Biomedical subjects

R Dennis Vigil

Publications and source records attributed to R Dennis Vigil.

5 recordsLinked to original sources

PubMed2006

Destructive aggregation: aggregation with collision-induced breakage.

Mean-field population balance equations are used to describe the evolution of particle size distributions in a wide variety of systems undergoing simultaneous aggregation and breakage. In this paper we develop a population balance that includes aggregation combined with collision-induced particle breakage for arbitrary fragment distribution functions, provided that this distribution function depends only on the total mass of the particles undergoing a collision. We then develop a specific distribution function for arbitrary two-body collisions by postulating that each collision produces a transition-state aggregate having the morphology of a linear polymer. The behavior of the resulting equation is then analyzed for the case in which the collision kernel is a constant, and partial analytical solutions are derived and compared to corresponding Monte-Carlo simulation results. The computer simulations are then used to validate a proposed scaling law for the steady-state particle size distribution. Lastly, the behavior of the aggregation with collision-induced-breakage population balance equation is compared and contrasted with the behavior of an analogous aggregation with linear-breakage population balance equation.

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PubMed2005

Vibration-induced mobilization of trapped oil ganglia in porous media: experimental validation of a capillary-physics mechanism.

The development of methods for mobilizing residual organic liquids trapped in porous media is becoming increasingly important as world demand for oil increases and because of the need to remediate aquifers degraded by slow-dissolving organic contaminants. Low-frequency elastic wave stimulation is one such technique, but until recently the lack of a mechanistic understanding of the effects of vibration on mobilization of oil ganglia has prevented the method from being applied predictably in the field. Recently, a simple capillary-physics mechanism has been developed to explain vibration-induced mobilization of a trapped non-wetting organic phase in porous media. Specific predictions that follow from this hypothesized mechanism are that vibrations will be most effective in mobilizing trapped oil when the acceleration amplitude is within an optimal range of values (that depend on the magnitudes of the capillary forces trapping the ganglia and the imposed static pressure gradients) and for sufficiently low vibration frequencies. In this paper we describe two-dimensional glass micromodel experiments that support these predictions.

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PubMed2005

CFD simulation of shear-induced aggregation and breakage in turbulent Taylor-Couette flow.

An experimental and computational investigation of the effects of local fluid shear rate on the aggregation and breakage of approximately 10 microm latex spheres suspended in an aqueous solution undergoing turbulent Taylor-Couette flow was carried out. First, computational fluid dynamics (CFD) simulations were performed and the flow field predictions were validated with data from particle image velocimetry experiments. Subsequently, the quadrature method of moments (QMOM) was implemented into the CFD code to obtain predictions for mean particle size that account for the effects of local shear rate on the aggregation and breakage. These predictions were then compared with experimental data for latex sphere aggregates (using an in situ optical imaging method). Excellent agreement between the CFD-QMOM and experimental results was observed for two Reynolds numbers in the turbulent-flow regime.

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PubMed2003

Quadrature method of moments for aggregation-breakage processes.

Investigation of particulate systems often requires the solution of a population balance, which is a continuity statement written in terms of the number density function. In turn, the number density function is defined in terms of an internal coordinate (e.g., particle length, particle volume) and it generates integral and derivative terms. Different methods exist for numerically solving the population balance equation. For many processes of industrial significance, due to the strong coupling between particle interactions and fluid dynamics, the population balance must be solved as part of a computational fluid dynamics (CFD) simulation. Such an approach requires the addition of a large number of scalars and the associated transport equations. This increases the CPU time required for the simulation, and thus it is clear that it is very important to use as few scalars as possible. In this work the quadrature method of moments (QMOM) is used. The QMOM has already been validated for crystal growth and aggregation; here the method is extended to include breakage. QMOM performance is tested for 10 different cases in which the competition between aggregation and breakage leads to asymptotic solutions.

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PubMed2002

Pore-scale study of nonaqueous phase liquid dissolution in porous media using laser-induced fluorescence.

Little quantitative, experimental pore-scale information exists regarding nonaqueous phase liquid (NAPL) ganglia undergoing dissolution in porous media. By using refractive index matched fluids and porous media, we have been able to nonintrusively visualize NAPL dissolution (at constant capillary numbers) in three dimensions using laser-induced fluorescence. The results provide dynamic, quantitative information regarding ganglia surface area, volume, position, and shape. It appears that ganglia smaller than a few pore volumes are spheroid, whereas larger ganglia exhibit a fractal area to volume scaling. Evidence of ganglia breakup is found for all capillary numbers studied. Mobilization, however, is only important at higher capillary numbers.

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