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Jets, Wakes, and Impingment Cooling

Effects of Rotation on Heat Transfer for a Single Row Jet Impingement Array With Crossflow

[+] Author and Article Information
Justin A. Lamont

Virginia Tech Department of Mechanical Engineering, 102 Randolph Hall, Blacksburg, VA 24061jalamont@vt.edu

Srinath V. Ekkad

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

Mary Anne Alvin

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

J. Heat Transfer 134(8), 082202 (May 29, 2012) (12 pages) doi:10.1115/1.4006167 History: Received June 21, 2011; Revised January 12, 2012; Published May 29, 2012; Online May 29, 2012

The effects of the Coriolis force are investigated in rotating internal serpentine coolant channels in turbine blades. For complex flow in rotating channels, detailed measurements of the heat transfer over the channel surface will greatly enhance the blade designers’ ability to predict hot spots so coolant may be distributed more effectively. The present study uses a novel transient liquid crystal technique to measure heat transfer in a rotating, radially outward channel with impingement jets. A simple case with a single row of constant pitch impinging jets with the crossflow effect is presented to demonstrate the novel liquid crystal technique and document the baseline effects for this type of geometry. The present study examines the differences in heat transfer distributions due to variations in jet Rotation number, Roj , and jet orifice-to-target surface distance (H/dj  = 1,2, and 3). Colder air, below room temperature, is passed through a room temperature test section to cause a color change in the liquid crystals. This ensures that buoyancy is acting in a similar direction as in actual turbine blades where walls are hotter than the coolant fluid. Three parameters were controlled in the testing: jet coolant-to-wall temperature ratio, average jet Reynolds number, Rej , and average jet Rotation number, Roj . Results show, such as serpentine channels, the trailing side experiences an increase in heat transfer and the leading side experiences a decrease for all jet channel height-to-jet diameter ratios (H/dj ). At a jet channel height-to-jet diameter ratio of 1, the crossflow from upstream spent jets greatly affects impingement heat transfer behavior in the channel. For H/dj  = 2 and 3, the effects of the crossflow are not as prevalent as H/dj  = 1: however, it still plays a detrimental role. The stationary case shows that heat transfer increases with higher H/dj values, so that H/dj  = 3 has the highest results of the three examined. However, during rotation the H/dj  = 2 case shows the highest heat transfer values for both the leading and trailing sides. The Coriolis force may have a considerable effect on the developing length of the potential core, affecting the resulting heat transfer on the target surface.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 6

(Top) Lengthwise view of the test section. (Bottom) View looking straight down the channel.

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Figure 7

Illustration on how the target wall changes when the test section is rotating

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Figure 8

Calibration curve relating hue to temperature. The relationship is approximately linear.

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Figure 9

Percent mass flow through each impingement jet

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Figure 10

Crossflow-to-jet mass flux ratio along the length of the channel

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Figure 11

H/dj  = 1. (Top left) Detailed measurements along the channel for the first seven jets. (Top right) Average heat transfer around each jet. (Bottom left) Maximum heat transfer values for each jet. (Bottom right) Midline rake along the channel length.

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Figure 5

Temperature response for the coolant inlet and the wall temperature used for calibration

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Figure 4

Illustration of test section and camera mount

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Figure 3

Schematic of the rotating rig

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Figure 2

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 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 12

H/dj  = 2. (Top left) Detailed measurements along the channel for the first seven jets. (Top right) Average heat transfer around each jet. (Bottom left) Maximum heat transfer values for each jet. (Bottom right) Midline rake along the channel length.

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Figure 13

H/dj  = 3. (Top left) Detailed measurements along the channel for the first seven jets. (Top right) Average heat transfer around each jet. (Bottom left) Maximum heat transfer values for each jet. (Bottom right) Midline rake along the channel length.

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Figure 14

(Top left) Stationary results for all H/dj cases. (Top right) Leading side results for all H/dj cases. (Bottom) Trailing side results for all H/dj cases.

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Figure 15

Illustrations of potential core development during rotation for all H/dj cases (top picture from Striegl and Diller [16])

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Figure 16

View inside of the impingement channel. The first jet experiences little to no crossflow. The later jets are bent due to crossflow. (Top) Velocity profile in the trailing side channel. (Bottom) Velocity profile in the leading side channel.

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