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RESEARCH PAPERS: Electronic Cooling

# Electronic Cooling Using Synthetic Jet Impingement

[+] Author and Article Information
Anna Pavlova

Mechanical, Aerospace and Nuclear Engineering Department, Rensselaer Polytechnic Institute, Troy, NY 12180

Michael Amitay1

Mechanical, Aerospace and Nuclear Engineering Department, Rensselaer Polytechnic Institute, Troy, NY 12180amitam@rpi.edu

1

Corresponding author.

J. Heat Transfer 128(9), 897-907 (Feb 20, 2006) (11 pages) doi:10.1115/1.2241889 History: Received September 14, 2005; Revised February 20, 2006

## Abstract

The efficiency and mechanisms of cooling a constant heat flux surface by impinging synthetic jets were investigated experimentally and compared to cooling with continuous jets. Effects of jet formation frequency and Reynolds number at different nozzle-to-surface distances $(H∕d)$ were investigated. High formation frequency $(f=1200Hz)$ synthetic jets were found to remove heat better than low frequency $(f=420Hz)$ jets for small $H∕d$, while low frequency jets are more effective at larger $H∕d$. Moreover, synthetic jets are about three times more effective in cooling than continuous jets at the same Reynolds number. Using particle image velocimetry, it was shown that the higher formation frequency jets are associated with breakdown and merging of vortices before they impinge on the surface. For the lower frequency jets, the wavelength between coherent structures is larger such that vortex rings impinge on the surface separately.

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## Figures

Figure 1

(a) Experimental setup and (b) detailed drawing of the synthetic jet

Figure 2

The change in the stagnation Nusselt number (with respect to free convection) as a function of the normalized distance, H∕d, for different Reynolds numbers: (a) f=420Hz and (b) f=1200Hz

Figure 3

The change in stagnation Nusselt number (with respect to free convection) as a function of the normalized distance, H∕d, for ReU0=445

Figure 4

Synthetic jet efficiency as a function of the normalized distance, H∕d, for ReU0=445

Figure 5

Time trace of the velocity at the synthetic jet exit plane. Rectified (dashed line) and derectified (solid line). ReU0=445.

Figure 6

Cross-stream distributions of the normalized time-averaged streamwise velocity component at x∕d=7.7. ReU0=190, f=1200Hz, and H∕d=9.5.

Figure 7

Cross-stream distributions of the normalized time-averaged streamwise velocity component at x∕d=5 and 7.7. (a)–(c) and (d)–(f) for jet operating frequencies of 420 and 1200Hz, respectively. ReU0=322 (a), 445 (b), and 598 (c) for the 420Hz jet, and ReU0=236 (d), 445 (e), and 740 (f) for the 1200Hz jet; H∕d=9.5.

Figure 8

Time-averaged spanwise vorticity fields for f=420Hz ((a)–(c)) and f=1200 ((d)–(f)). ReU0=322 (a), 445 (b), and 598 (c) for the 420Hz jet, and ReU0=236 (d), 445 (e), and 740 (f) for the 1200Hz jet. H∕d=9.5

Figure 9

Phase-averaged spanwise vorticity fields for f=420Hz ((a)–(c)) and f=1200 ((d)–(f)). ϕ=0deg ((a) and (d)), 120deg ((b) and (e)), and 240deg ((c) and (f)). ReU0=445 and H∕d=9.5.

Figure 10

Contour maps of time-averaged u′2∕U02 ((a) and (c)) and v′2∕U02 ((b) and (d)) for f=420Hz ((a) and (b)) and f=1200 ((c) and (d)). ReU0=445 and H∕d=9.5

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