Volume fraction

About: Volume fraction is a research topic. Over the lifetime, 16312 publications have been published within this topic receiving 374181 citations.

Thermal conductivity of porous materials

Abstract: Incorporation of porosity into a monolithic material decreases the effective thermal conductivity. Porous ceramics were prepared by different methods to achieve pore volume fractions from 4 to 95%. A toolbox of analytical relations is proposed to describe the effective thermal conductivity as a function of solid phase thermal conductivity, pore thermal conductivity, and pore volume fraction (νp). For νp 0.65, the thermal conductivity of kaolin-based foams and calcium aluminate foams was well described by the Hashin Shtrikman upper bound and Russell’s relation. Finally, numerical simulation on artificially generated microstructures yields accurate predictions of thermal conductivity when fine detail of the spatial distribution of the phases needs to be accounted for, as demonstrated with a bio-aggregate material.

Viscoelasticity of single wall carbon nanotube suspensions.

Abstract: We investigate the viscoelastic properties of an associating rigid rod network: aqueous suspensions of surfactant stabilized single wall carbon nanotubes (SWNTs). The SWNT suspensions exhibit a rigidity percolation transition with an onset of solidlike elasticity at a volume fraction of 0.0026; the percolation exponent is 2.3+/-0.1. At large strain, the solidlike samples show volume fraction dependent yielding. We develop a simple model to understand these rheological responses and show that the shear dependent stresses can be scaled onto a single master curve to obtain an internanotube interaction energy per bond approximately 40k(B)T. Our experimental observations suggest SWNTs in suspension form interconnected networks with bonds that freely rotate and resist stretching. Suspension elasticity originates from bonds between SWNTs rather than from the stiffness or stretching of individual SWNTs.

Nanofluid As a Coolant for Electronic Devices: Cooling of Electronic Devices

Abstract: Nanofluids are the suspension of ultrafine solid nanoparticles in a base fluid. Nanofluids are expected to be a promising coolant candidate for thermal management system of next generation high heat dissipation electronic systems. Nanofluids are used with different volume fractions. A minichannel heat sink with a 20 × 20 cm bottom is analyzed for SiC-water nanofluid and TiO2-water nanofluid turbulent flow as coolants through hydraulic diameters. The results showed that enhancement in thermal conductivity by dispersed SiC in water at 4% volume fraction was 12.44% and by dispersed TiO2 in water was 9.99% for the same volume fraction. It was found that by using SiC-water nanofluid as a coolant instead of water, an improvement of approximately 7.25%–12.43% could be achieved and by using TiO2-water 7.63%–12.77%. The maximum pumping power by using SiC-water nanofluid at 2 m/s and 4% vol. was 0.28 W and at 6 m/s and 4% volume equal to 5.39 W. By using TiO2-water nanofluid at 2 m/s and 4% vol. it was found to be 0.29 W and 5.64 W at 6 m/s with the same volume of 4%.

Fabrication and tribological properties of carbon nanotubes reinforced Al composites prepared by pressureless infiltration technique

Abstract: Aluminum composites reinforced with CNTs were fabricated by pressureless infiltration process and the tribological properties of the composites were investigated. Al has been infiltrated into CNTs–Mg–Al preform by pressureless infiltration in N2 atmosphere at 800 °C. By means of scanning electron microscope (SEM) and energy dispersive X-ray spectrometer (EDS), it was found that CNTs are well dispersed and embedded in the Al matrix. The friction and wear behaviors of the composite were investigated using a pin-on-disk wear tester under unlubricated condition. The tests were conducted at a sliding speed of 0.1571 m/s under an applied load of 30 N. The experimental results indicated that the friction coefficient of the composite decreased with increasing the volume fraction of CNTs due to the self-lubrication and unique topological structure of CNTs. Within the range of CNTs volume fraction from 0% to 20%, the wear rate of the composite decreased steadily with the increase of CNTs content in the composite. The favorable effects of CNTs on wear resistance are attributed to their excellent mechanical properties, being well dispersed in the composite and the efficiency of the reinforcement of CNTs.