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A numerical study of a novel discrete X-V baffle for heat transfer enhancement in duct heat exchangers
(2026-09-01)
Boonloi, Amnart
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Jedsadaratanachai, Withada
This study proposes a novel vortex generator, referred to as a discrete X-V baffle (DXVB), for enhancing heat transfer (H-T) in a square cross-section tube heat exchanger. The DXVB is developed by integrating the design concepts of a V-baffle and a V-orifice. A numerical approach based on the finite volume method is employed to investigate the thermal–hydraulic characteristics under turbulent flow conditions, with Reynolds numbers ranging from 3000 to 16,000. The effects of DXVB thickness and installation clearance are systematically examined. In addition, both co-current flow (+x direction) and counter-current flow (−x direction) configurations are considered. The results are presented in terms of dimensionless parameters, along with detailed analyses of flow structures (FS), H-T characteristics, and the underlying physical mechanisms occurring within the heat exchanger system. The findings reveal that the incorporation of DXVB significantly enhances the H-T rate, achieving a maximum increase of up to 6.29 times compared to a plain tube without inserts. Furthermore, the thermal enhancement factor (TEF), representing the overall performance, reaches a maximum value of 1.32.
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Thermal performance evaluation of a channel with twisted baffles installed: Effect of twisted baffle arrangement
(2026-03-01)
Eiamsa-ard, S.
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Pingta, S.
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Phila, A.
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Woncharee, K.
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Chamoli, S.
This research aims to introduce newly designed twisted baffle for enhancing heat transfer in solar air heater. This study examined the thermo-hydraulic performance of converging twisted baffles (C-TBs) and diverging twisted baffles (D-TBs) with different numbers of loops (n = 2, 4, 6, and 8) over a Reynolds number range (Re) of 6000–24,000. The results demonstrated that both converging twisted baffles and diverging twisted baffles significantly enhanced heat transfer compared to a smooth channel. The Nusselt number, friction factor, and thermal performance factor (TPF) increased as the number of loops decreased, attributed to stronger flow reattachment. Specifically, twisted baffles with 2, 4, 6, and 8 loops enhanced Nu by approximately 2.29–3.43, 2.02–3.05, 1.77–2.74, and 1.61–2.48 times, respectively, while the friction factor increased by 5.19–5.71, 4.61–5.01, 4.06–4.43, and 3.73–4.06 times, respectively. For a given number of loops, diverging twisted baffles consistently provided higher heat transfer enhancement than converging twisted baffles, albeit with slightly increased friction losses. Across the investigated range, the 2-loop diverging twisted baffles exhibited the best overall performance, achieving the highest Nusselt number ratio (Nu/Nu<inf>SC</inf> where Nu<inf>SC</inf> is the Nusselt number of the smooth channel) of 3.43 and a maximum thermal performance factor of 1.92 at Reynolds number of 6000, establishing it as the optimal configuration among those tested. This research contributes valuable design guidelines for selecting optimal baffle configurations, thereby supporting the development of more energy-efficient solar thermal systems.
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Thermal performance evaluation of a diamond-shaped roughened tube
(2025-12-01)
Chokphoemphun, Suriya
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Kamma, Panit
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Promvonge, Pongjet
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Promthaisong, Pitak
Thermal performance evaluation was examined numerically in a diamond-shaped roughened tube, which created recirculation and pair counter-rotation flows, which helped to disrupt the boundary layer, and increased fluid mixing led to improving the rate of heat transfer. The parameters studied, including relative depth ratio, e/D, DR, from 0.02 ≤ DR ≤ 0.14, and relative pitch ratio, p/D, PR, from 0.25 ≤ PR ≤ 1.5, under turbulent flow conditions, 3000 ≤ Re ≤ 20,000. Computed results included heat transfer (Nu/Nu<inf>0</inf>), frictional loss (f/f<inf>0</inf>) and thermal performance (in terms of thermal enhancement factor, TEF). The simulations showed that the velocity and heat transfer became fully developed periodic at around x/D ≈ 6–7.5. The pair counter-rotation flows increased the level of both the flow strength and the mixing of fluid, and disrupted the boundary layer, leading to an increase in heat transfer rate. The Nu/Nu<inf>0</inf>, f/f<inf>0</inf> and TEF were achieved in a range of 1.00–3.34, 1.21–24.00 and 0.69–1.56. The maximum TEF was found at 1.56 for DR = 0.08, PR = 0.50 and Re = 5000.
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Heat transfer performance evaluation of a solar air heater duct with multiple tapered V-baffles
(2025-12-01)
Thianpong, C.
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Kaewkosum, P.
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Woncharee, K.
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Keaitnukul, W.
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Maruyama, N.
This report aims to study the heat transfer enhancement, pressure loss characteristics, and thermal performance of a channel equipped with multiple tapered V-shaped baffles (MTVBs). The effects of up-facing and down-facing orientations, converging (C) and diverging(D) configurations, variations in the taper ratio (e<inf>CR</inf> and e<inf>DR</inf> = 0.0 and 0.5), and Reynolds number (6000 ≤ Re ≤ 24,000) are examined. The performance of UF-C-MTVBs, DF-C-MTVBs, UF-D-MTVBs, and DF-D-MTVBs is analyzed and compared with that of the conventional transverse baffles (TBs) and MVBs (e<inf>DR</inf> = 1.0). The experimental setup maintained a constant attack angle (α) of 45°, pitch ratio (p/H) of 1.5, width-shaped ratio (W<inf>b</inf>/W) of 0.25, and blockage ratio (e/H) of 0.3. Tests were conducted at a fixed Prandtl number of 0.71, and a thermochromic liquid crystal sheet was utilized to assess the local Nusselt number distribution on the wall installed with UF-C-MTVBs, DF-C-MTVBs, UF-D-MTVBs, and DF-D-MTVBs. The results reveal that the channel with MVBs (e<inf>DR</inf> = 1.0) achieves the greatest heat transfer rate, with a Nu/Nu<inf>s</inf> ratio of up to 4.37 while a f/f<inf>s</inf> ratio reaching 48.12. In contrast, D-MTVBs at e<inf>DR</inf> = 0.0, despite having a lower Nu/Nu<inf>s</inf> ratio (maximum 3.87), attain the maximum thermal performance of 1.39 at Re = 6000, owing to their optimized design that effectively enhances heat transfer while minimizing pressure drop.
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Numerical investigation of thermal profile and air-flow visualization in a tube heat exchanger with discrete X-V vortex inducers (DXVVI)
(2025-12-01)
Boonloi, Amnart
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Jedsadaratanachai, Withada
This study presents the implementation of discrete X-V vortex inducers (DXVVI) as a passive heat transfer enhancement technique in circular heat exchanger tubes. The DXVVI devices are introduced to improve the convective heat transfer coefficient, heat transfer rate, and thermal performance. Numerical simulations using a commercial CFD code were employed to investigate the flow structure and thermal behavior within the heat exchanger system. The DXVVI concept is developed based on a combination of the V-Orifice and V-shaped baffle, aiming to retain the thermal performance of the V-shaped baffle while maintaining the structural strength of the V-Orifice. The discrete configuration was selected to enhance turbulence levels and reduce pressure drop. Two DXVVI design groups, referred to as “GROUP 1” and “GROUP 2”, were proposed. Key parameters influencing the flow and thermal characteristics were investigated, including the pitch ratio (PRT), defined as the ratio of the longitudinal pitch or pitch distance (P) to the circular tube diameter (D), i.e., P/D, and the flow-blockage ratio (BKRT), defined as the ratio of the DXVVI thickness (b) to the circular tube diameter, i.e., b/D. The simulations were conducted under turbulent flow conditions with Reynolds numbers (Re) ranging from 3000 to 20,000, considering both co-flow (+x) and counter-flow (−x) directions. In GROUP 2, small gaps were introduced in various configurations to enhance turbulence intensity, increase the number of vortex cores, and further reduce pressure drop—leading to improved heat exchanger performance. The numerical model was validated using appropriate academic standards, confirming its reliability in predicting thermal and flow behaviors. The numerical results are performed in terms of fluid-flow structure (e.g., streamline plots in transverse planes and 3D flow visualizations) and thermal characteristics (e.g., fluid-temperature contours in cross-sectional planes and Nusselt number distributions on the tube surface). Performance evaluation was also carried out using dimensionless metrics, including the Nusselt number ratio (Nu/Nu₀), the friction factor ratio (f/f₀), and the thermal enhancement factor (TEF) under equal pumping power conditions. The best heat transfer rate augmentation was observed to be up to 8.07 times greater than the reference case (smooth tube). The highest TEF, equal to 3.14, was observed in GROUP 2 for configuration 5B5G5B with a pitch ratio (PRT) of 1.
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Experimental investigation and ANN prediction of heat transfer enhancement in a heat exchanger tube utilizing twin corrugated twisted tapes
(2025-12-01)
Du, Y.
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Wongcharee, K.
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Thianpong, C.
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Chuwattanakul, V.
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Chamoli, S.
This report introduces a novel twin-corrugated twisted tape (TC-TT) insert designed to enhance heat transfer in exchanger tubes. The key innovation lies in the twin-corrugated structure, which generates a twin-swirl flow effect. The corrugated surface synergistically increases flow disturbance and expands the effective heat transfer area. The studied parameters were twist ratios (y/w = 3.0, 3.5, and 4.0) and corrugation angles (θ = 45°, 60°, 75°, and 90°) at 6,000 ≤ Re ≤ 20,000. The results show that using twin-corrugated twisted tapes increases the average Nusselt number by roughly 60–135% compared to a plain tube and by 16–35% compared to a conventional single-twisted tape, confirming the effectiveness of this structural modification. This enhancement is primarily due to the combination of double swirling-flows and enhanced effective heat transfer generated by the corrugated surface. Reducing the corrugation angle (θ) and twist ratio (y/w) led to increases in the Nusselt number (Nu), friction factor (f), and thermal performance factor (TPF). Within the studied range, the Nusselt number, friction factor, and thermal performance factor reached maximum values of 5.18, 0.153, and 1.44, respectively, at a twist ratio of 3.0, a corrugation angle of 45°, and Re = 6,000. Regression analysis was utilized to develop correlations for the Nu and f, considering the Re, Pr, y/w, and θ as influencing variables. The proposed correlations for predicting the friction factor and Nusselt number have errors within ±3% and ±2%, respectively. In addition, an artificial neural network (ANN) was developed for predicting the thermal performance values occurring below the experimental study range. The optimal state ANN model shows remarkable prediction accuracy with R<sup>2</sup> of 0.965.
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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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Thermal effectiveness augmentation in heated tube with louver-punched delta winglets
(2025-09-01)
Promvonge, Pongjet
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Sripattanapipat, Somchai
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Promthaisong, Pitak
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Suchatawat, Maturose
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Nakhchi, Mahdi Erfanian
Louver-punched delta winglet (LPDW) vortex generators were presented as a way to increase convective heat transmission in a tubular exchanger. LPDW arrays were categorized as inline or staggered louver-punched delta winglets (I-LPDW and S-LPDW, respectively). Experimental and numerical research was carried out for Reynolds numbers varying from 4760 to 29,290 to analyze the thermal patterns and flow characteristics within a constant heat flux tube with LPDWs. The turbulence model adopted for the present research was the realizable k-ε model. For both I-LPDW and S-LPDW winglet arrangements, a single ratio of blockage (B<inf>R</inf> = e/D = 0.25), pitch ratio (P<inf>R</inf> = P/D = 1), and attack angle (α = 60°) was utilized as well as three ratios of louver length (L<inf>R</inf> = d/e = 0.24–0.56) and five flap angles (θ = 0°–90°). The research showed that when the θ and L<inf>R</inf> values fall, the LPDW's friction factor (f) and Nusselt number (Nu) grow since streamwise vortices that possess greater kinetic energy of turbulence promote fluid mixing. The winglet with θ = 45°, L<inf>R</inf> = 0.24 exhibited a peak TEF of 2.56 for I-LPDW and 2.63 for S-LPDW whereas the winglet with θ or L<inf>R</inf> = 0° had the largest Nu and f values, at 5.41 and 24.38 times, respectively. The numerical results illustrated that both LPDWs produce many longitudinal vortices throughout the tube. These flow patterns improved fluid mixing in the tube by raising the fluid's kinetic energy of turbulence. Additionally, the findings of the verification between the computational and experimental data were satisfactory. The Nu and f correlations for the I-LPDW and S-LPDW were also established using measured data.
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Performance Assessment of Solar Air Heater Channel with Inclined Groove Turbulators
(2025-05-19)
Koolnapadol, N.
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Promvonge, P.
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Khanoknaiyakarn, C.
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Promthaisong, P.
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Hoonpong, P.
An experimental investigation was carried out to explore the thermal performance and frictional loss features in a solar air heater (SAH) channel that was intentionally roughened on the absorber surface using multiple inclined groove turbulators. The working fluid, air, flows into the SAH channel, which has a consistent surface heat flux for Reynolds numbers (Re) varying between 5290 and 22,600 in the current research. Thermal characteristics at a single inclination angle (a = 45°) are investigated in this research by comparing the effects of three distinct relative groove frequencies (P/H=PR=0.8, 1.2 and 1.6) and groove depth ratios (D/H=DR=0.16, 0.24 and 0.32). The findings highlight that the employ of inclined grooves results in a noticeable rise in Nusselt number (Nu) from 1.24 to 2.82 times relative to the smooth absorber plate (smooth channel), as well as a 1.88 to 7.9 times increase in friction factor (f). The Nu and f show an increasing trend when Re increases, whereas the opposite pattern occurs as DR and PR increase. At PR = 0.8 and DR = 0.32, the inclined groove roughness has the largest thermal effectiveness factor (TEF) of around 1.64. The Nu and f correlations, which are functions of inclined groove features, have also been established.
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Enhanced thermal performance in solar receiver duct with louver-punched V-type winglets: Numerical and experimental study
(2025-03-01)
Suchatawat, Maturose
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Sripattanapipat, Somchai
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Promthaisong, Pitak
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Skullong, Sompol
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Promvonge, Pongjet
An experimental and computational research was performed to explore the augmentation of turbulent convection in a solar receiver channel by utilizing louver-punched V-type winglets (LPVWs) that were fixed to the absorber plate. The simulation utilized the realizable k-ε turbulent model, and the predicated outputs were verified by the relevant measured data. At a fixed attack angle (α) of 45°, the LPVW components were mounted on the absorber with the V-tip facing downstream. Using the LPVW, the newly developed absorber is intended to boost thermal performance by generating multiple flows of longitudinal vortices that induce impinging air streams onto the absorber, thereby enhancing heat transmission. The louvered hole on the winglet serves to reduce pressure loss while preserving the primary vortices. In the current investigation, the winglet parameters consisted of a single relative winglet height (B<inf>R</inf> = 0.4), four louver size ratios (R<inf>L</inf> = e<inf>1</inf>/b = 0.9, 0.7, 0.5, and 0.3), and five louver-flapped angles (β = 90°, 60°, 45°, 30°, and 0°). The LPVW with β > 0° substantially reduced the solid-winglet (β = 0°) friction loss, whereas the heat transmission was slightly declined, as indicated by the results. The solid winglet (β = 0°) exhibited the largest frictional loss and heat transmission, with values approximately 6.3 and 48.2 times the smooth flat duct, respectively. The optimal performance of the LPVW was roughly 2.58, at R<inf>L</inf> = 0.9 and β = 45° Furthermore, empirical correlations for heat transmission and frictional loss were established for this solar receiver duct system. To investigate the heat transmission and flow patterns, a 3-dimensional numerical simulation was implemented, and the predictions were verified against the measured data. The findings were in good accord between the numerical and measured data. For greater thermal performance, the LPVW is reconfigured by altering the locations of the louver holes. The revised LPVW exhibits a peak TEF of 2.7 at β = 35°, l<inf>2</inf>/l<inf>1</inf> = 0.15, l<inf>3</inf>/l<inf>1</inf> = -0.15 and R<inf>L</inf> = 0.9, about 4.65 % superior than the initial analysis.

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