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Carbon foam is known for its excellent insulation properties and is also regarded as an effective shock absorbing material. In the present work, a numerical parametric study has been performed to investigate and predict the merits of using carbon foam as an alternative material for firefighter garment and helmet. We considered open-cell non graphitic carbon foam because of its high porosity, better mechanical strength, and lower thermal conductivity. It absorbs impact-shocks efficiently and also provides adequate thermal insulation.In the present study, numerical simulations of flame test and impact test as designed by the National Fire Protection Association (NFPA) are performed on firefighter garment and helmet. In reference to the work done by Elgafy and Mishra [1], for the flame test on the garment, carbon foams with different thermal conductivity, porosity, and density are introduced to conduct a parametric study. Additionally, the thickness of the introduced carbon foam fabrics is varied to acquire optimum design [1]. Simulation is conducted for a square planar 2D geometry of the clothing consisting of different fabric layer and a transient double-precision pressure-based implicit solver is used. The new anticipated thermal protection system is tested under the harsh thermal environmental conditions to which firefighters are generally exposed. The parametric study [1] shows that employing carbon foam fabric with one set of designed parameters leads to weight reduction of 33% and 56% in the outer shell and the thermal liner respectively and a temperature reduction of 2% at the inner edge of the garment as compared to the traditional firefighter garment model used by Song et al. [2]. Carbon foam fabric with another set of designed parameters results in a weight reduction of 25% and 28% in the outer shell and thermal liner respectively and a temperature reduction of 6% at the inner edge of the garment [1]. Thus, carbon foam fabrics are seen to make the firefighter's garment thermally more protective and lighter in weight [1].Next, impact test simulation is conducted for a 3D hemispherical helmet model firmly seated on an aluminum headform. Parameters, such as porosity and density of carbon foam and thickness of the helmet, are varied to check their effects on the overall performance of the carbon-foam helmet. Crushable foam model of abaqus CAE software is used to define the carbon foams, and a dynamic explicit solver is used for the computation. The results of the simulation exhibit adequate impact resistance for the carbon-foam helmet. In addition, net helmet weight reduction of 56-61 % was achieved as compared to the currently used modern firefighter helmet. Finally, a flame test was conducted over the carbon-foam helmet thickness using a method similar to that used for the firefighter garment. Temperature is observed to drop along the thickness of the carbon-foam helmet, and reaches near-ambient temperature at the inner edge of the helmet.

The goal of this study is to evaluate thermally conductive graphite foams for use in thermal energy storage (TES) devices. A phase change material (PCM) can absorb heat during melting and release it during solidification. Most PCM have very low thermal conductivity values, which leads to slow melting rates. Therefore, a thermally conductive enhancer (TCE) is needed to melt the PCM at a faster rate. Graphite foams can be used as a TCE due to their high overall surface area, relatively low weight, and their ability to be manufactured with high thermal conductivity. This thesis examines the melt behavior of the PCM when infiltrated into graphite foam.The heat exchanger coupon used in this study is made of two blocks of foam separated by a parting plate. Two different materials are investigated as the parting plate: stainless steel and aluminum. Two different methods of bonding the foam to the parting plate are evaluated; they are bonding by epoxy, and a brazing method. The melting time of the PCM with different bonding methods are compared to the case when the foam coupons are not bonded to the parting plate. The experimental results indicate that the heat transfer rate is significantly influenced by the bonding method as well the thermal mass associated with the bonding material.

Multi-scale hierarchical carbon structures have been developed by growing strongly attached carbon nanotubes (CNT) on high surface area substrates having open, interconnected porosity. This investigation was developed on cellular carbon foams but the process is equally suitable for other geometries including flat, fibers, and other porous substrates (interconnected). It is also adaptable to other substrate materials such as metals, alloys or ceramic compounds. Multiwalled carbon nanotubes are grown using a floating catalyst chemical vapor deposition (CVD) method after pre-coating the substrate with a silica nano-layer. The silica-coated graphitic substrates are seen to grow 280 times more nanotubes per unit area compared to bare graphite. Detailed spectroscopic and microscopic studies indicate that this significant improvement can be attributed to improved adhesion and distribution of the iron catalysts and enhanced catalytic activity from substrate interactions. Failure analysis of the nanotube layer under several types of loading demonstrates strong adhesion between CNT and substrate, with failure occurring in the underlying substrate. Attachment of carbon nanotubes can result in more than two orders of magnitude increase in specific surface area as independently confirmed by modeling the microstructure and direct surface area measurement using Brunauer-Emmett-Teller (BET) technique. These hierarchical materials are tested as encapsulation structures for phase change materials (PCM). The CNT can act as nanofin radiators enhancing energy exchange between the thermally conductive encapsulation and the PCM, hence improving thermal response time. A heat cell was designed to compare the response times of foam encapsulation with and without CNT. Encapsulation with CNT is found to have and significantly faster thermal response. DSC measurements demonstrate that CNT/foam hierarchical encapsulation provides 15% higher storage of latent heat. The improvements in thermal responsiveness and storage capacity from CNT/foam encapsulation provide 150% higher specific power (W/g) while transferring the heat into the paraffin wax when compared to the foam without CNT.

Highly conductive graphitic foams are currently being studied for use as thermal conductivity enhancers (TCEs) in thermal energy storage (TES) systems. TES systems store energy using the latent heat capacity of phase change materials (PCMs). Due to the low thermal conductivity of most PCMs, TCEs are necessary to evenly distribute heat throughout the PCM. Graphitic foams have been used as TCEs due to their high thermal conductivity, high specific surface area, and low weight. This thesis describes the experimental research at Ohio University to determine the thermal conductivity and transient thermal response characteristics of foams infiltrated with PCMs. Methods have been developed to modify highly conductive open celled graphitic foam by filling them with epoxy. This allowed the testing of graphitic foams using classical experimental thermal measurement methods. Thermal conductivity of foams tested ranged from 12 W/mK to 135 W/mK. It was found that graphitic foams can increase the thermal diffusivity of PCMs by a factor of 400+. This leads to thermal responses 9 times lower when graphitic foams are used as TCEs.

A thermal energy storage device that uses pentaglycerine as a phase change material was developed. This solid-state phase change material was embedded in a carbon foam thermal conduction enhancer. This device and others identically constructed but using a paraffin phase change material were tested by imposing different input fluxes, 2.3 or 6.0 W/cm2 on one end, while the opposite end was either insulated or actively cooled with an output flux that varied from 3.1 to 5.4 W/cm2. The resulting temperature distributions within the devices were recorded at five locations; this information was used to determine the specific energy storage capacity, heating rate and the cycling performance of each device. It was found that the pentaglycerine/foam combination is capable of a specific storage capacity of 67 J/g; it demonstrated a storage capacity 174% of the paraffin/foam device, by eliminating the volume change and leakage problems associated with solid-liquid phase change materials.

The need for advanced thermal management materials is well recognized in the electronics and communication industries. An overall reduction in size of electronic components has lead to higher power dissipation and increased the necessity for innovative cooling designs. In response, material suppliers have developed and are continuing to develop, an increasing number of light weight thermal management materials. The new carbon foam is a low density and high thermal conductivity material which has the potential to radically improve heat transfer, thereby reducing size and weight of equipment while simultaneously increasing its efficiency and capabilities. However, carbon foam exhibits low strength and low heat capacity. The present work is intended to overcome these two main drawbacks using a combinatorial approach: (i) initially, copper coating was carried out to improve the thermo-mechanical properties of carbon foam. The thermal and mechanical properties of coated foam were measured using laser flash technique and compression test, respectively. An analytical model was developed to calculate the effective thermal conductivity. It was observed that the copper-coated carbon foam with 50% porosity can attain a thermal conductivity of 180 W/mK. The results from the analytical model were in a very good agreement with experimental results. The modulus increased from 4.5 MPa to 8.6 MPa and the plateau stress increased from 54 kPa to 171 kPa. The relationships between the measured properties and the copper weight ratio were determined. The above analyses demonstrated the significance of copper coating in tailoring carbon foam properties. (ii) Numerical and experimental studies were performed to analyze the phase change behavior of wax/foam composite encapsulated in metal casing. A two-energy equation model was solved using computational fluid dynamics software (CFD). Interfacial effects at the casing-composite junction and between the wax-foam surfaces and the capillary pressure within the foam matrix were investigated. These factors lowered the heat transfer rate considerably and the melting area was reduced by more than 23%. Two samples, coated and uncoated carbon foam, were infiltrated with PCM and subjected to a uniform heat load test in a vacuum. The coated foam showed excellent performance compared to the uncoated foam. (iii) Finally, the new engineered carbon foam was used as a heat sink and heat exchanger in a thermoelectric cooler for a cooling vest application. Using carbon foam as the core material for this application, the effective transfer of heat was significantly increased while reducing the size and weight of the heat exchanger.

Carbon foams are porous materials which are attractive for many engineering applications because their thermal and mechanical properties can be customized by varying manufacturing process parameters. However, a highly random geometry at pore level makes it very difficult to analyze the properties and the behavior of this material in an application. Published research work on the analysis of foams has employed various ideal geometries to approximate the pore microstructure. However, these models are unable to predict accurately the foam properties and behavior in engineering applications.The objective of this research work is to determine thermal and mechanical properties of carbon foam on the basis of its true microstructure. A new approach is proposed by creating a three dimensional (3D) solid model based on an accurate representation of the real geometry of carbon foam. Finite element models are then developed to investigate the bulk thermal and mechanical properties of carbon foam using the three dimensional solid model. On the basis of the true 3D model of carbon foam, a study is undertaken to examine the effect of the unique microstructure on the flow field within the foam pores and the resultant convective heat transfer. A finite volume model is developed using the accurate representation of carbon foam microstructure inside a flow channel. The fluid flow and heat transfer is simulated to evaluate pressure drop and heat transfer capabilities. The carbon foam permeability, inertial coefficient and friction coefficient are determined and found to be in good agreement with experimental and semi-empirical models. The results also show a large enhancement in the heat transfer due to the presence of carbon foam in the channel. These results are comparable to the experimental results available in published literature.Another application that has been analyzed in this study is the use of carbon foam as tooling material for manufacturing advanced composite materials. Finite element simulations are carried out to predict the process induced residual stresses and deformations when a composite part is manufactured on conventional tooling versus carbon foam tooling. The results show that both the lower coefficient of thermal expansion and the elastic modulus of carbon foam contribute to the reduction of residual stress and deformation of the composite part.

Carbon foam has many applications in the fields of thermal management, net-shape composites and electronic cooling due to its porous structure, low density, electrical and thermal conductivities. However it is prone to oxidation at high temperatures in air. Whereas some previous studies have reported oxidation protective coatings on other carbon structures such as graphite parts and fibers, there is very limited work on foam. Moreover, earlier methods have used vapor phase techniques such as Plasma Vapor Deposition (PVD) and Chemical Vapor Deposition (CVD). There is no known study involving such coatings using simple scalable liquid phase method. This thesis reports our results on such coatings obtained on carbon foam. Boron Nitride was chosen as the coating material. Several solvents and processes were investigated. Finally a two step process using PVP binder in alcohol-based solution is found to be most effective. Unlike other available methods this technique does not involve toxic precursors or by-products. This method is simple and can be obtained at atmospheric pressure. Different coating combinations using various particle sizes were applied and their surface morphologies were studied using SEM (Scanning Electron Microscopy) and FESEM (Field Emission Scanning Electron Spectroscopy). It was observed that coating formed using 1µ BN followed by 0.7µ size BN particles has the best performance so far. The surface chemistry of this coating was studied using X-ray Photo Spectroscopy (XPS) and found to be that of pure BN after heat treatment. This coating was tested on several grades of aerospace foams having different porosities and cell sizes. The testing shows that this layer enhances the oxidation resistance of all foams to a certain extent. However it is most effective on the foams that have ridged ligaments compared to those having smooth ligaments. On carbon foams having high surface roughness this layer could suppress oxidation even at 800 C and enhance the survivability by 333%. This coating approach therefore shows promise as a scalable, environmentally friendly way of inhibiting oxidation in porous carbon structures.

Pulikollu, Rajasekhar Venkata. Ph.D., Department of Mechanical and Materials Engineering, Wright State University, 2005. Nano-coatings on Carbon Structures for Interfacial Modification. Surface modification of materials is a rapidly growing field as structures become smaller, more integrated and complex. It opens up the possibility of combining the optimum bulk properties of a material with optimized surface properties such as enhanced bonding, corrosion resistance, reactivity, stress transfer, and thermal, optical or electrical behavior. Therefore, surface functionalization or modification can be an enabling step in a wide variety of modern applications. In this dissertation several surface modification approaches on carbon foam and carbon nano-fibers will be discussed. These are recently developed sp 2 graphitic carbon based structures that have significant potential in aerospace, automotive and thermal applications. Influence of surface modification on composite formation and properties have also been investigated. Two types of property changes have been investigated: one for enhancing the surface reactivity and another for surface inertness. Characterization techniques such as X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM), Contact Angle Measurement, Scanning Electron Microscope (SEM), Transmission Electron Microscope(TEM), and mechanical testing are used in this study to find out the influence of these coatings on surface composition, chemistry, and morphology. Mechanical testing has been performed on composites and stand-alone foam to study the influence of surface modification on physical and mechanical properties of the composite materials. The effectiveness of these coatings on metallic/graphite interface has also been investigated for metal-matrix composite related applications. Additionally, the influence of plasmacoatings on nucleation and growth of nanotubes on larger carbon structures (to produce multiscale, multifunctional materials) have also been studied. It is seen that the liquid phase activation treatment introduces oxygen functional groups on the surface, but may cause severe enough degradation that damages the ligaments and cell walls of carbon foam. This results in higher elastic modulus but lower strength. So, to get any benefit from such approaches the optimization window may be very narrow and marginal in controllability. An alternative solution would be to synthesize ultra thin film coatings without etching the surfaces. It is observed that plasma assisted coatings having thickness in the range of few nanometers (4-5nm) are completely covering the graphite substrates. The coating surface, chemistry, and morphology information is based upon XPS and AFM studies on pyrolytic graphite substrate. Two types of plasma surface modification techniques have been attempted: one is to make the surface more reactive for structural components and the other is to make the surface more inert for stand-alone structures. In order to achieve these goals, plasma assisted oxide and fluorocarbon coatings are studied in detail. The synthesized oxide and fluorocarbon coating chemistries are comparable to conventional silica (SiO2) and polytetrafluoroethylene (PTFE, –CF2-). It is seen that the fluorocarbon coatings provide moisture resistance to graphitic foam by making the surface inert at the nanometer scale. On the other hand, plasma assisted oxidecoating is a feasible and effective means of improving the wettability and dispersion of foam and nanofibers in organic polymer matrix material. Surface analysis as well as microstructural studies and mechanical tests have shown encouraging results. The interface reactions between graphite (coated and uncoated) and epoxy have also been studied in detail. Nano-scale plasma coatings have also been applied for metal matrix composites and semiconductor related applications. The fluorocarbon coating promotes delamination/exfoliation of the metal on graphite, hence may be used for patterning or lithography. Oxide coatings seem to enhance the adhesion and metallic diffusion between graphite and metal, hence can be used for the development of metalmatrix composites. Additionally, oxide coating seems to enhance the length and density of nanotubes synthesized on carbon structures, desired for the design of advanced nano-composites.