Theoretical study of the effective thermal conductivity of graphite foam based on a unit cell model

Leong, K.C.; Li, H.Y.

doi:10.1016/j.ijheatmasstransfer.2011.07.042

Cited by 37 publications

(10 citation statements)

References 20 publications

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“…Porosity is widely represented as the void ratio (ε), which is used to represent the volume fraction occupied by the voids (pore volume). The equation for representing ε is shown as follows [27]:…”

Section: Porositymentioning

confidence: 99%

“…Furthermore [27]. The unit cell model developed by Tee (shown in Figure 5.1) incorporated the anisotropic thermal conductivity of graphite layers [48].…”

Section: The Effective Thermal Resistance Of the Graphitic Foammentioning

confidence: 99%

“…A thermal and electrical resistance analogy is widely used to calculate effective thermal conductivity for different models. Furthermore, the unit cell (a tetrakaidecahedron) model is a popular method to analyze the relationship between the pore structure and the effective thermal conductivity[27]. Further discussion of the tetrakaidecahedron cell is covered in section 3.1.…”

mentioning

confidence: 99%

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Heat Transfer Interface to Graphitic Foam

Lin

Anderssen

Yee

2019

Volume 8: Heat Transfer and Thermal Engineering

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Thermal interface materials (TIMs) used for bonding components are important for creating a thermally conductive path which improves heat dissipation. Low density, porous carbon foams are commonly used for thermal management applications and devices. Their high surface area to volume ratio enables cooling more effectively via different heat transfer methods. Many studies have adopted different methods to analytically or computationally analyze the effective thermal conductivity of carbon foams. Others have studied the participation of TIMs used in composite materials. However, very few studies have analyzed the microscale effects in heat transfer of the interaction between TIM and carbon foams. The amount of contact between a carbon foam and a bonded surface has hardly been reported in the literature. In this study, the carbon foam is deposited with thin layers of graphene until reaching the desired foam density; this type of foam is known as the graphitic foam. Graphene’s highly anisotropic thermal properties result in high thermal conductivity in the planar direction but low in the normal direction. With these anisotropic thermal characteristics, the objective of this study is to determine the effect of TIM thickness on thermal conductivity of the graphitic foam. It was hypothesized that the direction which heat enters the graphitic foam and the size of the cross-sectional area normal to the heat flux direction would affect the overall effective thermal conductivity. As commonly known, a gap created between ligands (foam structure) and the bonded surface would likely reduce the overall effective thermal conductivity. At the gap, heat is transferred via the TIMs or the graphitic foam through conduction, depending on if a direct contact exists between the graphitic foam and the bonded surface. The filler types used for the TIMs are hypothesized to play a critical role in the heat portion transferred via the TIMs. The heat transfer in 2-D becomes extremely complicated while anisotropic materials (graphene coating) and isotropic materials (TIMs) interact. Furthermore, the non-uniform structure of the carbon foam introduces more complexity to the heat transfer at the interface. A computational model using ANSYS finite element program was developed in this study to help the analysis. The results demonstrate that the parameters at the interface can be optimized to improve the overall effective thermal conductivity of the interface.

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Section: Porositymentioning

confidence: 99%

“…Furthermore [27]. The unit cell model developed by Tee (shown in Figure 5.1) incorporated the anisotropic thermal conductivity of graphite layers [48].…”

Section: The Effective Thermal Resistance Of the Graphitic Foammentioning

confidence: 99%

mentioning

confidence: 99%

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Heat Transfer Interface to Graphitic Foam

Lin

Anderssen

Yee

2019

Volume 8: Heat Transfer and Thermal Engineering

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“…The CFD results were compared with experimental results obtained using a uniform microstructure, which yielded excellent agreement. Leong and Li [7] determined the effective thermal conductivity of a unit cell which may be described as the Boolean subtraction of eight spheres from a cubic shell, where the spheres are centered on the vertices of the cube. James et al [8] presented a novel approach for the generation of spherical-void phase (SVP) porous media wherein bubble diameters and interferences are chosen based on known probability distribution functions.…”

Section: Introductionmentioning

confidence: 99%

A new approach to digital generation of spherical void phase porous media microstructures

Dyck

Straatman

2015

International Journal of Heat and Mass Transfer

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a b s t r a c tThis work describes a novel approach for obtaining digital samples of porous media based on a statistical knowledge of the microstructure of interest. The present formulation introduces a contact law based on bubble physics that is capable of handling interferences among spherical primitives of different diameter placed in a representative elemental volume, while the volume is compressed to yield a target porosity. The result is a statistically accurate mathematical model of a permeable, spherical-void-phase porous material that has the added feature of being spatially periodic in all principal directions. To validate the approach, digital samples of spherical-void-phase carbon foam were generated and discretized for use in hydraulic and thermal Computational Fluid Dynamics simulations. Relevant transport properties were computed from the simulation results, and compared to similar data found in the literature.

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“…In fact, development of graphite foam [29,30] with nearly spherical interconnected pores provided even more oppor tunities for heat transfer enhancement in TES systems due to its high thermal conductivity [31,32]. Upon foaming and graphitization, the resulting graphite foams have low densities (ranging from 0.2 to 0.6 g/cnr), and high bulk thermal conductivities (from 40 to 150 W/m • K varied proportional to the density) which make them attractive for a variety of applications [29,30,33].…”

Section: Introductionmentioning

confidence: 99%

Solidification of Phase Change Materials Infiltrated in Porous Media in Presence of Voids

Sedeh

Khodadadi

2014

Journal of Heat Transfer

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Infiltration of phase change materials (PCM) into highly conductive porous structures effectively enhances the thermal conductivity and phase change (solidification and melt ing) characteristics of the resulting thermal energy storage (TES) composites. However, the infiltration process contributes to formation of voids as micron-size air bubbles within the pores of the porous structure. The presence of voids negatively affects the thermal and phase change performance of TES composites due to the thermophysical properties of air in comparison with PCM and porous structure. This paper investigates the effect of voids on solidification of PCM, infiltrated into the pores of graphite foam as a highly con ductive porous medium with interconnected pores. A combination of the volume-of-fluid (VOF) and enthalpy-porosity methods was employed for numerical investigation o f solid ification. The proposed method takes into account the variation of density with tempera ture during phase change and is able to predict the volume shrinkage (volume contraction) during the solidification of liquids. Furthermore, the presence of void and the temperature gradient along the liquid-gas interface (the interface between void and PCM) can trigger thermocapillary effects. Thus, Marangoni convection was included during the solidification process and its importance was elucidated by comparing the results among cases with and without thermocapillary effects. The results indicated that the presence of voids within the pores causes a noticeable increase in solidification time, with a sharper increase for cases without thermocapillary convection. For verification purposes, the amount of volume shrinkage during the solidification obtained from numer ical simulations was compared against the theoretical volume change due to the variation o f density for several liquids with contraction and expansion during the freezing process. The two sets of results exhibited good agreement.

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Theoretical study of the effective thermal conductivity of graphite foam based on a unit cell model

Cited by 37 publications

References 20 publications

Heat Transfer Interface to Graphitic Foam

Heat Transfer Interface to Graphitic Foam

A new approach to digital generation of spherical void phase porous media microstructures

Solidification of Phase Change Materials Infiltrated in Porous Media in Presence of Voids

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