Papers by Keyword: Thermal Conductivity (TC)

Abstract: Based on the nonequilibrium Molecular Dynamics method, interfacial thermal resistances of Si/3C-SiC/grphene composite films are investigated. The dependencies of interfacial thermal resistances of Si/3C-SiC and 3C-SiC/grphene on temperatures and the thickness of buffer layers are simulated separately. The results indicate that the interfacial thermal resistances of Si/3C-SiC and 3C-SiC/grphene increase with the increase of temperatures at the range of 100~700K, and converge to 3.4×10-9 Km²/W. In the Si/3C-SiC/grphene composite film, 3C-SiC connects Si substrate with grphene sheets. The results show the relationships between interfacial thermal resistances and the thickness are not prominent, and the maximum value of interfacial thermal resistance locates at 24×3.35 Å.

Abstract: Zinc and aluminum powders were used as foaming agents and organosilane was innovatively used as a modifier to synthesize a foamed geopolymer. The produced foamed geopolymer with enhanced compressive strength and low thermal conductivity is an ideal material for fire protection, sound absorption and thermal insulation. The low thermal conductivity was achieved by increasing the porosity in the foamed geopolymer and the enhanced compressive strength was realized by adding the modifier. The pore numbers in the foamed geopolymer were greatly increased by releasing the hydrogen gas, which was produced from the chemical reaction of zinc and aluminum powders in a base solution. The modifier decreased the foaming reaction rate and generated homogeneously-distributed small pores in the foamed geopolymer with improved compressive strength.

Abstract: Si/Al composites with different Si particle sizes were fabricated using spark plasma sintering process for electronic packaging. The density, thermal conductivity, coefficient of thermal expansion and flexural strength of the composites were investigated. Effect of Si particle size on structure and properties of the Si/Al composites were studied. The results showed that the Si/Al composites synthesized by spark plasma sintering were composed of Si and Al. Al was uniformly distributed among the Si phase, leading to a high thermal conductivity (>120 W/m·k). The relative density of the Si/Al composites decreased with increasing Si particle size. Small Si particle size produced small grains, leading to a low coefficient of thermal expansion and a high strength. There is an optimal matching among the thermal conductivity, coefficient of thermal expansion and flexural strength when the Si particle size was 44 um.

Abstract: A new type of insulation wall is developed based on waste foam glasses. Performance tests small particle size (1~10mm) foam glass block with mass ratio of 30%~50% shows that the coefficient of thermal conductivity and compressive strength of insulation block are blow 0.2w/(m.K) and above 3.10MPa, respectively. This indicates a well insulation performance and mechanical property however the density and strength are not good enough. If the large particle size (20~65mm) are used with the mass ratio of 50~80%, the density can be lower than 400kg/m³ and the coefficient of thermal conductivity and compressive strength of insulation block are 0.2w/(m.K) and 0.5MPa, respectively. This indicates a lighter weight and better insulation performance. If the 44.7% construction waste are added to the insulation walls, the compressive strength can be improved more than 90% and meet the requirement of bearing walls.

Abstract: Currently higher requirements in thermal performance is needed for the quality of building materials especially fired clay bricks. Thermal conductivity is an important criterion as it will influences the heat losses from building. The objective of this study is to validate the estimation value of thermal conductivity by using theoretical value with the experimental work conducted in the laboratory. The experiment data was collected in order to compare with a theoretical model that obtained the thermal conductivity value based on it relationship with dry density of fired clay bricks. Different percentages of CBs (0%, 2.5% and 5.0%) were incorporated into fired clay bricks. Different heating rates were applied during firing stage, which are 1°C/min, 3°C/min and 5°C/min respectively. All samples were fired up to 1050°C. The experimental work for thermal conductivity was carried out using the Hot Guarded Plate Method. Meanwhile, the theoretical result was obtained from the previous study using model developed. Throughout statistical analysis, some trend of thermal conductivity and dry density were revealed. The analysis results show that as the dry density decreased, thermal conductivity also decreased.

Abstract: Natural insulation materials have great potential of development given the contemporary requirements of the society in terms of reducing the energy demands of the production of building materials and the reduction of CO₂ emissions. Natural fibers are characteristic by their high moisture absorption and combustibility. The paper describes the results of research in the field of heat and moisture transfer within the structure of insulating materials based on natural fibers (hemp). The results of the experiments provided input data for computational simulations of hygrothermal behavior of hemp based fiber insulation applied in building envelopes.

Abstract: The polyimide foam (PIF) was prepared by the foaming of precursor derived from dimethyl ester of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 4,4′-diaminodiphenyl methane (MDA). The structure and properties of polymers were investigated by FTIR, ¹H NMR, TG, DSC, SEM and mechanical testing. The findings show the PIF developed is of glass transition temperature of about 309°C, weight loss 5wt% at 517°C, density of 0.0018 g/cm³, cell structure of about 150μm, open-cell of 20%, thermal conductivity of 0.0277W/cm·K suitable for thermal insulation foam.

Abstract: Thermal insulation materials are among the simplest ways of decreasing heat loss in the buildings. When insulation materials are installed in the walls, floors and roof of a building to prevent heat loss from the building, materials must be used with the appropriate structural and thermal properties. In this paper, a laboratory test of the thermal conductivity and cell structure of building insulation materials was conducted. From the experiment results, the correlation expression between thermal conductivity and density was derived. In the case of the insulation materials that were made of expanded polypropylene (EPP), as the density increased, the thermal conductivity tended to decrease; and in the case of ethylene-vinyl acetate co-polymer (EVA) and polyethylene (PE), as the density of the insulation materials increased, the thermal conductivity tended to also increase.

Abstract: Miniaturisation of electronic chips which have increasing functionality within the same package size has induced significant increases in requirements for extraction of heat from the integrated circuit (IC). Packaging materials therefore have to be capable to conduct heat efficiently and at the same time have low coefficient of thermal expansion (CTE) to minimize the thermal stress and warping. In the present study, copper silicon carbide was selected with an aim to solve thermal management problem presented by current IC systems. Powder metallurgy routes were chosen to fabricate the MMC based on this materials system. Copper and silicon carbide powders were mixed together in a planetary ball mill, and the green articles were then compacted and sintered to produce the final product of CuSiC. The sintering parameters were investigated for their effects towards the thermal conductivity of the composite. Sintering parameters investigated included temperature, heating duration and the gaseous environment. Upon sintering, the CuSiC particle bond to one another giving a higher strength and a possibility in attaining desirable density. Thus to achieve good thermal conductivity, the recommended sintering parameter suggests that the CuSiC composite should be sintered at 950°C for 7 hours in nitrogen gas.

Abstract: In order to improve the thermal performance and wear resistance of the polymer, foamed copper filled by the curable epoxy-matrix composite are developed as tribological materials. Graphite and multi-walled carbon nanotubes (MWCNTs) were incorporated the contents as friction additives. The tribological properties of the foamed-copper reinforced composites were investigated on an UMT-2 friction and wear tester. An electric field was imposed between the specimen and disc to monitor the formation of transfer film by means of contact resistance. It is found that the foamed-copper reinforced composites possess better wear resistance than homologous polymers, and the smaller is the aperture, the better the wear resistance. While the friction coefficients increase for the local direct contact between the copper and the steel disc. The copper skeletons contribute to the timely transfer of friction heat and the load-sharing. The foamed-copper unit was modeled from the foaming mechanism of the polyurethane foam. Two parameters of the surface area density of foamed copper and the area ratio of copper at the friction interface were quantized based on two kinds of typical contact models. The modeling analysis can lead to a better understand the influence of metallic skeletons on the wear performance of composite.