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Evaluation of Heat Transfer Augmentation in a Tube Fitted with Grooved Twisted Tapes: A Comparative Thermal-Hydraulic Performance Study
(2026-06-01)
Du, Yuexiang
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Liengsirikul, Sathaporn
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Phila, Arnut
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Wongcharee, Khwanchit
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Pimsarn, Monsak
A computational fluid dynamics (CFD) analysis is conducted to systematically investigate heat transfer enhancement in tubes fitted with grooved twisted tapes and to identify the groove geometry that provides the best thermo-hydraulic performance. Three grooved twisted tape configurations—circular-grooved twisted tapes (CGTT), rectangular-grooved twisted tapes (RGTT), and triangular-grooved twisted tapes (TGTT)—are evaluated and compared with a smooth tube and a conventional twisted tape over a Reynolds number range of 5000–20,000 under isothermal wall conditions. The grooved twisted tapes enhance heat transfer through the combined effects of swirl-induced secondary flows and groove-generated flow disturbances, which intensify turbulent mixing and reduce the thickness of the thermal boundary layer. Compared with the plain tube, the grooved configurations increase the Nusselt number by 1.472–1.98 times while increasing the friction factor by 3.21–3.58 times. Relative to the conventional twisted tape, the grooved designs provide an additional 8.0–12.1% enhancement in heat transfer with only a marginal increase of 0.2–1.5% in friction factor. The thermodynamic analysis indicates that the CGTT configuration exhibits the lowest entropy generation rate and exergy loss throughout the investigated Reynolds number range. In particular, the CGTT achieves a Bejan number of 0.999841 at Re = 5000, demonstrating an excellent balance between heat transfer enhancement and frictional losses. Furthermore, the CGTT attains the highest thermal performance factor (TPF) of 1.294 at Re = 5000 and maintains TPF > 1.0 over the entire Reynolds number range. The overall performance ranking is consistently established as CGTT > TGTT > RGTT based on comprehensive analyses of velocity fields, streamline patterns, turbulent kinetic energy distributions, temperature contours, and thermodynamic characteristics. Although the present study identifies the circular-groove configuration as the optimal design for a twist ratio (y/W) of 3.0, further parametric investigations involving variations in twist ratio, groove dimensions, and groove pitch are required to develop generalized design guidelines.
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Numerical Investigation of Thermodynamic Performance in Gradient-Pitch Twisted Square Ducts with Variable Aspect Ratio
(2026-04-01)
Samruaisin, Prachya
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Liengsirikul, Sathaporn
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Phila, Arnut
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Maruyama, Naoki
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Shoon Wai, Thiri
This study numerically investigates heat transfer and thermodynamic behavior in twisted square and rectangular air ducts while keeping a constant hydraulic diameter (D<inf>h</inf> = 30 mm). Three aspect ratios are considered (AR = 1.00, 0.75, and 0.50). The heated test section (900 mm) is divided into three equal segments, and three pitch patterns are examined: a uniform pitch (400–400–400 mm, P444) and two axial gradients (300–400–500 mm, P345; 500–400–300 mm, P543). All results are compared to a standard reference, the straight square duct (SD-AR1.00), to ensure fair comparisons across all cases with Reynolds numbers between 5000 and 20,000. Among the twisted ducts, the strongest rectangularity combined with the increasing pitch sequence, TSD-AR0.50-P345, provides the best overall balance. Its heat transfer rises from Nu = 39.39 to 88.62, giving Nu/Nu<inf>0</inf> = 1.493 → 1.433, while the pressure penalty increases to f/f<inf>0</inf> = 1.345 → 1.405. Under cube-root weighting of friction, this case maintains the highest thermal performance factor, TPF = 1.352 at Re = 5000 and TPF = 1.279 at Re = 20,000. Second-law trends support the same ranking: exergy destruction decreases from 12.81 W (baseline) to 8.44 W at Re = 5000 (≈34% reduction) and from 6.54 W to 4.84 W at Re = 20,000 (≈26% reduction). The Bejan number remains high at low Reynolds numbers (≈0.998), indicating heat-transfer irreversibility dominance, but drops at higher Reynolds numbers (≈0.87) as frictional effects become more important. In general, the results show that adding a small axial pitch increase to rectangularity can improve near-wall mixing while reducing losses downstream. This leads to a clear improvement in both first-law performance and exergy-based measures.
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Thermal performance enhancement of a circular tube fitted with inclined perforated disk inserts
(2026-03-01)
Mehta, Rajesh
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Gupta, Anirudh
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Kumar, Nitin
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Eiamsa-ard, Smith
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Thianpong, Chinaruk
Heat exchangers are crucial devices in industries, and enhancing their thermal performance while controlling pressure losses remains a significant challenge. This paper examines the idea that inclined perforated disk (IPD) inserts can be effectively used to improve heat transfer in circular tubes with constant heat flux conditions at acceptable levels of hydraulic penalties. Turbulent airflow with Reynolds numbers (Re) ranging from 5000 to 21,000 was examined in experiments, and three perforation indices (PI = 0.21, 0.24, and 0.27) were tested to determine the effects of hole density on thermal and hydraulic performance. Evidence showed that the Nusselt number (Nu) had been improved by over 86 % compared to plain tubes, with the thermal enhancement factor (TEF) reaching as high as 1.53 at PI = 0.27 and Re = 5000. Particle swarm optimization (PSO) and neural network modelling multi-objective optimization were used to test the results of the experiment and determine the best operating conditions at PI = 0.21. The paper has demonstrated that inclined perforated disk inserts can form a viable passive method for enhancing the efficiency of heat exchangers, as the swirl and jet flow patterns created by the perforations effectively break the thermal boundary layer, thereby increasing the rate of convective heat transfer.
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Thermodynamic performance analysis of a round tube fitted with gradient quadruple twisted tapes
(2026-03-01)
Samruaisin, Prachya
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Liengsirikul, Sathaporn
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Thianpong, Chinaruk
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Chuwattanakul, Varesa
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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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Influence of Wired Twisted Tape on Heat Transfer Enhancement, Friction Factor and Thermal Performance Behaviors in a Heat Exchanger Tube
(2026-03-01)
Lin, Jianyu
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Laphirattanakul, Ponepen
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Bhattacharyya, Suvanjan
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Thapmanee, Piphatpong
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Wongcharee, Khwanchit
This study experimentally investigates the thermal–hydraulic performance of heat exchanger tubes fitted with wired twisted tapes, with particular emphasis on the effects of the hole spacing-to-width ratio (s/W) and edge margin-to-width ratio (e/W). Experiments were conducted over a Reynolds number range of 6000–20,000, and the results were compared with those of plain tubes and tubes equipped with conventional twisted tapes. The findings revealed that the incorporation of wires significantly enhanced heat transfer due to the combined action of longitudinal eddies generated by wire protrusions and swirling flow induced by the twisted tape. At identical Reynolds numbers, tubes with a smaller hole spacing (s/W = 0.16) exhibited superior heat transfer performance, achieving Nusselt number enhancements of up to 107.7% relative to plain tubes and 51.6% relative to conventional twisted tapes. Similarly, reducing the edge margin ratio intensified near-wall eddies and further disrupted the boundary layer. The friction factor was found to increase with decreasing hole spacing and edge margin, primarily due to additional flow obstructions and enhanced near-wall shear stresses. For wired twisted tapes with s/W = 0.16, the friction factor reached nearly six times that of a plain tube. Despite this penalty, the thermal performance factor (TPF) remained favorable, with values of up to 1.2, indicating that the heat transfer benefits outweighed the corresponding pressure losses.
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Influence of perforated twisted tapes with vortex generator wings on heat transfer performance and entropy in a heat exchanger tube
(2026-01-01)
Mehta, Rajesh
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Gupta, Anirudh
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Kumar, Nitin
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Eiamsa-ard, Smith
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Pimsarn, Monsak
This study conducts an investigative exploration of thermal and hydraulic performance regarding hybrid inserts which combine perforated twisted tapes with vortex generator wings mounted inside circular tubes. The insert design makes use of both swirl flow and secondary vortex generation which breaks up the thermal boundary layer and boosts convective heat transfer rates. During this investigation, researchers utilized water as the working fluid at Reynolds number (Re) from 3000 to 21,000 to study the effect of three perforation diameter ratio (d/D) 0.143, 0.19, and 0.238 and respective Vortex generator (VG) edge cut ratio (a/D) 0.143, 0.19, and 0.238. Nusselt number (Nu) reach 182.3 % and thermal enhancement factor (TEF) achieve 1.68 at Re = 15,000 when using the enhanced tube compared to a smooth tube. The industrial application of larger VG openings at standard spacing produced a beneficial relationship between thermal performance and flow resistance when the pressure rise reached 345 %. The analysis of entropy generation showed heat transfer irreversibility gave way to frictional irreversibility when both perforation dimension and Re became larger. System design optimization prerequisites involved trade-offs which met Bejan number (Be) analysis trends. The Random Forest machine learning model combined with ANN and Linear Regression models contributed to thermal parameter prediction (Nu, f, TEF) by delivering a predictive accuracy level with less than 6.6 % deviation. The research leads to vital knowledge needed for developing compact heat exchangers integrating passive enhancement methods.
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Analysis of fluid flow across a 2D bluff body in a tandem arrangement with varying aspect ratios near a moving wall
(2026-01-01)
Kumar Pant, Pawan
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Chamoli, Sunil
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Pant, Naval
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Joshi, Hitesh
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Rana, Saurav
This study numerically investigates the flow characteristics around single and tandem cylinders positioned in close proximity to a moving wall at a Reynolds number of Re = 100. Using the finite volume method, simulations were performed for aspect ratios (AR) ranging from 1 to 5, while maintaining a fixed gap ratio (G/A = 0.5) and spacing ratio (S/A = 0.5). The results demonstrate that the moving wall significantly influences flow dynamics and stabilizes the wake. For an aspect ratio of 1, the merging of shear layers leads to the formation of elongated, steady vortices. As the aspect ratio increases from 2 to 5, the wake becomes increasingly smooth and the magnitude of positive vortices decreases, resulting in steady wake formation without significant oscillations. Force analysis reveals that the upstream cylinder exhibits chaotic drag (C<inf>d</inf>) and lift (C<inf>L</inf>) coefficients, whereas the downstream cylinder shows a consistent trend. Notably, the upstream cylinder maintains a higher drag coefficient than the downstream cylinder, with both being lower than that of a single isolated cylinder. The observed suppression of vortex shedding is primarily attributed to the interaction and coupling of shear layers between the moving wall and the cylinders, identifying shear alignment rather than viscous damping as the core mechanism of wake control.
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A comprehensive review on femtosecond laser polishing of silicon nitride: fundamentals, current progress, and industrial outlook
(2026-01-01)
Jian, Huang
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Pimsarn, Monsak
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Chuwattanakul, Varesa
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Eiamsa-ard, Smith
Silicon nitride ((Formula presented.)) ceramics are indispensable in aerospace bearings and semiconductor substrates due to their exceptional mechanical and thermal properties. However, achieving damage-free, atomic-level surface finishes remains problematic. Traditional mechanical polishing induces subsurface microcracks, while chemical mechanical polishing (CMP) is plagued by low material removal rates and environmental toxicity. This review critically evaluates femtosecond laser polishing as a transformative, “green” non-contact alternative. We first elucidate the laser-matter interaction mechanisms specific to wide-bandgap (Formula presented.) ((Formula presented.) eV), clarifying how multiphoton absorption enables “cold ablation” by suppressing the heat-affected zone (HAZ) via the two-temperature model (TTM) dynamics. A distinct material removal mechanism driven by rapid thermal decomposition ((Formula presented.)) and phase explosion is highlighted. Synthesizing recent experimental data, we establish a quantitative process window. Operating slightly above the ablation threshold ((Formula presented.)) with high spot overlap (70%–90%) is critical to balance surface leveling against the incubation effect, which otherwise triggers porosity. Furthermore, we address the unique challenges of inducing periodic structures (LIPSS) on dielectric surfaces and propose a hybrid manufacturing strategy—integrating high-speed laser roughing with CMP finishing—to resolve efficiency constraints. Finally, an industrial roadmap involving high-throughput polygon scanners and AI-driven closed-loop control is outlined, providing a comprehensive reference for advancing femtosecond laser polishing toward scalable, high-precision manufacturing.
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Correction: Analysis of fluid flow across a 2D bluff body in a tandem arrangement with varying aspect ratios near a moving wall ((2026), (Front. Mech. Eng.), 11, 1727981, (10.3389/fmech.2025.1727981))
(2026-01-01)
Pant, Pawan Kumar
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Chamoli, Sunil
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Pant, Naval
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Joshi, Hitesh
;
Rana, Saurav
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Evaluation of heat transfer performance of a heat exchanger tube mounted with an I-rib twisted tape and twisted winglets
(2025-12-01)
Qiu, Wenxuan
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Samruaisin, Prachya
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Chuwattanakul, Varesa
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Maruyama, Naoki
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Hirota, Masafumi
This study aims to improve the efficiency of heat exchangers and explore the enhancement mechanism of the thermal performance characteristics of heat exchange tubes by I-rib twisted tapes and twisted winglets (I-RTTW) through experimental research and numerical simulation. The I-RTTW structure consists of a central I-type rib and an edge twisted winglet. The key geometric parameters of the edge twisted winglet include the wing depth ratio (d/W = 0.096, 0.13, 0.16), the wing width ratio (w/W = 0.096, 0.13, 0.16), and a fixed twist angle of 45°. The study uses air as the working fluid to systematically analyze the heat transfer performance of the I-RTTW over a range of Reynolds numbers (Re) of 6,000–20,000. The experimental results reveal that the I-RTTW significantly improves heat transfer through a dual mechanism. First, the edge twisted winglet effectively disrupts the fluid boundary layer by inducing secondary flows. Second, the central I-type rib can promote radial mixing of the fluid. Further in-depth analysis of the experimental data revealed that a greater winglet depth ratio (d/W) increases the longitudinal size of the cutting winglet, thereby disturbing the fluid more deeply and increasing boundary layer disruption. An increased winglet width ratio (w/W) significantly enhances the fluid mixing effect by expanding the lateral coverage, thereby reducing thermal resistance and enhancing heat transfer between the pipe wall and the fluid. In terms of flow resistance characteristics, a greater winglet depth ratio directly leads to an increased longitudinal size of the cutting winglet. This strengthens the disturbance of fluid, resulting in increased boundary layer separation and greater eddy losses. Similarly, an increased winglet width ratio leads to greater lateral flow resistance, so that the fluid needs to overcome a larger shear force and higher collision losses. This leads to an increased friction coefficient (f). In the current study, the heat transfer rate of a pipe equipped with I-RTTWs is about 7 to 26% and 68 to 99% higher than that of a pipe equipped with typical tape (TT) and the plain tube, respectively. The friction coefficient is 1.15–1.37 times and 3.46–4.12 times that of a TT and plain tube, respectively. The comprehensive thermal performance index of the pipe with an I-RTTW is as high as 1.29.

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