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RESEARCH PAPERS: SPECIAL ISSUE ON BOILING AND INTERFACIAL PHENOMENA: Electronic Cooling

Thermal and Flow Performance of a Microconvective Heat Sink With Three-Dimensional Constructal Channel Configuration

[+] Author and Article Information
R. M. Moreno

Department of Mechanical and Materials Engineering, Florida International University, Miami, FL 33174

Y.-X. Tao

Department of Mechanical and Materials Engineering, Florida International University, Miami, FL 33174taoy@fiu.edu

J. Heat Transfer 128(8), 740-751 (Mar 06, 2006) (12 pages) doi:10.1115/1.2211630 History: Received April 27, 2004; Revised March 06, 2006

The design, performance, manufacturing, and experimental validation of two convective heat sinks with scalable dimensions are presented. The heat sinks consist of an array of elemental units arranged in parallel. Each elemental unit is designed as a network of branching channels whose dimensions follow a group of geometric relations that have been derived from physiological fluid transport systems and the constructal method. The goal of these relations is to optimize both the point-to-point temperature difference within the heat sink and the pressure drop across the device under imposed geometric constraints. The first branching network is a generic three-dimensional (3-D) structure that was analyzed to push the limit of the heat sinks capability. The second is a heat sink that was designed specifically with the tape-casting fabrication method in mind. The heat sink has a branching network embedded within low temperature cofire ceramic (LTCC) and the same network embedded within thick film silver, which has the ability of being cofired with low temperature cofired ceramic substrates. The performance is evaluated using both a channel-level lumped model and a CFD model. The performance for different heat sink materials (low-temperature cofired ceramic and silver) is presented. The key results are then compared with the experimental results of the two scaled models. The results show good agreement within the experimental uncertainty. This validation confirms that the thermal performance and pumping efficiency of the constructal heat sink is superior compared to porous metal and conventional microchannel heat sinks under the same operating conditions, and that the designs are only limited by manufacturing techniques.

Copyright © 2006 by American Society of Mechanical Engineers
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References

Figures

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Figure 5

Outlet surface temperature and maximum tube surface temperature as a function of heat flux: Constant heat flux boundary condition: Tc,in=6°C, and constructal heat sink size=10×10×1mm

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Figure 6

Scaled-up unit-model prototype: (a)–(c) channel features of three inner layers

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Figure 7

Measurement results for the scaled-up unit prototype under two controlled ambient temperatures (Fluid: water, single phase): (a) Heat transfer rate compared with the prediction. (b) Pressure drop comparison.

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Figure 1

A 3-D microconstructal flow system: (a) Schematic of four-level construction of one path in a unit connected to the manifold: (b) the outer view of the unit with one inlet port and four outlet ports; and (c) inner channel network (solid rendering where the dark ones are similar to the artery and the light ones are to the vein)

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Figure 2

Illustrating how multiple unit elements are connected in parallel by a manifold to cover the area requiring thermal management. The top layer of the manifold has been omitted so that the manifold channels, inlet, and exit holes are visible.

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Figure 3

Control volume for a piping segment where Ti represents the inlet temperature for the segment i

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Figure 4

A comparison of cooling capacity between a micro constructal heat sink and a 2-D microchannel: the benchmark condition: Tw=120°C; Tc,in=6°C, heat sink size=10×10×1mm. Note: m.c.—2-D microchannel; c.c.—constructal channels.

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Figure 13

Temperature contours at the bottom surface of one unit element of the LTCC heat sink in degrees Kelvin at (a) Re=25, (b) Re=200 (c) Re=500, (d) Re=700, and (e) Re=1000

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Figure 14

The thermal resistance and pressure drop as a function of flow rate for the LTCC heat sink

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Figure 15

Variation of the average bottom surface temperature with the heat flux into the surface of the silver tape heat sink: Re=500

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Figure 16

Microscope picture showing the channel structure of one unit element stacked on a layer of silver magnified 100X

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Figure 17

Thermal resistance and pressure drop as a function of flow rate for the silver heat sink

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Figure 18

Thermal resistance curves using the effective thermal conductivity assumption with series arrangement of Kapton® and silver

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Figure 8

Schematic of the elemental volume with the critical dimensions (H0=202μm and the hydraulic diameter=152μm). The channel of fluid is shown as the outline through the center of the elemental volume.

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Figure 9

(a) One layer of the heat sink channel structure that contains a total of 12 elemental volumes connected together by two first constructs, and (b) the solid unit element of the heat sink with the channel structure shown in (a) and the manifold on top. The top layer of the manifold has been omitted so that the manifold channels, inlet, and exit holes are visible.

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Figure 10

Schematic of the process of firing tape with kapton inserts to form embedded channels: (a) the layered structure during the stacking and lamination of the tape/kapton substrate; (b) the vaporization of the insert material during the firing and sintering stage; and (c) the finished substrate with an embedded channel structure

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Figure 11

Thermal resistance (R) and pressure drop values (implied in the pumping power PP) normalized by Eq. 14 for the LTCC heat sink. The minimum pressure drop and thermal resistance occurs between Re=300–400.

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Figure 12

Temperature contours at the cross section in (a) of one unit element of the LTCC heat sink in degrees Kelvin at (b) Re=25, (c) Re=200 (d) Re=500, (e) Re=700, and (f) Re=1000

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