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# Thermal Management of Low Profile Electronic Equipment Using Radial Fans and Heat Sinks

[+] Author and Article Information
Ed Walsh

Stokes Institute, University of Limerick, Limerick, Irelandedmond.walsh@ul.ie

Pat Walsh

Stokes Institute, University of Limerick, Limerick, Irelandpat.walsh@ul.ie

Ronan Grimes

Stokes Institute, University of Limerick, Limerick, Irelandronan.grimes@ul.ie

Vanessa Egan

Stokes Institute, University of Limerick, Limerick, Irelandvanessa.egan@ul.ie

J. Heat Transfer 130(12), 125001 (Sep 25, 2008) (8 pages) doi:10.1115/1.2977602 History: Received October 29, 2007; Revised June 13, 2008; Published September 25, 2008

## Abstract

There is an increasing need for low profile thermal management solutions for applications in the range of $5–10W$, targeted at portable electronic devices. This need is emerging due to enhanced power dissipation levels in portable electronics, such as mobile phones, portable gaming machines, and ultraportable personal computers. This work focuses on the optimization of such a solution within the constraints of the profile and footprint area. A number of fan geometries have been investigated where both the inlet and exit rotor angles are varied relative to the heat conducting fins on a heat sink. The ratio of the fan diameter to the heat sink fin length was also varied. The objective was to determine the optimal solution from a thermal management perspective within the defined constraints. The results show a good thermal performance and highlight the need to develop the heat sink and fan as an integrated thermal solution rather than in isolation as is the traditional methodology. An interesting finding is that the heat transfer scales are in line with turbulent rather than laminar correlations despite the low Reynolds number. It is also found that while increasing the pumping power generally improves the thermal performance, only small gains are achieved for relatively large pumping power increases. This is important in optimizing portable systems where reduced power consumption is a competitive advantage in the marketplace.

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## Figures

Figure 1

Inlet and exit velocity triangles of tested configurations for the indicated blade in each image of the heat sink and rotors employed, the arrow over thick arrows represent the rotational direction in each case. N.B. Pictures or velocity triangles are not to scale and for visualization purposes only.

Figure 2

Picture of experimental setup, this setup was placed within an enclosure for all results presented in this paper

Figure 3

Schematic of the experimental setup for thermal resistance measurements

Figure 4

(Left) Flow rate measurement facility for fans and the (right) thermal solution setup to measure the flow rate

Figure 5

Experimental setup for flow rate measurement (not to scale)

Figure 6

Covers manufactured to investigate the effect of the cover design on flow rates for small scale fans

Figure 7

Relative volumetric flow rate for the cases described in Table 1 for varying exit flow angles at 7500rpm

Figure 8

Thermal resistance in °C∕W for the cases described in Table 1 for varying exit flow angles at 7500rpm

Figure 9

Effect of varying the rotor diameter with a fixed internal fin diameter of 25mm and 33mm at a speed of 7500rpm

Figure 10

Effect of the rotation speed on the thermal performance for different rotor diameters with the heat sink fin diameter starting at 33mm

Figure 11

Average heat transfer coefficient for the heat sink with the fin length starting at a radius of 33mm

Figure 12

Scaling of the Nusselt number and Reynolds number for a range of rotor diameters and speeds

Figure 13

Percentage flow rate and heat transfer relative to no cover; black and grey columns represent the flow rate and Nusselt number, respectively, and K refers to the case of no blockage

## Errata

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