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Research Papers

Experimental and Numerical Heat Transfer Investigation of an Impinging Jet Array on a Target Plate Roughened by Cubic Micro Pin Fins1

[+] Author and Article Information
Robin Brakmann, Bernhard Weigand

Institute of Aerospace Thermodynamics (ITLR),
University of Stuttgart,
Pfaffenwaldring 31,
Stuttgart 70569, Germany

Lingling Chen

Institute of Aerospace Thermodynamics (ITLR),
University of Stuttgart,
Pfaffenwaldring 31,
Stuttgart 70569, Germany
e-mail: lingling.chen@itlr.uni-stuttgart.de

Michael Crawford

Siemens Energy, Inc.,
Fossil Power Generation,
4400 Alafaya Trail,
MC Q3-031, Orlando, FL 32826

2Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received April 12, 2016; final manuscript received April 26, 2016; published online June 28, 2016. Editor: Kenneth C. Hall.

J. Turbomach 138(11), 111010 (Jun 28, 2016) (9 pages) Paper No: TURBO-16-1087; doi: 10.1115/1.4033670 History: Received April 12, 2016; Revised April 26, 2016

A generic impingement cooling system for turbomachinery application is modeled experimentally and numerically to investigate heat transfer and pressure loss characteristics. The experimental setup consists of an array of 9 × 9 jets impinging on a target plate with cubic micro pin fins. The cubic micro pin fins have an edge length of 0.22 D and enlarge the target area by 150%. Experimentally heat transfer is measured by the transient liquid crystal (TLC) method. The transient method used requires a heated jet impinging on a cold target plate. As reference temperature for the heat transfer coefficient, we use the total jet inlet temperature which is measured via thermocouples in the jet center. The computational fluid dynamics (CFD) model was realized within the software package ANSYS CFX. This model uses a Steady-state 3D Reynolds-averaged Navier–Stokes (RANS) approach and the shear stress transport (SST) turbulence model. Boundary conditions are chosen to mimic the experiments as close as possible. The effects of different jet-to-plate spacing (H/D = 3–5), crossflow schemes, and jet Reynolds number (15,000–35,000) are investigated experimentally and numerically. The results include local Nusselt numbers as well as area and line averaged values. Numerical simulations allow a detailed insight into the fluid mechanics of the problem and complement experimental measurements. A good overall agreement of experimental and numerical behavior for all investigated cases could be reached. Depending on the crossflow scheme, the cubic micro pin fin setup increases the heat flux to about 134–142% compared to a flat target plate. At the same time, the Nusselt number slightly decreases. The micro pin fins increase the pressure loss by not more than 14%. The results show that the numerical model predicts the heat transfer characteristics of the cubic micro pin fins in a satisfactory way.

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Figures

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Fig. 1

Schematic of test rig and crossflow schemes

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Fig. 2

Cubic micro pin fin target plate and close up with dimensions

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Fig. 3

Computational domain and boundary conditions for the maximum crossflow setting

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Fig. 4

Detailed view of the computational hybrid mesh

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Fig. 5

GCI analysis of the H/D = 3, maximum crossflow, and Re = 35,000 case

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Fig. 6

Experimental and numerical Nusselt number distribution and spanwise averaged values—smooth target plate, H/D = 3, Re = 35,000, and maximum crossflow condition

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Fig. 7

Experimental and numerical Nusselt number contour plots for maximum, medium, and minimum crossflow condition; H/D = 3; and Re = 35,000

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Fig. 8

Experimental and numerical spanwise averaged Nusselt number for H/D = 3, Re = 35,000, and maximum crossflow condition (bottom part); numerical Nusselt number distribution for smooth and pin fin target plate in the top part

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Fig. 9

Numerical Nusselt number contour and streamlines at different locations for jet 5 and 6; H/D = 3; Re = 35,000; maximum crossflow; yellow margins indicate the spanwise area the green and blue streamlines are passing

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Fig. 10

H/D = 3; maximum crossflow; Re = 35,000; area-averaged numerical Nusselt number values; smooth target and micro cubic pin fins

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Fig. 11

H/D = 3; maximum crossflow; Re = 15,000, 25,000, and 35,000; spanwise averaged experimental and numerical Nusselt number values

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Fig. 12

H/D = 3–5; maximum crossflow; Re = 35,000; area-averaged experimental and numerical Nusselt number values; for the data points marked with “all pin fin surface included” heat transfer from both prime surface and the extended surfaces (pins) were evaluated (only possible for CFD)

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Fig. 13

H/D = 3; medium crossflow; Re = 35,000; spanwise averaged experimental and numerical Nusselt number values

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Fig. 14

H/D = 3; minimum crossflow; Re = 35,000; spanwise averaged experimental and numerical Nusselt number values

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