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Author: search.filters.author.Jedsadaratanachai, WithadaSubject: search.filters.subject.Turbulent flow

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    Numerical investigation on turbulent forced convection and heat transfer characteristic in spirally semicircle-grooved tube
    (2016-12-01)
    Promthaisong, Pitak
    ;
    Boonloi, Amnart
    ;
    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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    Numerical investigation on turbulent forced convection and heat transfer characteristic in a square channel with discrete combined V-baffle and V-orifice
    (2016-09-01)
    Boonloi, Amnart
    ;
    Jedsadaratanachai, Withada
    Turbulent forced convection, heat transfer and performance improvement in a square channel with discrete combined baffles (DCB), which combined V-baffle and V-orifice, are investigated numerically. The influences of the flow blockage ratios (BR=0.05, 0.10 and 0.15) and V-tip directions (V-tip pointing downstream called "V-Downstream" and V-tip pointing upstream called "V-Upstream") are examined with a single pitch spacing ratio, PR=1, and attack angle, α=30<sup>o</sup>, for the Reynolds number, Re=5000-20,000. The computation results are reported in terms of flow visualizations, heat transfer characteristics, performance assessments. The results are compared with the smooth channel and the previous works. As the results, the DCB enhances the heat transfer rate and thermal efficiency due to the disturbance of the thermal boundary layer. The improvement of the heat transfer rate is around 2.8-6 times higher than the smooth channel depended on BR, V-tip directions and Re. In addition, the computational result reveals that the optimum thermal enhancement factor, TEF, is around 1.72 at BR=0.1, Re=3000 and V-Upstream.
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    Flow and heat transfer profiles in a square channel with 45° V-downstream orifices
    (2016-01-01)
    Jedsadaratanachai, Withada
    ;
    Boonloi, Amnart
    Flow and heat transfer profiles in a square channel heat exchanger inserted with 45° V-orifices are presented. The influences of Reynolds number (Re = 3000-10,000) and blockage ratio (BR = 0.05, 0.10, 0.15, 0.20 and 0.25) on periodic concepts are investigated numerically. The computational domain is solved with the finite volume method and SIMPLE algorithm. As the numerical results, the periodic profiles on flow and heat transfer are found when inserted the 45° Vorifices in the square duct. The configurations on flow and heat transfer in the heating section can separated into two sections; periodic profile and fully developed periodic profile. The patterns on flow and heat transfer are similar, but the values are not equal, called "periodic profiles", while the identical on both profiles and values, called "fully developed periodic profiles". In addition, the periodic structures depends on the parameters of the vortex generator, position in the channel and Reynolds number.
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    Turbulent forced convection in a heat exchanger square channel with wavy-ribs vortex generator
    (2015-08-01)
    Boonloi, Amnart
    ;
    Jedsadaratanachai, Withada
    Turbulent forced convective heat transfer and flow configurations in a square channel with wavy-ribs inserted diagonally are examined numerically. The influences of the 30° and 45° flow attack angles for wavy-ribs, blockage ratio, R<inf>B</inf> = b/H = 0.05-0.25 with single pitch ratio, R<inf>P</inf> = P/H = 1 are investigated for the Reynolds number based on the hydraulic diameter of the square channel, Re = 3000-20000. The use of the wavy-ribs, which inserted diagonal in the square channel, is aimed to help to improve the thermal performance in heat exchange systems. The finite volume method and SIMPLE algorithm are applied to the present numerical simulation. The results are presented on the periodic flow and heat transfer profiles, flow configurations, heat transfer characteristics and the performance evaluations. The mathematical results reveal that the use of wavy-ribs leads to a higher heat transfer rate and friction loss over the smooth channel. The heat transfer enhancements are around 1.97-5.14 and 2.04-5.27 times over the smooth channel for 30° and 45° attack angles, respectively. However, the corresponding friction loss values for 30° and 45° are around 4.26-86.55 and 5.03-97.98 times higher than the smooth square channel, respectively. The optimum thermal enhancement factor on both cases is found at R<inf>B</inf> = 0.10 and the lowest Reynolds number, Re = 3000, to be about 1.47 and 1.52, respectively, for 30° and 45° wavy-ribs.
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    Numerical simulation of Al2O3-water nanofluid flow and heat transfer in a tube with angled rings
    (2014-01-01)
    Promvonge, Pongjet
    ;
    Sripattanapipat, Somchai
    ;
    Jedsadaratanachai, Withada
    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.