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Research Papers

Performance of an Air-Cooled Heat Sink Channel With Microscale Dimples Under Transitional Flow Conditions

[+] Author and Article Information
Krishna Kota

Department of Mechanical and
Aerospace Engineering,
New Mexico State University,
P. O. Box 30001/MSC 3450,
Las Cruces, NM 88003-8001
e-mail: kkota@nmsu.edu

Ludovic Burton

e-mail: ludovic@gatech.edu

Yogendra Joshi

e-mail: yogendra.joshi@me.gatech.edu

Microelectronics and Emerging
Technologies Thermal Laboratory,
The George W. Woodruff School
of Mechanical Engineering,
Georgia Institute of Technology,
771 Ferst Drive NW,
Atlanta, GA 30332-0405

Contributed by the Heat Transfer Division of ASME for publication in the Journal of Heat Transfer. Manuscript received April 1, 2012; final manuscript received September 28, 2012; published online September 23, 2013. Assoc. Sujoy Kumar Saha.

J. Heat Transfer 135(11), 111005 (Sep 23, 2013) (9 pages) Paper No: HT-12-1147; doi: 10.1115/1.4024598 History: Received April 01, 2012; Revised September 28, 2012

The objective of this effort is to pursue artificial microscale surface roughness features in the form of dimples, on the walls of an air-cooled heat sink channel, as a passive option to energy-efficiently augment heat transfer in forced convection flows. High fidelity numerical simulations were employed for realizing an optimized dimple configuration and to comprehend the behavior of microsized dimples under high velocity (∼17 m/s) transitional flow conditions. Fully developed flow simulations were performed, and design of experiments with response surface methodology was employed for the numerical optimization. The results showed ∼30% heat transfer improvement and ∼15% pressure drop increase in the fully developed region compared to a smooth-walled channel. Practicability of manufacturing 200 μm deep dimples on a 600 μm thin aluminum fin was demonstrated. Experiments were also carried out to assess the performance of the aforementioned optimized configuration in a custom built setup in the laboratory, which showed up to 10.5% heat transfer improvement and ∼12% pressure drop increase over a corresponding smooth-walled channel. The above results indicate that the performance of dimples is allied with the flow development characteristics. In addition, experiments performed at Reynolds numbers other than one at which the dimples were optimized showed inferior performance showing that application-specific optimization of dimples is crucial. With further exploration of shape and design parameters, dimples might have the potential to improve thermal performance passively and form an attractive candidate to realize high-performance air-cooled heat sinks in the future.

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Figures

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Fig. 1

(a) Dimple simulation domain, (b) meshing strategy and boundary conditions, and (c) structured boundary layer mesh near the wall

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Fig. 2 Left

SEM image of the milled dimple (∼200 μm deep); Right: 200 μm deep dimples milled on a 600 μm thin aluminum sheet in a staggered pattern

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Fig. 3

Experimental setup for testing the overall performance of dimples

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Fig. 4

Simulation showing negligible temperature gradients in the vicinity of dimple

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Fig. 5

Test-section with SLA fabricated holders and dimpled fins

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Fig. 6

Response function (PF) trend

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Fig. 7

Enhanced local wall Nusselt number at dimple exits

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Fig. 8

Velocity (in m/s) vectors showing secondary flow in the dimple

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Fig. 9

Local pressure (in Pa) rise at dimple exit

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Fig. 10

Measured wall temperatures; x is the axial location in the flow direction

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Fig. 11

Comparison of wall temperature profile obtained from the numerical simulation and experimental results for the dimple walled channel; experiment: wall temperature = 321.26 K at x = 0, simulation: wall temperature = 321.55 K at x = 0

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Fig. 12

Local wall Nu plotted on the right symmetry face (see Fig. 1)

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Fig. 13

Experimentally measured wall temperatures of dimpled and smooth channels at various flow Re

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Fig. 14

Performance of a dimpled channel (as characterized by PF obtained from experiments) a function of flow Re

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