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Research Papers

Hotspot Thermal Management With Flow Boiling of Refrigerant in Ultrasmall Microgaps

[+] Author and Article Information
Mohamed H. Nasr, Craig E. Green, Peter A. Kottke, Yogendra K. Joshi

George W. Woodruff School
of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332

Xuchen Zhang, Thomas E. Sarvey, Muhannad S. Bakir

School of Electrical and Computer Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332

Andrei G. Fedorov

George W. Woodruff School
of Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332
e-mail: AGF@gatech.edu

1Corresponding author.

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received August 12, 2016; final manuscript received November 30, 2016; published online January 5, 2017. Assoc. Editor: M. Baris Dogruoz.

J. Electron. Packag 139(1), 011006 (Jan 05, 2017) (8 pages) Paper No: EP-16-1097; doi: 10.1115/1.4035387 History: Received August 12, 2016; Revised November 30, 2016

As integration levels increase in next generation electronics, high power density devices become more susceptible to hotspot formation, which often imposes a thermal limitation on performance. Flow boiling of R134a in two microgap heat sink configurations was investigated as a solution for hotspot thermal management: a bare microgap and inline micro-pin fin populated microgap, both with 10 μm gap height, were tested in terms of their ability to dissipate heat fluxes approaching 5 kW/cm2 at the heat source. Additional parameters investigated include mass fluxes up to 3000 kg/m2 s at inlet pressures up to 1.5 MPa and exit qualities approaching unity. The microgap testbeds investigated consist of a silicon layer which is heated from the bottom using resistive heaters and capped with glass to enable visual observation of two-phase flow regimes. Wall temperature, device thermal resistance, and pressure drop results are presented and mapped to the dominant flow regimes that were observed in the microgap.

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Figures

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Fig. 1

Overview of bare microgap and pin fin microgap devices

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Fig. 2

Schematic of experimental system

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Fig. 3

Exploded view of test section and hermetic package. Flow visualization obtained from a top-down view of the microgap with microscope. Flow visualization was obtained from a top-down view of the microgap with microscope.

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Fig. 4

Vapor plume and liquid slug flow regime visualization in bare microgap device

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Fig. 5

Vapor plume and liquid slug flow regime visualization in pin fin microgap device

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Fig. 6

Wall temperature versus microgap wall heat flux for the bare microgap and pin fin microgap at (a) 2000 kg/m2 s and (b) 3000 kg/m2 s mapped into flow regimes described in Figs. 4 and5

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Fig. 7

Comparison of device thermal resistance versus heater heat flux between the bare microgap and pin devices at: (a) G = 1000 kg/m2 s, (b) G = 2000 kg/m2 s, and (c) G = 3000 kg/m2 s, mapped into flow regimes described in Figs. 4 and 5. The dashed arrows represent expected trends of thermal resistance trends beyond the tested heat fluxes showing that thermal resistance would continue to increase as the liquid film wetting the microgap surface dries out. Note that no liquid slugs were observed in the pin fin microgap at 3000 kg/m2 s.

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Fig. 8

Pressure drop versus heat flux (a) bare microgap device and (b) pin fin device at 820 kPa system pressure (downstream of microgap). Dashed lines indicate flow regime transitions. “VP” denotes vapor plume domain and “LS” denotes liquid slug domain.

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Fig. 9

Pumping power versus heater heat flux in the bare microgap and pin fin microgap at a mass flux of 3000 kg/m2 s in the vapor plume regime

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