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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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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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Path Optimization Using an Improved APF-RRT* Algorithm
(2026-01-01)
Zheng, Yongyang
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Pimsarn, Monsak
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Chuwattanakul, Varesa
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Chokphoemphun, Suriya
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Eiamsa-Ard, Smith
Path planning remains a critical research area in mobile robotics, yet current approaches often suffer from suboptimal path quality, limited sampling efficiency, and inadequate adaptability across diverse operational scenarios. To address these issues, this paper proposes an improved algorithm combining Artificial Potential Field (APF) and Restricted Path Time (RRT*) approaches. This algorithm employs an optimization model that combines dynamic sampling with potential field guidance, constructing a two-stage dynamic sampling mechanism. During sampling, candidate nodes with Gaussian noise are generated along the resultant force direction. Finally, path cost comparison and parent node reselection are performed within the dynamic optimization radius to ensure asymptotic optimality of the path. Experimental results show that in complex maps, path length is reduced by 33.41% and 26.64%, respectively, and planning time is reduced by 21.36% and 86.32%, respectively; in narrow passages, path length is reduced by 49.6% and 49.8%, respectively. The results confirm the effectiveness of the two-stage dynamic sampling mechanism, which not only preserves the probabilistic completeness of the RRT* algorithm but also adaptively adjusts the sampling strategy, improving both planning length and time.
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Recent Advances in Welding Processes for High-Entropy Alloys: A Comprehensive Review
(2026-01-01)
Li, Min
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Pimsarn, Monsak
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Chuwattanakul, Varesa
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Eiamsa-Ard, Smith
High-Entropy Alloys (HEAs) have gained attention for their exceptional mechanical properties, corrosion resistance, and unique microstructure. However, welding HEAs remains challenging, attributed to intricate microstructures, inadequate thermal conductivity, and elevated melting points. This review systematically summarizes recent advances in metal welding of HEAs with both similar and dissimilar alloys, including stainless steel, titanium alloys, aluminum alloys, and nickel-based alloys. Welding techniques, including Gas Metal Arc Welding (GMAW), Laser Welding (LW), Electron Beam Welding (EBW), and Gas Tungsten Arc Welding (GTAW) are critically compared in terms of joint microstructure, mechanical performance, and corrosion behavior. The influence of filler composition, heat treatment, and process parameters on weld quality are discussed. Key challenges, including microstructure evolution under complex service conditions and controlling brittle intermetallic phases, are identified. Finally, potential research directions and application prospects of HEA welding in advanced manufacturing are outlined.
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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
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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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Characterization of Heat Transfer Enhancement and Flow Topology in a Three-Start Spirally Corrugated Tube
(2025-12-01)
Du, Yuexiang
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Phila, Arnut
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Promthaisong, Pitak
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Chuwattanakul, Varesa
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Eiamsa-ard, Smith
The article provides a numerical analysis of the heat transfer characteristics and laminar periodic flow in a three-dimensional 3-start spirally corrugated tube. The working fluid is air, with a flow rate in terms of Reynolds numbers (Re) that ranges from 200 to 2,000. The investigation is conducted at six different pitch ratios (PR = 0.75, 1.0, 1.25, 1.5, 2.0, and 2.5) and five different depth ratios (DR = 0.02, 0.04, 0.06, 0.08, and 0.10). The results indicated that the spiral flow along the tube length was generated by the 3-start spirally corrugated tube. The swirl flow is divided into two components: the primary swirl flow, which is visible at the core, and the secondary swirl flow, which is visible at the near wall. These components contribute to the enhancement of fluid mixing, boundary layer disruption, and heat transfer on the tube wall. The Nusselt number (Nu) and friction factor (f) were increased as a result of the decrease in PR and the increase in Re and DR. The range of the Nu/Nu₀, f/f₀, and thermal performance factor (TPF) in a range analysis is 1.02 - 15.90, 0.97 - 5.52, and 0.73 - 2.33, respectively. At Re = 2,000, the corrugated tube with DR = 0.10 exhibited the greatest TPF of 2.33. Additionally, the results indicate that the 3-start spirally corrugated tube significantly improves heat transfer compared to the corresponding straight tube. The findings suggest that the structural characteristics of the flow path within the tube can be changed by a suitable PR and DR to optimize the overall heat transfer rate and thermal performance factor.

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