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Influence of perforated twisted tapes with vortex generator wings on heat transfer performance and entropy in a heat exchanger tube
(2026-01-01)
Mehta, Rajesh
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Gupta, Anirudh
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Kumar, Nitin
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Eiamsa-ard, Smith
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Pimsarn, Monsak
This study conducts an investigative exploration of thermal and hydraulic performance regarding hybrid inserts which combine perforated twisted tapes with vortex generator wings mounted inside circular tubes. The insert design makes use of both swirl flow and secondary vortex generation which breaks up the thermal boundary layer and boosts convective heat transfer rates. During this investigation, researchers utilized water as the working fluid at Reynolds number (Re) from 3000 to 21,000 to study the effect of three perforation diameter ratio (d/D) 0.143, 0.19, and 0.238 and respective Vortex generator (VG) edge cut ratio (a/D) 0.143, 0.19, and 0.238. Nusselt number (Nu) reach 182.3 % and thermal enhancement factor (TEF) achieve 1.68 at Re = 15,000 when using the enhanced tube compared to a smooth tube. The industrial application of larger VG openings at standard spacing produced a beneficial relationship between thermal performance and flow resistance when the pressure rise reached 345 %. The analysis of entropy generation showed heat transfer irreversibility gave way to frictional irreversibility when both perforation dimension and Re became larger. System design optimization prerequisites involved trade-offs which met Bejan number (Be) analysis trends. The Random Forest machine learning model combined with ANN and Linear Regression models contributed to thermal parameter prediction (Nu, f, TEF) by delivering a predictive accuracy level with less than 6.6 % deviation. The research leads to vital knowledge needed for developing compact heat exchangers integrating passive enhancement methods.
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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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Heat transfer and turbulent flow friction in a round tube with staggered-winglet perforated-tapes
(2016-04-01)
Skullong, Sompol
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Promvonge, Pongjet
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Thianpong, Chinaruk
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Pimsarn, Monsak
The article deals with thermal and flow resistance characteristics in a tubular heat exchanger fitted with staggered-winglet perforated tapes (WPT). The experiment was conducted in the test tube having a constant wall heat-flux for turbulent airflow, Reynolds number (Re) from 4180 to 26,000. The aim of using the WPT is to generate longitudinal vortex flows to disrupt thermal boundary layer on the tube wall and to provide stronger fluid mixing. The WPT having an winglet inclination angle of 30° was inserted into the test tube at five different winglet blockage ratios (B <inf>R</inf> = 0.1, 0.15, 0.2, 0.25 and 0.3) and three winglet pitch ratios (P <inf>R</inf> = 0.5, 1.0 and 1.5). To find an optimum thermal performance condition, the effect of B <inf>R</inf> and P <inf>R</inf> on the heat transfer and pressure loss due to flow friction in the tube is examined. The experimental results reveal that Nusselt number (Nu) and friction factor (f) for the WPT increase with the increment of B <inf>R</inf> but the reduction of P <inf>R</inf> . The highest thermal enhancement factor (TEF) of 1.71 is achieved by utilizing the WPT with B <inf>R</inf> = 0.15, P <inf>R</inf> = 1.0 at Re = 4180. Compared to staggered-winglet typical non-perforated tape (WTT), the WPT yields the TEF of about 1.2 times higher than the WTT. Correlations of Nu, f and TEF for the WPT and the WTT are also proposed.
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Heat transfer augmentation in a circular tube with winglet vortex generators
(2015-04-01)
Chokphoemphun, Suriya
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Pimsarn, Monsak
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Thianpong, Chinaruk
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Promvonge, Pongjet
The article presents the influence of winglet vortex generators (WVGs) placed in the core flow area on thermal performance enhancement of a tube heat exchanger. The experiment was carried out in a uniform wall heat-fluxed tube by varying turbulent airflow for Reynolds number ranging from 5300 to 24000. In the present work, the WVGs with an attack angle of 30° were inserted into the test tube at four different winglet pitch ratios (R<inf>P</inf> = P/D) and three winglet-width or blockage ratios (R<inf>B</inf> = e/D). The experimental results at various R<inf>P</inf> and R<inf>B</inf> values were evaluated and compared with those for smooth tube and tubes with twisted tape or wire coil. The measurement reveals that the WVGs enhance considerably the heat transfer and friction loss above the plain tube, wire coil and twisted tape. The Nusselt number and friction factor increase with the increment of R<inf>B</inf> and Re but with the decreasing R<inf>P</inf>. The average Nusselt numbers for the WVGs with various R<inf>B</inf> are in the range of 2.03-2.34 times above the plain tube. The thermal performance for the WVGs is found to be much higher than that for the wire coil and twisted tape and is in a range of 1.35-1.59. Also, a numerical investigation is conducted to study the flow structure and heat transfer enhancement mechanisms in the winglet-inserted tube.
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Thermal characterization in a circular tube fitted with inclined horseshoe baffles
(2015-01-22)
Promvonge, Pongjet
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Tamna, Sombat
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Pimsarn, Monsak
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Thianpong, Chinaruk
In the present study, the influence of inclined horseshoes baffles placed repeatedly in a tubular heat exchanger on heat transfer rate, friction factor and thermal enhancement factor are experimentally determined. The horseshoe baffle elements with an inclination angle of 20° were inserted periodically into the test tube at three different baffle-pitch ratios (P<inf>R</inf> = 0.5, 1.0 and 2) and -width or blockage ratios (B<inf>R</inf> = 0.1, 0.15 and 0.2). The experiment was conducted in the test tube having a uniform heat-fluxed wall by varying turbulent airflow to obtain Reynolds number in a range of 5300-24,000. The experimental results revealed that the tube fitted with inclined horseshoes baffles provides considerable improvement of the heat transfer rate over the plain tube around 92-208% while the friction factor is increased at about 1.76-6.37 times. To access the real benefits for the inclined horseshoes baffles inserted in plain tube, thermal performance factor is examined and found to be in the range of 1.34-1.92 at which the maximum obtained at P<inf>R</inf> = 0.5 and B<inf>R</inf> = 0.1 is considerably higher than that for published inserted devices. Correlations for Nusselt number and friction factor for the oblique horseshoe-baffled tube are also proposed.

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