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TECHNICAL PAPERS

# Enhanced Impingement Heat Transfer: The Influence of Impingement X/D for Interrupted Rib Obstacles (Rectangular Pin Fins)

[+] Author and Article Information
G. E. Andrews, R. A. A. Abdul Hussain, M. C. Mkpadi

Energy and Resources Research Institute, School of Process, Environment and Materials Engineering, The University of Leeds, Leeds LS2 9JT, UK

J. Turbomach 128(2), 321-331 (Mar 01, 2004) (11 pages) doi:10.1115/1.1860574 History: Received October 01, 2003; Revised March 01, 2004

## Abstract

Impingement flat wall cooling, with 15.2 mm pitch square hole arrays, was investigated in the presence of an array of interrupted rib obstacles. These ribs took the form of rectangular pin-fins with a 50% blockage to the cross flow. One side exit of the air was used, and there was no initial cross flow. Three hole diameters were investigated, which allowed the impingement wall pressure loss to be varied at constant coolant mass flow rate. Combustor wall cooling was the main application of the work, where a low wall cooling pressure loss is required if the air is subsequently to be fed to a low $NOx$ combustor. The results showed that the increase in surface average impingement heat transfer, relative to that for a smooth wall, was small and greatest for an $X∕D$ of 3.06 at 15%. The main effect of the interrupted ribs was to change the influence of cross flow, which produced a deterioration in the heat transfer with distance compared to a smooth impingement wall. With the interrupted ribs the heat transfer increased with distance. If the heat transfer was compared at the trailing edge of the test section, where the upstream cross flow was at a maximum, then at high coolant flow rates the increase in heat transfer was 21%, 47%, and 25% for $X∕D$ of 4.66, 3.06, and 1.86, respectively.

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## Figures

Figure 3

In-line and offset impingement jet

Figure 1

Rectangular pin-fin obstacle configuration

Figure 2

Pressure loss as a function of G for the smooth and rectangular pin-fin impingement flow for X∕D=1.86, 3.06, and 4.66

Figure 12

Influence of square array impingement jet X∕D on Nusselt versus impingement jet Reynolds number plot, X=15.2mm and Z=9mm. Impingement surface with rectangular pin-fin array with one fin in-line with each impingement jet and offset midway between the jets.

Figure 4

Influence of G on the surface-averaged impingement heat transfer coefficient for X∕D=1.86. Comparison of in-line and offset jets.

Figure 5

The influence of G on the surface-averaged impingement heat transfer coefficient for X∕D=4.66, Z∕D=2.75, Uj∕Uc=1.8. Comparison of in-line and offset jets relative to the rectangular pin obstacles.

Figure 6

hr∕hs as a function of G for X∕D 1.86, 3.06, and 4.66

Figure 13

Variation of the impingement heat transfer coefficient with axial distance from the leading edge. Comparison of smooth surface impingement heat transfer with a rectangular pin-fin rough surface, X∕D=1.86, G=1.91kg∕sm2.

Figure 14

Impingement heat transfer coefficient as a function of axial distance from the leading edge. Comparison between smooth wall and rough wall rectangular pin-fin array impingement heat transfer, X∕D=3.06, G=1.9kg∕sm2.

Figure 15

Impingement heat transfer coefficient as a function of the axial distance from the leading edge. Comparison of smooth surface and rough rectangular pin-fin arrays with square array impingement jets, X∕D=4.66, G=1.92kg∕sm2.

Figure 7

Comparison of the surface-averaged impingement heat transfer coefficient as a function of G for smooth and rectangular pin-fin surface roughness, X∕D=1.86, Uj∕Uc=0.29

Figure 8

Comparison of the surface-averaged impingement heat transfer coefficient as a function of G for smooth and rectangular pin-fin roughness for in-line jets, X∕D=3.06, Z∕D=1.8, Uj∕Uc=0.78

Figure 9

Surface-averaged impingement heat transfer for smooth and rectangular pin-fin rough surfaces, as a function of G for X∕D=4.66

Figure 10

Influence of X∕D on surface-averaged impingement heat transfer as a function of G

Figure 11

Ratio of rough rectangular pin-fin surface to smooth surface-averaged impingement heat transfer coefficient as a function of G. Comparison of the influence of square array impingement hole X∕D.

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