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Author: search.filters.author.Promvonge, PongjetSubject: search.filters.subject.Pressure drop

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    Experimental study on heat transfer and pressure drop in a channel with triangular v-ribs
    (2010-01-01)
    Jansangsuk, Dumri
    ;
    Khanoknaiyakarn, Chitakorn
    ;
    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
    ;
    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.