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Research Papers: Flows in Complex Systems

The Effect of Reynolds Number on Microaxial Flow Fan Performance

[+] Author and Article Information
David Quin

 Cameron Systems Ireland, Longford, Irelanddavid.quin@c-a-m.com

Ronan Grimes

 Stokes Research Institute, Limerick, Irelandronan.grimes@ul.ie

J. Fluids Eng 130(10), 101101 (Sep 02, 2008) (10 pages) doi:10.1115/1.2953300 History: Received October 06, 2007; Revised May 11, 2008; Published September 02, 2008

Microscale axial flow fans were investigated in response to the growing cooling requirements of the electronics industry. The two main challenges of this investigation were manufacture of a fully functional fan at the microscale, and performance reduction due to Reynolds number effect. Manufacture of a fully functional axial microfan complete with three-dimensional blade geometry was proven possible using microelectrodischarge machining techniques. Experimental performance measurements proved that Reynolds number effect was not prohibitive at the microscale, and dimensional analysis thereof derived a novel linear scaling method, which quickly and accurately predicted the Reynolds number effect at any fan scale.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Test fans. (a) Datum fan. 30cm rulers included for scale. (b) 1∕3 scale fan. 30cm rulers included for scale. (c) 1∕20 scale fan. Pencil tip and European 1 cent coin (∅16mm) included for scale.

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Figure 2

μEDM of the 1∕20 scale rotor

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Figure 3

1∕20 scale fan components. European 1 cent coin included for scale

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Figure 4

Fan characterization rigs. (a) Schematic of fan characterization rigs. (b) Exploded view of microfan characterization rig. (c) Assembled microfan characterization rig. 30cm rulers included for scale.

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Figure 5

Dimensionless fan performance. Ψ and ϕ are defined by Eqs. 4,5, respectively.

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Figure 6

Static performance characteristics for the 1∕20 scale fan; power of the flow rate axis Q has been adjusted to decompose the performance characteristic into three lines. (a) Static performance characteristics for the 1∕20 scale fan. (b) Flow rate axis raised to the power of 0.2 to linearize the progressive stall regime. (c) Flow rate axis raised to the power of 2 to linearize the normal operating regime.

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Figure 7

Pressure flow characteristic, divided into three operating regimes (abrupt stall, progressive stall, and normal operation)

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Figure 8

Linear trend in the normal operating regime of the 1∕3 scale fan. (a) Static performance characteristics for the 1∕3 scale fan. (b) Flow rate Q axis raised to the power of 2 to linearize the normal operating regime.

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Figure 9

Linear trend in the normal operating regime of the datum scale fan. (a) Static performance characteristics for the datum fan. (b) Flow rate Q axis raised to the power of 2 to linearize the normal operating regime.

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Figure 10

Dimensionless fan performance; ϕ axis has been raised to the power of 2 to display linear trends

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Figure 11

Plot of RH* against the Reynolds number. The points represent measurements and the continuous line represents empirical correlation (Eq. 12). The results for all fan scales are shown in (a) and the results for the 1∕20 scale fan are shown more clearly in (b).

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Figure 12

Plot of SH* against the Reynolds number. The points represent measurements and the continuous line represents empirical correlation (Eq. 13). The results for all fan scales are shown in (a) and the results for the 1∕20 scale fan are shown more clearly in (b).

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Figure 13

Plot of the maximum flow coefficient ϕmax against the Reynolds number. The points represent measurements and the continuous line represents empirical correlation.

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Figure 14

Dimensionless 1∕20 scale fan performance characteristics at low Reynolds number, showing distortion of the characteristic shape. (a) Re=850. (b) Re=567. (c) Re=283.

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