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Research Papers

Effects of Pin Detached Space on Heat Transfer in a Rib Roughened Channel

[+] Author and Article Information
Minking K. Chyu

e-mail: mkchyu@pitt.edu
Department of Mechanical Engineering and Materials Science,
University of Pittsburgh,
Pittsburgh, PA 15261

Mary Anne Alvin

National Energy Technology Laboratory,
U.S. Department of Energy,
Pittsburgh, PA 15236

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received August 17, 2011; final manuscript received September 23, 2011; published online November 8, 2012. Editor: David Wisler.

J. Turbomach 135(2), 021029 (Nov 08, 2012) (9 pages) Paper No: TURBO-11-1186; doi: 10.1115/1.4006567 History: Received August 17, 2011; Revised September 23, 2011

An experimental study is performed to investigate the heat transfer characteristics and frictional losses in a rib roughened channel combined with detached pin-fins. The overall channel geometry (W = 76.2 mm, E = 25.4 mm) simulates an internal cooling passage of wide aspect ratio (3:1) in a gas turbine airfoil. With a given pin diameter, D = 6.35 mm = [1/4]E, three different pin-fin height-to-diameter ratios, H/D = 4, 3, and 2, were examined. Each of these three cases corresponds to a specific pin array geometry of detachment spacing (C) between the pin-tip and one of the endwalls, i.e., C/D = 0, 1, 2, respectively. The rib height-to-channel height ratio is 0.0625. Two newly proposed cross ribs, namely the broken rib and full rib are evaluated in this effort. The broken ribs are positioned in between two consecutive rows of pin-fins, while the full ribs are fully extended adjacent to the pin-fins. The Reynolds number, based on the hydraulic diameter of the unobstructed cross section and the mean bulk velocity, ranges from 10,000 to 25,000. The experiment employs a hybrid technique based on transient liquid crystal imaging to obtain distributions of the local heat transfer coefficient over all of the participating surfaces, including the endwalls and all pin elements. The presence of ribs enhances local heat transfer coefficient on the endwall substantially by approximately 20% to 50% as compared to the neighboring endwall. In addition, affected by the rib geometry, which is a relatively low profile as compared to the overall height of the channel, the pressure loss seems to be insensitive to the presence of the ribs. However, from the overall heat transfer enhancement standpoint, the baseline cases (without ribs) outperform cases with broken ribs or full ribs.

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References

Figures

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Fig. 1

Schematic layout of test setup

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Fig. 2

Top view of (a) broken rib, (b) full rib array, and (c) staggered pin-fin configuration (side view)

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Fig. 3

Local heat transfer coefficient h (W/m2 K) distribution for endwall and pin-fins (C/D = 2; H/D = 2) at Re = 25,000

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Fig. 4

Local heat transfer coefficient h (W/m2 K) distribution for endwall and pin-fins (C/D = 1; H/D = 3) at Re=25,000

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Fig. 5

Schematic of row in the pin-fin array

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Fig. 6

Row-resolved average Nusselt number for endwall and pin-fins (C/D = 2; H/D = 2): (a) baseline, (b) pin-fins with broken ribs, and (c) pin-fins with full ribs

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Fig. 7

Row-resolved average Nusselt number for endwall and pin-fins (C/D = 1; H/D = 3): (a) baseline, (b) pin-fins with broken ribs, and (c) pin-fins with full ribs

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Fig. 8

Endwall heat transfer enhancement versus Re

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Fig. 9

Overall heat transfer enhancement versus Re

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Fig. 10

Pressure loss coefficient versus Re

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Fig. 11

Performance index versus Re

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