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Research Papers

Natural Convection Immersion Cooling With Enhanced Optical Performance of Light-Emitting Diode Systems

[+] Author and Article Information
Enes Tamdogan

Department of Mechanical Engineering,
Faculty of Engineering,
Ozyegin University,
Cekmekoy,
Istanbul 34794, Turkey
e-mail: enestamdogan@gmail.com

Mehmet Arik

Department of Mechanical Engineering,
Faculty of Engineering,
Ozyegin University,
Cekmekoy,
Istanbul 34794, Turkey
e-mail: mehmet.arik@ozyegin.edu.tr

1Corresponding author.

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received October 11, 2014; final manuscript received August 28, 2015; published online October 15, 2015. Assoc. Editor: Shi-Wei Ricky Lee.

J. Electron. Packag 137(4), 041006 (Oct 15, 2015) (8 pages) Paper No: EP-14-1089; doi: 10.1115/1.4031480 History: Received October 11, 2014; Revised August 28, 2015

Electronics driven at high currents may experience local hot spots, which may cause thermal degradation or even catastrophic failures. This common problem occurs at light-emitting diode (LED) chips and it is not easily observed by end-users. Driving over 700 mA over a 1 mm2 chip is expected to generate local temperature gradients. In addition, bonding failures at manufacturing or during operation (cracks, delamination, etc.) may also lead to local hot spots. Therefore, possible hot spots over an LED chip have turned attention to direct cooling with dielectric liquids comprises the current study. Computational and experimental studies have been performed to understand the impact of conduction and alternatively convection with various dielectric fluids to abate local hot spots in a multichip LED light engine. To capture the local temperature distributions over the LED light engine with a dome in the domain especially over the LED chip; first, computational models have been built with a commercial computational fluid dynamics (CFD) software. Later, attention has been turned into experimental validation by using a multichip high brightness LED (HB LED) light engine. An optothermal evaluation has been made at single and multiphase heat transfer modes with dielectric fluids (LS5252, HFE7000, and silicone oil, etc.) to compare with a series of CFD models and experimental studies. While multiphase liquid-cooled LED system has a better cooling performance but lower optical extraction, single-phase liquid-cooled LED system has shown a reasonable thermal performance with a 15% enhancement at light extraction.

Copyright © 2015 by ASME
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References

Figures

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Fig. 1

Schematic of CFD domain for the light engine with dome

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Fig. 2

Chosen grid for analysis (mesh 1)

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Fig. 3

Grid refinements through three different mesh structures and comparison of present CFD analysis with Mehmet et al. [14] experimental results

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Fig. 4

Thermal and optical experimental setup

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Fig. 5

Single- and multiphase natural convection experimental setup

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Fig. 6

Spectral fluxes for three test samples at various currents

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Fig. 7

Comparison of lumen extraction for various fluids

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Fig. 8

Computational comparison of thermal capability of air and silicone

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Fig. 9

Temperature distributions for air (left) and silicone (right) filled domes

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Fig. 10

Computational comparison of thermal capability of air and HFE7200

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Fig. 11

Computational comparison of thermal capability of air and FC72

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Fig. 12

Temperature contour plots for each liquids and also silicone in comparison to dome with air: (a) system with open and close dome, (b) dome filled with air and silicone, (c) dome filled with air and water, (d) dome filled with air and HFE7000, (e) dome filled with air and HFE7200, and (f) dome filled with air and FC72

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Fig. 13

Optical degradation with boiling

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Fig. 14

Light extraction enhancement by liquid

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Fig. 15

Effect of boiling over optical power

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Fig. 16

Temperature rise over ambient for different liquids at various driving conditions

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Fig. 17

Temperature rise over ambient for air, water, and NS15 at various driving conditions

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Fig. 18

Nu and Pr values for dielectric liquids with NS fluids

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Fig. 19

Nu and Gr values for dielectric liquids with NS15

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