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Research Papers: Flows in Complex Systems

Exit Flow Behavior of Axial Fan Flows With/Without Impingement

[+] Author and Article Information
D. Sui, S. S. Wang, J. R. Mao

School of Energy and Power Engineering, Xi’an Jiatong University, Xi’an 710049, P.R.C.

T. Kim

MOE Key Laboratory for Strength and Vibration, Xi’an Jiaotong University, Xi’an 710049, P.R.C.tongbeum@gmail.com

T. J. Lu

MOE Key Laboratory for Strength and Vibration, Xi’an Jiaotong University, Xi’an 710049, P.R.C.tjlu@mail.xjtu.edu.cn

J. Fluids Eng 131(6), 061103 (May 14, 2009) (7 pages) doi:10.1115/1.3130246 History: Received June 19, 2008; Revised April 13, 2009; Published May 14, 2009

The exit flow patterns of an axial flow fan widely used in electronics cooling are experimentally characterized both in free exit and in the presence of a flat impingement plate. The axial fan is rotated with 12.0 V input from a dc power supply, leading to a nominal Reynolds number of Re=9.0×103 based on fan diameter. One shear layer each is found to form between the exit flow from the axial fan and the surrounding fluid at rest, and between the exit flow and the flow along the fan axis. In addition to creating a highest wall pressure region (the primary stagnation region), the presence of the flat plate induces a flow recirculation zone (the secondary stagnation region) at the plate center. When the fan exit-to-plate spacing normalized by fan diameter (H/D) equals to about 0.6, the wall pressure is minimized in the secondary stagnation region due to the maximized “recirculation” as a result of intensified flow interaction. Within the range considered (0.2H/D2.0) and with the case of H/D0.6 serving as a reference, the flow interaction tends to be suppressed by the proximity of the plate at H/D=0.2 and weakened due to the momentum dissipation at H/D2.0.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

An axial fan and fin heat sink utilized for central processing unit cooling

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Figure 2

Schematic of fan exit flow test rig and particle image velocimetry measurement planes

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Figure 3

Overall exit flow structures obtained from PIV measurements for Re=9.0×103: (a) ensemble average velocity vectors and (b) radial profiles of axial velocity, at five selected axial planes

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Figure 4

Radial distributions of (a) radial and (b) tangential velocity components obtained from PIV measurements for Re=9.0×103

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Figure 5

The r-z plane velocity vectors for varying exit-to-plate spacings: (a) H/D=1.0, (b) H/D=0.5, and (c) H/D=0.25

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Figure 6

Radial distributions of axial and radial velocity components of the axial fan flow for a fixed relative axial location, e.g., z/H=0.9 within the exit-to-plate spacings (H/D=0.25, 0.5, and 1.0); (a) axial velocity profile and (b) radial velocity profile

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Figure 7

Distributions of wall pressure coefficient Cp: (a) radial distribution, and (b) variation in Cp at the secondary stagnation point (r/D=0) with the exit-to-plate spacing

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Figure 8

Sketch of overall exit flows emerging from an axial flow fan

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