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Research Papers

Detailed Heat Transfer Measurements Inside Rotating Ribbed Channels Using the Transient Liquid Crystal Technique

[+] Author and Article Information
Justin A. Lamont

Department of Mechanical Engineering,  Virginia Tech, 106 Randolph Hall, Blacksburg, VA 24061jalamont@vt.edu

Srinath V. Ekkad

Department of Mechanical Engineering,  Virginia Tech, 106 Randolph Hall, Blacksburg, VA 24061sekkad@vt.edu

Mary Anne Alvin

 National Energy Technology Laboratory, Department of Energy, 626 Cochrans Mill Road, Pittsburgh, PA 15236Maryanne.Alvin@netl.doe.gov

J. Thermal Sci. Eng. Appl 4(1), 011002 (Feb 24, 2012) (11 pages) doi:10.1115/1.4005604 History: Received June 28, 2011; Revised August 09, 2011; Published February 21, 2012; Online February 24, 2012

Coolant flow in rotating internal serpentine channels is highly complex due to the effects of the Coriolis force and centrifugal buoyancy. Detailed knowledge of the heat transfer over a surface will greatly enhance the blade designers’ ability to predict hot spots so coolant may be distributed effectively. The present study uses a novel transient liquid crystal technique to measure heat transfer on a rotating two-pass channel surface with chilled inlet air. The present study examines the differences in heat transfer distributions on channel surfaces with smooth walls, 90 deg rib and W-shaped rib turbulated walls. The test section is made up of two passes to model radially inward and outward flows. To account for centrifugal buoyancy, cold air is passed through a room temperature test section. This ensures that buoyancy is acting in a similar direction to real turbine blades. The inlet coolant-to-wall density ratio is fixed at 0.08, Re = 16,000, and Ro = 0.08. The present study shows that the W-shaped ribs enhance heat transfer in all cases (stationary and rotating) approximately 1.75 times more than the 90 deg ribs. The W-shaped rib channel is least affected by rotation, which may be due to the complex nature of the secondary flow generated by the geometry. A higher pressure drop is associated with the W-shaped ribs than the 90 deg ribs, however, the overall thermal-hydraulic performance of the W-shaped ribs still exceeds that set by the 90 deg ribs.

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Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 5

Typical temperature step response of the air in the test section when the flow direction is switched

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Figure 6

The test sections used for the present study. Schematic of the test section with: (top) smooth wall, (middle) 90 deg ribbed walls, and (bottom) w-shaped ribbed walls.

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Figure 7

Side view of the ribs. “P” is the pitch of the ribs, “e” is the height of the ribs, and “H” is the height of the channel.

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Figure 8

W-shaped rib geometry. The flow path is from bottom to top of the rib.

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Figure 9

A typical calibration curve relating the hue of the liquid crystal to the wall temperature

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Figure 10

(a) Leading side, stationary, and trailing side heat transfer results due to rotation. (b) Area average heat transfer along the flow path of the smooth wall channel. (c) (Top) low heat transfer region in the leading side turn. (Bottom) heat transfer in the trailing side turn region. The trailing side heat transfer appears to concentrate more in the center of the wall.

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Figure 11

(a) Leading side, stationary, and trailing side heat transfer results due to rotation for 90 deg ribbed channel. (b) Area average heat transfer along the flow path of the 90 deg ribbed channel.

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Figure 12

(a) Leading side, stationary, and trailing side heat transfer results due to rotation for W-shaped rib channel. (b) Area average heat transfer along the flow path of the W-shaped ribbed channel. (c) (left) How the coolant passes over the W-shaped rib and how the flow is shed. (right) shows a cross sectional view of the vortices generated due to W-shaped ribs. Vortices are labeled 1, 2, 3, and 4. This helps explain the heat transfer pattern seen at locations A, B, and C.

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Figure 13

(a) Stationary comparison for the smooth wall, 90 deg rib, and W-shaped rib walls. The presence of ribs greatly increases the heat transfer, especially the W-shaped ribs. (b) Trailing side comparison for the smooth wall, 90 deg rib, and W-shaped rib walls. The presence of ribs greatly increases the heat transfer, especially the W-shaped ribs. (c) Leading side comparison for the smooth wall, 90 deg rib, and W-shaped rib walls. The presence of ribs greatly increases the heat transfer, especially the W-shaped ribs.

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Figure 1

A standard turbine blade with internal coolant channels. (Left) cross section of blade. (Right) Cutaway view of coolant channels (modified from Parsons [4]).

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Figure 2

(Top) Schematic of the test section. First-pass is where the coolant air enters. Second-pass is where the coolant air exits. Average heat transfer calculations are made in regions 1–12. Region 13 is for calibration. (Bottom) View of the test section looking down the channels.

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Figure 3

Computer aided drafting (CAD) drawing of the rotating rig support frame. The shown test section is arbitrary, as many types may be inserted.

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Figure 4

Schematic of the test rig. A camera is mounted onto the test section for filming the liquid crystal color change.

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