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Author: search.filters.author.Eiamsa-Ard, S.Subject: search.filters.subject.Twisted tape

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    Intensification of convective heat transfer and heat exchanger performance by the combined influence of a twisted tube and twisted tape
    (2019-09-01)
    Samruaisin, P.
    ;
    Kunlabud, S.
    ;
    Kunnarak, K.
    ;
    Chuwattanakul, V.
    ;
    Eiamsa-Ard, S.
    Twisted tubes and twisted tapes are swirl flow generators utilized for increasing thermal performance. The combined effects of twisted tubes and twisted tapes on heat transfer, pressure drop and thermal performance were experimentally investigated. Experiments were performed using a trapezoidal shaped twisted tube and twisted tapes having various twist ratios (y/w=2.0, 3.0, 4.0 and 5.0). Water was used as the test fluid in a turbulent regime (4500<Re<16,000). A simulation of velocity, temperature contours and local Nusselt number plots was also performed to gain information about fluid flow and heat transfer. The results of the combined devices are studied with those of a smooth circular tube and a twisted tube alone, for comparison. The experimental results show that at a given Re, the Nusselt number (Nu), friction factor (f) and thermal performance of a twisted tube mounted with a twisted tape are consistently higher than those of the twisted tube alone and a smooth circular tube. Additionally, the heat transfer, friction loss and thermal performance factor increase with a reduction of the twist ratio (y/w) since the tape with a smaller y/w gives stronger and more consistent swirl flow.
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    A case study on thermal performance assessment of a heat exchanger tube equipped with regularly-spaced twisted tapes as swirl generators
    (2014-01-01)
    Eiamsa-Ard, P.
    ;
    Piriyarungroj, N.
    ;
    Thianpong, C.
    ;
    Eiamsa-Ard, S.
    Effects of the regularly-spaced twisted tape (RS-TT) on the heat transfer, friction factor and thermal performance factor behaviors in a heat exchanger are reported along with those of a full length twisted tape. The full length (or typical) twisted tapes with two different twist ratios (y=P/W = 6.0 and 8.0), and the regularly-spaced twisted tape (RS-TT) with two different twist ratios (y=6.0 and 8.0) and three free space ratios (s=S/P = 1.0, 2.0, and 3.0) were employed for comparative study. The article also presents the application of a mathematical model for numerical simulation of the swirling flow in a tube induced by regularly-spaced twisted tape (RS-TT) insertion. The numerical simulation was performed in order to gain an understanding of physical behavior of the fluid flow (decaying swirling flow field), fluid temperature and local Nusselt number characteristics of a tube fitted with RS-TT in the turbulent flow regime. The Navier-Stokes equation in common with the energy equation was solved using the SIMPLE technique with the RNG k-ε turbulence model. The experimental results show that heat transfer rate and friction increased with decreasing twist ratio and space ratio. At similar conditions, full length twisted tapes (s=0) offered higher heat transfer rate, friction factor and thermal performance factor than RS-TT ones (s = 1.0, 2.0 and 3.0) as they induced more consistent swirling flows and thus turbulence. This reveals that it is possible to gain promising tradeoff between enhanced heat transfer and increased friction by selecting the twisted tape with proper geometries.
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    Thermohydraulic characteristics of co/counter swirl flow through a round tube fitted with helical screw tape and twisted tape
    (2013-03-01)
    Eiamsa-Ard, S.
    ;
    Yongsiri, K.
    ;
    Nanan, K.
    ;
    Thianpong, C.
    Influence of co/counter swirl flow on the characteristics of friction, heat transfer and thermal performance factor in heat exchanger tubes has been experimentally investigated. Each twisted tape is inserted into a helical screw tape and then these combined tapes are subsequently equipped in a heat exchanger tube for generating the swirl flow. The combined tapes are arranged in two different forms, namely (i) co-swirl arrangement in which their twist are in the same direction and (ii) counter-swirl arrangement in which their twists directions are in the opposite directions. The experiments using helical tapes alone are also performed for assessment. The helical screw tapes are used at three different tape-twist ratios (PR = p/D = 1.0, 1.5 and 2.0), each with three different tape-width ratios (WR = w/D = 0.15, 0.2 and 0.25), while twisted tapes are used at three different twist ratios (YR = y/W = 3, 4 and 5). The results show the maximum thermal performance factor of 1.49 for helical tape alone with PR=2.0 and WR=0.2. At similar conditions, the heat transfer rate associated with the combined tapes in counter-swirl arrangement is 3.4% and 10% higher than those in co-swirl arrangement and helical tape alone.
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    Effect of perforated twisted-tapes with parallel wings on heat transfer enhancement in a heat exchanger tube
    (2012-01-01)
    Thianpong, C.
    ;
    Eiamsa-Ard, P.
    ;
    Promvonge, P.
    ;
    Eiamsa-Ard, S.
    This article reports an experimental investigation on heat transfer and pressure drop characteristics of turbulent flow in a heating tube equipped with perforated twisted tapes with parallel wings (PTT) for Reynolds number between 5500 and 20500. The design of PTT involves the following concepts: (1) wings induce an extra turbulence near tube wall and thus efficiently disrupt a thermal boundary layer (2) holes existing along a core tube, diminish pressure loss within the tube. The parameters investigated were the hole diameter ratio (d/W = 0.11, 0.33 and 0.55) and wing depth ratio (w/W = 0.11, 0.22 and 0.33). A typical twisted tape was also tested for an assessment. Compared to the plain tube, the tubes with PTT and TT yielded heat transfer enhancement up to 208% and 190%, respectively. The evaluation of overall performance under the same pumping power reveal that the PTT with d/W = 0.11 and w/W = 0.33, gave the maximum thermal performance factor of 1.32, at Reynolds number of 5500. Empirical correlations of the heat transfer, friction factor and thermal performance for tubes with PTTs were also developed. In addition, the swirling/axial flow patterns of tube with PTT were visualized using dye injection technique. © 2011 Published by Elsevier Ltd.
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    Heat transfer enhancement in a rectangular channel with twisted tape inserts
    (2009-01-01)
    Nuthong, W.
    ;
    Eiamsa-Ard, S.
    ;
    Nanan, K.
    ;
    Eiamsa-Ard, P.
    ;
    Thianpong, C.
    Experimental investigation of heat transfer and friction factor behaviors in a rectangular channel with multiple twisted tapes (MTTs) is carried out. In each run, five MTTs are simultaneously used as the swirl flow generators in a test section. The lower wall of the channel is subjected to uniform heat flux conditions while the upper wall is insulated. Parametric runs are made for Reynolds numbers ranging from 2700 to 9000, the tapes with twist-length to twist-width ratios (y/w) of 3, 4 and 5 while the aspect ratio of AR = W/H = 10 is fixed throughout. Experiments using smooth channel are also performed for comparison. The experimental results reveal that heat transfer in the channels with MTTs at twist ratios (y/w) of 3, 4 and 5 are respectively increased around 55%, 37% and 22% over those in the smooth channel. In addition, the empirical correlations of the Nusselt number and friction factor in the developed flow region for the channels fitted with MTTs are also derived.
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    Turbulent heat transfer through a heat exchanger with porous twisted tape inserts
    (2009-01-01)
    Eiamsa-Ard, S.
    ;
    Wongcharee, K.
    ;
    Rattanawong, S.
    ;
    Eiamsa-Ard, P.
    ;
    Pimsarn, M.
    In this present work, the influences of the porous twisted tape (PT) on the heat transfer and the pressure loss are studied experimentally. The comparative experiments are conducted in the tube fitted with the PT or typical twisted tape (TT) at different twist ratios, y/w = 4.0 and 5.0, in the Reynolds number ranging from 4800 to 16,000 under uniform heat flux conditions. In the experiments, the PT inserts generate swirls that modify the near wall velocity profile resulted in improvement of the heat transfer rate. The experimental results reveal that the heat transfer rates increase with decreasing twist ratio (y/w) for all twisted tapes used in the experiments. The heat transfer rates increase up to 71% with the help of the PT. The increases in average Nusselt numbers of using PT and TT are found to be 48% and 22%, respectively, over those of the corresponding plain tube. However, PT causes a considerable increase in friction factor. The mean increases of friction factors for PT and TT are respectively, about 3.14 and 2.45 times in comparison with that for the plain tube. Mean friction factor and Nusselt number for PT, are respectively 28% and 21% higher than those for TT. In addition, the empirical correlations of the Nusselt number and friction factor are also reported.