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Author: search.filters.author.Nanan, K.Subject: search.filters.subject.Heat exchanger

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    Heat transfer enhancement by tapered twisted tape inserts
    (2015-10-01)
    Piriyarungrod, N.
    ;
    Eiamsa-ard, S.
    ;
    Thianpong, C.
    ;
    Pimsarn, M.
    ;
    Nanan, K.
    The effects of inserted tapered twisted tapes, their taper angle and twist ratio on heat transfer rate, pressure drop and thermal performance factor characteristics have been reported. The experiments were carried out by using the tapered twisted tapes with 4 different taper angles which θ= 0.0° (typical twisted tape), 0.3°, 0.6° and 0.9°. At each taper angle, the tapered twisted tapes were twisted at three different twist ratios (y/W) of 3.5, 4.0 and 4.5. All tapes were tested under turbulent flow regime for Reynolds numbers between 6000 and 20,000. A twist ratio is defined as the ratio of twist length (y) to twisted tape width at the large end (W). The plain tube was also tested for comparison. Heat transfer enhancement and friction loss increased with decreasing taper angle and twist ratio. Thermal performance factor tended to increase with increasing taper angle and decreasing tape twist ratio. For the present range, the tube with the tape with taper angle (θ) of 0.9° and twist ratio (y/W) of 3.5 yielded the maximum thermal performance factor of 1.05 at Reynolds number (Re) of 6000.
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    Heat transfer augmentation by helically twisted tapes as swirl and turbulence promoters
    (2012-10-01)
    Eiamsa-ard, S.
    ;
    Yongsiri, K.
    ;
    Nanan, K.
    ;
    Thianpong, C.
    This paper describes heat transfer enhancement attributed to helically twisted tapes (HTTs). Each helically twisted tape was fabricated by twisting a straight tape to form a typical twisted tape then bending the twisted tape into a helical shape. The experiments were performed using HTTs with three twist ratios (y/. W) of 2, 2.5 and 3, three helical pitch ratios (p/. D) of 1, 1.5 and 2 for Reynolds number between 6000 and 20,000. The conventional helical tape (CHT) was also tested for comparison. The obtained results reveal that at similar conditions (y/. W and . p/. D), HTTs give lower Nusselt number and friction but higher thermal performance factor than CHTs. Heat transfer rate and friction factor increase as the tape twist ratio and helical pitch ratio decrease, while the thermal performance shows opposite trend. In the present range, the highest thermal performance factor of 1.29 is achieved by utilizing the tape with the largest twist ratio (y/. W=3) and helical pitch ratio (p/. D=2) at Reynolds number of 6000. © 2012 Elsevier B.V.
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    Thermal performance evaluation of heat exchangers fitted with twisted-ring turbulators
    (2012-07-01)
    Thianpong, C.
    ;
    Yongsiri, K.
    ;
    Nanan, K.
    ;
    Eiamsa-ard, S.
    Heat transfer, friction factor and thermal performance characteristics in a tube equipped with twisted-rings (TRs) are experimentally investigated. The experiments were conducted using TRs with three different width ratios (W/D. =. 0.05, 0.1 and 0.15) and three pitch ratios of (p/D. =. 1, 1.5 and 2) for Reynolds numbers ranging from 6000 to 20,000 using air as a test fluid. The typical circular rings (CRs) were also tested for an assessment. The experimental results reveal that most TRs yield lower Nusselt numbers and friction factor than CRs, except at the largest width ratio (W/D. =. 0.15) and the smallest pitch ratio (p/D. =. 1.0). In addition, Nusselt number and friction factor increase as width ratio increases and pitch ratio decreases. However, a maximum thermal performance factor is associated by TRs with the smallest width ratio and pitch ratio. The empirical correlations of the heat transfer (Nu) and friction factor (f) are also included in this paper. © 2012 Elsevier Ltd.