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.

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.

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.

Thermographic Studies of Aerogel Composites

2020 ◽  
Vol 15 (2) ◽  
Author(s):  
K. Keerthi Sanghamitra ◽  
A. Yamini ◽  
A. Venu Vinod ◽  
Neha Hebalkar
Keyword(s):  
Thermal Conductivity ◽  
Silica Aerogel ◽  
Cold Water ◽  
High Porosity ◽  
Fiber Mats ◽  
Aerospace Applications ◽  
Thermal Insulating ◽  
Wide Range ◽  
Composite Form ◽  
Insulation Performance

AbstractAerogels are regarded as the superior thermal insulating materials for wide range of temperatures, from cryogenic insulation, cold water diving garments to high temperature applications and even to defense and aerospace applications. For most of such applications, the aerogels are used in composite form rather than monolithic form as aerogels are fragile in nature due to its high porosity of up to 98%. These composites constitute aerogel infiltrated fiber mats to give flexibility, on the other hand, compromises on the insulation performance due to reinforcing aerogel with fibers that have comparatively higher thermal conductivity than silica aerogel. To increase the efficiency, density of the fiber mat needs to be reduced to incorporate higher loading of silica aerogel. Many techniques are being used to study the insulation performance of these composites. This paper presents about the study of insulation performance of fibre mats with different aerogel content and composition using a well-known thermography technique. The morphological, compositional, thermal and physical studies of the fiber mats and its composites using FESEM, EDAX, BET, thermal conductivity etc., are discussed.

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.

Effect of SiC Whiskers on the Microstructure and Thermal Conductivity of Carbon Foam

2018 ◽  
Vol 917 ◽  
pp. 106-111 ◽  
Author(s):  
Sheng Jie Yu ◽  
Zhao Feng Chen ◽  
Yang Wang
Keyword(s):  
Thermal Conductivity ◽  
Random Distribution ◽  
Chemical Vapor ◽  
Carbon Foam ◽  
Laser Flash ◽  
Homogeneous Distribution ◽  
Silicon Carbide Whiskers ◽  
Sic Whiskers ◽  
Flash Diffusivity ◽  
Insulation Performance

This paper describes the modification of ultralight flexible carbon foam by chemical vapor deposition (CVD) of silicon carbide whiskers (SiCw). The effect of SiC whiskers on the microstructure and the thermal conductivity of carbon foam were investigated by scanning electron microscopy (SEM) and laser flash diffusivity method in a Netzsch LFA427. The results show that the macro-pores (~30 μm) of the carbon foam were divided by the random distribution of SiC whiskers. The diameter of SiC whiskers decreased with decreasing catalyst concentration which resulted in the improved microstructure with a smaller pore diameter (4~6 μm) and a more homogeneous distribution of the pores. The carbon foam reinforced by SiCw exhibits better insulation performance than the pristine carbon foam when the temperature exceeds 200°C.

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.

Preparation and Characterization of Resin-Derived Carbon Foams Containing Hollow Microspheres

2014 ◽  
Vol 941-944 ◽  
pp. 318-323 ◽  
Author(s):  
Bin Wang ◽  
He Jun Li ◽  
Yun Yu Li ◽  
Man Hong Hu ◽  
Jing Xian Xu ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Hollow Microsphere ◽  
Carbon Foam ◽  
Hollow Microspheres ◽  
Vitreous Carbon ◽  
Compressive Property ◽  
Fracture Characteristics ◽  
Compressive Fracture ◽  
Carbon Foams

Resin-derived carbon foams with closed hollow spherical structure were prepared from mixtures of hollow phenolic microspheres and phenolic resin, followed by curing and carbonization. The resultant carbon foam had a bulk density of 0.45 g·cm-3. Effects of hollow microsphere on the on the compressive property and thermal conductivity of carbon foams were investigated. The results revealed that the hollow microspheres played an important role in improving compressive fracture toughness and lowering the thermal conductivity of carbon foams. The compressive fracture characteristics of carbon foam exhibited gradient brittle fracture, and the compressive strength was 10.93 MPa. The thermal conductivity of the carbon foam was 0.907 W·m-1·K-1 at room temperature, which was lowered by 49.67 % in comparison with phenolic-based vitreous carbon.

TEM study of boron additions to cobalt aluminide

1988 ◽  
Vol 46 ◽  
pp. 546-547
Author(s):  
Gerald B. Feldewerth
Keyword(s):  
High Temperature ◽  
Turbine Engines ◽  
Major Drawback ◽  
University Of Missouri ◽  
Specific Strength ◽  
Aerospace Applications ◽  
Wide Range ◽  
Ordered Alloys ◽  
The University ◽  
Very High

In recent years an increasing emphasis has been placed on the study of high temperature intermetallic compounds for possible aerospace applications. One group of interest is the B2 aiuminides. This group of intermetaliics has a very high melting temperature, good high temperature, and excellent specific strength. These qualities make it a candidate for applications such as turbine engines. The B2 aiuminides exist over a wide range of compositions and also have a large solubility for third element substitutional additions, which may allow alloying additions to overcome their major drawback, their brittle nature.One B2 aluminide currently being studied is cobalt aluminide. Optical microscopy of CoAl alloys produced at the University of Missouri-Rolla showed a dramatic decrease in the grain size which affects the yield strength and flow stress of long range ordered alloys, and a change in the grain shape with the addition of 0.5 % boron.

OLIN C197

Alloy Digest ◽  
1999 ◽  
Vol 48 (1) ◽  
Keyword(s):  
Thermal Conductivity ◽  
Wear Resistance ◽  
Physical Properties ◽  
Tensile Properties ◽  
High Performance ◽  
Corrosion And Wear ◽  
Contact Forces ◽  
High Current ◽  
Lower Strength ◽  
Current Carrying Capability

Abstract Olin C197 is a second-generation high performance alloy developed by Olin Brass. It has a strength and bend formability similar to C194 (see Alloy Digest Cu-360, September 1978), but with 25% higher electrical and thermal conductivity. High conductivity allows C197 to replace brasses and bronzes in applications where high current-carrying capability is required. Also, the strength of C197 provides higher contact forces when substituted for many lower strength coppers. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion and wear resistance as well as forming and joining. Filing Code: CU-627. Producer or source: Olin Brass.

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