Research Papers: Heat Transfer Enhancement

Effect of Rotation on Detailed Heat Transfer Distribution for Various Rib Geometries in Developing Channel Flow

[+] Author and Article Information
Justin A. Lamont

e-mail: jalamont@vt.edu

Srinath V. Ekkad

e-mail: sekkad@vt.edu
Department of Mechanical Engineering,
Virginia Tech,
Blacksburg, VA 24061

Mary Anne Alvin

DOE-National Energy Technology Laboratory,
Pittsburgh, PA 15236
e-mail: Maryanne.Alvin@NETL.DOE.GOV

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received September 25, 2012; final manuscript received July 26, 2013; published online October 25, 2013. Assoc. Editor: Phillip M. Ligrani.

J. Heat Transfer 136(1), 011901 (Oct 25, 2013) (10 pages) Paper No: HT-12-1523; doi: 10.1115/1.4025211 History: Received September 25, 2012; Revised July 26, 2013

The effects of Coriolis force and centrifugal buoyancy have a significant impact on heat transfer behavior inside rotating internal serpentine coolant channels for turbine blades. Due to the complexity of added rotation inside such channels, detailed knowledge of the heat transfer will greatly enhance the blade designer's ability to predict hot spots so coolant may be distributed more effectively. The effects of high rotation numbers are investigated on the heat transfer distributions for different rib types in near entrance and entrance region of the channels. It is important to determine the actual enhancement derived from turbulating channel entrances where heat transfer is already high due to entrance effects and boundary layer growth. A transient liquid crystal technique is used to measure detailed heat transfer coefficients (htc) for a rotating, short length, radially outward coolant channel with rib turbulators. Different rib types such as 90 deg, W, and M-shaped ribs are used to roughen the walls to enhance heat transfer. The channel Reynolds number is held constant at 12,000 while the rotation number is increased up to 0.5. Results show that in the near entrance region, the high performance W and M-shaped ribs are just as effective as the simple 90 deg ribs in enhancing heat transfer. The entrance effect in the developing region causes significantly high baseline heat transfer coefficients thus reducing the effective of the ribs to further enhance heat transfer. Rotation causes increase in heat transfer on the trailing side, while the leading side remains relatively constant limiting the decrement in leading side heat transfer. For all rotational cases, the W and M-shaped ribs show significant effect of rotation with large differences between leading and trailing side heat transfer.

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Fig. 1

A standard turbine blade with internal coolant channels. (Left) cross section of blade. (Right) cutaway view of coolant channels (from Ref. [5]).

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Fig. 2

Illustration of the rotating rig support frame

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Fig. 3

Schematic of the rotating rig. A camera is mounted onto the test section to view the color change in the liquid crystals.

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Fig. 4

Wall and mainstream temperature history for the transient test

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Fig. 5

Test section used for the present study. This has a large cross section to achieve high rotation numbers at relatively slow rotational speeds. The crosshatching indicates the honeycomb laminators to break down entrance asymmetries.

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Fig. 6

The two types of W/M shaped ribs used in the present study

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Fig. 7

Definition of W/M shaped ribs. (Left) W-shaped ribs. (Right) M-shaped ribs

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Fig. 8

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

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Fig. 9

Heat transfer distribution for the smooth, stationary baseline case

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Fig. 10

(Left) spanwise Nusselt number average along the length of the channel. (Right) spanwise Nusselt number average normalized to the Dittus–Boelter equation along the length of the channel.

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Fig. 11

Detailed results for the 90 deg ribs for stationary and rotational cases

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Fig. 12

Detailed results for the 45 deg W-shaped ribs for stationary and rotational cases

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Fig. 13

Detailed results for the 45 deg M-shaped ribs for stationary and rotational cases

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Fig. 14

Detailed results for the 30 deg W-shaped ribs for stationary and rotational cases

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Fig. 15

Detailed results for the 30 deg M-shaped ribs for stationary and rotational cases

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Fig. 16

Swirling flow shed from the W/M-shaped ribs. This is speculative, but may explain the heat transfer distribution.

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Fig. 17

Spanwise averaged Nusselt number ratios (Nu/Nus) for all cases with and without rotation

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Fig 18

Average Nu/Nus for each case before (1) and after (2) the center rib of the detailed plots




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