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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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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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Influences of the punched delta winglet vortex generators in a circular tube heat exchanger on thermo-hydraulic performance
(2015-01-01)
Jedasadaratanachai, Withada
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Boonloi, Amnart
Numerical investigations on flow topology, heat transfer behavior and thermal performance evaluation in a circular tube heat exchanger with the punched delta winglet vortex generators (PDWVG) inserted in the middle of the test section are presented. The effects of the flow attack angles that converging to the center of the tube; α = 0˚, 5˚, 10˚, 15˚, 20˚, 25˚, and flow directions; winglet tips pointing downstream and upstream, are investigated for the Reynolds numbers; Re = 100 – 2000. The finite volume method and SIMPLE algorithm are used for the current study. The results are presented in terms of flow configuration, heat transfer behavior and thermal performance assessments and also compared with the smooth tube with no PDWVG. As numerical results, the use of PDWVG inserted in the tube can help to improve heat transfer rate and thermal performance in the heat exchanger by creating the vortex flows through the test section. The rise of the flow attack angle and Reynolds number leads to increase in heat transfer, friction loss and thermal performance. The optimum TEF is around 2.33 at Re = 2000, α = 25˚ for winglet tip pointing downstream.
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Effects of blockage ratio and pitch ratio on thermal performance in a square channel with 30° double V-baffles
(2014-11-01)
Jedsadaratanachai, Withada
;
Boonloi, Amnart
This article presents flow configurations and heat transfer characteristics in an isothermal square channel with 301 double V-baffles. The influences of blockage ratios (b/H, BR=0.05-0.25) and pitch ratios (L/H, PR=1-2) for Reynold numbers, Re=100-1200 are investigated numerically. The 30° double V-baffles are placed on both two opposite walls of the square channel with in-line arrangement and each V-tip pointing downstream. The numerical results are presented in four parts; accuracy validations, flow structures, heat transfer behaviors and performance evaluations. It is found that the use of the double V-baffles performs higher heat transfer rate and pressure loss than the smooth channel with no baffle. The rise of the blockage ratio and reducing the pitch ratio lead to the increase in heat transfer rate and pressure loss. The optimum thermal enhancement factor is found to be about 3.2 at PR=1, BR=0.10 and Re=1200.
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Thermal performance assessment for laminar forced convection with downstream Reformed-V and Reformed-Double-V generators
(2014-01-01)
Jedsadaratanachai, Withada
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Boonloi, Amnart
Thermal assessments for laminar flow in an isothermal wall square channel over downstream Reformed-V (RV) and Reformed-Double-V (RDV) generators inserted diagonally are presented numerically in three dimensional. The RV and RDV are designed to comfort for forming and installing in the heat exchanger channel. The effect of RV and RDV height is investigated in terms of blockage ratio, b/H, BR = 0.05-0.30 for Reynolds number based on the hydraulic diameter of the square channel, Re = 100-1200. The SIMPLE algorithm, finite volume method and the periodic condition are used in the current computational domain. The mathematical results show that the uses of RV and RDV provide higher heat transfer rate than the smooth square channel with no generators. The RV gives higher on both heat transfer rate and friction factor values than the RDV case for all BR and Re values. The maximum heat transfer rate and friction factor are found around 20.5 and 420 times over the smooth square channel, respectively, at BR = 0.30 for RV case. The optimum thermal enhancement factor, TEF, is found at BR = 0.1, Re = 2000 around 2.95 for RDV case.

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