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RESEARCH PAPERS: Jets, Wakes, and Impingment Cooling

Local Convective Heat Transfer From a Constant Heat Flux Flat Plate Cooled by Synthetic Air Jets

[+] Author and Article Information
M. B. Gillespie

 Progress Energy, 8202 West Venable Street, Crystal River, FL 34429mark.gillespie@pgnmail.com

W. Z. Black

George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405william.black@me.gatech.edu

C. Rinehart

George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405gt1479b@mail.gatech.edu

A. Glezer

George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405ari.glezer@me.gatech.edu

J. Heat Transfer 128(10), 990-1000 (Feb 22, 2006) (11 pages) doi:10.1115/1.2345423 History: Received March 29, 2005; Revised February 22, 2006

The effects of a small-scale, rectangular synthetic air jet on the local convective heat transfer from a flat, heated surface were measured experimentally. The synthetic jet impinges normal to the surface and induces small-scale motions by zero-net mass flux, time-periodic entrainment, and ejection of ambient air at frequencies whose periods are far higher than the characteristic thermal time scale. The velocity field between the jet orifice and the target plate is measured in planar cross sections using particle image velocimetry and is related to the local heat transfer from the plate. The present work suggests that synthetic jets can lead to substantial enhancement of the local heat transfer from heated surfaces by strong mixing that disrupts the surface thermal boundary layer. The dependence of the local heat transfer coefficient on the primary parameters of jet motion is characterized over a range of operating conditions.

Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Synthetic jet actuator with a rectangular orifice of width S and length W, impinging on a foil heater of length 2L and width W

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Figure 2

Schematic of experimental apparatus

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Figure 6

Streamwise variation of: (a) jet width at 50% of centerline velocity (∎major axis by, 엯minor axis bx) and (b) normalized centerline velocity

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Figure 7

Cross-stream distributions of streamwise velocity in the free jet, (a) minor axis and (b) major axis. z∕S=∎5, 엯10, ▴15, —20, ◆25, and ×30.

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Figure 8

Power spectra of the jet centerline velocity: (a)z∕S=5, (b)z∕S=15, and (c)z∕S=25

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Figure 9

Velocity field and spanwise vorticity concentrations for jet impinging surface at Zp∕S=10, (a) minor axis, and (b) major axis. Two vorticity contours are marked with dashed lines: ζ=●●●●100,gray circles−100(1∕s).

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Figure 11

As in Fig. 9 for Zp∕S=20

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Figure 12

Spanwise distributions of local time-averaged Nusselt number, Zp∕S=(a) 3.6, (b) 14.5, (c) 22.7. Re≕∎108, 엯254, ▴309, ×367, and ◆396.

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Figure 13

Variation of the average Nusselt number with orifice-to-plate separation. Re=∎108, 엯254, ▴309, ×367, and ◆396.

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Figure 16

Comparison of the average Nusselt number based on ambient and cavity temperatures: ∎(Tp−T∞), ∘(Tp−Tj)

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Figure 15

Variation of air temperature in the synthetic jet actuator cavity, Tj, with orifice-to-plate separation

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Figure 3

Time trace of synthetic jet velocity at the orifice (f=300Hz)

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Figure 4

Variation of jet Reynolds number with frequency

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Figure 5

Velocity field and spanwise vorticity concentrations for a free jet, (a) minor axis, and (b) major axis. Two vorticity contours are marked with dashed lines: ζ=●●●●100,gray circles−100(1∕s).

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Figure 10

As in Fig. 9 for Zp∕S=15

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Figure 14

Variation of the average Nusselt number with synthetic jet frequency. Zp∕S=∎3.6, •5.4, ▴7.3, —9.1, ◆10.9, ×12.7, ◻14.5, 엯18.1, ▵22.7, and ◇45.4.

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