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    Numerical simulation of Al2O3-water nanofluid flow and heat transfer in a tube with angled rings
    (2014-01-01) ;
    Sripattanapipat, Somchai
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    A numerical investigation has been conducted to examine turbulent flow and heat transfer characteristics in a three-dimensional isothermal tube mounted with 60° angled rings (AR). The ARs with pitch spacing ratio, PR=1.0 and various blockage ratios (BR) ranging from 0.025-0.1 are introduced. The computations are based on a finite volume method and the SIMPLE algorithm has been implemented. The fluid flow and heat transfer characteristics are presented for Reynolds number (Re) ranging from 3000 to 12000. To generate a main counter-vortex pair flow in the tube, ARs at an attack angle of 60° are mounted repeatedly in the tube. Effect of different BRs at a single PR and nanofluid, Al<inf>2</inf>O<inf>3</inf>-water, with volume fractions 1% and 5% on heat transfer and friction loss is investigated. It is apparent that two main vortex flows created by the ARs exist and help to induce impinging flows on the tube wall leading to drastic increase in heat transfer rate over the tube. The increment in the BR gives rise to the increase in the Nusselt number and friction factor. The computational results reveal that the maximum thermal enhancement factor for the AR with BR=0.025 is found to be 1.8 at Re =3000. The results show that nanofluid, Al<inf>2</inf>O<inf>3</inf> -water, can increase the thermal performance when increasing volume fraction to 5%. © (2014) Trans Tech Publications, Switzerland.
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    Heat transfer and flowfriction behaviors in a channel with multiple 30° V-ribs
    (2014-01-01)
    Khanoknaiyakarn, C.
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    The paper presents an experimental study on heat transfer and flow friction characteristics in a rectangular channel fitted with periodically rectangular V-ribs. The multiple V-rib turbulators are tested in the channel having an aspect ratio (width to height ratio), AR=10 and height, H= 30 mm, with three rib-to-channel height ratios (e/H=0.2, 0.3, and 0.4), two rib-pitch to channel-height ratios (PR=P<inf>1</inf>/H= 3 and 4) and a single attack angle (α=30°). The upper plate of channel is uniformly heated at a constant heat-flux. The experiment has been conducted by varying airflow velocity in order to obtain the Reynolds number range from 5000 to 24,000. The experimental results show a significant effect of the presence of the ribs on the heat transfer rate and pressure drop over the smooth channel. The measured data indicates that the V-rib turbulators with e/H = 0.4 and PR =3 yields the highest heat transfer rate and friction loss. All the V-rib turbulators perform much higher than the smooth channel with no rib. © 2014 Asian Institute of Technology.
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    Numerical investigations on flow structure and heat transfer in a square duct equipped with double V-orifice
    (2020-01-01)
    Boonloi, Amnart
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    Numerical predictions on heat transfer characteristic, flow topology and thermal performance assessment in a square duct are presented. The passive technique, insertion of the vortex generator, is opted to develop the heat transfer rate in the square duct heat exchanger. The vortex generator of the present research is Double V-Orifice (DVO). The square duct equipped with DVO is tested with various parameters. The influences of DVO height, b, to the duct height, H, or b/H, gap spacing between the outer edge of the orifice and the duct wall, s, to the duct height or s/H and flow directions (tip-pointing-Downstream and tip-pointing-Upstream) on flow pattern and heat transfer profile are considered for laminar flow regime with similar pitch, P, to duct height or P/H of 1. The Reynolds number, Re, based on the hydraulic diameter, D<inf>h</inf>, of the square duct around 100 – 2000 is discussed. The numerical model is solved with the commercial software (finite volume method). As the numerical result, the square duct inserted with the DVO offers greater Nusselt number, Nu, than the plain duct around 1.00 – 14.80 times. The maximum thermal enhancement factor, TEF, for the square duct inserted with the DVO is found to be about 3.60 depended on s/H, b/H and flow direction. The flow and heat transfer profiles in the square duct inserted with the DVO are also illustrated.
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    Thermal characteristics in turbulent channel flows with V-baffle vortex generators
    (2014-01-01)
    Kaewkohkiat, Y.
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    Eiamsa-Ard, P.
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    Eiamsa-Ard, S.
    Experimental work has been performed to examine the effects of V-baffle vortex generators on the heat transfer and friction characteristics in a channel under a constant heat flux boundary condition. In the experiments, V-baffles at different pitch ratios (PR=P/e = 4.0, 6.0 and 8.0) were carried out. Measurements were carried out for a channel of one aspect ratio, AR = W/H = 4.0 and duct height, H= 40 mm with baffle height, e = 8 mm. Experiments were conducted for the Reynolds number range of 6000 to 22,000. The distributions of temperature and local Nusselt number on bottom channel wall were observed with thermochromic liquid crystal (TLC) sheet. Isothermal friction factors were also taken and presented. The obtained results demonstrate that heat transfer increases with the increase of Reynolds number, whereas friction factor (f) shows the opposite trend. Experimental results also show that the channels with V-baffle at the highest pitch ratio (PR = 8.0) provide highest heat transfer than others. © 2014 Asian Institute of Technology.
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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) ;
    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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    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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    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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    Heat transfer improvement in a square duct with diagonal inclined ribs
    (2014-01-01)
    Suwannapan, Supattarachai
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    Poomsalood, Ratsak
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    Limkul, Thitipat
    This research presents a numerical study of turbulent periodic flow and heat transfer in three-dimensional isothermal-fluxed square duct with diagonal inclined rib inserted. The fluid flow and heat transfer characteristics are presented for Reynolds numbers in the range of 4000 to 20,000. The computations based on the finite volume method, and the SIMPLE algorithm has been implemented. Effects of rib pitch ratios (0.5 to 2) at a single blockage ratio of 0.2 and attack angle of 60° on heat transfer and friction factor in the duct are examined and their results of the inclined rib are also compared with those of the smooth duct. It is found that the inclined rib provides higher heat transfer rate and friction factor than the smooth duct for all cases. In addition, the decreasing of the pitch ratio leads to the rise in the Nusselt number and friction factor. © (2014) Trans Tech Publications, Switzerland.
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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) ;
    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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    3D simulation on flow behavior and heat transfer in a circular tube with inclined different arrangement of thin rib
    (2013-01-28)
    Boonloi, Amnart
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    This work deals with periodic flow, friction loss and heat transfer characteristics in a constant temperature-surfaced circular tube fitted with rib vortex generators (RVG). The computations are based on the finite volume method with the SIMPLE algorithm implemented. The fluid flow and heat transfer behaviors are presented for Reynolds numbers ranging from 100 to 1000. To generate two main vortex flows through the tested section, the 45<sup>o</sup> RVGs are mounted repeatedly in in-line arrangements on the top and bottom walls and in the central area of the tested section. Effects of different RVG heights, BR in a range from 0.1D to 0.3D with a single pitch of 1.5D on heat transfer and friction losses in the test section are examined. It is apparent that the vortex flows created by the RVG exist and help to induce periodically impinging flows on a sidewall leading to drastic increase in the heat transfer rate over the test section. The computational results reveal that the optimum thermal performance is about 2.38 for using the RVG height of 0.2D for the RVG placed on the tube walls at the highest Re value. © (2013) Trans Tech Publications, Switzerland.
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    Numerical investigation on turbulent forced convection in heating channel inserted with discrete V-shaped baffles
    (2016-01-01)
    Boonloi, Amnart
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    The numerical examinations on flow visualization, heat transfer characteristic and performance improvement in a square duct inserted with discrete V-shaped baffles (DVB) are reported. The DVB is designed to reduce the pressure loss when compared with the V-shaped baffle. The influences of the flow blockage ratios (b/H, BR = 0.05-0.20), V-tip directions (V-Downstream and V-Upstream) are investigated for Reynolds number, Re = 3000-20,000, with a single pitch ratio and flow attack angle of 1 and 30°, respectively. As the results, the DVB can generate the vortex flow and impinging flow through the test section that assists to develop the thermal efficiency. The augmentations on the heat transfer coefficient and pressure drop are around 2.5-5.75 and 4-22.5 times above the smooth duct, respectively. The best thermal efficiency in forms of thermal enhancement factor, TEF, around 2.32 is detected at Re = 3000, BR = 0.10 and V-Upstream.