• Title/Summary/Keyword: Divergent channel

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Heat Transfer and Frictions in the Rectangular Divergent Channel with Ribs on One Wall

  • Lee, MyungSung;Ahn, SooWhan
    • International Journal of Aeronautical and Space Sciences
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    • v.17 no.3
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    • pp.352-357
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    • 2016
  • An investigation of ribbed divergent channel was undertaken to determine the effect of rib pitch to height ratio on total friction factor and heat transfer results in the fully developed regime. The ribbed divergent rectangular channel with the channel exit hydraulic diameter ($D_{ho}$) to inlet channel hydraulic diameter ($D_{hi}$) ratio of 1.16 with wall inclination angle of 0.72 deg, at which the ratios (p/e) of 6,10, and 14 are considered. The ribbed straight channel of $D_{ho}/D_{hi}=1.0$ were also used. The ribbed divergent wall is manufactured with a fixed rib height (e) of 10 mm and the ratio of rib spacing (p) to height 6, 10, and 14. The measurement was run with range of Reynolds numbers from 24,000 to 84,000. The comparison shows that the ratio of p/e=6 has the greatest thermal performance in the divergent channel under two constraints; identical mass flow rate and identical pressure drop.

Effect of Rib Angle on Thermal Performance in a Two Wall Convergent/Divergent Channel with Ribs on One Wall (양측면 수축/확대 사각채널에서 한면에 설치된 리브의 각도가 열성능에 미치는 효과)

  • Ahn, Soo Whan;Lee, Myung Sung;Bae, Sung Taek
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.27 no.4
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    • pp.195-200
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    • 2015
  • The thermal performance in the channels with two-wall rectangular convergent/divergent cross-sectional areas along the axial distance was investigated experimentally. The ribbed rectangular convergent/divergent channels were manufactured with a fixed rib height (e) = 10 mm and the ratio of rib spacing (p) to height (e) = 10. Three different parallel angled ribs (a = $30^{\circ}$, $45^{\circ}$, and $60^{\circ}$) were each placed on the channel's one sided wall only. The convergent channel of $D_{ho}/D_{hi}=0.67$ and the divergent channel of $D_{ho}/D_{hi}=1.49$ were considered. The ribbed divergent channel produced better thermal performance than the ribbed convergent channel in three different restrictions; identical flow rate, identical pumping power, and identical pressure loss.

Measurement of the Film Cooling Effectiveness using Pressure Sensitive Paint on Convergent/Divergent Channel (압력감응페인트를 이용한 확대/축소 유로에서의 막냉각 효율 측정)

  • Park, Seoung-Duck;Lee, Ki-Seon;Kim, Sung-Ha;Kim, Hark-Bong;Kwak, Jea-Su;Kim, Chun-Teak;Yang, Gyae-Byung
    • The KSFM Journal of Fluid Machinery
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    • v.11 no.6
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    • pp.31-37
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    • 2008
  • Film cooling effectiveness on the convergent or divergent channel was measured by pressure sensitive paint technique. The channel convergent or divergent angle was changed from $-5^{\circ}$ to $10^{\circ}$ and the tested blowing ratios were 0.5, 1 and 2. Results showed that the film cooling effectiveness on the convergent channel was not much affected by the convergent angle. With divergent film cooled surface, the film cooling effectiveness near the injection hole decreased as the divergent angle increases. However, the film cooling effectiveness at far downstream from the hole showed opposite trend. For the non-film cooled surface inclined case, the film cooling effectiveness was not much affected by the divergent angle.

Effect of Rib Pitch on Heat Transfer and Friction Factor in a Two Wall Divergent Channel (2벽면 확대 사각채널에서 리브 피치가 열전달과 마찰계수에 미치는 효과)

  • Ahn, Soo Whan;Lee, Myung Sung;Jeong, Seong Soo;Bae, Sung Taek
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.26 no.4
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    • pp.175-180
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    • 2014
  • Experimental investigations of the heat transfer and friction factors in the ribbed divergent rectangular channel with the channel exit hydraulic diameter to inlet hydraulic diameter ratio of 1.16 were performed. The surface heaters were mounted onto the two opposite walls. The main experimental parameter is the ratio of rib pitch (p) to height (e), at which the ratios (p/e) of 6, 10, and 14 are considered in the channel with ribs on one wall only. The straight ribbed square channel is also considered as a comparison. The major findings are that the ratio of p/e = 6 shows the highest values in the heat transfer and the ratio of p/e = 10 indicates the greatest friction factor in the ribbed divergent channel. Editor's note:No major changes or corrections needed. Well written.

Effect of Inclined Wall Number on Heat Transfer and Friction in the Smooth Channel (매끈한 사각채널에서 경사 벽면 수가 열전달과 마찰에 미치는 효과)

  • Lee, Myung-Sung;Ahn, Soo-Whan
    • Journal of Power System Engineering
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    • v.18 no.3
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    • pp.66-72
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    • 2014
  • The local heat transfer and pressure drop of developed turbulent flows in the smooth convergent/divergent channels with rectangular and square cross-sectional areas along the axial distance have been investigated experimentally. The measurement was conducted within the range of Reynolds numbers from 15,000 to 89,000. The channel hydraulic diameter ratios of 0.67 and 1.49 in the rectangular channel with 2 inclined walls and the ratios 0.75 and 1.33 in the square channel with 4 inclined walls are considered. The comparison showed that among the four channels the square divergent channel has the highest thermal performance at the identical mass flow rate, at the identical pumping power, and at the static pressure drop.

Heat Transfer and Frictions in the Convergent/divergent Channel with Λ/V-shaped Ribs on Two Walls

  • Kim, Beom-soo;Lee, Myung-sung;Ahn, Soo-whan
    • International Journal of Aeronautical and Space Sciences
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    • v.18 no.3
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    • pp.395-402
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    • 2017
  • The local heat transfer and total pressure drops of developed turbulent flows in the ribbed rectangular convergent/divergent channels with ${\Lambda}/V-shaped$ ribs have been investigated experimentally. The channels have the exit hydraulic diameter ($D_{ho}$) to inlet hydraulic diameter ($D_{hi}$) ratios of 0.67 for convergence and 1.49 for divergence, respectively. The ${\Lambda}/V-shaped$ ribs with three different flow attack angles of $30^{\circ}$, $45^{\circ}$, and $60^{\circ}$ are manufactured with a fixed rib height (e) of 10 mm and the ratio of rib spacing (S) to height (e) of 10 on the walls. Thermal performances of the ribbed rectangular convergent/divergent channels are compared with the smooth straight tube under identical pumping power. The results show that the flow attack angle of $45^{\circ}$ with ${\Lambda}-shaped$ rib has the greatest thermal performance at all the Reynolds numbers studied in the convergent channel; whereas, the flow attack angle of $60^{\circ}$ with V-shaped rib has the greatest thermal performance over Reynolds number of 30,000 in the divergent channel.

Turbulent Heat Transfer and Friction in Four-Wall Convergent/Divergent Square Channels with One Ribbed Wall (한면에 리브가 설치된 4벽면 수축/확대 채널의 난류 열전달과 유체마찰)

  • Ahn, Soo Whan;Lee, Myung Sung
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.39 no.10
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    • pp.773-778
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    • 2015
  • The local heat transfer and pressure drop of developed turbulent flows in convergent/divergent channels with square axial cross-sectional areas were experimentally investigated to improve the channel design, such as a gas turbine cooling system. Square convergent/divergent channels with one ribbed wall were manufactured with a fixed rib height e of 10 mm and a ratio of rib spacing p to height e of 10. The measurement was conducted for Reynolds numbers from 15,000 to 89,000. Convergent, divergent, and straight channels with ratios $D_{ho}/D_{hi}$ of 0.75, 1.33, and 1.0, respectively, are considered. Of the three channel types, the ribbed divergent channel was found to produce the best thermal performance under identical flow rate, pumping power, and pressure loss conditions.

Heat Transfer Enhancement in a Divergent Passage with 30° Inclined Ribs (30° 경사 리브가 있는 확대 채널 통로 내의 열전달 증가)

  • Lee, Myung Sung;Ahn, Soo Whan
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.29 no.8
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    • pp.401-407
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    • 2017
  • The effect of different rib geometries such as V-shaped continuous (case A), parallel broken (case B), and V-shaped broken (case C) ribs on local heat transfer distributions and pressure drops in a divergent channel with $30^{\circ}$ inclined ribs on one wall or two walls was investigated for Reynolds numbers from 22,000 to 75,000. Top and bottom walls were insulated; two side walls were uniformly heated in the divergent channel. Heated walls were composed of 10 isolated coper sections and length-to-outlet hydraulic diameter ratio of 10. Rib height-to-outlet hydraulic diameter ratio was 0.1, and rib pitch-to-height ratio equaled 10. Results revealed that V-shaped continuous rib (case A) produced approximately 1.4 times higher average Nussselt number than in the parallel broken rib (case B), and V-shaped broken rib (case C) in the channel with two ribbed walls at Re = 54,000.

Effect of Rib Arrangement on Heat Transfer in the Divergent Channel (확대 채널에서 리브 배열이 열전달에 미치는 효과)

  • Lee, Myung-Sung;Lee, Gyeong-Ju;Kim, Sang-Moon;Min, Se-Chan;Bae, Jae-Moon;Hwang, Jun-Su;Park, Cheol-O;Kim, Dong-Chan;Jung, Jung-Hyeon;Ahn, Soo-Whan
    • Journal of Power System Engineering
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    • v.21 no.5
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    • pp.35-40
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    • 2017
  • The effects of the different rib geometries such as V-shaped continuous (case A), parallel broken (case B), and V-shaped broken (case C) ribs on the heat transfer and pressure drops in a divergent channel with $45^{\circ}$ inclined ribs on one wall or two walls are checked out. The top and bottom walls are adiabatic; two side walls are uniformly heated in the divergent rectangular channel. The tested Reynolds numbers are ranged from 22,000 to 75,000. The channel with two opposite walls inclined only has the length of test section of 1 m and the channel divergence ratio of $D_{ho}/D_{hi}=1.49$, corresponding to $1.43^{\circ}$ inclined walls. The results show in the identical pumping power that the V-shaped continuous rib (case A) with two ribbed walls is the greatest, but the parallel broken rib (case B) with one ribbed wall is the worst in the thermal performance.

Interaction of turbulences with non-breaking divergent waves in an open channel

  • Hwang, Ayoung;Seok, Woochan;Lee, Sang Bong
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.13 no.1
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    • pp.35-49
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    • 2021
  • This paper presents a direct numerical simulation of turbulent flows over a bump in an open channel to examine the turbulence characteristics near divergent waves emanating from the bump and to investigate the interaction of the turbulences with the divergent waves. To verify the reliability of the simulations, the mean velocity profile and root-mean-square of velocity fluctuations are compared with previous data. The anisotropic invariant maps show that the ratio of the streamwise to spanwise velocity fluctuations plays an important role in characterizing the anisotropic nature of the separated shear layer behind the bump in the vicinity of the free surface. The vortex identification discloses a large-scale streamwise vortical structure from the mean velocity field and a cluster of small coherent structures from the instantaneous velocity field, which are responsible for the anisotropic characteristics of the turbulence beneath the free surface.