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Investigations on thermal profiles and flow structures in a square channel equipped with staggered vortex turbulators
(2024-09-01)
Boonloi, Amnart
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Lewpiriyawong, Nuttawut
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Jedsadaratanachai, Withada
Given the escalating energy demands today, improving the efficiency of engineering equipment is crucial for optimizing energy use. This study focuses on enhancing heat exchanger performance through passive methods, particularly by installing vortex turbulators. Passive techniques can effectively manage energy costs while enhancing efficiency. The research examines thermal profiles and airflow structures within a square channel heat exchanger (SCHE) equipped with staggered vortex turbulators (SVTs). SVTs feature a unique design combining rectangular winglets and V-pattern baffles. The installation of SVTs aims to intensify vortex strength, thereby increasing SCHE efficiency, convective heat transfer coefficients, and overall heat transfer potential. The study investigates the effects of SVT dimensions (b<inf>1</inf>/H and b<inf>2</inf>/H), airflow directions (+x and -x), installation patterns (pattern no. 1 and 2), pitch to height ratios (P/H = 1, 1.5, and 2), and flow attack angles (α = 20°, 30°, and 45°). Computational simulations using the finite volume method with a commercial code (FLUENT) under laminar flow conditions (Reynolds number of 100–2000) provide insights into thermal profiles, fluid temperature distributions, and flow configurations within the SCHE. Staggered arrangement and gap spacing are employed to reduce pressure loss and enhance airflow strength. The results highlight flow structures and heat transfer characteristics in the heat exchanger channels, elucidating the underlying mechanisms of the heat exchange process. Understanding these behaviors is crucial for developing more efficient heat exchangers and vortex generators in the future. Simulation findings demonstrate that SVTs significantly enhance convective heat transfer over smooth channels due to increased vortex strength. Notably, pattern no. 2 SVTs (b<inf>1</inf>/H = b<inf>2</inf>/H = 0.20) achieve the highest Nu/Nu<inf>0</inf> of 19.21 in the +x flow direction at Re = 2000, α = 30°, and P/H = 1. In conclusion, the study identifies a maximum thermal enhancement factor of 4.38. It underscores the potential of pattern no. 2 SVTs for optimizing heat exchanger performance, offering valuable insights for future developments in thermal management technologies.
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Performance improvement in a heat exchanger tube using discrete X–V baffle (DXVB) turbulators
(2024-02-01)
Boonloi, Amnart
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Lewpiriyawong, Nuttawut
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Jedsadaratanachai, Withada
Thermal performance improvement in a heating tube (HT) using discrete X–V baffle (DXVB) as turbulators is presented. The DXVB is designed with three main goals: 1. To decrease the pressure drop in the tested tube and 2. To increase the mixing quality in the heat exchanger tube and 3. To produce powerful vortex flows. Lower pressure drop, generated vortex flows and higher mixing quality will augment a heat transfer rate and thermo-hydraulic efficiency. This study examines effects of DXVB structures, DXVB distances and placements on laminar air flow and thermal structure with Reynolds number from 100 to 2000. The current problem is numerically investigated using the finite volume technique of a commercial program/code (ANSYS-FLUENT V.2022). The created model of the HT fitted with the DXVB is numerically validated. From the numerical results, the DXVB installed affects the air flow structure in the tested tube. The vortex streams are observed. The change in fluid flow influences thermal characteristics. The vortex streams destroy some parts of the thermal boundary layer and help to increase mixing quality. These perturbed thermal boundary layer (TB-layer) and better mixing quality are two important factors that contribute to convective heat transfer enhancement. In addition, the maximum heat transfer rate and pressure loss are 10.17 and 45.75 times upper than that in the circular plain tube, respectively, while the best thermal enhancement factor (TEF) of 3.09 is observed at 15b5g, +x at Re = 2000.
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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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Numerical assessments of flow pattern and heat transfer profile for the round tube equipped with different configurations of the dual-inclined baffle
(2021-10-01)
Boonloi, Amnart
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Jedsadaratanachai, Withada
Numerical studies of the heat exchanger tube (HXT) equipped with the dual-inclined baffle (DIB) on fluid streams and heat transfer profiles are reported. The DIB configurations can be separated into three types: 1. The DIB is inserted in the middle of the HXT called “type I″, 2. The DIB is placed on the HXT wall called “type II” and 3. The combination of the type I and II DIB called “type III”. The three DIB types are designed with the main purpose to create three different flow profiles. The influences of DIB height with a single pitch distance (P/D = 1) and DIB attack angle of 30° for heat transfer characteristics and fluid streams are discussed in a laminar flow region at Re = 100–2000 (considered at the entry condition). The numerical problem of the HXT inserted with the DIB is solved with a commercial code (the finite volume method). The computation domain is validated to confirm the reliability and accuracy of the simulated results. The flow configurations: streamlines in transverse planes (y-z planes), and heat transfer behaviors: temperature contours in transverse planes (y-z planes) and local Nusselt number contours (Nu<inf>x</inf>), in the HXT equipped with the DIB are proposed in the simulated-result section. The relations of the average Nusselt number ratio (Nu/Nu<inf>0</inf>), friction factor ratio (f/f<inf>0</inf>) and thermal enhancement factor (TEF) with the Reynolds numbers in the HXT inserted with the DIB are presented. As the simulated results, the equipment of the DIB in the HXT brings upper heat transfer rate and thermal performance than those of the smooth tube because of the creations of the vortex streams and impinging streams. The different flow profiles are detected when varying the DIB types that impact for the variations of the heat transfer profile. For the studied range, the increased heat transfer rate in the HXT installed with the DIB is observed to be around 1.03–17.46 times above the plain tube depended on the DIB type, DIB blockage and Reynolds number. Additionally, the maximal TEF of 3.70 is found for the type II DIB at b/D = 0.25 and Re = 2000.
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Thermal performance assessment in a circular tube fitted with various sizes of modified v-baffles: A numerical investigation
(2021-01-01)
Boonloi, Amnart
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Jedsadaratanachai, Withada
This research reports numerical examinations on fluid flow, heat transfer behavior and thermal performance analysis in a circular tube equipped with modified V-baffles (CTMVB). The modified V-baffle (MVB) is a combination vortex generator between V-baffles/V-orifices which are placed on the tube wall and V-baffles which are inserted at the core of the tested tube. The MVB height is separated into two parts; b1 represents the MVB height on the tube wall, while b2 represents the MVB height at the core of the tested round tube. The MVB height to tube diameter ratios, b/D, are adjusted; b1/D = 0.05, 0.1, 0.15 and 0.2, and b2/D = 0.025, 0.05, 0.075 and 0.1. The Reynolds numbers of about 100 – 2000 (laminar regime) are considered. The flow directions in the tested section; V-tip directing downstream and V-tip directing upstream, are discussed. The flow attack angles for the MVB, α, of about 20<sup>o</sup> and 30<sup>o</sup> are compared. The finite volume method with SIMPLE algorithm (a commercial code) is opted to analyze the present investigation. The computational domain of the CTMVB is validated (grid independence and smooth tube validations). It is found that the MVB generates many vortex cores in the tested section. The vortex flows near the tube wall disrupt thermal boundary layer, while the vortex flows at the center of the tube help superior fluid blending. The disturbed thermal boundary layer and the better fluid blending are main two causes for heat transfer augmentation. In addition, the best thermal enhancement factor of the CTMVB is found to be around 3.92.
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The effects of gap spacing ratio on flow structure and heat transfer characteristic for the v-orifice in the square channel heat exchanger
(2019-01-01)
Boonloi, Amnart
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Jedsadaratanachai, Withada
The variations of flow and heat transfer in the square channel heat exchanger inserted with various parameters of V-orifice are investigated numerically. The influences of flow directions (V-Downstream and V-Upstream), gap spacing ratios (g/H or GR = 0, 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30) and blockage ratios (b/H or BR = 0.05, 0.10, 0.15, 0.25 and 0.30) on flow topology and heat transfer behavior are reported. The laminar flow regime with the Reynolds number in the range 100 – 2000 is considered. The numerical results are presented in terms of flow and heat transfer structure in the heat exchanger channel. The thermal performance assessments in the square channel with V-orifice are also concluded. As the numerical results, the gap between the V-orifice and channel walls changes the flow and heat transfer mechanisms in the channel. The gap can reduce the friction loss in the channel and also helps to increase the turbulence of the flow. The optimum gap spacing ratio may help to increase the thermal performance of the square channel heat exchanger.
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Numerical predictions on flow and heat transfer in heat exchanger tube equipped with various flow attack angles of inclined-wavy surface
(2018-01-01)
Boonloi, Amnart
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Jedsadaratanachai, Withada
Numerical analysis on flow configuration, heat transfer behavior and thermal performance in the heat exchanger tube equipped with various flow attack angles of the inclined wavy surface are presented. The laminar flow (Re = 100 – 1200) and turbulent flow (Re = 3000 – 10000) are considered for the present investigation. The flow attack angles of the inclined wavy surface are varied as 15° – 60°. The finite volume method with SIMPLE algorithm is selected to evaluate the current problem. The numerical results are reported in terms of flow and heat transfer mechanisms. The performance evaluations in forms of the Nusselt number ratio (Nu/Nu<inf>0</inf>), friction factor ratio (f/f<inf>0</inf>) and thermal enhancement factor (TEF) are also concluded. As the results, the vortex flow, impinging flow and thermal boundary layer disturbance are detected when inserted the inclined wavy surface in the heat exchanger tube. These behaviors effect for the augmentation of the heat transfer rate, pressure loss and thermal performance. The optimum flow attack angle of the inclined wavy surface for the laminar and turbulent flows are also concluded.
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Effect of location in transverse plane for 45-degree V-baffle on flow and heat transfer mechanisms in a square channel
(2018-01-01)
Boonloi, Amnart
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Jedsadaratanachai, Withada
Numerical predictions on flow and heat transfer in a square channel heat exchanger placed with V-baffle are examined. The gap spacing between the V-baffle and channel wall is varied for all baffle heights. The laminar regime with Re = 100 - 1000 is considered. The numerical model for the square channel heat exchanger placed with V-baffle is validated. The preliminary result reveals that the computational domain has reliability to predict flow and heat transfer in the channel. The mechanisms on flow and heat transfer in the heat exchanger channel are illustrated at the numerical result section. The thermal performance analysis of the heating section when inserted with the V-baffle is also reported in forms of the Nusselt number ratio (Nu/Nu0 or NuR), friction factor ratio (f/f0 or fR) and thermal enhancement factor (TEF). As the results, it is found the gap spacing has extremely effect for flow structure and heat transfer behavior in the test section. The optimum gap spacing ratio may help to reduce the pressure loss or improves the heat transfer rate in the channel heat exchanger. The selection for the gap spacing ratio in the heating section at various baffle heights is also concluded. In addition, the gap spacing ratio around 5 - 10% is suggested for the range investigation.
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3D numerical investigation on laminar forced convection and heat transfer in a circular tube inserted with right triangular wavy surfaces
(2017-01-01)
Jedsadaratanachai, Withada
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Boonloi, Amnart
Numerical investigations on flow and heat transfer characteristics in a circular tube heat exchanger inserted with right triangular wavy surfaces are reported. The configurations of the wavy surfaces; incline and V-shape, are studied with flow attack angles of 30°, 45° and 60° for the Reynolds numbers, Re = 100-2000. The numerical results are compared with the smooth circular tube. The mechanisms on flow and heat transfer in the tube heat exchanger with the wavy surface are presented. As the results, the wavy surface can generate the vortex flow and impinging flow through the test section that helps to improve the heat transfer rate and thermal performance. The impingement of the flow on the tube wall disturbs the thermal boundary layer that is an important factor to enhance the heat transfer rate. The V-Downstream wavy surface can create the highest strength of the impinging flow that leads to the highest heat transfer rate. In the range investigate, the augmentations are around 1.2-7.6 and 4-43.6 times above the smooth tube for the heat transfer and friction loss, respectively. In addition, the optimum thermal enhancement factor, TEF, is around 2.42 for the V-Downstream wavy surface at α = 30° and Re = 2000.
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Flow topology, heat transfer characteristic and thermal performance in a circular tube heat exchanger inserted with punched delta winglet vortex generators
(2016-01-01)
Boonloi, Amnart
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Jedsadaratanachai, Withada
To improve the heat transfer rate and thermal performance, the punched delta winglet vortex generators, DWVGs, were inserted in the middle of the circular tube heat exchanger. The effects of the flow attack angles and the flow directions were investigated numerically for the Reynolds number Re = 100–2000. The finite volume method and the SIMPLE algorithm were used to study. The results are reported in terms of the flow structure, heat transfer behavior and thermal performance evaluation and also compared with the smooth tube with no vortex generators. As the numerical results, the use of the DWVGs in the tube can improve the heat transfer rate and thermal performance by creating the vortex flow through the tested section. The rise of the flow attack angle results in the increasing strength of the vortex flows. The flow attack angle of 25° performs the highest heat transfer rate and thermal performance, while the flow attack angle of 0o gives the reversed results. The computational results reveal that the optimum thermal enhancement factor is around 2.80 at Re = 2000, α = 25°, with the winglet tip pointing downstream. The correlations on both the Nusselt number ratio and friction factor ratio for the DWVG in the tube heat exchanger are presented.

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