Volume fraction

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

Computational modeling of gas/particle flow in a riser

Abstract: Axial solid velocity, solid volume fraction, and solid shear viscosity were computed in the riser of a circulating fluidized-bed reactor using a two-phase 2-D computational fluid dynamic model. The time-averaged model predictions agree well with the experimental data of Miller and Gidaspow (1992). The model predicts a core-annulus flow in the riser, similar to that found experimentally. The maximum velocity in the core agrees well with the measurements, but the downflow in the annulus is somewhat overpredicted. The solid volume fractions profiles agree well in both core and annulus, with discrepancy in the core at the level close to the inlet. The radial profile of solid shear viscosity computed by the turbulent kinetic energy model is ten times lower in the core than that found experimentally, but with a linear function of solid volume fraction in the measurement, the computed profile agrees well with experiments.

Heat- and mass-transport in aqueous silica nanofluids

Abstract: Using the transient hot wire and pulsed field gradient nuclear magnetic resonance methods we determined the thermal conductivity and the solvent self-diffusion coefficient (SDC) in aqueous suspensions of quasi-monodisperse spherical silica nanoparticles. The thermal conductivity was found to increase at higher volume fraction of nanoparticles in accordance with the effective medium theory albeit with a smaller slope. On the other hand, the SDC was found to decrease with nanoparticle volume fraction faster than predicted by the effective medium theory. These deviations can be explained by the presence of an interfacial heat-transfer resistance and water retention by the nanoparticles, respectively. We found no evidence for anomalous enhancement in the transport properties of nanofluids reported earlier by other groups.

Effects of Radiative Electro-Magnetohydrodynamics Diminishing Internal Energy of Pressure-Driven Flow of Titanium Dioxide-Water Nanofluid due to Entropy Generation.

Abstract: The internal average energy loss caused by entropy generation for steady mixed convective Poiseuille flow of a nanofluid, suspended with titanium dioxide (TiO2) particles in water, and passed through a wavy channel, was investigated. The models of thermal conductivity and viscosity of titanium dioxide of 21 nm size particles with a volume concentration of temperature ranging from 15 °C to 35 °C were utilized. The characteristics of the working fluid were dependent on electro-magnetohydrodynamics (EMHD) and thermal radiation. The governing equations were first modified by taking long wavelength approximations, which were then solved by a homotopy technique, whereas for numerical computation, the software package BVPh 2.0 was utilized. The results for the leading parameters, such as the electric field, the volume fraction of nanoparticles and radiation parameters for three different temperatures scenarios were examined graphically. The minimum energy loss at the center of the wavy channel due to the increase in the electric field parameter was noted. However, a rise in entropy was observed due to the change in the pressure gradient from low to high.

Effects of shear induced crystallization on the rheology and ageing of hard sphere glasses

Abstract: The rheological properties of highly concentrated suspensions of hard sphere particles are studied with particular reference to the rheological response of shear induced crystals. Using practically monodisperse hard spheres, we prepare shear induced crystals under oscillatory shear and examine their linear and non-linear mechanical responses in comparison with their glassy counterparts at the same volume fraction. It is evident, that shear induced crystallization causes a significant drop in the elastic and viscous moduli due to structural rearrangements that ease flow. For the same reason the critical (peak of G″) and crossover (overlap of G′ and G″) strain are smaller in the crystal compared to the glass at the same volume fraction. However, when the distance from the maximum packing in each state is taken into account the elastic modulus of the crystal is found to be larger than the glass at the same free volume, suggesting a strengthened material due to long range order. Finally, shear induced crystals counter-intuitively exhibit similar rheological ageing to the glass (with a logarithmic increase of G′), indicating that the shear induced structure is not at thermodynamic equilibrium.

Experimental Study on Hybrid Fiber-Reinforced Concrete Subjected to Uniaxial Compression

Abstract: This paper presents the uniaxial compression behavior of steel-polypropylene hybrid fiber–reinforced concrete (HFRC). A total of 30 batches of specimens with different fiber-reinforcement indices in terms of volume fraction and aspect ratio are investigated by the orthogonal experimental method. A variance analysis is conducted to obtain the optimum proportion of hybrid fiber in terms of compressive strength and corresponding peak strain. It is observed from the experimental results that the uniaxial compression behavior of plain concrete can be improved by inclusion of hybrid fibers; it is also noted that the hybrid effect between volume fraction and aspect ratio of steel fiber as well as the volume fraction of polypropylene fiber should be considered as influential factors on uniaxial compressive strength. Furthermore, in comparison to single fiber-reinforced concrete, HFRC exhibits more ductility at postpeak performance. Subsequently, the results are used to develop predictive equations for the...