Values Of Solid Fraction Research Articles

Computer-aided cooling curve analysis of A356 aluminum alloy

Computer aided cooling curve analysis (CA-CCA) is very useful in the foundry industry for easy and fast evaluation of a variety of properties. Typical applications include the prediction of the temperatures and amounts of different phases appearing during solidification and monitoring of the quality of melt in terms of Si- modification, grain refinement, inoculation, and graphite spheoridization. The use of cooling curve analysis can be extended to many other areas of solidification also, assuming the calculated values are reasonably accurate. The calculation of zero curve, which is vital in cooling curve analysis, offers many problems however. In this study, an attempt was made to investigate the problems of zero curve calculation and a new method is suggested to minimize calculation errors. An in-house developed computer program was used for a complete analysis of aluminum alloy A356 to determine the latent heat and solid fraction values.

Cake collapse in frontal filtration of colloidal aggregates: mechanisms and consequences

Microstructures of cakes formed on ultrafiltration membrane as a result of packing of colloidal aggregates generated in rapid coagulation have been investigated though small angle neutron scattering experiments. Scattering curves show an extensive collapse of fractal structure of colloidal aggregates due to their packing in the cake. Accordingly experimental values of solid fraction in the cake are higher than expected from gentle packing of fractal aggregates. Different densification features have been detected both at small and large scale depending on the friction forces between the particles and the strength of inter-particles bonds.

Collisional particle pressure measurements in solid–liquid flows

Experiments were conducted to measure the collisional particle pressure in both cocurrent and countercurrent flows of liquid–solid mixtures. The collisional particle pressure, or granular pressure, is the additional pressure exerted on the containing walls of a particulate system due to the particle collisions. The present experiments involve both a liquid-fluidized bed using glass, plastic or steel spheres and a vertical gravity-driven flow using glass spheres. The particle pressure was measured using a high-frequency-response flush-mounted pressure transducer. Detailed recordings were made of many different particle collisions with the active face of this transducer. The solids fraction of the flowing mixtures was measured using an impedance volume fraction meter. Results show that the magnitude of the measured particle pressure increases from low concentrations (<10% solid volume fraction), reaches a maximum for intermediate values of solid fraction (30–40%), and decreases again for more concentrated mixtures (>40%). The measured collisional particle pressure appears to scale with the particle dynamic pressure based on the particle density and terminal velocity. Results were obtained and compared for a range of particle sizes, as well as for two different test section diameters.In addition, a detailed analysis of the collisions was performed that included the probability density functions for the collision duration and collision impulse. Two distinct contributions to the collisional particle pressure were identified: one contribution from direct contact of particles with the pressure transducer, and the second one resulting from particle collisions in the bulk that are transmitted through the liquid to the pressure transducer.

Particle Mixing and Volumetric Expansion in a Vibrated Granular Bed

The present experiments are an investigation of the expansion and mixing that occur in a horizontal bed of particles subjected to vibrational accelerations in the direction parallel to gravity. The particles are colored-glass balls of uniform size; three different bed heights are examined of 6, 9, and 12 particle diameters. The vibrational frequency and amplitude are controlled separately to cover a range of acceleration levels from 1 to 5.5 times gravitational acceleration. The expansion results show that above a critical frequency, the bed begins to expand and the bed solid fraction decreases. This result is independent of the vibrational amplitude. Above a second critical frequency, the thickest beds show a further decrease in solid fraction; the minimum value of solid fraction for all bed heights is approximately 0.21 ± 0.03. The mixing results indicate that the mixing times decrease significantly with the expansion of the bed. However, the mixing times are greater as the bed depth increases. Unlike the expansion results, the mixing times depend on the amplitude of the vibration. A simple analysis of the flow is performed using a self-diffusion coefficient developed from dense-gas kinetic theory. The analysis qualitatively agrees with the experiments for the largest vibrational velocities and for the thinnest beds.

Analysis of the Fully Developed Chute Flow of Granular Materials

Existing constitutive relations and governing equations have been used to solve for fully developed chute flows of granular materials. In particular, the results of Lun et al. (1984) have been employed and the boundary value problem has been formulated with two parameters (the coefficient of restitution between particles, and the chute inclination), and three boundary values at the chute base wall, namely the values of solid fraction, granular temperature, and mean velocity at the wall. The boundary value problem has been numerically solved by the “shooting method.” The results show the significant role played by granular conduction in determining the profiles of granular temperature, solid fraction, and mean velocity in chute flows. These analytical results are also compared with experimental measurements of velocity fluctuation, solid fraction, and mean velocity made by Ahn et al. (1989), and with the computer simulations by Campbell and Brennen (1985b).