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Numerical heat transfer study of square duct equipped with novel flapped V-baffles
(2024-03-01)
Thianpong, Chinaruk
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Promvonge, Pongjet
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Skullong, Sompol
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Promthaisong, Pitak
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Nakhchi, Mahdi Erfanian
The paper describes a computational study of heat transfer enhancement inside a square duct with V-shaped flapped baffles located repeatedly on the bottom and top walls for fluid flowing with Reynolds numbers (Re) from 3000 to 21,000. The basic goal of this work is to attain the largest relative Nusselt number (Nu/Nu<inf>0</inf>) whilst maintaining the highest thermal performance to improve energy savings. A finite volume method was used in the computations, along with the Realizable k‒ε turbulent model. The variable baffle parameters considered first in the current simulation were the relative height/blockade ratio (B<inf>R</inf> = 0.05−0.2) and the flap angle of the baffle hole (β = 0° − 90°), while the fixed parameters included the attack angle (α = 60°), hole diameter ratio (d<inf>R</inf> = 0.5), and pitch ratio (P<inf>R</inf> = 0.5). To accomplish this goal, the previously mentioned parameters providing the best thermal performance were investigated further by extending the values of B<inf>R</inf> to 0.25−0.3, d<inf>R</inf> to 0.8 and α to 45°−30°. The simulation results indicate that the jet flowing from the flapped hole, as well as the vortices created by the baffle, can boost heat transfer and friction loss in comparison to the plain duct. In comparison, using a flapped baffle with β > 0° results in less friction loss, a greater thermal enhancement factor (TEF), and a higher Nusselt number than using a baffle with no flap. The first investigation disclosed that for B<inf>R</inf> = 0.2 and β = 20°, the greatest TEF of 2.19 with Nu/Nu<inf>0</inf> of 7.9 times are obtained. The extended study, on the other hand, showed that the highest TEF of roughly 2.49 with Nu/Nu<inf>0</inf> of 8.4 times are seen for α = 45°, d<inf>R</inf> = 0.8, B<inf>R</inf> = 0.25 and β = 20° at lowest Re. Thus, the flapped baffle provides a significant increase in Nu/Nu<inf>0</inf> and TEF over the baffle alone.
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Effect of louvered curved-baffles on thermohydraulic performance in heat exchanger tube
(2023-02-01)
Jayranaiwachira, Nuthvipa
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Promvonge, Pongjet
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Thianpong, Chinaruk
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Promthaisong, Pitak
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Skullong, Sompol
The paper presents an experimental study of convection enhancement in a tube heat exchanger using louvered curved-baffle (LCB) vortex generator (VG). The heat transfer and pressure loss of air as a working fluid, flowing in an isothermal-fluxed tube were measured having Reynolds numbers (Re) between 4760 and 29,300. The LCB elements were arrayed on two tape sides in a V-shape with a 30° attack angle. At a fixed baffle height, the LCB had three axial pitch ratios (PR) from 0.5 to 1.5 and six louver angles (θ) from 0° to 90°. Thermal enhancement factor (TEF), Nusselt number (Nu), and friction factor (f) are often utilized to analyze the effect of VG geometrical variables on thermohydraulic performance. The measured results demonstrated that the LCB-inserted tube has a significantly larger Nu and f than a plain tube functioning alone, and that the Nu and f tend to rise when PR and θ decline. Using the LCB increases Nu and f by approximately 2.59-4.66 and 3.8-39.37 times, respectively. The maximal TEF is achieved for the LCB at PR = 1, θ = 45° and lower Re. Empirical correlations for Nu and f were evaluated and found to fit measured data well, with discrepancies by ± 9% and ±10%, respectively.
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Thermal-hydraulic performance of solar receiver duct with inclined punched-ribs and grooves
(2022-11-01)
Jayranaiwachira, Nuthvipa
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Promvonge, Pongjet
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Thianpong, Chinaruk
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Skullong, Sompol
The article presents an experimental study on turbulent airflow friction and thermal behaviors in a solar receiver heat exchanger duct mounted with combined inclined chamfered-groove and turbulators. The experimental work was conducted for Reynolds numbers from 5,300 to 24,000, based on the hydraulic duct diameter. The 45°-inclined punched-ribs and grooves were placed periodically on the absorber plate. The punched-rib parameters were four inclination angles (β = 0°, 45°, 90° and 135°) of the punched holes and three relative rib pitches (PR = 1, 1.5 and 2) whereas only a rib blockage ratio (BR = 0.5) and an angle of attack (α) of 45° were fixed. Similarly, the parameters of the grooves included only three groove-pitch ratios (PR), similar to the rib pitches and one groove blockage ratio (BR = 0.2). The experimental result has revealed that the combination of rib-groove turbulators at β = 0° (solid rib) and PR = 1 gives the maximum heat transfer rate and friction loss while the greatest thermal enhancement factor of 2.1 was found at β = 45°, PR = 1. Moreover, the friction loss and heat transfer correlations for this thermal system were determined.
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Thermal performance in solar air heater with perforated-winglet-type vortex generator
(2018-08-01)
Skullong, Sompol
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Promthaisong, Pitak
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Promvonge, Pongjet
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Thianpong, Chinaruk
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Pimsarn, Monsak
An experimental and numerical study of turbulent convective heat transfer in a solar air heater duct with winglet-type vortex generators (WVGs) placed on the absorber plate is presented. Air as the test fluid enters the duct having a uniform wall heat-flux applied on the upper wall or the absorber plate with Reynolds number from 4100 to 25,500. Two types of WVGs are introduced: rectangular (RWVG) and trapezoidal (TWVG) WVGs, in order to create multiple vortex flows along the duct. The WVG parameters in the present study include two relative height (B<inf>R</inf> = e/H = 0.2 and 0.48), three longitudinal pitch ratios (P<inf>R</inf> = P<inf>l</inf>/H = 1, 1.5 and 2) and a single attack angle, α = 30°. The experimental result reveals that the RWVG with B<inf>R</inf> = 0.48 and P<inf>R</inf> = 1 provides the highest heat transfer and friction factor at about 7.1 and 109.5 times above the flat duct, respectively while the TWVG with B<inf>R</inf> = 0.2 and P<inf>R</inf> = 1.5 yields the maximum thermal performance around 1.84. Then, to improve the performance by reducing the substantial pressure loss, both the WVGs with B<inf>R</inf> = 0.48 and P<inf>R</inf> = 1.5 are modified to be perforated rectangular and trapezoidal winglet-type vortex generators (P-RWVG and P-TWVG) with four different punched hole/pore diameters (d = 1, 3, 5 and 7 mm) on their central area. The investigation indicates that among the perforated WVGs, the P-RWVG at d = 1 mm yields the highest heat transfer and friction factor up to 6.78 and 84.32 times higher than the smooth duct but the best thermal performance of about 2.01 is found for the P-TWVG with d = 5 mm. To explore the flow and heat transfer pattern, a 3D numerical flow simulation is performed and validated with available measurements where both the numerical and measured results are in good agreement.
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Thermal performance of heat exchanger tube inserted with curved-winglet tapes
(2018-01-25)
Skullong, Sompol
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Promvonge, Pongjet
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Thianpong, Chinaruk
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Jayranaiwachira, Nuthvipa
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Pimsarn, Monsak
The paper deals with the effect of curved-winglet (CW) inserts on thermal and flow behaviors in a constant heat-fluxed tube. A straight tape is used to support the 45° CWs mounted repeatedly on both tape sides to generate two pairs of longitudinal counter-rotating vortices along the test tube in order to assist the chaotic flow mixing and to disrupt the boundary layer leading to faster rate of heat transfer. The airflow and heat transfer behaviors in the tube are examined for Reynolds number (Re) in the range of 4150–25,400. The curved-winglet tape (CWT) parameters involved are the winglet attack angle of 45° three relative winglet heights (b/D = B<inf>R</inf> = 0.1, 0.2 and 0.3) and winglet pitches, (P/D = P<inf>R</inf> = 0.5, 1.0 and 2.0). The investigation reveals that the maximum thermal enhancement factor (TEF) of the CWT is about 1.62 at B<inf>R</inf> = 0.1 and P<inf>R</inf> = 1.0. For further improvement, the CWT at B<inf>R</inf> = 0.1 and P<inf>R</inf> = 1.0 is modified by punching the CW to be the perforated-curved-winglet tape (P-CWT) to reduce the pressure loss. The P-CWT characteristics include five different punched hole diameters (d = 1.0, 1.5, 2.0, 2.5 and 3.0 mm). The experimental results show that TEF of all the P-CWTs is higher than that of the CWT and the maximum TEF of 1.76 higher than the CWT around 9% is found for d = 1.5 mm. To understand the flow pattern and heat transfer mechanism, a three-dimensional CFD investigation is also performed and for validation, the good agreement between numerical and experimental results is found. For experimental data, empirical correlations for Nu, f and TEF for the CWT and P-CWT inserts are also determined.
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Heat transfer characterization in a tubular heat exchanger with V-shaped rings
(2017-01-05)
Chingtuaythong, Witoon
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Promvonge, Pongjet
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Thianpong, Chinaruk
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Pimsarn, Monsak
This article presents the influence of V-shaped rings (or V-ring) placed in a uniform heat-fluxed tube on heat transfer and flow resistance characteristics. In the current experiment, the V-ring elements with attack angle of 30° are inserted into the tube with four relative ring-pitches (R<inf>P</inf> = P/D = 0.5, 1.0, 1.5 and 2.0) and three ring blockage ratios (R<inf>B</inf> = e/D = 0.1, 0.15 and 0.2). Air as the test fluid flows through the tube for Reynolds number of about 5000–25,000. The experimental results reveal that the V-ring can considerably enhance the heat transfer rate up to 5.8 times above the plain tube whereas the friction factor is up to 82 times. The increase in R<inf>B</inf> leads to higher heat transfer and friction loss while the increment in R<inf>P</inf> provides the reversing trend. The thermal enhancement factor of the V-ring is in the range of 1.36–1.63 where its maximum regarded as the optimum point is at R<inf>B</inf> = 0.1 and R<inf>P</inf> = 1.0. In comparison with other vortex-flow devices, the V-ring yields much higher thermal performance than the published inclined rings, wire-coils and twisted tapes. Nusselt number and friction factor correlations for the V-ring are also determined.
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Thermal behaviors in a round tube equipped with quadruple perforated-delta-winglet pairs
(2017-01-01)
Skullong, Sompol
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Promvonge, Pongjet
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Thianpong, Chinaruk
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Jayranaiwachira, Nuthvipa
The article deals with an experimental investigation of enhancing convective heat transfer in a heated circular tube with pairs of perforated-delta-winglets placed repeatedly on a perforated-cross-tape (PW-XT). The perforated-delta-winglets are placed in inline array and a triangular-hole is punched on each winglet to reduce the friction loss. The aim at using the PW-XT insert is to produce streamwise-vortex flows in the tube to reduce the thickness of thermal boundary layer and to increase fluid mixing of the flow. The involved winglet parameters are composed of relative winglet height or blockage ratio, (B<inf>R</inf> = b/D = 0.1, 0.15, 0.2 and 0.25) and relative winglet pitch or pitch ratio, (P<inf>R</inf> = P/D = 0.5, 1.0, 1.5 and 2.0) and those are performed at a single delta-winglet inclination/attack angle, α = 30° and a winglet porosity ratio, A<inf>p</inf>/A<inf>w</inf> = 0.359 for Reynolds number from 4180 to 26,000. The present results of heat transfer and pressure loss displayed in terms of respective Nusselt number (Nu) and friction factor (f) show that Nu increases with increasing B<inf>R</inf>but with decreasing P<inf>R</inf>. Nu for the PW-XT insert is in a range of 1.96–5.06 times while f increases around 2.06–35.68 times above the plain tube alone. To estimate the real merits of the PW-XT, the thermal enhancement factor (TEF) is evaluated and found to be a maximum around 1.902 at B<inf>R</inf> = 0.15, P<inf>R</inf> = 1.0. In comparison, the PW-XT gives considerably higher TEF than the typical four delta-winglet pairs placed on the cross-tape (TW-XT) having the highest TEF around 1.72.
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Heat transfer augmentation in a solar air heater channel with combined winglets and wavy grooves on absorber plate
(2017-01-01)
Skullong, Sompol
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Promvonge, Pongjet
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Thianpong, Chinaruk
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Jayranaiwachira, Nuthvipa
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Pimsarn, Monsak
An investigation on heat transfer characteristics in a solar air heater channel using wavy grooves incorporated with pairs of trapezoidal-winglets (TW) placed on the absorber plate has been experimentally conducted. Air as the test fluid entered the test section having a constant heat-flux on the absorber plate while the Reynolds numbers obtained by controlling the airflow rate is in a range of 4500–22,000. The TW characteristics include three relative winglet-pitches (P<inf>R</inf>) and five relative winglet height or blockage ratios (B<inf>R</inf>) at a single attack angle of 45° whereas the wavy rectangular-groove parameters are three relative groove-pitch lengths (P<inf>R</inf>) similar to the TW case but at a fixed width and height. The investigation shows that the TW together with the groove provides the substantial increase in heat transfer over the smooth channel. The TW alone gives much higher heat transfer but the groove yields considerably lower pressure drop. The combined groove and TW devices at a given B<inf>R</inf>, perform the highest heat transfer and friction factor at smaller P<inf>R</inf> and also provides considerably higher thermal performance than the single device acting alone. At P<inf>R</inf> = 1, the compound device with B<inf>R</inf> = 0.28 offers the highest heat transfer and friction factor while the one with B<inf>R</inf> = 0.24 gives the maximum thermal performance.
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Experimental and numerical heat transfer investigation in a tubular heat exchanger with delta-wing tape inserts
(2016-11-01)
Skullong, Sompol
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Promvonge, Pongjet
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Jayranaiwachira, Nuthvipa
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Thianpong, Chinaruk
Effects of insertion of a straight tape with double-sided delta wing pairs (called “delta-wing tape”, DWT) used as a longitudinal vortex generator (LVG) on forced convective heat transfer and flow friction characteristics in a uniform heat-flux heat exchanger tube are investigated experimentally and numerically in the present work. The experiment is conducted for turbulent airflow with the Reynolds number (Re) from 4200 to 25,500. The delta wings are in a forward-wing arrangement with three wing inclination angles (α = 30°, 45° and 60°) and with five ratios of wing-pitch to tube-diameter (P/D = PR = 0.5, 1.0, 1.5, 2.0 and 2.5). Influences of the DWT insert on heat transfer in terms of Nusselt number (Nu) and pressure drop in the form of friction factor (f) are examined. The results indicate that the DWT provides the increases in Nu and f up to 505% and 69 times above the plain tube, respectively and the maximum thermal enhancement factor (TEF) is at 1.49. The 60° DWT with PR = 0.5 yields the highest Nu and f but the 30° one with PR = 1.0 gives the best TEF. To understand the flow structure and heat transfer mechanism, a three dimensional CFD simulation of the inserted tube is also performed. The simulated results are validated and are in good agreement with the current measurements. A simulated heat transfer and fluid flow structure is also reported.
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Thermal performance in solar air heater channel with combined wavy-groove and perforated-delta wing vortex generators
(2016-05-05)
Skullong, Sompol
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Promvonge, Pongjet
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Thianpong, Chinaruk
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Pimsarn, Monsak
An experimental investigation on thermal performance improvement in a solar air heater channel with combined wavy-groove and delta-wing vortex generator (WVG) placed on the absorber plate having a uniform wall heat-flux is carried out. The Reynolds number based on the hydraulic diameter of the channel ranges from 4800 to 23,000. The effect of the combined groove and WVG on the heat transfer and pressure drop in the channel in terms of respective Nusselt number and friction factor is examined. Investigated parameters of the WVG mounted on the grooved absorber are three wing porosity area ratios (called porosity ratio, A<inf>h</inf>/A<inf>w</inf> = 0.031, 0.085 and 0.167) and four groove-wing distance to channel-height ratios (g/H = 0.4, 0.5, 0.75 and 1) at a single attack angle (α = 45°). The experimental result reveals that at g/H = 0.5, the smaller A<inf>h</inf>/A<inf>w</inf> provides the highest Nusselt number and friction factor around 6 and 30 times over the smooth channel, respectively, but the optimum thermal performance is at A<inf>h</inf>/A<inf>w</inf> = 0.085 and g/H = 0.5. The combined devices give the thermal performance augmentation at about 37.7-46.3% higher than the groove alone and also at about 1.5-12.5% above the combined groove and non-perforated WVG (without hole).

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