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Start date: 2020Subject: search.filters.subject.Twisted tape

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    Thermodynamic performance analysis of a round tube fitted with gradient quadruple twisted tapes
    (2026-03-01)
    Samruaisin, Prachya
    ;
    Liengsirikul, Sathaporn
    ;
    Thianpong, Chinaruk
    ;
    Chuwattanakul, Varesa
    ;
    Chamoli, Sunil
    Air-cooled heat exchangers employing twisted-tape passive inserts exist in many forms; however, designing tapes that are practical to manufacture while enhancing heat transfer without incurring excessive pressure drop remains challenging. This study therefore introduces gradient quadruple twisted tapes (GQTT), which gradually vary the pitch across four tapes to control swirl and mix along the tube. In addition, the turn count changes in steps along the four tapes, which triggers extra turbulence near each change and keeps the flow well mixed downstream. This simple and manufacturable pattern aims to boost heat transfer while keeping the added friction under control. Our objective is to evaluate whether GQTT can improve overall performance while keeping the pressure drop within a practical range, in comparison with a plain tube and a constant-turn tape. A realizable k-ε turbulence model, rigorously validated against benchmark data, was applied to eight GQTT variants and benchmarked against a plain tube and a constant-turn tape for Reynolds numbers (Re) between 5000 and 19,000. Spatial second-order schemes, grid-independence testing, and strict residual criteria ensured solution accuracy. Among the candidates, the descending-opposite-pitch configuration (Ds-OPSD) consistently delivered the highest performance. First-law analysis reveals a peak thermal performance factor (TPF) of 1.42 at Re = 5000, equating to a 42 % gain in overall thermo-hydraulic efficiency over the plain tube, with the Nusselt number (Nu) climbing from 57.5 to 100 across the examined Re window. Second-law metrics corroborate this superiority. At the same Re of peak TPF, the Ds-OPSD cuts exergy destruction from 291.4 to 62 W (≈79 % reduction versus the plain tube and ≈22 % versus the constant-turn tape). Total entropy generation remains minimal and nearly constant (S<inf>total</inf> ≈ 0.206–0.212), while the Bejan number stays high (≈0.999–0.971), indicating that the enhancement is achieved without excessive frictional penalties.
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    Investigation of turbulent thermal-hydraulic behaviors of a heat exchanger tube with U-cut twisted-tape
    (2025-03-01)
    Wongcharee, K.
    ;
    Chuwattanakul, V.
    ;
    Chamoli, S.
    ;
    Maruyama, N.
    ;
    Hirota, M.
    This study examines the influences of U-cut twisted tapes (U-TTs) on thermal-hydraulic behaviors in a circular tube with uniform heat flux. The geometric parameters studied include six U-cut ratios (s/t = 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0) and two twist ratios (y/w = 3.5 and 4.0). Experimental results revealed that their U-cut ratios highly influenced heat transfer enhancement. U-TTs with U-cut ratios (s/t) of 0.5, 1.0, 1.5, and 2.0 achieved higher Nusselt numbers than conventional twisted tapes (TTs). In contrast, U-TTs with larger U-cut ratios (s/t = 2.5 and 3.0) showed reduced Nusselt numbers. However, friction losses with all U-TTs were consistently higher than those with TTs. Due to their excellent heat transfer enhancement, U-TTs with s/t ratios of 0.5 and 1.0 exhibited significantly higher thermal performance factors (TPF) than conventional TTs. The highest TPF, 1.28, was achieved by U-TTs with an s/t ratio of 0.5 and a y/w of 3.5 at a Reynolds number of 6000.
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    Effect of sparsely placed twisted tapes installed with multiple-transverse twisted-baffles on heat transfer enhancement
    (2020-05-01)
    Samruaisin, P.
    ;
    Kunnarak, K.
    ;
    Chuwattanakul, V.
    ;
    Eiamsa-ard, S.
    The influences of sparsely placed twisted tapes installed with multiple-transverse twisted-baffles on heat transfer and thermal enhancement factor characteristics of tubes were experimentally studied. The tests were performed using sparsely placed twisted tapes with a twist ratio (y/W) of 3.0, a tape width (W) of 60 mm and a space width-to-tape width ratio (S/W) of 0.8. Each twisted tape was installed with multiple-transverse twisted-baffles. The study encompassed multiple-transverse twisted-baffles with four twist ratios (s/w) of 2.0, 2.5, 3.0 and 3.5 and five width ratios (w/W) of 0.10, 0.13, 0.16, 0.19 and 0.22. A typical twisted tape was also tested for assessment. The results showed that twisted tapes installed with transverse twisted-baffles gave higher heat transfer rates, friction factors and thermal enhancement factors (η) than a typical twisted tape. This is attributed to the combined actions of swirl flow caused by the twisted tape inserts and an additional flow disturbance caused by the multiple-transverse twisted-baffles. For the tube with compound devices, the heat transfer rate, friction loss and thermal enhancement factor increased with increasing s/w and w/W of multiple-transverse twisted-baffles. The tube with sparsely placed twisted tapes installed with multiple-transverse twisted-baffles yielded the highest thermal enhancement factor of 1.32.