Thermodynamic optimization of a heat exchanger tube mounted with integrated-winglet twisted-tapes

This study introduces integrated-winglet twisted tapes (IWTTs) as passive enhancers for constant-flux air flow in a circular tube, targeting simultaneous gains in both first- and second-law metrics. A realizable k-ε RANS model with second‑order spatial discretization, tight residual criteria, and grid‑independence checks was employed over 5,000 ≤  Re  ≤ 20,000. The results are benchmarked against a plain tube (PT) and a traditional twisted tape (TTT). Eleven cases were assessed, spanning three winglet lengths and lifts. Among them, the IWTT-Lr0.033-Hr0.017 consistently delivered the best integrated performance. First‑law evaluation shows a peak thermal performance factor ( TPF ) = 1.58 at Re  = 5,000. The TPF for the IWTT-Lr0.033-Hr0.017 remains above unity (1.58→1.01) throughout the range. For the same case, the Nusselt number increases from 51.39 to 91.64 across the examined window, with Nu/Nu₀ values of up to 2.82, exceeding the TTT counterpart by 8% at Re  = 5,000. Second‑law indicators corroborate these gains. Exergy destruction is reduced from 316.52 W (PT) to 79.89 W (Lr0.033-Hr0.017) at Re  = 5,000 (a 75% reduction) and remains 7–12% lower than the TTT over the range. Total entropy generation for the Lr0.033-Hr0.017 remains low and weakly varies ( S _total ≈ 0.266–0.304), while the Bejan number is high (≈ 0.9997–0.9875), indicating the dominance of heat‑transfer over frictional irreversibility. This performance is attributed to winglet‑induced secondary swirl flow that disrupts the near‑wall boundary layer and augments convection while moderating pressure penalties under cube‑root weighting in TPF . Collectively, these findings establish the IWTT‑ Lr0.033-Hr0.017 as the most effective option in the present matrix and a promising insert for compact, air‑cooled heat exchangers where dual‑law (energy and exergy) improvements are required.