KMITL

Permanent URI for this communityhttps://dspace.kmitl.ac.th/handle/123456789/1

Browse

Search Results

Now showing 1 - 10 of 19

Some of the metrics are blocked by your
consent settings
Evaluation of Heat Transfer Augmentation in a Tube Fitted with Grooved Twisted Tapes: A Comparative Thermal-Hydraulic Performance Study
(2026-06-01)
Du, Yuexiang
;
Liengsirikul, Sathaporn
;
Phila, Arnut
;
Wongcharee, Khwanchit
;
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.
Some of the metrics are blocked by your
consent settings
Influence of divergence tapered V-baffles on heat transfer behaviors in a rectangular channel
(2026-05-15)
Keaitnukul, Warin
;
Pingta, Supapat
;
Phila, Arnut
;
Wongcharee, Khwanchit
;
Maruyama, Naoki
This study examines the effects of Divergence Tapered V-Baffle (henceforth DT-VB) regarding the heat transfer and friction loss behavior within the rectangle-shaped duct. The baffle attack angles (α) were set at 45°, 60°, 75°, and 90°. The experimental results indicated that as Reynolds numbers increased, the Nusselt numbers exhibited an upward trend, while the friction values showed a corresponding decrease. The Nusselt number improved consistently as the attack angle decreased, with baffles at a 60° attack angle producing the highest friction loss, followed by those at 45°, 75°, and 90°. Among the configurations tested, the 45° attack angle demonstrated the best thermal performance due to its relatively low friction loss and enhanced heat transfer. The highest thermal performance factor (TPF) of 2.13 was attained at a 45° attack angle and a Reynolds number of 6,000.
Some of the metrics are blocked by your
consent settings
Numerical Investigation of Thermodynamic Performance in Gradient-Pitch Twisted Square Ducts with Variable Aspect Ratio
(2026-04-01)
Samruaisin, Prachya
;
Liengsirikul, Sathaporn
;
Phila, Arnut
;
Maruyama, Naoki
;
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.
Some of the metrics are blocked by your
consent settings
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
;
Samruaisin, Prachya
;
Chuwattanakul, Varesa
;
Maruyama, Naoki
;
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.
Some of the metrics are blocked by your
consent settings
Heat Transfer Intensification in a Heat Exchanger Tube with Continuous V-Rib Twisted Tapes Installed
(2025-05-01)
Du, Yuexiang
;
Wongcharee, Khwanchit
;
Chuwattanakul, Varesa
;
Naphon, Paisarn
;
Maruyama, Naoki
This article reports the effect of twisted tapes with continuous V-ribs on the thermal performance index characteristics of a heat exchanger tube. Numerical and experimental studies were conducted to investigate the influence of V-rib attack angles (β = 15°, 30°, and 45°) in forward and backward arrangements. This investigation employed 0.9 mm thick, continuous V-rib twisted tapes (CVRTs) made from aluminum sheets formed with a twist ratio of y/w = 4.0. The experimental results indicated that a continuous V-rib twisted tape (CVRT) was more effective in heat transfer improvement than a typical twisted tape (TT). This was due to swirl and longitudinal vortex flows that helped increase flow mixing and reduce boundary layer thickness. Decreased V-rib attack angles (β) led to greater heat transfer enhancement, pressure drop, and thermal performance index values due to the greater turbulent mixing of fluid. The numerical result revealed that a continuous V-rib twisted tape created strong longitudinal vortex flow, especially with higher attack angles. The Turbulent Kinetic Energy (TKE) and core fluid temperature increased with the insertion of CVRTs. Local Nusselt numbers also remained relatively high for heat exchanger tubes with CVRTs. The experimental study illustrated that a tube with a CVRT installed augmented heat transfer. In the experimentally studied cases, a backward arrangement had more heat transfer, a greater friction factor, and a better thermal performance index. Compared to a plain tube, a tube with CVRT installed, having β = 15°, 30°, and 45°, showed 76.8, 71.6, and 66.2% improved heat transfer, respectively. CVRTs with these three β-values, respectively, exhibited higher thermal performance than a TT. Among the investigated CVRTs, the backward-arranged tape with β = 15° offered the maximum thermal performance index, 1.13 at Re = 6000. The results are congruent with the simulation outcomes, hence supporting the CFD analysis.
Some of the metrics are blocked by your
consent settings
Numerical Methodology for Enhancing Heat Transfer in a Channel with Arc-Vane Baffles
(2025-03-01)
Thapmanee, Piphatpong
;
Phila, Arnut
;
Wongcharee, Khwanchit
;
Maruyama, Naoki
;
Hirota, Masafumi
This study numerically investigates flow and heat transfer in a channel with arc-vane baffles at various radius-to-channel high ratios (r/H = 0.125, 0.25, 0.375, and 0.5) for Reynolds numbers between 6000 and 24,000, focusing on solar air-heater applications. The calculations utilize the finite volume method, and the SIMPLE algorithm is executed with the QUICK scheme. For the analysis of turbulent flow, the finite volume method with the Renormalization Group (RNG) k-ε turbulence model was used. The results show that arc-vane baffles create double vortices along the axial direction, promoting flow reattachment on the heated surface and enhancing heat transfer. Baffles with smaller r/H ratios strengthen flow reattachment, reduce dead zones, and improve fluid contact with the heat transfer surface. The baffles with the smallest r/H ratio achieve a Nusselt number ratio (Nu/Nu<inf>s</inf>) of 4.91 at Re = 6000. As r/H increases, the friction factor (f) and friction factor ratio (f/f<inf>s</inf>) rise due to increased baffle curvature and surface area. The highest thermal performance factor (TPF) of 2.28 occurs at r/H = 0.125 and Re = 6000, reflecting an optimal balance of heat transfer and friction losses. Arc-vane baffles with a r/H ratio of 0.125 yield a TPF exceeding unity, indicating potential energy savings. These findings provide valuable insights for optimizing baffle designs to enhance thermal performance in practical applications.
Some of the metrics are blocked by your
consent settings
Evaluation of heat transfer performance of a channel mounted with square-wing perforated V-type baffles
(2025-01-01)
Eiamsa-Ard, Smith
;
Phila, Arnut
;
Thianpong, Chinaruk
;
Chuwattanakul, Varesa
;
Maruyama, Naoki
The current study examines the aerothermal performance behaviors of a rectangular-channel with square-wing perforated V-type baffles (SW-PVBs). The SW-PVBs were attached to lower channel walls at five attack angles, θ = 0° (solid V-type baffle), 22.5°, 45°, 67.5° and 90°. The heat transfer and pressure drop results of a channel without SW-PVBs were performed to normalize the results of the SW-PVBs and evaluate thermal performance factors (TPFs). It can be observed that as the attack angles decreased, the heat transfer and pressure loss rose. Among the SW-PVBs that were tested, those characterized by θ = 22.5° exhibited the most significant improvement in heat transfer, whereas SW-PVBs with θ = 45° gave the highest thermal performance factors. Additionally, the SW-PVBs with θ = 45° offered the highest TPF, as high as 1.93.
Some of the metrics are blocked by your
consent settings
Thermal performance augmentation in a solar air heater with twisted multiple V–baffles
(2024-11-01)
Chompookham, Teerapat
;
Eiamsa-ard, Smith
;
Buanak, Kalong
;
Promvonge, Pongjet
;
Maruyama, Naoki
A 3D numerical investigation of thermal performance augmentation of a twisted multiple V–baffles in a solar air heater is presented. Two important functions of the twisted multiple V–baffles are to generate multiple impinging flows upon the wall to improve the convective heat transfer (compared with a smooth channel) and reduce the pressure drop (compared with a typical multiple V–baffles). These outcomes enhance thermal performance. The results of heat transfer (in terms of a Nusselt number ratio), pressure drop (in terms of a friction factor ratio) and thermal performance (in terms of a thermal enhancement factor) of a twisted multiple V–baffles were compared with both a smooth channel and a typical multiple V–baffles. Eighty–one cases including those with a pitch ratio of PR = 0.4–2.0; blockage ratio, BR = 0.10–0.20; angle of attack, α = 30o – 60o and a fixed number of twisted loops, n = 2, were investigated in turbulent flow. The results revealed that the twisted multiple V–baffles created multiple impinging jets at the heated wall and help accelerate heat transfer between the wall and the fluid. Compared to a typical multiple V–baffles, the friction factor showed a large decrease while the Nusselt number was slightly lower leading to better thermal performance. Over the study range, PR = 0.4, BR = 0.20, and α = 60o appeared to yield the highest thermal enhancement factor, 2.81 at Re = 3000.
Some of the metrics are blocked by your
consent settings
Enhanced heat transfer performance in channel with delta-wing perforated V-type baffles
(2023-10-01)
Eiamsa-ard, Smith
;
Phila, Arnut
;
Thianpong, Chinaruk
;
Chuwattanakul, Varesa
;
Maruyama, Naoki
The article examines the influence of delta-wing V-type baffles (DW-PVBs) on the average Nusselt number, local Nusselt number distribution, pressure losses, and thermal performance behaviors in a channel. Delta-wing perforated V-type baffles (DW-PVBs) mounted in a regular manner on the bottom of a channel produced two pairs of longitudinal counter-rotating vortices to enhance chaotic fluid mixing and destabilize the boundary layer, hence boosting the heat transfer. The geometric characteristics of the delta-wing V-type baffle (DW-PVBs) located on the bottom of the channel were examined at relative baffle blockage and pitch ratios (BR = h/H = 0.3 and p/H = 1.5), and five delta-wing attack angles, θ = 0o (solid V-shaped baffle), 22.5°, 45°, 67.5°, and 90°. The present DW-PVBs mounted on the channel were designed to mitigate pressure loss due to flow blockage. The experiment was done by permitting air to flow through a channel at Reynolds numbers (Re) ranging from 6000 to 24,000. The present results show that the friction factor using the DW-PVBs decreased considerably with increasing θ values. The experimental results revealed that small θ values yielded greater heat transfer and resistance than large θ values. The DW-PVBs with θ = 22.5° performed better than inserts with other θ values in terms of heat transfer rate. It was also observed that the DW-PVBs with θ = 45° gave the maximum thermal performance factor (TPF), while presenting a 13.64–17.26% lower friction factor than the solid V-shaped baffle. Furthermore, it was also found that the DW-PVBs with θ = 0°, 22.5°, 45°, 67.5°, and 90° gave peak TPF values of up to 1.87, 1.89, 1.91, 1.87, and 1.84 at the lowest Reynolds number, 6000.
Some of the metrics are blocked by your
consent settings
Thermal performance and exergy analysis in a round tube with louvered trapezoidal winglets
(2023-09-15)
Promvonge, Pongjet
;
Eiamsa-ard, Smith
;
Skullong, Sompol
;
Maruyama, Naoki
;
Hirota, Masafumi
An experiment was performed to investigate the influence of inserting a louver-punched trapezoidal-winglet (LPTW) into a uniform heat-fluxed tube in order to create a longitudinal vortex generator. This research aims to maximize both the thermal performance to increase energy savings, and the relative Nusselt number (Nu<inf>R</inf>) at the optimal performance to reduce heat exchanger sizes. Therefore, the experimental result was emphasized on the thermal and pressure loss characteristics including entropy, and exergy analysis of the turbulent tube flow for Reynolds numbers (Re) that extended from 4760 to 29,280. The LPTWs were arranged by letting V-tip direct downstream with three attack angles (α = 30°, 45° and 60°) and five louver angles (θ<inf>1</inf> = 0°, 25°, 30°, 45° and 90°), all at a single relative winglet pitch (P<inf>R</inf> = 1.0) and height (B<inf>R</inf> = 0.25). According to the findings, it revealed that the friction factor (f) and Nusselt number (Nu) of the LPTW at α= 60° and θ<inf>1</inf> = 0° are, respectively, up to 29.1 and 5.5 times above those of the plain tube. With decreasing Re and θ<inf>1</inf>, the entropy generation (S˙′<inf>gen</inf>) was reduced to a lower value and the maximum exergy efficiency (η<inf>Ex</inf>) was obtained for the LPTW at α = 60° and θ<inf>1</inf> = 0° The peak thermal performance around 2.5 together with Nu<inf>R</inf> = 4.68 was found at a= 60°, θ<inf>1</inf> = 45° and the lowest Re. However, the optimal condition at α= 60°, θ<inf>1</inf> = 30° was preferable because it provides the greatest Nu<inf>R</inf> = 5.04 at TEF = 2.47. Additionally, correlations for f and Nu were derived and presented for the range of parameters that were taken into consideration.

KMITL

Browse

Filters

Settings

Sort By

Results per page

Search Results