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Research Papers: Electronic Cooling

An Experimental Study on the Design of Miniature Heat Sinks for Forced Convection Air Cooling

[+] Author and Article Information
Vanessa Egan

Department of Mechanical and Aeronautical Engineering, Stokes Institute, University of Limerick, Limerick, Irelandvanessa.egan@ul.ie

Jason Stafford

Department of Mechanical and Aeronautical Engineering, Stokes Institute, University of Limerick, Limerick, Irelandjason.stafford@ul.ie

Pat Walsh

Department of Mechanical and Aeronautical Engineering, Stokes Institute, University of Limerick, Limerick, Irelandpat.walsh@ul.ie

Ed Walsh

Department of Mechanical and Aeronautical Engineering, Stokes Institute, University of Limerick, Limerick, Irelandedmond.walsh@ul.ie

J. Heat Transfer 131(7), 071402 (May 06, 2009) (9 pages) doi:10.1115/1.3110005 History: Received July 14, 2008; Revised February 12, 2009; Published May 06, 2009

An experimental study is performed on one of the smallest commercially available miniature fans, suitable for cooling portable electronic devices, used in conjunction with both finned and finless heat sinks of equal exterior dimensions. The maximum overall footprint area of the cooling solution is 534mm2 with a profile height of 5 mm. Previous analysis has shown that due to fan exit angle, flow does not enter the heat sinks parallel to the fins or bounding walls. This results in a nonuniform flow rate within the channels of the finned and finless heat sinks along with impingement of the flow at the entrance giving rise to large entrance pressure losses. In this paper straightening diffusers were attached at the exit of the fan, which resulted in aligning the flow entering the heat sinks with the fins and channel walls. Detailed velocity measurements were obtained using particle image velocimetry, which provided a further insight into the physics of the flow in such miniature geometries and in designing the straightening diffusers. The thermal analysis results indicate that the cooling power of the solution is increased by up to 20% through the introduction of a diffuser, hence demonstrating the need for integrated fan and heat sink design of low profile applications.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of finned and finless heat sinks outlining the overall dimensions and the optimized parameters b and tfin

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Figure 2

Velocity triangle showing fan exit angle

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Figure 3

Photograph of the experimental configuration employing the straightening diffusers with the finned and finless heat sinks

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Figure 4

PIV Experimental setup showing camera and laser positions with respect to fan and heat sink. The diffuser is inserted between the fan and heat sink.

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Figure 5

Normalized PIV velocity magnitude plot, from Ref. 13, of flow in the entrance region of both finless (a) heat sink and channel (1–4) of finned (b) heat sink with no diffuser. All velocities are normalized with respect to the maximum velocity.

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Figure 6

PIV velocity magnitude plots depicting flow within the diffuser and heat sink entrance for both finned and finless geometries with diffuser angles of 25–60 deg

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Figure 7

PIV velocity magnitude plots depicting the flow within the diffuser and finless heat sink for a fan speed of 5500 rpm. Flow is from left to right. The respective velocity scale bar is in m/s. The dashed line represents the entrance to the heat sink from the diffuser.

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Figure 8

PIV velocity magnitude plots of flow in finned heat sink and 50 deg straight diffuser at 3000 rpm, 5500 rpm, and 8000 rpm. Respective scale bars for velocities in m/s are given above each result. Flow is from left to right. Regions in gray are shadows from the heat sink fins, which result from the laser light entering from the right.

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Figure 9

Plot of forced convection thermal resistance with varying rpm. Also indicated are the effects due to secondary cooling mechanisms (losses).

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Figure 10

The forced convection heat transfer coefficient for both finned and finless heat sinks

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Figure 11

Graph depicting the volumetric flow rates through heat sink measured using the PIV data presented in Fig. 8 and Ref. 13 over the three fan speeds tested

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