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Research Papers: Micro/Nanoscale Heat Transfer

Nanocapillarity in Graphene Oxide Laminate and Its Effect on Critical Heat Flux

[+] Author and Article Information
Ji Min Kim

Division of Advanced Nuclear Engineering,
POSTECH,
San 31, Hyoja-dong, Nam-gu,
Pohang 37673, Kyungbuk, South Korea
e-mail: erskarin@postech.ac.kr

Ji Hoon Kim

Department of Mechanical Engineering,
Incheon National University,
Songdo 1(il)-dong, Yeonsu-gu,
Incheon 22012, South Korea
e-mail: Kimjiihoon123@inu.ac.kr

Moo Hwan Kim

Division of Advanced Nuclear Engineering,
POSTECH,
San 31, Hyoja-dong, Nam-gu,
Pohang 37673, Kyungbuk, South Korea
e-mail: mhkim@postech.ac.kr

Massoud Kaviany

Department of Mechanical Engineering,
University of Michigan,
Ann Arbor, MI 48109
e-mail: kaviany@umich.edu

Ho Seon Ahn

Department of Mechanical Engineering,
Incheon National University,
Songdo 1(il)-dong, Yeonsu-gu,
Incheon 22012, South Korea
e-mail: hsahn@inu.ac.kr

1Corresponding author.

Manuscript received August 19, 2016; final manuscript received March 9, 2017; published online April 25, 2017. Assoc. Editor: Ronggui Yang.

J. Heat Transfer 139(8), 082402 (Apr 25, 2017) (9 pages) Paper No: HT-16-1525; doi: 10.1115/1.4036282 History: Received August 19, 2016; Revised March 09, 2017

The nanocapillarity phenomenon involves ultralow frictional flow of water molecules through nanoscale channels, and here we study this using exceptionally large number of nanochannels within graphene oxide (GO) laminates. The nanoconfined water molecules in GO nanochannels form square lattice (as in the ice bilayer), which melts and jumps across the channels, similar to slip flow, with mean speed of the order of 1 m/s. This ease of liquid spreading in GO laminate is used to delay the critical heat flux (CHF) phenomenon in water pool boiling, by preventing formation/growth of dry spots. The water nanocapillarity speed is derived based on the measured water penetration flux, and the CHF enhancement (up to 140%) is demonstrated on a 1-μm-thick GO laminate. The GO laminate offers efficient surface modifications for increased transport efficiency (and safety margin) of pool boiling heat transfer systems.

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References

Figures

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Fig. 4

Morphology of the GO laminate formed by boiling: (a) GO-coated surface (gray) after experiments, (b) atomic force microscopy (AFM) image of GO film and GO flakes (inset). Scanning electron microscopy (SEM) images of, (c) the top view of a region damaged by critical heat flux (CHF), and (d) its cross section, providing evidence that GO has a well-aligned laminate structure.

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Fig. 3

(a) Pool-boiling experimental apparatus, (b) image of nucleate boiling on the main heater, (c) upper side, and (d) underside view of the main heater, showing the mirror-polished silicon plate with a platinum film heater on its underside

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Fig. 2

(a) Schematic diagram of the water penetration experiment with vacuum suction and (b) thickness of GO laminate versus area density of GO (inset) an image of a GO laminate film on a membrane filter

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Fig. 1

(a) Graphene oxide (GO) colloids showed a transparent brown color, (b) GO flakes showed a two-dimensional (2D) monolayer structure in transmission electron microscopy (TEM) images, where the hexagonal sp2 bonding structure of carbon atoms was damaged in the chemical oxidation process, as seen in, and (c) the selected area electron diffraction (SAED) image

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Fig. 6

CHF as a function of the thickness of the GO laminate and its prediction by nanocapillarity using Eq. (6). (Inset) schematic diagram of nanocapillary inflow into a dry-out zone during bubble growth on the GO laminate.

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Fig. 5

Boiling curve; case of 1 mg/L, 5 mg/L, and 10 mg/L [13]

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Fig. 7

Effect of a GO laminate film on CHF enhancement: high-speed visualization images of boiling under near-CHF conditions using de-ionized (DI) water on (a) a bare surface (700 kW/m2) and (b) the prepared GO laminate (1200 kW/m2), indicating that it could delay CHF, despite a higher area of vapor stems. Schematic diagram of nanocapillary inflow via the GO laminate underneath the mushroom, (c) top view, (d) side view in a unit cell, and (e) evaporation on top of the GO laminate. (See figure online for color.)

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Fig. 8

Plot of the measured X-ray diffraction (XRD) pattern of the GO laminate by boiling and by filtration

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Fig. 9

Water penetration flux according to thickness of the GO laminate and evaluation of the nanocapillary speed of water molecules. (Inset graph) nanocapillary speed according to depth of the GO laminate. (Inset schematics) the water molecules should penetrate the longer (shorter) effective nanochannels to reach the boiling surface according to the depth of the GO laminate film, as indicated by the lower (upper) line, which causes as reduction in their speed.

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Fig. 10

Comparison of liquid inflow to evaluate the equivalent thickness of a GO laminate on wire heater geometry: (a) a wire heater and (b) a plate heater (arrow inside bubble: liquid evaporation, arrow outside bubble: liquid supply)

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