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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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Heat transfer mechanism in turbulent channel flow with V-tapered-baffles: Effect of convergence and divergence direction V-baffles
(2026-01-01)
Chokphoemphun, S.
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Phila, A.
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Promthaisong, P.
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Chamoli, S.
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Maruyama, N.
Solar air heaters are equipment that is utilized in a variety of applications including engineering and agriculture. Improving the transfer performance of heat exchangers is necessary to benefit from efficient energy consumption. The purpose of this work is to examine the effect of novel design V-tapered-baffles on the thermal performance of solar air heaters. The experiment was conducted with the expectation of a constant wall heat flux. In turbulent flow, air serves as the testing fluid with a Reynolds number range of 6,000 to 24,000. Two V-tapered-baffle types were employed in the experiment: convergent (C-VB) and divergent (D-VB) direction V-baffles, which were employed with fixed baffle pitch length of 60 mm and four different convergent and divergent edge baffle heights of 0, 3, 6, and 9 mm. The experimental results are compared with traditional V-baffles (T-VB) and the smooth surface channel. The investigation discovered that installing V-baffles provided a better thermal performance factor than traditional V-baffles. The important factor is that the V-baffles can reduce the friction factor by about 11–50 % compared to the traditional V-baffles under the same conditions. The maximum thermal enhancement factor values for the C-VB and D-VB were 2.19 and 2.13, respectively.
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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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Turbulent forced convection in a square duct heat exchanger (SDHX) equipped with combined vortex turbulators (CVT): A numerical investigation
(2025-02-01)
Boonloi, Amnart
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Jedsadaratanachai, Withada
This research presents a numerical study on flow structures, heat transfer, and thermal performance evaluation in a square duct heat exchanger (SDHX) equipped with combined vortex turbulators (CVTs). The aim of installing CVTs is to create vortex flow, impinging flow, and disrupt the thermal boundary layer, thereby enhancing the convective heat transfer coefficient and increasing the heat transfer ability and SDHX performance. V-shaped ribs and rectangular winglets are selected as CVTs due to their effectiveness in enhancing heat transfer rates. The study investigates the effects of CVT height (the values of a/H and b/H range from 0.05 to 0.20.), flow direction (V-apex pointing downstream (V-Downstream) and V-apex pointing upstream (V-Upstream)), and CVT arrangement (in-line and staggered arrangements) on flow structure and heat transfer characteristics. A comparison between V-shaped ribs and rectangular winglets is presented in terms of CVT types (A and B). The study focuses on turbulent flow with Reynolds numbers ranging from 3000 to 20,000. The results demonstrate that the flow behavior aligns with the proposed hypotheses, leading to increased heat transfer rates, which are 1.24 to 7.71 times greater than those of the empty duct. For thermal performance evaluation, the highest thermal enhancement factor (TEF) value of 1.77 is observed with type A CVT, in a staggered arrangement, and with the V-Upstream flow direction, when considering a Reynolds number (Re) of 3000. Additionally, the results of the study are presented in the form of TEF contours and correlations to assist in the design of vortex turbulators for heat exchange systems.
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Evaluation of aerothermal performance of a round tube with regularly-spaced multi-channel twisted tape elements installed
(2024-06-01)
Phila, Arnut
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Chuwattanakul, Varesa
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Thianpong, Chinaruk
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Bhattacharyya, Suvanjan
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Naphon, Paisarn
This article presents a study of aerothermal performance of tubes with regularly-spaced multi-channel twisted tape elements (RS-MTT) installed. This research aimed to find the proper design RS-MTTs that induce swirl flow which potentially improves fluid mixing between the core fluid and the fluid near the tube wall, thereby accelerating the heat transfer rate. Additionally, the effects of Reynolds numbers and free-spacing ratios (s/y) on heat transfer, friction loss, and thermal performance behaviors were examined. The RS-MTTs having different free-spacing ratios (s/y) of 0.0, 0.25, 0.5, 0.75, and 1.0 were tested. Air was utilized as the testing fluid in experiments with Reynolds numbers (Re) spanning from 6000 to 20,000. The utilization of RS-MTTs with s/y = 0.0, 0.25, 0.5, 0.75, and 1.0 augmented heat transfer rates up to 1.74, 1.80, 1.85, 1.90, and 2.15 times given by the plain tube alone while the friction factors increased by 4.22, 4.61, 3.87, and 4.05 times, respectively. At the lowest Reynolds number of 6000, the thermal enhancement factors of the tube containing the RS-MTTs with s/y = 0.0, 0.25, 0.5, 0.75, and 1.0 reached the maximum values of 1.42, 1.35, 1.31, 1.27, and 1.23, respectively. Among the RS-MTTs tested, the RS-MTT with s/y = 0.0 showed the best thermal enhancement factor of 4.56%, corresponding to the heat transfer augmented of 11.52% with a friction penalty of 8.71%.
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Numerical predictions of flow topology and heat transfer in a square duct with staggered V-ribs
(2022-12-01)
Boonloi, Amnart
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Jedsadaratanachai, Withada
Performance augmentation of a square duct heat exchanger by a passive technique is numerically investigated. V-pattern ribs are used as vortex turbulators to enhance heat exchanger performance. The V-rib arrangement is designed with two important factors: 1. to increase the heat transfer coefficient by disturbing thermal boundary layers and to expedite fluid mixing and 2. to remain or decline the friction loss across the ribbed duct when compared with a typical in-line V-rib arrangement. The effects of rib heights (b/H = 0.05–0.20), rib pitch (P/H = 1–2) and flow paths (+x and -x) on fluid structure and thermal characteristics are studied within a laminar flow regime. Numerical analysis using the finite volume method (FVM) is chosen to predict the fluid structure and thermal mechanisms within the ribbed duct. Validating topics: smooth duct validation and grid independence, are firstly investigated. Simulation results are analyzed in forms of fluid structure and thermal behaviors. Performance assessment (thermal enhancement factor, friction factor ratio and Nusselt number ratio) within the tested section are also concluded. The simulation results show that the best TEF is found to be around 4.5, while the maximum Nusselt number ratio is around 19.39.
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3D-numerical predictions of flow structure and heat transfer behavior in heat exchanger tubes inserted with different patterns of double-V baffles
(2022-11-01)
Boonloi, Amnart
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Jedsadaratanachai, Withada
3D-simulation of convective heat transfer and laminar flows at an isothermal wall of a circular tube heat exchanger (CTHE) inserted with different configurations of double-V baffles (DVB) are presented. The insertion of DVB is done with the objective to produce vortex flows and impinging flows to perturb the thermal boundary layer (TBL) over the isothermal wall, thus increasing convective heat transfer coefficient and efficiency. Various DVB parameters which contribute to the best thermal efficiency are considered. Effects of six DVB shapes (Type A-F), DVB height (b/D = 0.05-0.30) and flow directions (+x, -x) on air stream and thermal mechanisms with Reynolds number within 100-2000 (calculated with the inlet condition) are compared. Simulation results of flow structure (streamline structures in transverse planes) and heat transfer characteristics (fluid temperature distributions and local Nusselt number (Nux) contours) are reported. Insights into the flow pattern and heat transfer are key to improve heating and cooling system performance. The improvement of the CTHE inserted with the DVB is presented in terms of the Nusselt number (Nu) and the thermal enhancement factor (TEF), while the pressure loss is presented by the friction factor (f). Simulation results show that the DVB creates vortex and impinging flow over the surface of the circular tubes in the CTHE of all investigated tests. The best TEF and the best Nusselt number ratio are 3.55 and 22.42, respectively.
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EFFECTS OF BLOCKAGE LOCATIONS FOR ENHANCED HEAT TRANSFER AND FLOW VISUALIZATION IN A TESTED DUCT WITH DUAL-INCLINED BAFFLES (DIB): A CFD ANALYSIS
(2022-01-01)
Boonloi, Amnart
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Jedsadaratanachai, Withada
Numerical analysis of fluid flow mechanism and heat transfer in a heat exchanger duct (HXD) with dual-inclined baffles (DIB) are reported. Three DIB types are examined: 1. “Type A” is located at the center of the HXD, 2. “Type B” is located on the upper-lower duct walls (as an orifice) and 3. “Type C” is a combination of the type A and B (as double orifices). The impacts of the ratio of DIB heights (b) to the square duct height (H; b/H) on increased heat transfer and friction loss are analyzed. Laminar flow (Re = 100 – 2000 based on the entry condition of the tested duct) is discussed. The simulated problems of the HXD equipped with various DIB types are analyzed by a commercial code (the finite volume method). To confirm accuracy results, the simulated domain of the HXD with the DIB is validated (optimum grid check and smooth duct validation). The simulated solutions are illustrated in terms of heat transfer and flow features. The performance assessments of the HXD with different DIB types are also presented in terms of thermal enhancement factor, Nusselt number and friction factor. It is interesting that the changed DIB position at an identical flow-blockage-ratio leads to the changed flow structure that impacts the variations of both the Nusselt number and pressure drop of the HXD. It is found that type C DIB provides the greatest thermal potentiality. The heat transfer rate of the HXD equipped with type A, B and C DIB is 1.38 – 13.93, 1.00 – 14.19 and 1.31– 14.45 times higher than that of the smooth duct, respectively, depending on the DIB height and Reynolds number. Additionally, the best thermal enhancement factor (TEF) of 4.04 is found for the HXD with the type C DIB at b<inf>1</inf>/H = 0.05 and b<inf>2</inf>/H = 0.15 at Re = 2000.
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Thermal and swirl flow topologies in a twisted square duct with a multi-twisted tape installed
(2020-01-01)
Promthaisong, Pitak
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Chuwattanakul, Varesa
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Eiamsa-Ard, Smith
This paper presents 3D numerical investigation of the turbulent flow and heat transfer characteristics of a twisted square duct installed with multi-twisted tapes. Air was used as the working fluid with flow rates in terms of Reynolds numbers ranging from 3000 to 20,000. The effects of (1) multi-twisted tape width ratios (w/H) of 0.2 to 1.0 and (2) the number of channels (N = 2 and 4) on heat transfer and flow mechanisms were studied at constant twist ratio of y/D = 3.5. The numerical results showed that twisted square duct combined with twisted tape caused swirl flows which effectively promoted fluid mixing and provided heat transfer over those of both a straight smooth square duct and twisted square duct. Increasing w/H led to increases in both heat transfer and the friction factor. At a given multi-twisted tape width ratio (w/H), the heat transfer and friction factor with N = 4 were higher than those with N = 2, while thermal enhancement factor showed the opposite trend. A maximum thermal enhancement factor of 1.93 was obtained at tape width ratio of w/H = 1.0, channel number of N = 2 and Re = 3000.
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Heat transfer augmentation in a circular tube with winglet vortex generators
(2015-04-01)
Chokphoemphun, Suriya
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Pimsarn, Monsak
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Thianpong, Chinaruk
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Promvonge, Pongjet
The article presents the influence of winglet vortex generators (WVGs) placed in the core flow area on thermal performance enhancement of a tube heat exchanger. The experiment was carried out in a uniform wall heat-fluxed tube by varying turbulent airflow for Reynolds number ranging from 5300 to 24000. In the present work, the WVGs with an attack angle of 30° were inserted into the test tube at four different winglet pitch ratios (R<inf>P</inf> = P/D) and three winglet-width or blockage ratios (R<inf>B</inf> = e/D). The experimental results at various R<inf>P</inf> and R<inf>B</inf> values were evaluated and compared with those for smooth tube and tubes with twisted tape or wire coil. The measurement reveals that the WVGs enhance considerably the heat transfer and friction loss above the plain tube, wire coil and twisted tape. The Nusselt number and friction factor increase with the increment of R<inf>B</inf> and Re but with the decreasing R<inf>P</inf>. The average Nusselt numbers for the WVGs with various R<inf>B</inf> are in the range of 2.03-2.34 times above the plain tube. The thermal performance for the WVGs is found to be much higher than that for the wire coil and twisted tape and is in a range of 1.35-1.59. Also, a numerical investigation is conducted to study the flow structure and heat transfer enhancement mechanisms in the winglet-inserted tube.

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