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Influence of divergence tapered V-baffles on heat transfer behaviors in a rectangular channel
(2026-05-15)
Keaitnukul, Warin
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Pingta, Supapat
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Phila, Arnut
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Wongcharee, Khwanchit
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Maruyama, Naoki
This study examines the effects of Divergence Tapered V-Baffle (henceforth DT-VB) regarding the heat transfer and friction loss behavior within the rectangle-shaped duct. The baffle attack angles (α) were set at 45°, 60°, 75°, and 90°. The experimental results indicated that as Reynolds numbers increased, the Nusselt numbers exhibited an upward trend, while the friction values showed a corresponding decrease. The Nusselt number improved consistently as the attack angle decreased, with baffles at a 60° attack angle producing the highest friction loss, followed by those at 45°, 75°, and 90°. Among the configurations tested, the 45° attack angle demonstrated the best thermal performance due to its relatively low friction loss and enhanced heat transfer. The highest thermal performance factor (TPF) of 2.13 was attained at a 45° attack angle and a Reynolds number of 6,000.
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How can the appropriate near-wall grid size for gas cyclone CFD simulation be estimated?
(2022-01-01)
Bumrungthaichaichan, Eakarach
In this paper, one of the frequently asked questions for gas cyclone CFD simulation, that “How can the proper near-wall grid size be estimated?”, has been answered. The wall y+ definition was adopted to estimate the near-wall grid sizes. The velocities and friction factors for barrel and cone were obtained by simplifying the previous cyclone pressure drop prediction model to estimate near-wall grid sizes. The representative positions for cyclone cones have been investigated to simplify the near-wall grid estimation. Moreover, new correlations for velocities inside the vortex finder have been developed. The gas cyclones were properly simulated and compared to the previous works to assess the capability of this grid size estimation method. The CFD models developed by the estimated near-wall grid sizes represented the reasonable mean flow properties. Finally, this research concludes that the proposed near-wall grid size estimation method is essential and suitable for gas cyclone CFD simulation.
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HEAT TRANSFER AND FLOW PROFILES IN ROUND TUBE HEAT EXCHANGER EQUIPPED WITH VARIOUS V-RINGS
(2022-01-01)
Boonloi, Amnart
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Jedsadaratanachai, Withada
This study numerically investigates pressure loss, heat transfer and thermal efficiency in round tube heat exchangers attached with various types of V-rings. A typical type A V-ring is compared with two types of modified V-rings (type B and C). The impacts of blockage ratios, b/D = 0.05, 0.10, 0.15 and 0.20 for all V-ring types in the turbulent region are discussed (Re = 3000 – 20,000). Flow directions in the round pipe attached with the V-rings are varied. The V-apex setting downstream is referred to as “V-Downstream, while the V-apex setting upstream is referred to as “V-Upstream”. The flow and heat transfer profiles in the tested section are analyzed using the finite volume method (a commercial code with the SIMPLE algorithm). The thermal performance of the tested tube is measured in terms of dimensionless variables: thermal enhancement factor (TEF), Nusselt number (Nu) and friction factor (f). Numerical results reveal that type B and C V-rings can reduce pressure drop compared with type A V-ring. Additionally, the V-Upstream of type C V-ring yields the maximum TEF of 3.10 at b/D = 0.05.
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The difference in flow pattern, heat transfer and pressure drop characteristics of mini-channel flow boiling in horizontal and vertical orientations
(2018-04-01)
Saisorn, Sira
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Wongpromma, Pakorn
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Wongwises, Somchai
Flow pattern, heat transfer, and pressure drop data for different flow orientations was presented in this study. The data was obtained based on flow boiling experiments with R-134a flow through a 1 mm diameter channel which was aligned in different orientations, i.e. horizontal flow, vertical upward flow, and vertical downward flow. A constant surface heat flux condition was performed under a saturation pressure of 8 bar, a heat flux range of 1–60 kW/m2, and a mass flux range of 250–820 kg/m2s. The experimental results showed the importance of the change in the flow direction. The shape of the gas slug during horizontal flow did not look the same as in the vertical orientations. Heat transfer coefficient and pressure drop became increased when the refrigerant flowed in the vertical downward direction. The experimental data was also compared with the existing prediction methods.
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Numerical investigation on turbulent forced convection and heat transfer characteristic in spirally semicircle-grooved tube
(2016-12-01)
Promthaisong, Pitak
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Boonloi, Amnart
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Jedsadaratanachai, Withada
Turbulent forced convection and heat transfer structure in the spirally semicircle-grooved tube heat exchanger are numerically examined. The computational problem is solved by finite volume method (FVM) with the SIMPLE algorithm. The influences of groove depth and helical pitch on heat transfer, pressure loss, and thermal performance are investigated for turbulent regime, Re = 5000–20,000. As a result, the swirling flow is found through the test section due to the groove on the tube wall. The flow structure in the spirally semicircle-grooved tube can separate into two types: main and secondary swirling flows. The main swirling flow is found in all cases, while the secondary swirling flow is detected when DR ≥ 0.06. The swirling flow disturbs the thermal boundary layer on the tube wall that is an important reason for heat transfer augmentation. In range studies, the enhancements on heat transfer and friction loss are around 1.16–1.96 and 1.2–10.8 time above the smooth tube, respectively. The optimum thermal performance is around 1.11, which detected at DR = 0.06, PR =1.4,andRe = 5000. The correlations of the Nusselt number and friction factor for the spirally semicircle-grooved tube with PR =1.4 are produced to help to design the tube heat exchanger.
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Adiabatic two-phase gas-liquid flow behaviors during upward flow in a vertical circular micro-channel
(2015-12-01)
Saisorn, Sira
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Wongwises, Somchai
A two-phase air-water flow experiment was carried out to obtain flow pattern, void fraction, and pressure drop data from a vertical micro-channel, which was a fused silica tube with a diameter of 0.53. mm and a length of 320. mm. The adiabatic two-phase flow behaviors during vertical upward direction were experimentally investigated, and consequently, a buoyancy effect can be detected in this work. A flow visualization study was performed, leading to observation of slug flow, throat-annular flow, churn flow, annular flow, and annular-rivulet flow. The shape of the interfacial surface in the slug flow pattern was deformed during vertical upward flow, which was different from the bullet-shaped gas slug observed in the horizontal channel. The flow visualization results also indicate that the flow pattern map for vertical upward flow is not completely compatible with that for horizontal flow. Image analysis was performed to determine the void fraction, which increases linearly with increasing volumetric quality. The vertical upward flow gave a lower void fraction than the horizontal flow. The frictional pressure drop can be increased when the churn flow is formed in the channel. In addition, vertical upward flow can result in higher pressure drop when compared with the horizontal channel.
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A critical review of recent investigations on two-phase pressure drop in flow boiling micro-channels
(2012-01-01)
Saisorn, Sira
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Wongwises, Somchai
Two-phase pressure drop during flow boiling has been studied for several decades. Obviously, the publications available on micro-channels are relatively small compared with those for ordinarily sized channels. Although the use of micro-channels yields several advantages, the pressure drop taking p lace in these extremely small channels is higher than that in the ordinarily sized channels because of the increased wall friction. The knowledge of the two-phase pressure drop characteristics in addition to heat transfer phenomena is essential to the design and evaluation of the micro-systems. In this paper, recent research on the flow boiling pressure drop in micro-scale channels is reviewed. The experimental results as well as the relevant prediction methods based on different researchers are presented.
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Two-phase air-water flow in micro-channels: An investigation of the viscosity models for pressure drop prediction
(2011-02-01)
Saisorn, Sira
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Wongwises, Somchai
Adiabatic two-phase air-water flow is experimentally studied in this work. Two channels, made of fused silica, with different diameters of 0.53 and 0.15. mm are used as test sections. The void fraction data for both tubes are obtained by image analysis. For the larger channel, the void fraction is found to be a linear relationship with the volumetric quality. In the case of the smaller one, however, the non-linear void fraction is obtained. The measured frictional pressure drop data are compared with the predictions regarding the homogeneous flow assumption. Several well-known two-phase viscosity models are subsequently evaluated for applicability to micro-channels. © 2010 Elsevier Ltd.
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Experimental study on heat transfer and pressure drop in a channel with triangular v-ribs
(2010-01-01)
Jansangsuk, Dumri
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Khanoknaiyakarn, Chitakorn
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Promvonge, Pongjet
The paper presents an experimental study on heat transfer and pressure drop characteristics in a rectangular channel fitted with periodic triangular v-pattern ribs. The ribs are tested for pointing downstream (v-down) to the flow. The channel has an aspect ratio (width to height ratio), AR = 10 and height, H = 30 mm; the rib-to-channel height, e/H = 0.1, 0.2, and 0.3; the rib pitch to channel height, PR=P/H = 3 and 4; the attack angle (α) of 30° relative to the flow direction. The experiment has been conducted by varying air flow velocity in order to adjust Reynolds number range from 5000 to 20,000. The upper plate of channel is uniformly heated as a constant heat flux while the whole test section is covered with insulation to reduce heat loss to surroundings. These boundary conditions correspond closely to those founded in solar air heaters. The experimental results show a significant effect of the presence of the ribs on the heat transfer rate and pressure drop over the plain channel. The measured data indicates that the triangular v-type rib with e/H = 0.3 and PR =3 yields higher heat transfer rate in terms of Nusselt number, Nu, and the pressure drop in the form of friction factor, f, than the others and also much higher than the smooth wall channel.
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Enhancement of heat transfer in a tube with regularly-spaced helical tape swirl generators
(2005-01-01)
Eiamsa-ard, Smith
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Promvonge, Pongjet
Influence of helical tapes inserted in a tube on heat transfer enhancement is studied experimentally. A helical tape is inserted in the tube with a view to generating swirl flow that helps to increase the heat transfer rate of the tube. The flow rate of the tube is considered in a range of Reynolds number between 2300 and 8800. The swirling flow devices consisting of: (1) the full-length helical tape with or without a centered-rod, and (2) the regularly-spaced helical tape, are inserted in the inner tube of a concentric tube heat exchanger. Hot air is passed through the inner tube whereas cold water is flowed in the annulus. The experimental data obtained are compared with those obtained from plain tubes of published data. Experimental results confirmed that the use of helical tapes leads to a higher heat transfer rate over the plain tube. The full-length helical tape with rod provides the highest heat transfer rate about 10% better than that without rod but it increased the pressure drop. To overcome this, different free-spacing ratio (s = L <inf>s</inf>/L<inf>h</inf>) of 0.5, 1.0, 1.5, and 2.0 were examined. It was found that the space ratio value should be about unity for Re < 4000. The regularly-spaced helical tape inserts at s = 0.5 yields the highest Nusselt number which is about 50% above the plain tube. © 2004 Elsevier Ltd. All rights reserved.

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