• Title/Summary/Keyword: Discrete Rib Turbulators

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An Investigation of Angled Discrete Rib-Turbulators for Cooling Enhancement of Gas Turbine Blades (가스 터빈 블레이드 냉각 성능 향상을 위한 경사요철의 단락 효과)

  • Wu, Seong-Je;Lee, Sei-Young;Cho, Hyung-Hee
    • Proceedings of the KSME Conference
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    • 2001.06d
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    • pp.782-789
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    • 2001
  • Local heat/mass transfer and friction loss in a square duct roughened with various types of continuous and discrete rib turbulators are investigated. The combined effects of the gap flows of the discrete ribs and the secondary flows are examined for the purpose of the reduction of thermally weak regions and the promotion of the uniformity of heat/mass transfer distributions as well as the augmentation of average heat/mass transfer. The rib-to-rib pitch to the rib height ratio (p/e) of 8 and the rib angles of 90 and 60 deg are selected with $e/D_{h}=0.08$. The vortical structure of the secondary flows induced by the parallel angled arrays are quite distinct from that induced by the cross angled arrays. This distinction influences on heat/mass transfer and friction loss in all the tested cases. The gap flows of the discrete ribs reduce the strength of the secondary flows but promote local turbulence and flow mixing. As a result, the fairly uniform heat/mass transfer distributions are obtained with two row gaps.

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Effects of Discrete Rib-Turbulators on Heat/Mass Transfer Augmentation in a Rectangular Duct (사각 덕트 내부 열전달 향상을 위한 요철의 단락 효과)

  • Kwon, Hyuk-Jin;Wu, Seong-Je;Cho, Hyung-Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.5
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    • pp.744-752
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    • 2000
  • The influence of arrangement and length of discrete ribs on heat/mass transfer and friction loss is investigated. Mass transfer experiments are conducted to obtain the detailed local heat/mass transfer information on the ribbed wall. The aspect ratio (width/height) of the duct is 2.04 and the rib height is one tenth of the duct height, such that the ratio of the rib height to hydraulic diameter is 0.0743. The ratio of rib-to-rib distance to rib height is 10. The discrete ribs were made by dividing each continuous rib into 2, 3 or 5 pieces and attached periodically to the top and the bottom walls of the duct with a parallel orientation The combined effects of rib angle and length of the discrete ribs on heat/mass transfer ae considered for the rib angles $({\alpha})\;of\;90^{\circ}\;and\;45^{\circ}$. As the number of the discrete ribs increases, the uniformity of the heat/mass transfer distributions increases. For $(\alpha})=90^{\circ}$, the heat/mass transfer enhancement with the discrete ribs is remarkable, while the heat/mass transfer performances are slightly higher than that of the transverse continuous ribs due to the accompanied high friction loss penalty. For $(\alpha})=90^{\circ}$, the average heat/mass transfer coefficients and the heat/mass transfer performances decrease slightly with the discrete ribs compared to the case of the angled continuous ribs.

Heat/Mass Transfer and Friction Characteristic in a Square Duct with Various Discrete Ribs -In-Lined Gap Arrangement Ribs- (덕트내 요철의 단락위치 변화에 따른 열/물질전달 및 압력강하 특성 - 정렬 단락배열 요철 -)

  • Lee, Sei-Young;Choi, Chung;Rhee, Dong-Ho;Cho, Hyung-Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.11
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    • pp.1640-1649
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    • 2001
  • The present study investigates the effects of various rib arrangements on heat/mass transfer in the cooling passage of gas turbine blades. A complex flow structure occurs in the cooling passage with rib turbulators which promote heat transfer on the wall. It is important to increase not only the heat transfer rates but also the uniformity of heat transfer in the cooling passage. A numerical computation is performed using a commercial code to calculate the flow structures and experiments are conducted to measure heat/mass transfer coefficients using a naphthalene sublimation technique. A square channel (50 mm $\times$ 50 mm) with rectangular ribs (4 mm $\times$ 5 mm) is used fur the stationary duct test. The experiments focus on the effects of rib arrangements and gap positions in the discrete ribs on the heat/mass transfer on the duct wall. The rib angle of attack is 60°and the rib-to-rib pitch is 32 mm, that is 8 times of the rib height. With the inclined rib angle of attack (60°), the parallel rib arrangements make a pair of counter rotating secondary flows in the cross section, but the cross rib arrangements make a single large secondary flow including a small secondary vortex. These secondary flow patterns affect significantly the heat/mass transfer on the ribbed wall. The heat/mass transfer in the parallel arrangements is 1.5 ∼2 times higher than that in the cross arrangements. However, the shifted rib arrangements change little the heat/mass transfer from the inline rib arrangements. The gap position in the discrete rib affects significantly the heat/mass transfer because a strong flow acceleration occurs locally through the gap.

Heat/Mass Transfer Augmentation in a Square Duct . Roughened with Angled Discrete Ribs Having Narrow Gaps (정사각 덕트 내에서 열/물질전달 촉진을 위한 경사진 단락 요철의 좁은 틈새 효과)

  • Wu, Seong-Je;Lee, Sei-Young;Choi, Chung;Cho, Hyung-Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.1
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    • pp.150-158
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    • 2002
  • Local heat/mass transfer and friction loss in a square duct roughened with various types of continuous and discrete rib turbulators are investigated. The combined effects of the gap flows of the discrete ribs and the secondary flows are examined for the purpose of the reduction of thermally weak regions and the promotion of the uniformity of heat/mass transfer distributions as well as the ;augmentation of average heat/mass transfer. The rib-to-rib pitch to the rib height ratio (p/e) of 8 and the rib angles of 90° and 60° are selected with e/D$\_$h/=0.08. The vortical structure of the secondary flows induced by the parallel angled arrays are quite distinct from that induced by the cross angled arrays. This distinction influences on heat/mass transfer and friction loss in all the tested cases. The gap flows of the discrete ribs reduce the strength of the secondary flows but promote local turbulence and flow mixing. Consequently, the angled discrete ribs with the small gaps provide a more uniform heat/mass transfer distribution sustaining high average heat/mass transfer.

Experimental Study of Heat/Mass Transfer in Rotating Cooling Passages with Discrete Ribs (단락 요철이 설치된 내부 냉각유로에서 회전에 따른 열/물질전달 특성 연구)

  • Kim Kyung Min;Kim Sang In;Lee Dong Ho;Cho Hyung Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.5 s.236
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    • pp.590-598
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    • 2005
  • The present study has been conducted to investigate the effect of discrete ribs and rotation on heat/mass transfer characteristics in a two-pass square duct with $90^{\circ}-rib$ turbulators. The rib turbulator has a square cross section of 1.5 mm. The rib height-to-hydraulic diameter ratio $({e/D_{h})$ is 0.056, and the rib pitch-to-rib height ratio (p/e) is 10. The gap width is the same as the rib height. The rotation number ranges from 0.0 to 0.2 while Reynolds number is fixed to 10,000. In a stationary duct, the heat/mass transfer on the surfaces with discrete ribs is enhanced because the gap flow promotes local turbulence and flow mixing near the ribbed surface. In a rotating duct, the gap flow affects differently the heat/mass transfer on leading and trailing surfaces with discrete ribs. On the leading surface of the first pass, heat/mass transfer is increased due to the gap flow. On the trailing surface of the first pass, however, heat/mass transfer is decreased because the gap flow disturbs reattachment of main flow. The phenomenon, that is, the difference of heat transfer between the leading and the trailing surfaces is distinctly presented by rotation.