angle α, branching distance h, branching angle β, curvature coefficient ε, and pitch P) on the thermo-hydraulic performance and irreversibility are systematically examined. The Nusselt number increases to 3.34–9.47 times that of the smooth tube, while the friction factor rises to 2.59–10.23 times. The maximum performance evaluation criteria (PEC) reaches 4.63. Furthermore, geometric parameters of BASPs are optimized based on the dissipation minimization principle. A design on the obtained Pareto front achieves a Nusselt number enhancement of 8.71 times, surpassing all training cases under the same Reynolds number, and the compromise solution also attains a PEC value of 4.12, confirming the theoretical guidance provided by the dissipation minimization principle.