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Research Papers

Impingement Heat Transfer From Jet Arrays on Turbulated Target Walls at Large Reynolds Numbers

[+] Author and Article Information
Shantanu Mhetras

Siemens Energy, Inc.,
5101 Westinghouse Boulevard,
Charlotte, NC 28273

Je-Chin Han

Department of Mechanical Engineering,
Texas A&M University,
College Station, TX 77843
e-mail: jc-han@tamu.edu

Michael Huth

Siemens AG,
Mellinghofer Street 55,
Muelheim an der Ruhr 45473, Germany

Manuscript received June 28, 2013; final manuscript received September 3, 2013; published online November 8, 2013. Assoc. Editor: Srinath V. Ekkad.

J. Thermal Sci. Eng. Appl 6(2), 021003 (Nov 08, 2013) (10 pages) Paper No: TSEA-13-1106; doi: 10.1115/1.4025665 History: Received June 28, 2013; Revised September 03, 2013

Experiments to investigate heat transfer and pressure loss from jet array impingement are performed on the target wall at high Reynolds numbers. Reynolds numbers up to 450,000 are tested. The presence of a turbulated target wall and its effect on heat transfer enhancement against a smooth surface is investigated. Two different jet plate configurations are used with closely spaced holes and with angled as well as normal impingement holes. The test section cross-section is designed to expand along the streamwise direction maintaining the jet plate to target wall distance in order to reduce cross-flow effects. The jet plate holes are chamfered or filleted to minimize pressure loss through the jet plate. Heat transfer and pressure loss measurements are performed on a smooth target wall as well as turbulated target walls. Three turbulators configurations are used with streamwise riblets, short pins, and spherical dimples. A steady-state heat transfer measurement method is used to obtain the heat transfer coefficients while pressure taps located in the plenum and at several streamwise locations are used to record the pressure losses across the jet plate. Experiments are performed for a range of Reynolds numbers from 50,000 to 450,000 based on average jet hole diameters to cover the incompressible as well as compressible flow regimes. A target wall with short pins provides the best heat transfer with the dimpled target wall giving the lowest heat transfer among the three turbulators geometries studied. Addition of turbulators though does not significantly increase the pressure losses in the test section over the smooth target wall.

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Figures

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Fig. 1

Layout of the flow loop along with the test section

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Fig. 2

Schematic of the two impingement jet plates

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Fig. 3

Exploded view of impingement test section

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Fig. 4

Turbulated target wall design

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Fig. 5

Representative heat loss characteristic for jet plate 1 with smooth target wall

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Fig. 6

Nusselt number distributions for all regions on smooth target wall with jet plate 1

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Fig. 7

Row-wise mass flow and jet Mach number distributions through streamwise jet rows for jet plate 1

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Fig. 8

Nusselt number distributions for all regions on smooth target wall with jet plate 2

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Fig. 9

Mass flow distributions and jet Mach numbers through streamwise jet rows for jet plate 2

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Fig. 10

Nusselt number distributions for all regions on target wall with riblets and jet plate 2

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Fig. 11

Nusselt number distributions for all regions on target wall with short pins and jet plate 2

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Fig. 12

Nusselt number distributions for all regions on target wall with dimples and jet plate 2

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Fig. 13

Comparison of average Nusselt numbers for all regions between all cases

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Fig. 14

Nusselt number enhancement from turbulated target walls compared to smooth walls

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Fig. 15

Comparison of loss coefficient from plenum to test section exit between all cases

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