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RESEARCH PAPERS

Heat Transfer Contributions of Pins and Endwall in Pin-Fin Arrays: Effects of Thermal Boundary Condition Modeling

[+] Author and Article Information
M. K. Chyu, Y. C. Hsing, T. I.-P. Shih

Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213

V. Natarajan

The BOC Group Technical Center, Murray Hill, NJ 07947

J. Turbomach 121(2), 257-263 (Apr 01, 1999) (7 pages) doi:10.1115/1.2841309 History: Received February 01, 1998; Online January 29, 2008

Abstract

Short pin-fin arrays are often used for cooling turbine airfoils, particularly near the trailing edge. An accurate heat transfer estimation from a pin-fin array should account for the total heat transfer over the entire wetted surface, which includes the pin surfaces and uncovered endwalls. One design question frequently raised is the actual magnitudes of heat transfer coefficients on both pins and endwalls. Results from earlier studies have led to different and often contradicting conclusions. This variation, in part, is caused by imperfect or unrealistic thermal boundary conditions prescribed in the individual test models. Either pins or endwalls, but generally not both, were heated in those previous studies. Using a mass transfer analogy based on the naphthalene sublimation technique, the present experiment is capable of revealing the individual heat transfer contributions from pins and endwalls with the entire wetted surface thermally active. The particular pin-fin geometry investigated, S/D = X/D = 2.5 and H/D = 1.0, is considered to be one of the optimal array arrangement for turbine airfoil cooling. Both inline and staggered arrays with the identical geometric parameters are studied for 5000 ≤ Re ≤ 25,000. The present results reveal that the general trends of the row-resolved heat transfer coefficients on either pins or endwalls are somewhat insensitive to the nature of thermal boundary conditions prescribed on the test surface. However, the actual magnitudes of heat transfer coefficients can be substantially different, due to variations in the flow bulk temperature. The present study also concludes that the pins have consistently 10 to 20 percent higher heat transfer coefficient than the endwalls. However, such a difference in heat transfer coefficient imposes very insignificant influence on the overall array-averaged heat transfer, since the wetted area of the uncovered endwalls is nearly four times greater than that of the pins.

Copyright © 1999 by The American Society of Mechanical Engineers
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