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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
;
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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Enhancing convective heat transfer coefficient in a circular heat exchanger tube mounted with modified V-orifice (MVO): CFD analysis and correlations
(2026-01-01)
Boonloi, Amnart
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Jedsadaratanachai, Withada
This study investigates the airflow dynamics and heat transfer (HT) profiles in a circular heat exchanger tube (CHET) mounted with a modified V-orifice (MVO) acting as a turbulator/vortex generator, which is a passive technique to enhance HT. A numerical modeling approach based on the finite volume method using a commercial software package was employed to provide detailed insights into the air flow profile, which is essential for the design of both the turbulator and the CHET system. The MVO is a turbulator derived from the orifice concept, an established engineering device, and has been adapted in combination with a V-shaped structure to effectively generate vortices and enhance HT. Key parameters expected to influence the flow and HT behavior were investigated. These include the ratio of the MVO thickness, b, to the CHET diameter, D (referred to as the blockage ratio, B-R), which was studied in the range of 0.05–0.30, and the ratio of the MVO spacing, P, to the CHET diameter (pitch ratio, P-R), which was considered at values of 1, 1.5, and 2. Attack angles of 30°, 45°, and 60° were examined for both + x and–x flow directions. The study covered turbulent flow conditions corresponding to Reynolds numbers in the range of 3,000–16000, representative of the operating conditions at the CHET inlet. The results indicate that MVO installation in the CHET acts as a flow obstruction, generating a pressure difference that induces vortex formation. These vortices play a key role in modifying the HT behavior, resulting in increased convective HT coefficients. The outcomes are summarized in forms of dimensionless variables. The highest observed HT enhancement reached 9.93 times that of the plain CHET, while the maximum thermal enhancement factor (TEF) was 1.92, obtained at an attack angle of 30°, P-R = 1, B-R = 0.25, in the +x fluid-flow direction at Re = 3,000.
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Intensification of Thermal Performance of a Heat Exchanger Tube with Knitted Wire Coil Turbulators Installed
(2025-12-01)
Wongcharee, K.
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Shoon Wai, T.
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Maruyama, N.
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Hirota, M.
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Chuwattanakul, V.
This study reports on heat transfer augmentation by knitted wire coil turbulators in a fully developed turbulent regime. Four knitted wire coil turbulators with different wire loop number densities (N = 6, 8, 10, and 12 loops per pitch, with 1.0 pitch = 6.8 mm) were tested. Each was made by winding a 0.7 mm copper wire around a 1.0 mm core rod. Experiments were conducted under a constant 600 W/m<sup>2</sup> wall heat flux. The flow behaviors observed through a dye injection technique revealed that the wire coil induced secondary flows and developed shear layers, contributing to enhanced heat transfer. Heat transfer improved with increasing wire loop number density. Application of knitted wire coil turbulators increased the Nusselt number (Nu) by 86, 95.4, 103.2, and 109.3% for N = 6, 8, 10, and 12, respectively. This corresponded to increased friction factors (f) by 1.77, 1.97, 2.15, and 2.31 times, respectively. The tube with coils having N = 12 yielded the highest thermal performance index (TPI), 1.4, at a Reynolds number of 5000. The empirical correlations for Nu, f, and TPI showed deviations within ±2.1, ±0.68, and ±2.28%, respectively.
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Numerical Methodology for Enhancing Heat Transfer in a Channel with Arc-Vane Baffles
(2025-03-01)
Thapmanee, Piphatpong
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Phila, Arnut
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Wongcharee, Khwanchit
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Maruyama, Naoki
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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.
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Turbulent Airflow and Thermal Analysis in a Circular Tube Heat Exchanger Fitted With Turbulence-Inducing Vortex Generators (X-V Baffles)
(2025-01-01)
Boonloi, Amnart
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Jedsadaratanachai, Withada
The research presents an investigation into airflow configuration, thermal behavior, and convective heat transfer enhancement in a circular heat exchanger tube fitted with turbulence generators. These turbulence generators, referred to in this study as X-V baffles (XVBs), were developed to generate swirling flow within the heat exchanger tube, which is directly related to the enhancement of heat transfer rates and the overall performance of the heat exchanger. Additionally, the XVBs were designed with consideration for practical application and ease of maintenance in real-world industrial settings. The study examines the variables influencing airflow topology and thermal structure, including the blockage ratio (g/D = 0.05–0.20), pitch ratio (P/D = 1–2), flow direction (FD-VD and FD-VU), and types of turbulence generators (Type S and Type T XVBs). The research was conducted within the turbulent flow regime, with Reynolds numbers ranging from 3000 to 12,000 (Re = 3000–12000). The results are presented in terms of observed flow behavior within the test tube, such as cross-flow streamlines, streamwise flow streamlines, Nusselt number distribution, and fluid temperature distribution. The findings clearly show the formation of swirling flow in the heat exchanger tube when XVBs are installed. An increase in the blockage ratio and a decrease in the pitch ratio lead to a more intense swirling flow. The intensity of this swirling flow is directly correlated with the degree of disturbance in the thermal boundary layer (TH-BL). The maximum enhancements in Nusselt number and friction factor due to XVB installation are 7.24 and 58.01 times greater, respectively, compared to a smooth tube without XVBs. The maximum thermal enhancement factor (TEF) achieved is 2.27, obtained from the case with the Type T XVB at a blockage ratio of g/D = 0.05, a pitch ratio of P/D = 1, and a flow direction in the FD-VD configuration.
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Heat Transfer Intensification in a Heat Exchanger by Means of Twisted Tapes in Rib and Sawtooth Forms
(2022-12-01)
Poonpakdee, Pasu
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Samutpraphut, Boonsong
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Thianpong, Chinaruk
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Chokphoemphun, Suriya
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Eiamsa-ard, Smith
This experimental study aimed to intensify the aerothermal performance index (API) in a round tube heat exchanger employing twisted tapes in rib and sawtooth forms (TTRSs) as swirl/vortex flow generators. The TTRSs have a constant twist ratio of 3.0, a constant rib pitch ratio (p/e) of 1.0, and six different sawtooth angles (α = 20°, 30°, 40°, 50°, 60°, and 70°). Experiments were carried out in an open flow using air as the working fluid for Reynolds numbers between 6000 and 20,000 in the current study, which was conducted in a heated tube under conditions of uniform wall heat flux. A typical twisted tape (TT) was also tested for comparison. The experimental results suggest that TTRSs yield Nusselt numbers ranging from 1.42 to 2.10 times of those of a plain tube. TTRSs with larger sawtooth angles (α) offer superior heat transfer. The TTRSs with α = 20°, 30°, 40°, 50°, 60°, and 70° respectively, enhance average Nusselt numbers by 158%, 162%, 166%, 172%, 180%, and 187% with average friction factors of 3.51, 3.55, 3.60, 3.67, 3.75 and 3.82 times higher than a plain tube. Additionally, TTRSs with sawtooth angles (α) of 20°, 30°, 40°, 50°, 60°, and 70° offer APIs in the ranges of 0.99 to 1.19, 1.01 to 1.21, 1.03 to 1.26, 1.05 to 1.31, 1.07 to 1.42, and 1.09 to 1.48, respectively, which are higher than those of the typical twisted tape (TT) by around 5%, 7%, 11%, 16%, 25%, and 31%, respectively. This demonstrates that twisted tapes in rib and sawtooth form (TTRSs), with appropriate geometries, give a promising trade-off between enhanced heat transfer and an increased friction loss penalty.
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Thermal performance evaluation of heat exchanger tubes equipped with coupling twisted tapes
(2013-10-20)
Eiamsa-Ard, S.
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Nanan, K.
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Thianpong, C.
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Eiamsa-Ard, P.
The present work has been conducted to investigate the effect of coupling twisted tapes on heat transfer enhancement in a heat exchanger. The effects of (1) twisted tape orientation (co-coupling twisted tapes or counter-coupling twisted tapes), (2) width ratio, and (3) twist ratio were also examined. Results of coupling twisted tapes were also compared to those of a typical twisted tape. Experimental results showed that the use of counter-coupling twisted tapes resulted in higher heat transfer, friction loss, and thermal performance factor than that of co-coupling twisted tapes and typical twisted tapes. Thermal performance factor increased as twist ratio and Reynolds number decreased while width ratio increased. © 2013 Taylor & Francis Group, LLC.
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Influences of twisted-tape with parallel rectangular-wing on thermal performance of a heat exchanger
(2012-12-01)
Eiamsa-Ard, P.
;
Thianpong, C.
;
Eiamsa-Ard, S.
The present paper reports heat transfer enhancement and friction factor characteristics in the tubes inserted with rectangular-winged twisted-tapes (TT-RWs). The wing-depth ratio (d/W) was varied from 0.1 to 0.3 while the tape-twist ratio was kept constant at y/W = 4.0. The experiments were conducted under uniform heat flux condition for Reynolds number between 5500 and 20,200 (based on the inner diameter, D), using water as the working fluid. The tubes with typical twisted tape (TT) and twisted tape with alternate-axis (TA) as well as a plain tube were also tested for assessment. The obtained results demonstrate that the utilization of the tubes with TT-RWs leads to the increases of both Nusselt number and friction compared to those from the uses of the tubes with TT, TA and the plain tube. In addition, Nusselt number increases as a wing-depth ratio of the twisted tape increases. The improvement of Nusselt number is directly related to the superior destruction of the boundary layer which is responsible by the stronger swirl flow and turbulence intensity. According to the results, the TT-RW with d/W = 0.3 yields the highest Nusselt number which is around 100% higher than that of the plain tube, corresponding to the thermal performance factor of 1.36 at constant pumping power. © 2011 IEEE.

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