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Research Papers: Heat and Mass Transfer

Study of Microstructure-Based Effective Thermal Conductivity of Graphite Foam

[+] Author and Article Information
Y. Chai, X. H. Yang, Z. Y. Chen, X. Z. Meng

School of Human Settlement
and Civil Engineering,
Xi'an Jiaotong University,
Xi'an 710049, China

M. Zhao

School of Human Settlement
and Civil Engineering,
Xi'an Jiaotong University,
Xi'an 710049, China;
China Northwest Architecture Design and
Research Institute Co. Ltd.,
Xi'an 710018, China

L. W. Jin

School of Human Settlement
and Civil Engineering,
Xi'an Jiaotong University,
Xi'an 710049, China
e-mail: lwjin@mail.xjtu.edu.cn

Q. L. Zhang

School of Environment and Energy
Engineering,
Beijing University of Civil Engineering
and Architecture,
Beijing 100044, China

W. J. Hu

School of Environment and Energy Engineering,
Beijing University of Civil Engineering
and Architecture,
Beijing 100044, China

1Corresponding author.

Presented at the 2016 ASME 5th Micro/Nanoscale Heat & Mass Transfer International Conference. Paper Number MNHMT2016-6721. Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received June 19, 2016; final manuscript received February 3, 2017; published online March 7, 2017. Assoc. Editor: Zhuomin Zhang.

J. Heat Transfer 139(5), 052004 (Mar 07, 2017) (9 pages) Paper No: HT-16-1403; doi: 10.1115/1.4036002 History: Received June 19, 2016; Revised February 03, 2017

As a relatively new type of functional material, porous graphite foam exhibits unique thermophysical properties. It possesses the advantages of low density, high specific surface area, and high bulk thermal conductivity and could be used as the core component of compact, lightweight, and efficient heat exchangers. Effective thermal conductivity serves one of the key thermophysical properties of foam-based heat exchangers. The complex three-dimensional topology and interstitial fluids significantly affect the heat conduction in the porous structure, reflecting a topologically based effective thermal conductivity. This paper presents a novel geometric model for representing the microstructure of graphite foams with simplifications and modifications made on the realistic pore structure, where the complex surfaces and tortuous ligaments were converted into a simplified geometry with cylindrical ligaments connected between cuboid nodes. The multiple-layer method was used to divide the proposed geometry into solvable areas, and the series–parallel relation was used to derive the analytical model for the effective thermal conductivity. To explore heat conduction mechanisms at the pore scale, direct numerical simulation was also conducted on the realistic geometric model. Achieving good agreement with experimental data, the simplified geometric model was validated. The numerically simulated conductivity followed the simplified model prediction that the two geometries are equivalent from thermal aspect. It validates further that the simplified model is capable of reflecting the internal microstructure of graphite foam, which would benefit the understandings of the thermophysical mechanisms of pore-scaled heat conduction and microstructures of graphite foam.

Copyright © 2017 by ASME
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References

Figures

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Fig. 1

Electron micrograph of porous graphite foam

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Fig. 2

(a) Face-centered cubic model and (b) body-centered cubic model

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Fig. 4

(a) Parallel resistance model and (b) series resistance model

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Fig. 5

Chipping unit cell model

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Fig. 6

(a) Graphite foam pore structure under SEM and (b) proposed model

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Fig. 7

Simplified unit cell model

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Fig. 8

Simplification process between two models

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Fig. 9

One eighth representative section

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Fig. 10

Region division of each layer

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Fig. 11

Six regions in y direction

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Fig. 12

Numerical models with different porosities of (a) solid phase, (b) fluid phase, and (c) assembled model of graphite foam

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Fig. 13

(a) Representative mesh and (b) thermal boundary condition

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Fig. 14

Heat flux distribution on the top face of (a) solid phase and (b) fluid phase of graphite foam

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Fig. 15

Temperature distribution within (a) the solid phase and (b) the fluid phase of graphite foam

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Fig. 16

Variation of interior surface area to volume ratio with the porosity

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Fig. 17

Variations of the effective thermal conductivity with the porosity

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