Model of Multiscale Transport in Carbon Foams

2003 ◽  
Author(s):  
C. Druma ◽  
M. K. Alam ◽  
A. M. Druma
Keyword(s):  
Thermal Conductivity ◽  
Numerical Models ◽  
Carbon Foam ◽  
Compact Heat Exchanger ◽  
High Concentration ◽  
Element Analysis ◽  
Bulk Properties ◽  
Heat Spreaders ◽  
Carbon Foams ◽  
Different Shapes

A number of carbon foam products are being developed for use as insulation, heat spreaders, and compact heat exchanger cores. Such foams have voids that are typically of the order 100 microns, and pore walls are about 10 microns. Within the walls of the pores, the graphene planes are arranged anisotropically so that the thermal transport is highly dependent on the orientation of the bulk foam. This results in bulk conductivities that range from 1 W/mK to 200 W/mK. The bulk properties of such a porous medium are difficult to determine analytically, particularly for the case of high concentration of non-spherical pores, or when the porous material is anisotropic or non-homogeneous. A finite element analysis has been developed to calculate the bulk thermal conductivity of carbon foams containing micropores of different shapes. The effective thermal conductivity is then evaluated by comparing the results of the analytical and numerical models.

Numerical Analysis of Conduction in a Foam

2002 ◽  
Author(s):  
A. M. Druma ◽  
M. K. Alam ◽  
C. Druma
Keyword(s):  
Thermal Conductivity ◽  
Porous Medium ◽  
Numerical Models ◽  
High Porosity ◽  
Material Microstructure ◽  
Element Analysis ◽  
Empirical Parameter ◽  
Bulk Properties ◽  
Heat Spreaders ◽  
Homogeneous Models

Porous organic materials are being developed for use as insulation, heat spreaders, and compact heat exchanger cores. The bulk properties of such a porous medium are difficult to determine analytically, particularly for the case of high porosity or when the porous material is not isotropic or homogeneous. Models that predict thermal conductivity of foams often use an empirical parameter to account for the effect of pore shape and material microstructure on the conduction process. A finite element analysis has been developed to calculate the thermal conductivity of a porous medium containing micropores. The effective thermal conductivity and the empirical conduction parameter are evaluated by comparing the results of the analytical and numerical models.

Measurement of Thermal Conductivity of Carbon Foams

2003 ◽  
Author(s):  
M. K. Alam ◽  
A. M. Druma
Keyword(s):  
Thermal Conductivity ◽  
Carbon Foam ◽  
Lower Strength ◽  
Aerospace Applications ◽  
Wide Range ◽  
Heat Spreaders ◽  
Carbon Foams ◽  
Interface Contact ◽  
Flash Diffusivity ◽  
Graphitic Foam

A number of carbon foam products are being developed for use as insulation, heat spreaders, and compact heat exchanger cores. The application of carbon foams in aerospace applications is advantageous due to the high thermal conductivity and low density of the graphitic foam. However, the measurement of thermal conductivity has been difficult due the problems of interface contact and lower strength of the foam. The flash diffusivity method has been used to find thermal conductivity of a wide range of materials. Because of the porous nature of the foam, errors may be introduced with the flash diffusivity method. An analytical and experimental study has been carried out to determine the validity of the flash diffusivity method for foam specimen.

Mechanical Properties of Microscale Graphitic Carbon Foam Ligaments and Nodes

2009 ◽  
Author(s):  
S. Ganguli ◽  
A. K. Roy ◽  
R. Wheeler
Keyword(s):  
Thermal Conductivity ◽  
Thermal Management ◽  
Thermal Protection ◽  
Solid Phase ◽  
Coefficient Of Thermal Expansion ◽  
Carbon Foam ◽  
High Thermal Conductivity ◽  
Uniform Size ◽  
Open Cell ◽  
Carbon Foams

Carbon foam is recognized as having the greatest potential to replacement for metal fins in thermal management systems such as heat exchangers, space radiators, and thermal protection systems [1–5]. Carbon foam refers to a broad class of materials that include reticulated glassy, carbon and graphitic foams that are generally open-cell or mostly open-cell. They can be tailored to have low or high thermal conductivity with a low coefficient of thermal expansion and density. These foams have high modulus but low compression and tensile strength. Among the carbon foams, the graphitic foam offers superior thermal management properties such as high thermal conductivity. Graphitic foams are made of a network of spheroidal shell segments. Each cell has thin, stretched ligaments in the walls that are joined at the nodes or junctions. The parallel arrangement of graphene planes in the ligaments confers highly anisotropic properties to the walls of the graphitic foams. The graphene planes tend to be oriented with the plane of the ligaments but become disrupted at the junctions (nodes) of the walls. Since conduction is highest along parallel graphene planes, the thermal conductivity is highest in the plane of the ligaments or struts, and much lower in the direction transverse to the plane of these ligaments. In a previous study [6] extensive mechanical and thermal property characterization of carbon foams from Kopper Inc. (L1) and POCO Graphite, Inc. (P1) were reported. These foams were graphitic ones that are expected to have high thermal conductivity. Figure 1 shows sections of light microscopy images of the three foams of four foams. The most important thing to notice is that the images were not at the same magnification. The large cells in the GrafTech foam have an average diameter of only ∼100 μm but have a bimodal distribution cells with many small closed-cells few micrometers in diameter. Changes in density in the GrafTech foam was accompanied by a change in the large cells’ diameter — larger diameter giving greater porosity and lower density without changing the smaller cells’ sizes that filled the solid phase between the larger bubbles. The POCO foam has a fairly uniform size cell distribution of a few hundred micrometers. The Koppers’ foams show larger cells yet with the left (“L” precursor) having a uniform size while the right-hand (“D” precursor) is a less uniform and lower porosity.

Study of Miniaturization of a Silicon Vapor Chamber for Compact 3D Microelectronics, via a Hybrid Analytical and Finite Element Method

2019 ◽  
Vol 6 (5) ◽  
pp. 01-18
Author(s):  
Ma Yue ◽  
Shirazy Mahmoud ◽  
Coudrain Perceval ◽  
Colonna Jean-Phulippe ◽  
Souifi Abdelkader ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Numerical Models ◽  
Computational Cost ◽  
Vapor Chamber ◽  
Cooling Systems ◽  
Heat Spreaders ◽  
Operating Limits ◽  
Silicon Vapor ◽  
Core Height ◽  
Low Computational Cost

The interest in silicon vapor chambers (SVCs) has increased in the recent years as they have been identified as efficient cooling systems for microelectronics. They present the advantage of higher thermal conductivity and smaller form factor compared to conventional heat spreaders. This work aims to investigate the potential miniaturization of these devices, preliminary to integration on the backside of mobile device chips, located as close as possible to hotspots. While detailed numerical models of vapor chamber operation are developed, an easy modeling with low computational cost is needed for an effective parametric study.  Based on the study of the operating limits, this paper shows the thinning potential of a water filled micropillar for a device operating below 10 W and identify the corresponding vapour core height, and wick thickness.

scholarly journals Study of Miniaturization of a Silicon Vapor Chamber for Compact 3D Microelectronics, via a Hybrid Analytical and Finite Element Method

2019 ◽  
Vol 7 (6) ◽  
pp. 1-16
Author(s):  
Yue MA ◽  
M. R. S. Shirazy ◽  
Q. Struss ◽  
P. Coudrain ◽  
J.P. Colonna ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Numerical Models ◽  
Computational Cost ◽  
Vapor Chamber ◽  
Cooling Systems ◽  
Heat Spreaders ◽  
Operating Limits ◽  
Silicon Vapor ◽  
Core Height ◽  
Low Computational Cost

The interest in silicon vapor chambers (SVCs) has increased in the recent years as they have been identified as efficient cooling systems for microelectronics. They present the advantage of higher thermal conductivity and smaller form factor compared to conventional heat spreaders. This work aims to investigate the potential miniaturization of these devices, preliminary to integration on the backside of mobile device chips, located as close as possible to hotspots. While detailed numerical models of vapor chamber operation are developed, an easy modeling with low computational cost is needed for an effective parametric study.  Based on the study of the operating limits, this paper shows the thinning potential of a water filled micropillar for a device operating below 10 W and identify the corresponding vapour core height, and wick thickness.

Fabrication and properties of carbon/carbon-carbon foam composites

2019 ◽  
Vol 89 (21-22) ◽  
pp. 4452-4460
Author(s):  
Bin Wang ◽  
Bugao Xu ◽  
Hejun Li
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
Thermal Insulation ◽  
Bonding Strength ◽  
Carbon Foam ◽  
Shear Load ◽  
Foam Composite ◽  
Final Failure ◽  
Carbon Foams ◽  
Insulation Performance

This paper was focused on the development of a new composite for high thermal insulation applications with carbon/carbon (C/C) composites, carbon foams and an interlayer of phenolic-based carbon. The microstructure, mechanical properties, fracture mechanism and thermal insulation performance of the composite was investigated. The experiment results showed that the bonding strength of the C/C-carbon foam composite was 4.31 MPa, and that the fracture occurred and propagated near the interface of the carbon foam and the phenolic-based carbon interlayer due to the relatively weak bonding. The shear load-displacement curves were characterized by alternated linear slopes and serrated plateaus before a final failure. he experiment revealed that the thermal conductivity of the C/C-carbon foam composite was 1.55 W·m−1ċK−1 in 800℃, which was 95.8% lower than that of C/C composites, proving that the thermal insulation of the new foam composite was greatly enhanced by the carbon foam with its porous hollow microstructure.

scholarly journals Latent Heat Storage and Thermal Efficacy of Carboxymethyl Cellulose Carbon Foams Containing Ag, Al, Carbon Nanotubes, and Graphene in a Phase Change Material

Nanomaterials ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 158 ◽  
Author(s):  
Hong Kim ◽  
Yong-Sun Kim ◽  
Lee Kwac ◽  
Hee Shin ◽  
Sang Lee ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Carbon Nanotubes ◽  
Phase Change ◽  
Latent Heat ◽  
Carbon Foam ◽  
Phase Change Temperature ◽  
Carbon Foams ◽  
Change Temperature ◽  
Latent Heat Loss ◽  
Change Material

Carbon foam was prepared from carboxymethyl cellulose (CMC) and Ag, Al and carbon nanotubes (CNTs), and graphene was added to the foam individually, to investigate the enhancement effects on the thermal conductivity. In addition, we used the vacuum method to impregnate erythritol of the phase change material (PCM) into the carbon foam samples to maximize the latent heat and minimize the latent heat loss during thermal cycling. Carbon foams containing Ag (CF-Ag), Al (CF-Al), CNT (CF-CNT) and graphene (CF-G) showed higher thermal conductivity than the carbon foam without any nano thermal conducting materials (CF). From the variations in temperature with time, erythritol added to CF, CF-Ag, CF-Al, CF-CNT, and CF-G was observed to decrease the time required to reach the phase change temperature when compared with pure erythritol. Among them, erythritol added to CF-G had the fastest phase change temperature, and this was related to the fact that this material had the highest thermal conductivity of the carbon foams used in this study. According to differential scanning calorimetry (DSC) analyses, the materials in which erythritol was added (CF, CF-Ag, CF-Al, CF-CNT, and CF-G) showed lower latent heat values than pure erythritol, as a result of their supplementation with carbon foam. However, the latent heat loss of these supplemented materials was less than that of pure erythritol during thermal cycling tests because of capillary and surface tension forces.

Thermal Performance of Natural Graphite Heat Spreaders With Embedded Thermal Vias

2007 ◽  
Author(s):  
Martin Smalc ◽  
Prathib Skandakumaran ◽  
Julian Norley
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Thermal Performance ◽  
Numerical Models ◽  
Accelerated Aging ◽  
High Heat ◽  
High Heat Flux ◽  
Natural Graphite ◽  
Heat Spreaders ◽  
Graphite Heat

Natural graphite heat spreaders are in use in electronic cooling applications where heat flux density is low. Natural graphite is an anisotropic material, with a high thermal conductivity in the plane of the spreader combined with a much lower thermal conductivity through its thickness. This low through-thickness thermal conductivity poses a problem when attempting to cool heat sources with relatively high heat flux densities. This problem can be overcome by embedding a thermal via in the graphite material. This via is made from an isotropic material with a thermal conductivity significantly higher than the through-thickness graphite conductivity. This paper examines the thermal performance of a natural graphite heat spreader with an embedded thermal via. The work is primarily experimental although numerical models were used to guide the experiments. The thermal performance of these spreaders is compared to that of spreaders made from conventional isotropic materials. The effect of accelerated aging tests on the performance of these graphite spreaders is reviewed. Finally, two applications are examined; first cooling an ASIC module and second, cooling an FB-DIMM memory card.

scholarly journals Heat Transfer Interface to Graphitic Foam

2019 ◽  
Author(s):  
Fang-Ming Lin ◽  
Eric Anderssen ◽  
Raymond K. Yee
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Heat Dissipation ◽  
Critical Role ◽  
Carbon Foam ◽  
Thin Layers ◽  
Uniform Structure ◽  
Carbon Foams ◽  
Graphitic Foam

Abstract 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.

Finite Element Analysis of Carbon Foams With Randomly Distributed Spherical Pores

2005 ◽  
Author(s):  
Adriana Druma ◽  
Khairul Alam ◽  
Calin Druma
Keyword(s):  
Thermal Conductivity ◽  
Finite Element Analysis ◽  
Finite Element ◽  
Thermal Management ◽  
Thermomechanical Properties ◽  
Element Analysis ◽  
Cellular Foams ◽  
Thermal Management Of Electronics ◽  
Carbon Foams ◽  
Potential Applications

Carbon foams have potential applications in thermal management of electronics and aerospace industries due to their low density and high thermal conductivity. These foams have open or closed pores that are approximately spherical. This paper presents a finite element analysis of the thermomechanical properties of carbon foams with randomly distributed spherical pores. The results are presented in nondimensional form and compared with theoretical and finite element analysis values obtained for cellular foams. The effect of pore distribution on the effective thermal conductivity of foams is also presented.

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