Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session EP: Particle-Laden Flows III |
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Chair: Mark Murray, U.S. Naval Academy Room: Salt Palace Convention Center 251 D |
Sunday, November 18, 2007 4:10PM - 4:23PM |
EP.00001: Computational Analysis of Sediment Entrainment in Three Dimensional Channel Flow Benjamin Yergey, Maria-Laura Beninati, Jeffrey Marshall, John Mousel A computational method that utilizes an unsteady Reynolds-averaged Navier-Stokes (RANS) code for the fluid phase together with a discrete-element method to simulate the transport of individual sediment particles in natural systems is applied within the near-bed region of a 3D channel flow. The coupling of the methods utilizes the interpolated fluid velocity at each particle and the resulting particle body force for each fluid cell. Sediment entrainment, the act of a fluid medium accelerating particles from within a fluidized bed, is relevant to a better understanding of river and coastal erosion as well as some biological and chemical transport applications. Initial conditions include coherent fluid structures over a bed of packed particles, where the fluid properties represent those of water, and the particle properties represent those of natural sediment. The effect of two-way coupling to particle momentum is quantified. The results and conclusions of this micro-scale study are necessary for further development of models including the effects of shielding on particles at the top of the bed which is essential to the study of sediment entrainment and bed-load transport. [Preview Abstract] |
Sunday, November 18, 2007 4:23PM - 4:36PM |
EP.00002: Velocity Fluctuations in Binary Particle Liquid Fluidized Beds Phil Segre, James Davidheiser, Elizabeth Baker We study particle velocities and concentration profiles of mixtures of $2$ different sized particles in concentrated liquid fluidized beds. For binary systems of particles of the same density, we find that there is always a complete phase separation in the bed. The larger particles occupy a zone in the lower part of the bed, and the smaller ones a zone in the upper part. For binary systems of particles of {\it different} density materials, conditions are found where the binary particles are either fully separated, partially mixed together, and at a single point called the inversion point, fully mixed into a one phase state. Results will be presented on the phase diagrams of binary suspensions as well as the properties of the velocity fluctuation magnitudes and spatial correlation lengths. [Preview Abstract] |
Sunday, November 18, 2007 4:36PM - 4:49PM |
EP.00003: Linking Radial Species Segregation and Bubbling Patterns in Gas-Fluidized Beds. Gustavo Joseph, Christine Hrenya, Joe Kozlowski Binary mixtures of gas-fluidized Geldart Group B particles with size and/or density differences were experimentally investigated at gas velocities up to 3 times the complete fluidization velocities ($u_{fc})$ of the mixtures. Steady state operation of the bed was ensured prior to data collection. Local bubbling information (mean bubble size, bubble rise velocity, and bubbling frequency) was obtained throughout the bed by means of a backscattered-light optical probe. Segregation data were obtained via bed ``freezing'' and subsequent sieving of layers. Monodisperse runs were also performed as benchmarks for the binary-mixture runs. Perceptible radial variations in species composition were encountered, with the less massive particles tending toward the bed center in most cases. For systems where the species differed in both size and density, the bottom layer presents a reversal of radial segregation pattern at gas velocities below 2$u_{fc}$. At velocities below 2$u_{fc}$, bubbling is seen predominantly at the bed periphery, with qualitative differences between monodisperse and mixed systems above 2$u_{fc}$. A detailed analysis of the bubbling patterns at the various compositions and gas velocities is presented, and links to the observed segregation behavior are made. [Preview Abstract] |
Sunday, November 18, 2007 4:49PM - 5:02PM |
EP.00004: Numerical Study of Particle Transport and Aggregates during Spin Coating of Ag Colloidal Suspension Yongli Zhao, Albert Ratner, Jeffrey Marshall A multiple time-step discrete-element approach is employed to model the transport, collision and adhesion of small Ag colloidal particles in a spin coating process. The computations are used to predict particle distribution and wall adhesion during the non-evaporative phase of spin coating of a thin film, which is important for controlling the abrasiveness, opacity, conductivity, and other properties of the film, as well as for using the deposited particles for growing new materials (e.g., nanotubes). The computations examine the particle distribution and the effect of particle adhesive force on particle deposition during spin coating. Particles are observed to preferentially collect within the film ridge just behind the moving contact line. Increase in the particle adhesive force is observed to lead to enhanced deposition of particles within an inner radius of the film and increase in the aggregate size. The aggregate size decreases with higher rotational speed. A more uniform distribution of particles can be obtained by decreasing the rotational speed. [Preview Abstract] |
Sunday, November 18, 2007 5:02PM - 5:15PM |
EP.00005: Modeling Reverse Osmosis Crossflow Filtration Laura Campo, Brent Houchens During the initial stages of crossflow filtration, a concentration polarization layer forms near the membrane surface, causing a decrease in clean water flux over time. Accurate modelling of this flux decline is essential to improving the design of filtration systems in applications including water purification, food processing, and desalination. A continuum model of reverse osmosis crossflow filtration is developed by numerically solving the coupled Navier-Stokes and Convection-Diffusion equations in two dimensions for an incompressible Newtonian fluid. The model treats diffusivity and viscosity as functions of local particle concentration. The dependence of viscosity on concentration is measured experimentally and a curve fit offers an empirical constitutive equation for the generalized Newtonian fluid. The numerical solution is obtained using a Chebyshev spectral collocation method with Gauss-Lobatto grid spacing in both the axial and transverse directions. [Preview Abstract] |
Sunday, November 18, 2007 5:15PM - 5:28PM |
EP.00006: Fluid-particle drag in binary suspensions under Stokes flow condition Xiaolong Yin, Sankaran Sundaresan In multi-fluid models for fluid-particle suspensions, the details of the fluid-particle interactions are supplied through various constitutive relations, among which the one for drag is particularly important. Drag correlations for binary suspensions with no mean relative motion between the two solid phases have been well established. However, multi-fluid models for flowing binary suspensions require more general drag correlations, where different types of particles can have different local averaged velocities relative to the interstitial fluid. The goal of this study is to construct such drag correlations from direct numerical simulations. We assumed that the particles have high St and small Re. The drag force is then related to the fluid-particle relative velocities by a proportionality matrix, the off-diagonal components of which represent the particle-particle drag due to hydrodynamic interactions and were found to give important contributions to the net drag force. The total particle volume fraction in our study ranged from 0.1 to 0.4. The size ratios of particles were varied from 1:1 to 1:4. [Preview Abstract] |
Sunday, November 18, 2007 5:28PM - 5:41PM |
EP.00007: Aging rates of glassy suspensions of thermosensitive microgel particles Frieder Mugele, Dirk van den Ende, Eko Purnomo We performed rheological measurements of the aging behaviour of soft microgel particle suspensions with a thermally controllable degree of glassiness. Linear measurements display aging at a rate that decreases upon approaching the glass transition. Applying the recently proposed non-linear strain rate frequency superposition (SRFS) principle, we identify the corresponding structural relaxation time at a frequency well below the range accessible in the linear measurements. Consistent with the linear measurements, we find that both the relaxation time increases with the sample life time and the corresponding aging rate vanishes at the glass transition. Except for the vicinity of the glass transition, the aging rate of the structural relaxation time agrees quantitatively with the predictions derived from the linear measurements using the soft glassy rheology model (SGR), thereby corroborating the validity and usefulness of both the SRFS principle and the SGR model. [Preview Abstract] |
Sunday, November 18, 2007 5:41PM - 5:54PM |
EP.00008: Particle capture by a freezing front in a binary alloy Justin Kao, Alexander Golovin, Stephen Davis We examine the interaction between a particle and a nearby solidification front in a binary alloy, subject to constitutional undercooling, Gibbs-Thomson effect, hydrodynamic lubrication, and van der Waals disjoining pressure. We solve for the shape of the front and obtain the particle velocity as a function of distance from the front, and quasi-steady traveling solutions as a function of velocity. We find scaling relations for the critical speed of solidification, which separates particle rejection and particle capture. It is shown that the presence of solute (e.g. impurities) in the system can lower the critical speed for capture by an order of magnitude, with the particle-front gap becoming dominated by constitutional undercooling rather than van der Waals premelting. [Preview Abstract] |
Sunday, November 18, 2007 5:54PM - 6:07PM |
EP.00009: Particle size concentration and meteorological parameter dynamics Andrew Duggleby, James Regens, Kenneth Ball A proper orthogonal decomposition of particle size concentration and meteorological parameter dynamics is performed on data collected from 12:45 pm CDT on 18 July 2004 until 1:00 pm CDT on 22 July 2004 using an Aerodynamic Particle Sizer spectrometer and a modular weather station. The sampling station was located at 60 feet above ground level on the roof of the College of Health Building on the University of Oklahoma Health Sciences Center campus in Oklahoma City, and it sampled data every 15 minutes. The effect of the meteorological conditions of temperature, humidity, pressure, wind speed, and wind direction on particle concentration dynamics is examined. Most of the dynamical fluctuations occur at particle sizes below 1 micron, temperature and humidity have the most effect on the dynamics, and the wind speed and direction have a smaller effect. Discussions will include the potential effects of rush-hour traffic and diurnal meteorological patterns on the particle size distributions. [Preview Abstract] |
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