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Research Papers: Jets, Wakes, and Impingement Cooling

# Full-Field Flow Measurements and Heat Transfer of a Compact Jet Impingement Array With Local Extraction of Spent Fluid

[+] Author and Article Information

Department of Mechanical Engineering, Stanford University, Stanford, CA 94305aonstad@stanford.edu

Christopher J. Elkins, Robert J. Moffat, John K. Eaton

Department of Mechanical Engineering, Stanford University, Stanford, CA 94305

1

Corresponding author.

J. Heat Transfer 131(8), 082201 (Jun 04, 2009) (8 pages) doi:10.1115/1.3109991 History: Received August 18, 2008; Revised February 18, 2009; Published June 04, 2009

## Abstract

Jet impingement cooling is widely used due to the very high heat transfer coefficients that are attainable. Both single and multiple jet systems can be used, however, multiple jet systems offer higher and more uniform heat transfer. A staggered array of 8.46 mm diameter impingement jets with jet-to-jet spacing of 2.34 D was examined where the spent fluid is extracted through one of six 7.36 mm diameter extraction holes regularly located around each jet. The array had an extraction area ratio $(Ae/Ajet)$ of 2.23 locally and was tested with a jet-to-target spacing $(H/D)$ of 1.18 jet diameters. Magnetic resonance velocimetry was used to both quantify and visualize the three dimensional flow field inside the cooling cavity at jet Reynolds numbers of 2600 and 5300. The spatially averaged velocity measurements showed a smooth transition is possible from the impingement jet to the extraction hole without the presence of large vortical structures. Mean Nusselt number measurements were made over a jet Reynolds number range of 2000–10,000. Nusselt numbers near 75 were measured at the highest Reynolds number with an estimated uncertainty of 7%. Large mass flow rate per unit heat transfer area ratios were required because of the small jet-to-jet spacing.

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## Figures

Figure 1

Two different types of impingement cooling with local extraction of spent fluid

Figure 2

View of the jet impingement geometry from the jet impingement exit plane. The geometry is a staggered array of 36 8.46 mm diameter injection holes surrounded by 6 7.29 mm diameter extraction holes.

Figure 3

Impingement apparatus. The working fluid enters through the inlet manifold and progresses through the impingement array. The fluid leaves the array entering the extraction plenum where it passes through one of four tubes before it is exhausted.

Figure 4

Cross section of the jet impingement geometry. The impinging jets pass in tubes through the extraction plenum striking the target surface creating primary stagnation regions. The fluid turns radially outward and interacts with adjacent jets creating a secondary stagnation zone. The fluid is then exhausted through spent fluid holes into the extraction plenum.

Figure 5

Cross-sectional view of the heat transfer surface

Figure 6

Laboratory air supply schematic

Figure 7

Velocity magnitude contours (in m/s) illustrating the full array spanwise cross section (y-z) at ReD=5300

Figure 8

Velocity magnitude contours in m/s and in-plane, (z-y), velocity vectors zoomed in to show the flow structure inside the cooling cavity at ReD=5300

Figure 9

Velocity magnitude contours in m/s and in-plane (x-y), velocity vectors shown for the plane orthogonal to that shown in Fig. 8

Figure 10

Nondimensional mass flow rate through each individual jet. Jets located at identical z locations are plotted as a group with the same symbol indicating the spanwise variation in jet mass flow rate.

Figure 11

Contours of velocity magnitude (m/s) and in-plane x-z, vectors showing the flow field 10 mm upstream of the impingement jets

Figure 12

Contours of velocity magnitude (m/s) in the x-z plane measured at y=9.5 mm, or at the start of the impingement jets

Figure 13

Contours of velocity magnitude (m/s) in the x-z plane measured at y=5 mm, or at the midplane of the impingement jet

Figure 14

Contours of velocity magnitude (m/s) in the x-z plane measured immediately above the target surface

Figure 15

Average Nusselt number as a function of the jet Reynolds number

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