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3D numerical analysis on mechanisms of flow and heat transfer in a square channel with right triangular wavy surfaces
(2018-05-01)
Jedsadaratanachai, W.
;
Boonloi, A.
Numerical investigations on thermo-hydraulic performance and mechanisms of flow and heat transfer in a square channel heat exchanger inserted with right triangular wavy surfaces are examined. The influence of the flow attack angles (30°, 45° and 60°) is investigated for laminar flow (Re = 100–2000). The configurations of the right triangular wavy surfaces are varied as inclined and V-shaped wavy surfaces (the pointing of V-tip with downstream and upstream called “V-downstream” and “V-upstream”, respectively). The insertions of the wavy surfaces in the channel heat exchanger are divided into two types: middle and diagonal insertions. The computational results reveal that the maximum thermal enhancement factor, TEF, is around 2.31 for the 30° V-downstream wavy surface with diagonal insertion at Re = 2000.
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3D Numerical study on the flow topology and heat transfer characteristics of turbulent forced convection in spirally corrugated tube
(2016-03-18)
Promthaisong, P.
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Jedsadaratanachai, W.
;
Eiamsa-Ard, S.
This paper presents a numerical analysis on flow configurations and heat transfer characteristics of turbulent forced convection in spirally corrugated tubes. The influences of corrugation depth (DR = 0.02-0.16), pitch ratio (PR = 0.10-1.00), and Reynolds number (Re = 5,000-20,000) on flow structure and heat transfer characteristics are described. Comparisons between the full length and periodic domains are also reported. The results show that spirally corrugated tubes induced vortex flows which helped to increase heat transfer due to enhanced fluid mixing. The maximum thermal enhancement factor of 1.16 was obtained by using the spirally corrugated tube with DR = 0.06, PR = 0.25 at Re = 5,000.
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Heat transfer enhancement of TiO2/water nanofluid in a heat exchanger tube equipped with overlapped dual twisted-tapes
(2015-09-01)
Eiamsa-ard, S.
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Kiatkittipong, K.
;
Jedsadaratanachai, W.
Titanium dioxide (TiO<inf>2</inf>) in water as nanofluid was employed for heat transfer enhancement together with overlapped dual twisted tapes (O-DTs). The study encompassed Reynolds numbers from 5400 to 15,200, O-DTs with overlapped twist ratios (y<inf>o</inf>/y) of 1.5, 2.0 and 2.5 and nanofluids with TiO<inf>2</inf> volume concentrations (ϕ) of 0.07%, 0.14% and 0.21%. The experimental and numerical results indicated that O-DTs with smaller overlapped twisted ratio delivered a stronger swirl intensity and higher turbulent kinetic energy (TKE). The use of O-DTs at the smallest overlapped twist ratio of 1.5 enhanced heat transfer rates up to 89%, friction factor by 5.43 times and thermal performance up to 1.13 times as compared to those of plain tube. In addition, heat transfer increased as TiO<inf>2</inf> volume concentration of nanofluid increased, owing to the increases of contact surface and thermal conductivity. The simultaneous use of the O-DTs having twist ratios 1.5 with the nanofluid with TiO<inf>2</inf> volume concentration of 0.21% resulted in heat transfer enhancement around 9.9–11.2% and thermal performance improvement up to 4.5% as compared to the use of O-DTs alone. The empirical correlations of heat transfer rate (Nu), friction factor (f) and thermal performance (η) in a constant wall heat flux tube equipped O-DTs at different overlapped twist ratios (y<inf>o</inf>/y) and volume concentrations of TiO<inf>2</inf> nanoparticles (ϕ) are also reported for heat transfer applications.
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Thermal characteristics in turbulent channel flows with V-baffle vortex generators
(2014-01-01)
Kaewkohkiat, Y.
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Jedsadaratanachai, W.
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Eiamsa-Ard, P.
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Promvonge, P.
;
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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Heat transfer and flowfriction behaviors in a channel with multiple 30° V-ribs
(2014-01-01)
Khanoknaiyakarn, C.
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Jedsadaratanachai, W.
;
Promvonge, P.
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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Heat transfer augmentation through the use of wire-rod bundles under constant wall heat flux condition
(2013-11-01)
Nanan, K.
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Pimsarn, M.
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Jedsadaratanachai, W.
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Eiamsa-ard, S.
This article reports an experimental investigation on heat transfer, friction factor and thermal performance characteristics of turbulent flow (6000. ≤. Re≤. 20,000) in heat exchanger tubes with wire-rod bundles as flow turbulators. The experiments were carried out at three different pitch ratios (P/D) of 1.0, 1.5 and 2.0 and three wire-rod number per bundle (N) of 4, 6 and 8. The experimental results show that Nusselt number increases with increasing Reynolds number and wire-rod number per bundle, and decreasing pitch ratio (P/D) of the turbulators. As compared to the results of the tube without wire-rod (the plain tube), heat transfer rate and friction factor are respectively increased in ranges of 3.5 to 68.8% and 156 to 353%, depending on the operating conditions. At the same pumping power, the use of wire-rod turbulators results in thermal performance factor up to 1.02 times of those of the plain tube. In addition, the correlations that developed from the present experimental data for Nusselt number, friction factor and thermal performance factor are also presented. © 2013 Elsevier Ltd.
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Laminar periodic flow and heat transfer in square channel with 30° inclined baffles
(2010-12-06)
Kwankaomeng, S.
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Jedsadaratanachai, W.
;
Promvonge, P.
A numerical investigation has been carried out to study laminar flow and heat transfer characteristics in a three-dimensional isothermal wall square-channel with 30° staggered angled-baffles. The computations are based on the finite volume method, and the SIMPLE algorithm has been implemented. The fluid flow and heat transfer characteristics are presented for Reynolds numbers based on the hydraulic diameter of the channel ranging from 100 to 1200. To generate a pair of stream wise counter-rotating vortex (P-vortex) flows through the tested channel, the baffles (like rectangular winglet) with the attack angle of 30° are mounted in tandem and staggered arrangement on both upper and lower walls of the test channel. Effects of different baffle heights at a single pitch ratio (PR=3) on heat transfer and pressure loss in the channel are studied. It is found that P-vortex flows created by the 30° baffle exist and help to induce impinging jets on a side wall and the upper and lower wall leading to drastic increase in heat transfer rate over the test channel. In addition, the increase in the baffle height results in the rise of Nusselt number and friction factor values. The computational results reveal that the optimum thermal enhancement factor of the baffle is about 2.9 at height of 0.15 times of the channel height.

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