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Heat Transfer Enhancement

Effects of Pin Detached Space on Heat Transfer and Pin-Fin Arrays

[+] Author and Article Information
Sin Chien Siw

Department of Mechanical Engineering and Materials Science,  University of Pittsburgh, Pittsburgh, PA 15261

Minking K. Chyu

Department of Mechanical Engineering and Materials Science,  University of Pittsburgh, Pittsburgh, PA 15261mkchyu@pitt.edu

Tom I.-P. Shih

Department of Aeronautics and Astronautics,  Purdue University, West Lafayette, IN 47907

Mary Anne Alvin

National Energy Technology Laboratory, U.S. Department of Energy, Pittsburgh, PA 15236

J. Heat Transfer 134(8), 081902 (Jun 05, 2012) (9 pages) doi:10.1115/1.4006166 History: Received June 13, 2011; Revised January 28, 2012; Published June 05, 2012; Online June 05, 2012

Heat transfer and pressure characteristics in a rectangular channel with pin-fin arrays of partial detachment from one of the endwalls have been experimentally studied. The overall channel geometry (W = 76.2 mm, E = 25.4 mm) simulates an internal cooling passage of wide aspect ratio (3:1) in a gas turbine airfoil. With a given pin diameter, D = 6.35 mm = ¼E, three different pin-fin height-to-diameter ratios, H/D = 4, 3, and 2, were examined. Each of these three cases corresponds to a specific pin array geometry of detachment spacing (C) between the pin tip and one of the endwalls, i.e., C/D = 0, 1, 2, respectively. The Reynolds number, based on the hydraulic diameter of the unobstructed cross-section and the mean bulk velocity, ranges from 10,000 to 25,000. The experiment employs a hybrid technique based on transient liquid crystal imaging to obtain the distributions of the local heat transfer coefficient over all of the participating surfaces, including the endwalls and all the pin elements. Experimental results reveal that the presence of a detached space between the pin tip and the endwall has a significant effect on the convective heat transfer and pressure loss in the channel. The presence of pin-to-endwall spacing promotes wall-flow interaction, generates additional separated shear layers, and augments turbulent transport. In general, an increase in detached spacing, or C/D, leads to lower heat transfer enhancement and pressure drop. However, C/D = 1, i.e., H/D = 3, of a staggered array configuration exhibits the highest heat transfer enhancement, followed by the cases of C/D = 0 and C/D = 2, i.e., H/D = 4 or 2, respectively.

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Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 12

Performance Index versus Re

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Figure 11

Normalized friction factor versus Re

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Figure 10

Heat transfer enhancement versus Re

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Figure 9

Local heat transfer coefficient, h (W/m2 K) at Re = 15,000 [22]

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Figure 8

Shear stress (Pa) on the top and bottom endwall at Re = 15,000 [22]

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Figure 7

Row-resolved average Nusselt number for “mixed” pin-fin cases: (a) pin fin and (b) endwall

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Figure 6

Row-resolved average Nusselt number: (a) staggered array and (b) inline array

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Figure 5

Local heat transfer coefficient, h, distribution on individual pins and endwall, Re = 25,000

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Figure 4

Pin-fin configuration for all staggered arrays (side view)

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Figure 3

(a) Inline and (b) staggered pin-fin array (top view)

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Figure 2

3-D view of test section assembly

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Figure 1

Schematic layout of test setup

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