Research Papers

Heat Transfer Enhancement in Narrow Diverging Channels

[+] Author and Article Information
Srinath V. Ekkad

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

Samir Salamah

General Electric Company,
Schenectady, NY 12345

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 13, 2012; final manuscript received September 17, 2012; published online June 5, 2013. Assoc. Editor: David Wisler.

J. Turbomach 135(4), 041017 (Jun 05, 2013) (7 pages) Paper No: TURBO-12-1145; doi: 10.1115/1.4007740 History: Received July 13, 2012; Revised September 17, 2012

Detailed heat transfer coefficient distributions have been obtained for narrow diverging channels with and without enhancement features. The cooling configurations considered include rib turbulators and concavities (or dimples) on the main heat transfer surfaces. All of the measurements are presented at a representative Reynolds number of 28,000. Pressure drop measurements for the overall channel are also presented to evaluate the heat transfer enhancement geometry with respect to the pumping power requirements. The test models were studied for wall heat transfer coefficient measurements using the transient liquid crystal technique. The model wall inner surfaces were sprayed with thermochromic liquid crystals and a transient test was used to obtain the local heat transfer coefficients from the measured color change. An analysis of the results shows that the choice of designs is limited by the available pressure drop, even if the design provides significantly higher heat transfer coefficients. Dimpled surfaces provide appreciably high heat transfer coefficients and a reasonable pressure drop, whereas ribbed ducts provide significantly higher heat transfer coefficients and a higher overall pressure drop.

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Fig. 1

Experimental set up

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Fig. 2

Wall temperature and hue matching (top). Resulting calibration of hue and temperature (bottom).

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Fig. 3

Step change in the mainstream temperature obtained from the mesh heater response

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Fig. 4

Test section geometry

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Fig. 5

Rib turbulator geometries

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Fig. 6

Dimple configurations used for testing

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Fig. 7

Detailed heat transfer coefficient distributions for the baseline smooth surface

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Fig. 8

Detailed heat transfer results. From top to bottom: 90 deg ribs, 60 deg ribs, 45 deg V-ribs; case 1, case 2, case 3, and case 4.

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Fig. 9

Comparing the overall heat transfer ratios with the overall pressure drop ratio for all cases (single sided only)




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