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Research Papers: Evaporation, Boiling, and Condensation

Experimental Characterization of Capillary-Fed Carbon Nanotube Vapor Chamber Wicks

[+] Author and Article Information
Suresh V. Garimella

e-mail: sureshg@purdue.edu
School of Mechanical Engineering
and Birck Nanotechnology Center,
Purdue University,
585 Purdue Mall,
West Lafayette, IN 47907

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the Journal of Heat Transfer. Manuscript received August 9, 2011; final manuscript received August 29, 2012; published online December 26, 2012. Assoc. Editor: Bruce L. Drolen.

J. Heat Transfer 135(2), 021501 (Dec 26, 2012) (7 pages) Paper No: HT-11-1388; doi: 10.1115/1.4007680 History: Received August 09, 2011; Revised August 29, 2012

The thermal performance of passive vapor chamber heat spreaders can be improved by enhancing evaporation from the internal wick structure. A wick structure that integrates conventional copper screen mesh and carbon nanotubes (CNTs) is developed and characterized for increased heat transport capability and reduced thermal resistance. The high-permeability mesh provides for a low-resistance liquid flow path while the carbon nanotubes, with their high thermal conductivity and large surface area, help reduce conduction and phase-change resistances. The wicks are fabricated by sintering a copper mesh on a multilayer substrate consisting of copper and molybdenum. CNTs are grown on to this mesh and a submicron layer of copper is evaporated on to the CNTs to improve wettability with water and wicking. Samples grown under varying degrees of positive bias voltage and varying thicknesses of post-CNT-growth copper evaporation are fabricated to investigate the effect of surface morphology variations. The resultant boiling curves indicate that micro/nano-integrated wicks fabricated with higher positive bias voltages during CNT synthesis coupled with thicker copper coatings produce lower wick thermal resistances. Notably, heat fluxes at the heater surface of greater than 500 W/cm2 were supported without a critical heat flux condition being reached.

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Figures

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Fig. 1

Schematic diagram of a vapor chamber featuring a CNT array in the evaporator section

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Fig. 2

Photograph of a sample after (a) mesh sintering on substrate, (b) deposition of trilayer catalyst, (c) CNT growth in MPCVD system, and (d) post CNT growth coating with copper

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Fig. 3

SEM images at different magnifications of (a) mesh region and (b) central evaporation region of copper mesh/substrate integrated sample

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Fig. 4

(a) Test facility heater block, chamber, and sample assembly. (b) Copper heater block temperature measurement locations and nomenclature.

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Fig. 5

Schematic diagram of the sealed interface between the vertically aligned test sample and chamber wall

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Fig. 6

Steady-state thermal performance data for the set of copper-coated CNT samples presented as (a) boiling curves and (b) thermal resistance curves. The maximum heat flux test points shown do not correspond to observed dryout or critical heat flux conditions.

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Fig. 7

Plot of the minimum thermal resistance, Rmin, achieved along the boiling curve versus the approximate CNT density of each sample tested. The minimum occurs at a heat flux above 450 W/cm2 for all instances.

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Fig. 8

Post-testing image and representative sketch of test sample highlighting a distinct ring formed in the CNT evaporator region

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