Particle Concentration (particle + concentration)

Distribution by Scientific Domains
Distribution within Chemistry


Selected Abstracts


Experimental determination of saltating glass particle dispersion in a turbulent boundary layer

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 14 2006
H. T. Wang
Abstract A horizontal saltation layer of glass particles in air is investigated experimentally over a flat bed and also over a triangular ridge in a wind tunnel. Particle concentrations are measured by light scattering diffusion (LSD) and digital image processing, and velocities using particle image velocimetry (PIV). All the statistical moments of the particle concentration are determined such as mean concentration, root mean square concentration fluctuations, skewness and flatness coefficients. Over the flat bed, it is confirmed that the mean concentration decreases exponentially with height, the mean dispersion height being a significant length scale. It is shown that the concentration distribution follows quite well a lognormal distribution. Over the ridge, measurements were made at the top of the ridge and in the cavity region and are compared with measurements without the ridge. On the hill crest, particles are retarded, the saltation layer decreases in thickness and concentration is increased. Downwind of the ridge, particle flow behaves like a jet, in particular no particle return flow is observed. Copyright © 2006 John Wiley & Sons, Ltd. [source]


Assessing the variability of hydrographic processes influencing the life cycle of the Sicilian Channel anchovy, Engraulis encrasicolus, by satellite imagery

FISHERIES OCEANOGRAPHY, Issue 1 2005
JESÚS GARCÍA LAFUENTE
Abstract Three oceanographic surveys carried out in the Sicilian Channel during the spawning season (June to July) of anchovy (Engraulis encrasicolus) showed a close relationship between anchovy reproductive strategy and important hydrographic structures. A time series of satellite-derived sea surface temperature images of the Sicilian Channel were analysed by means of empirical orthogonal functions and the dominant empirical modes were studied in detail. The first empirical mode captured much of the original variance and reproduced the trajectory of the Atlantic Ionian Stream (AIS), the principal hydrodynamic feature of the area. The time coefficients of modes 1 and 2 had seasonal signals which, when combined, accounted for the enhancement of the thermal front, clearly visible off Cape Passero (southernmost coast of Sicily) during summer. As the area constituted the principal nursery ground of the Sicilian Channel anchovy, the combination of the time coefficients of these modes was considered a potential indicator of the food particle concentration usually associated with oceanic fronts, which provided the energy requirements for larval growth. Mode 3 described the north/south displacements of the mean AIS trajectory, which modified the surface temperature regime of the anchovy spawning habitat. Therefore, the time coefficients of this mode were used as a potential indicator of anchovy spawning habitat variability. The capability of time coefficients of modes 2 and 3 to modify the main pattern depicted by mode 1 were tested successfully against in situ oceanographic observations. [source]


Predator-released compounds, ambient temperature and competitive exclusion among differently sized Daphnia species

FRESHWATER BIOLOGY, Issue 4 2006
JACOBUS VIJVERBERG
Summary 1. We studied the effects of fish water and temperature on mechanisms of competitive exclusion among two Daphnia species in flow-through microcosms. The large-bodied D. pulicaria outcompeted the medium sized D. galeata × hyalina in fish water, but not in the control treatment. Daphnia galeata × hyalina was competitively displaced 36 days earlier at 18 °C than at 12 °C. 2. It is likely that the high phosphorus content of fish water increased the nutritional value of detrital seston particles by stimulating bacterial growth. Daphnia pulicaria was presumably better able to use these as food and hence showed a more rapid somatic growth than its competitor. This led to very high density of D. pulicaria in fish water, but not in the controls. The elevated D. pulicaria density coincided with high mortality and reduced fecundity in D. galeata × hyalina, resulting in competitive displacement of the hybrid. 3. It is clear that the daphnids competed for a limiting resource, as grazing caused a strong decrease in their seston food concentration. However, interference may also have played a role, as earlier studies have shown larger Daphnia species to be dominant in this respect. The high density of large-bodied D. pulicaria in fish water may have had an allelopathic effect on the hybrid. Our data are inconclusive with respect to whether the reached seston concentration was below the threshold resource level (R*) of the hybrid, where population growth rate and mortality exactly balance, as it would be set in the absence of interference, or whether interference actually raised the hybrid's R* to a value above this equilibrium particle concentration. 4. Our results do clearly show that fish-released compounds mediated competitive exclusion among zooplankton species and that such displacement occurred at a greatly enhanced rate at an elevated temperature. Fish may thus not only structure zooplankton communities directly through size-selective predation, but also indirectly through the compounds they release. [source]


The scaling law in the hole erosion test with a constant pressure drop

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 13 2008
Stéphane Bonelli
Abstract A process called ,piping', which often occurs in the soil at dams, levees, and dykes, involves the formation and development of a continuous tunnel between upstream and downstream ends. The hole erosion test is commonly used to quantify the critical stress and the rate of piping erosion progression. The aim of this study is to draw up a model for interpreting the results of this test. A characteristic internal erosion time is defined and expressed as a function of the initial hydraulic gradient and the coefficient of surface erosion. It is established here that the product of the coefficient of erosion and the flow velocity is a significant dimensionless number: when this number is small, the kinetics of erosion are low, and the particle concentration does not have any effect on the flow. This finding applies to most of the available test results. Theoretical and experimental evidence is presented showing that the evolution of the pipe radius during erosion with a constant pressure drop obeys a scaling exponential law. Copyright © 2008 John Wiley & Sons, Ltd. [source]


Instabilities during batch sedimentation in geometries containing obstacles: A numerical and experimental study,

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2007
Rekha R. Rao
Abstract Batch sedimentation of non-colloidal particle suspensions is studied with nuclear magnetic resonance flow visualization and continuum-level numerical modelling of particle migration. The experimental method gives particle volume fraction as a function of time and position, which then provides validation data for the numerical model. A finite element method is used to discretize the equations of motion, including an evolution equation for the particle volume fraction and a generalized Newtonian viscosity dependent on local particle concentration. The diffusive-flux equation is based on the Phillips model (Phys. Fluids A 1992; 4:30,40) and includes sedimentation terms described by Zhang and Acrivos (Int. J. Multiphase Flow 1994; 20:579,591). The model and experiments are utilized in three distinct geometries with particles that are heavier and lighter than the suspending fluid, depending on the experiment: (1) sedimentation in a cylinder with a contraction; (2) particle flotation in a horizontal cylinder with a horizontal rod; and (3) flotation around a rectangular inclusion. Secondary flows appear in both the experiments and the simulations when a region of higher density fluid is above a lower density fluid. The secondary flows result in particle inhomogeneities, Rayleigh,Taylor-like instabilities, and remixing, though the effect in the simulations is more pronounced than in the experiments. Published in 2007 by John Wiley & Sons, Ltd. [source]


Numerical calculations of erosion in an abrupt pipe contraction of different contraction ratios

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 1 2004
M. A. Habib
Abstract Erosion predictions in a pipe with abrupt contraction of different contraction ratios for the special case of two-phase (liquid and solid) turbulent flow with low particle concentration are presented. A mathematical model based on the time-averaged governing equations of 2-D axi-symmetric turbulent flow is used for the calculations of the fluid velocity field (continuous phase). The particle-tracking model of the solid particles is based on the solution of the governing equation of each particle motion taking into consideration the effect of particle rebound behaviour. Models of erosion were used to predict the erosion rate in mg/g. The effect of Reynolds number and flow direction with respect to the gravity was investigated for three contraction geometries considering water flow in a carbon steel pipe. The results show that the influence of the contraction ratio on local erosion is very significant. However, this influence becomes insignificant when the average erosion rates over the sudden contraction area are considered. The results also indicate the significant influence of inlet velocity variations. The influence of buoyancy is significant for the cases of low velocity of the continuous flow. A threshold velocity below which erosion may be neglected was indicated. Copyright © 2004 John Wiley & Sons, Ltd. [source]


Effect of pressure on thermal aspects in the riser column of a pressurized circulating fluidized bed

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 3 2006
A. V. S. S. K. S. Gupta
Abstract In the present paper the effect of pressure on bed-to-wall heat transfer in the riser column of a pressurized circulating fluidized bed (PCFB) unit is estimated through a modified mechanistic model. Gas,solid flow structure and average cross-sectional solids concentration play a dominant role in better understanding of bed-to-wall heat transfer mechanism in the riser column of a PCFB. The effect of pressure on average solids concentration fraction ,c' in the riser column is analysed from the experimental investigations. The basic cluster renewal model of an atmospheric circulating fluidized bed has been modified to consider the effect of pressure on different model parameters such as cluster properties, gas layer thickness, cluster, particle, gas phase, radiation and bed-to-wall heat transfer coefficients, respectively. The cluster thermal conductivity increases with system pressure as well as with bed temperature due to higher cluster thermal properties. The increased operating pressure enhances the particle and dispersed phase heat transfer components. The bed-to-wall heat transfer coefficient increases with operating pressure, because of increased particle concentration. The predicted results from the model are compared with the experimentally measured values as well as with the published literature, and a good agreement has been observed. The bed-to-wall heat transfer coefficient variation along the riser height is also reported for different operating pressures. Copyright © 2005 John Wiley & Sons, Ltd. [source]


Effect of pressure and temperature on cluster and particle heat transfer in a pressurized circulating fluidized bed

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 14 2001
B. V. Reddy
Abstract The present work reports the influence of pressure and bed temperature on particle-to-wall heat transfer in a pressurized circulating fluidized bed (PCFB). The particle convection heat transfer plays a dominant role in determining the bed-to-wall heat transfer coefficient. So far, no information is reported on the effect of pressure and bed temperature on particle-to-wall heat transfer in a PCFB in the published literature. The present investigation reports some information in this direction. The effect of system pressure and bed temperature are investigated to study their influence on cluster and particle heat transfer. The particle convection heat transfer coefficient increases with system pressure and bed temperature due to higher cluster thermal conductivity. The increase in particle concentration (suspension density) results in greater cluster solid fraction and also the particle concentration near the wall is enhanced. This results in higher cluster and particle convection heat transfer between the bed and the wall. Higher particle convection heat transfer coefficient results in enhanced heat transfer between the bed and the wall. The results will also help to understand the bed-to-wall heat transfer mechanism in a better way in a PCFB. Copyright © 2001 John Wiley & Sons, Ltd. [source]


Quality control of protein standards for molecular mass determinations by small-angle X-ray scattering

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2010
Shuji Akiyama
Small-angle X-ray scattering (SAXS) is a powerful technique with which to evaluate the size and shape of biological macromolecules in solution. Forward scattering intensity normalized relative to the particle concentration, I(0)/c, is useful as a good measure of molecular mass. A general method for deducing the molecular mass from SAXS data is to determine the ratio of I(0)/c of a target protein to that of a standard protein with known molecular mass. The accuracy of this interprotein calibration is affected considerably by the monodispersity of the prepared standard, as well as by the precision in estimating its concentration. In the present study, chromatographic fractionation followed by hydrodynamic characterization is proposed as an effective procedure by which to prepare a series of monodispersed protein standards. The estimation of molecular mass within an average deviation of 8% is demonstrated using monodispersed bovine serum albumin as a standard. The present results demonstrate the importance of protein standard quality control in order to take full advantage of interprotein calibration. [source]


A thermal study on the use of immobilized penicillin G acylase in the formation of 7-amino-3-deacetoxy cephalosporanic acid from cephalosporin G

JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 10 2004
Jian-Liang Pan
Abstract Penicillin G acylase (PGA) is an important enzyme for the industrial production of 7-amino-3-deacetoxy cephalosporanic acid (7-ADCA) from cephalosporin G (Ceph-G), and 6-aminopenicillanic acid (6-APA) from penicillin G (Pen-G). These products are used for the manufacture of semi-synthetic cephalosporins and penicillins. In this study, immobilized PGA was utilized to catalyze the conversion of Ceph-G to 7-ADCA. The optimal conditions were found to be an operating temperature of 45 °C, 0.2 M phosphate buffer, a substrate concentration of 30 mg cm,3 and a catalyst particle concentration of 0.01 g cm,3 (specific activity of 623.2 U g,1). Up to 45 °C the reaction was characterized by an activation energy of 38.66 kJ mol,1. Beyond 57.5 °C there was a sharp decline of activity, characterized by a deactivation energy of 235.88 kJ mol,1. Copyright © 2004 Society of Chemical Industry [source]


Flow visualization and solute transport in evaporating droplets

AICHE JOURNAL, Issue 7 2010
Pallippadan Johny Jaijus
Abstract We have investigated the velocity field and associated particle transport in an evaporating water droplet using the tool of particle image velocimetry. Experiments were performed where single droplets containing polystyrene particles were exposed to evaporation. Our method applicable to droplets confined between two parallel surfaces differs from the conventional PIV techniques on the 3D droplets and removes many of the limitations associated with mapping of velocity field. To avoid refraction of light at the droplet surface we have studied the motion in a disc-shaped droplet which was prepared by confining the drop between two nonwetting surfaces and its base is pinned to a wetting surface. Experiments were carried out under the conditions where Marangoni flow creates convection cells and finally leading to deposition of particles toward the pinned edge. The contact angle, height of the droplet, velocity field, and the particle concentration inside the evaporating droplet was measured and its time evolution was recorded. © 2009 American Institute of Chemical Engineers AIChE J, 56: 1674,1683, 2010 [source]


Viscosity corrections for concentrated suspension in capillary flow with wall slip

AICHE JOURNAL, Issue 6 2010
Z. Y. Wang
Abstract Corrections for viscosity measurements of concentrated suspension with capillary rheometer experiments were investigated. These corrections include end effects, Rabinowitsch effect, and wall slip. The effects of temperature, particle concentration, and contraction ratio on the end effects were studied and their effects were accounted for using an entrance and exit losses model. The non-Newtonian effect and the nonlinearity of slip velocity against wall shear stress were described using a slip model. The true viscosity of a concentrated suspension with glass powder suspended in a non-Newtonian binder system was calculated as a function of shear rate and effective particle concentration, taking into consideration particle migration, which is calculated by a diffusive numerical model. Particle size was found to affect significantly the viscosity of the suspension with viscosity decreasing with increasing particle size, which can be reflected by a decrease in the value of the power-law index in the Krieger model. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source]


Influence of elevated pressure and particle lyophobicity on hydrodynamics and gas,liquid mass transfer in slurry bubble columns

AICHE JOURNAL, Issue 3 2010
Vinit P. Chilekar
Abstract This article reports on the influence of elevated pressure and catalyst particle lyophobicity at particle concentrations up to 3 vol % on the hydrodynamics and the gas-to-liquid mass transfer in a slurry bubble column. The study was done with demineralized water (aqueous phase) and Isopar-M oil (organic phase) slurries in a 0.15 m internal diameter bubble column operated at pressures ranging from 0.1 to 1.3 MPa. The overall gas hold-up, the flow regime transition point, the average large bubble diameter, and the centerline liquid velocity were measured along with the gas,liquid mass transfer coefficient. The gas hold-up and the flow regime transition point are not influenced by the presence of lyophilic particles. Lyophobic particles shift the regime transition to a higher gas velocity and cause foam formation. Increasing operating pressure significantly increases the gas hold-up and the regime transition velocity, irrespective of the particle lyophobicity. The gas,liquid mass transfer coefficient is proportional to the gas hold-up for all investigated slurries and is not affected by the particle lyophobicity, the particle concentration, and the operating pressure. A correlation is presented to estimate the gas,liquid mass transfer coefficient as a function of the measured gas hold-up: . © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source]


Mechanisms of particle dispersion in a turbulent, square duct flow

AICHE JOURNAL, Issue 7 2009
Michael Fairweather
Abstract Particle dispersion in a square duct flow is studied using large eddy simulation combined with Lagrangian particle tracking under conditions of one-way coupling. The flow has a bulk Re = 250 k, with six particle sizes ranging from 5 to 1000 ,m. Results obtained for the fluid phase show good agreement with experimental data. For particles, predictions demonstrate that secondary flows within the duct dominate small particle dispersion and result in a uniform distribution, whereas gravity promotes the deposition of large particles on the duct floor. For the largest particles, the secondary flows contribute to particle concentration in corners on the duct floor, with these particles also clustering in low-velocity regions close to the floor. A detailed analysis of the influence of the flow on particle distribution is provided through consideration of the particle dispersion function, with the mechanisms of particle dispersion elucidated using a dynamical analysis. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]


Particle-size analysis in mass crystallization from solutions

AICHE JOURNAL, Issue 7 2000
G. Zelmanov
The problem of product-size distribution exiting a crystallizer is addressed theoretically and experimentally. The distribution function of the particle size is solved and demonstrated experimentally as a function of fines destruction, solids content of feed, particle circulation ratio, feed particle sizes, particle concentration. Theoretical tools are given for estimation of various important parameters such as distribution moments, rate of growth, rate of nuclei production and particle-size distribution. A good agreement is shown between the theoretical model and the experimental results. [source]


Synthesis and Evaluation of Water-Soluble Fluorinated Dendritic Block-Copolymer Nanoparticles as a 19F-MRI Contrast Agent

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 14 2010
Michihiro Ogawa
Abstract Well-defined water-soluble fluorinated polymer nanoparticles (PNPs) with a high fluorine content and biocompatibility were successfully prepared by living radical polymerization (LRP) of 2,2,3,3-tetrafluoropropyl methacrylate (TFPMA) from the polyamidoamine dendrimer macroinitiator (PAMAM-Br), and successive block polymerization of carboxybetaine monomer (CMB). The obtained core,shell type PNPs (PAMAM- g -PTFPMA- b -PCMB) showed high solubility in water and a sphere-like structure with a diameter in the range of 15,80,nm in water. The short 19F-NMR spin,lattice relaxation time (T1) (<250,ms) of PAMAM- g -PTFPMA- b -PCMB allowed the use of fast repetition time. The spin,spin relaxation time (T2) was evaluated to be as low as 10 ms. 19F-MRI in vitro signals can be detectable even at concentrations lower than 1 µM (particle concentration). These results demonstrate that a new type of 19F-MRI contrast agent can be developed by the molecular design using the dendrimer-initiated LRP method. [source]


Gas-solid Two-phase Mixtures Flowing Upward through a Confined Packed Bed,

PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 3-4 2006
Yurong He
Abstract This paper deals with flows of a gas-solid two-phase mixture through a confined packed bed. Both experimental work and numerical modelling are performed on the behaviour of suspended particles within the packed bed. The experimental work is carried out with a non-intrusive Positron Emission Particle Tracking (PEPT) technique, which tracks particle motion at the single particle level for a prolonged period thus allows both the microscopic and macroscopic solids behaviour to be analysed under the steady-state conditions. A continuous based model is used to simulate the flow behaviour. The model uses a newly proposed porosity model and treats the suspended and packed particles as a binary mixture with the packed particles being at zero velocity. The results show that the model captures the main features of solids behaviour in terms of the radial distributions of the suspended particle concentration and the axial solids velocity. Both the experiments and modelling suggest that the wall effect on the motion of suspended particles be limited to a small region close to the wall (,0.5,1 packed particle diameter). However, deviations exist between the model predictions and experiments; more work is therefore proposed to improve the interaction terms in the model between the suspended and packed particles. [source]


Experimental Study on Particle Size Distribution and Concentration Using Transmission Fluctuation Spectrometry with the Autocorrelation Technique

PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 3 2005
Xiaoai Guo
Abstract Based on the statistical characteristics of the transmission fluctuations in the particle suspension, transmission fluctuation spectrometry with autocorrelation (TFS-AC) is described theoretically, with the assumptions of geometric ray propagation and completely absorbent particles in the suspension. The experiments presented here are realized in a focused Gaussian beam with the TFS-AC technique. The acquisition of transmission fluctuation signals is achieved by using a high-resolution digital oscilloscope. The transition function of TFS-AC is obtained by varying the autocorrelation time. With a modified iterative Chahine inversion algorithm, solving a linear equation retrieves information on the particle size distribution and particle concentration. Some experimental results on spherical and non-spherical particles are presented and discussed. The experiments cover a particle size range from 1,m to 1000,,m and a particle concentration of up to 12,%. [source]


Transmission Fluctuation Spectrometry in Concentrated Suspensions.

PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 1 2005
Part Three: Measurements
Abstract The theory of transmission fluctuation spectrometry (TFS) was developed for particle size analysis in flowing particle suspensions, whereby the statistical transmission fluctuations are used to extract the particle size distribution (PSD) and particle concentration. In the previous parts of this publication high concentration effects on TFS were investigated theoretically and by simulation. This work presents a study on TFS measurements in concentrated suspensions. By introducing an empirical correction to include the high concentration effects from both the monolayer structure and particle overlapping in the inversion algorithm, it is possible to obtain the particle size distribution and particle concentration over broad ranges of particle sizes and concentrations. [source]


Transmission Fluctuation Spectrometry in Concentrated Suspensions Part Two: Particle Overlapping

PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 6 2004
Ulrich Riebel
Abstract Transmission fluctuations measured on a flowing suspension of particles with a high spatial and temporal resolution can be used to measure the particle size distribution and particle concentration. The theory of transmission fluctuation spectrometry (TFS) was recently developed, whereby the statistical behavior of the entire suspension is described on the basis of a single monolayer, in combination with a layer model describing the suspension as a series of independent monolayers. As the monolayers are assumed to be statistically independent from each other, the transmission through the 3-dimensional suspension is modeled as the product of transmissions through the monolayers. [source]


Microwave absorption of ferrite powders in a polymer matrix

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2006
S. Kolev
Abstract The object of this work is to investigate the microwave absorbing properties of nanocomposite bulk samples. As filler we used magnetite with different particle size in a silicone rubber matrix and investigated the influence of the filler concentration and particle size in the polymer matrix on the microwave nonlinearity in a large frequency range (1 ÷ 13 GHz). We found that the intensity and the frequency at the reflection loss minimum depend on the particle size and particle concentration of magnetite in the samples. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Mass Transport Through PDMS/Clay Nanocomposite Membranes

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2007
Quan Liu
Abstract Poly(dimethylsiloxane)/clay nanocomposite membranes have been synthesized and mass transport properties through those nanocomposite membranes have been investigated. The effect of mechanical deformation on the transport properties of the PDMS (nanocomposite) membranes has also been studied. With the introduction of clay particles into the polymer matrix, mass transport is reduced, likely due to the longer diffusion path, which slows the diffusion process. The effect of membrane extension on diffusion is more complicated. Under small deformation, the permeation flux decreases, but under high deformation, it shows an enhanced diffusion. As the clay particle concentration increased, the effect of external deformation is reduced, and an enhanced diffusion is observed. On a synthétisé des membranes en nano-composites de polydiméthysiloxane et d'argile dans le but d'étudier leurs propriétés de transfert de matière. L'effet de la déformation mécanique sur les propriétés de transfert de ces membranes a également été étudié. Avec l'introduction des particules d'argile dans la matrice des polymères, le transfert de matière est réduit, probablement en raison du chemin de diffusion qui est plus long, ce qui ralentit le processus de diffusion. L'effet de l'extension des membranes sur la diffusion est plus compliqué. Sous faible déformation, le flux de perméation diminue, mais sous forte déformation, la diffusion est améliorée. Lorsque la concentration de particules d'argile augmente, l'effet de la déformation externe est réduit, et une meilleure diffusion est observée. [source]


Pressure buildup in gas-liquid flow through packed beds due to deposition of fine particles

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2002
Murray R. Gray
Abstract In order to understand the increase in pressure drop in hydrotreating reactors due to deposition of fine solids, experiments were conducted with a model suspension of kaolin clay in kerosene. The suspension was circulated through packed beds of catalyst pellets in the trickle-flow and pulse-flow regimes, and the increase in pressure drop measured as a function of particle concentration in the bed. The increase in pressure drop was linear with particle concentrations over the range 0,60 kg.m,3. A consistent approach to modeling the pressure drop behavior was to determine an effective porosity of the packed bed as a function of the concentration of fine particles, then use this porosity in the Ergun equation as a basis for calculating the two-phase pressure drop. Afin de comprendre l'augmentation de perte de charge causée par le dépôt de solides fins dans les réacteurs d'hydrotraitement, des expériences ont été menées avec une suspension modèle d'argile de kaolin dans du kérosène. On a fait circuler la suspension dans des lits garnis de pastilles de catalyseur en régime à écoulement ruisselant et à écoulement pulsé et on a mesuré l'augmentation de perte de charge en fonction de la concentration de particules dans le lit. L'augmentation de la perte de charge est linéaire pour des concentrations de particules se situant dans la gamme de 0,60 kg.m,3. Une façon cohérente de modéliser le comportement de la perte de charge consiste à déterminer une porosité effective du lit garni en fonction de la concentration de fines, puis d'utiliser cette porosité dans l'équation d'Ergun comme base pour calculer la perte de charge diphasique. [source]


Gas hold-up in bubble columns: Operation with concentrated slurries versus high viscosity liquid

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2000
Rajamani Krishna
Abstract The hydrodynamics of bubble columns with concentrated slurries of paraffin oil (density, ,L = 790 kg/m3; viscosity, ,L = 0.0029 Pa·s; surface tension, , = 0.028 N·m1) containing silica particles (mean particle diameter dp = 38 ,m) has been studied in columns of three different diameters, 0.1, 0.19 and 0.38 m. With increasing particle concentration, the total gas hold-up decreases significantly. This decrease is primarily caused by the destruction of the small bubble population. The hold-up of large bubbles is practically independent of the slurry concentration. The measured gas hold-up with the 36% v paraffin oil slurry shows remarkable agreement with the corresponding data obtained with Tellus oil (,L = 862 kg/m3; ,L = 0.075 Pa·s; , = 0.028 N·m,1) as the liquid phase. Dynamic gas disengagement experiments confirm that the gas dispersion in Tellus oil also consists predominantly of large bubbles. The large bubble hold-up is found to decrease significantly with increasing column diameter. A model is developed for estimation of the large bubble gas hold-up by introduction of an wake-acceleration factor into the Davies-Taylor-Collins relation (Collins, 1967), describing the influence of the column diameter on the rise velocity of an isolated spherical cap bubble. On a étudié dans des colonnes de trois diamètres différents, soient 0,1, 0,19 et 0,38 m, l'hydrodynamique de colonnes à bulles avec des suspensions concentrées d'huile de paraffine (masse volumique, ,L = 790 kg/m3; viscosité, ,L = 0,0029 Pa·s; tension de surface, , = 0,028 N·m,1) contenant des particules de silice (diamètre moyen des particules dp = 38 ,m). Lorsque la concentration de particules augmente, la rétention de gaz totale diminue considérablement. Cette diminution est principalement due à la destruction de la population de petites bulles. La rétention de grosses bulles est pratiquement indépendante de la concentration des suspensions. La rétention de gaz mesurée avec la suspension d'huile paraffine à 36% volumique concorde remarquablement bien avec les données correspondantes obtenues avec de l'huile de Tellus (,L = 86 kg/m,3; ,L = 0,075 Pa·s; , = 0,028 N·m,1) comme phase liquide. Des expériences de dégagement de gaz dynamiques confirment que la dispersion dans l'huile de Tellus se compose essentiellement de grosses bulles. On a trouvé que la rétention de grosses bulles diminuait de manière significative avec l'augmentation du diamètre de la colonne. On a mis au point un modèle pour l'estimation de la rétention de grosses bulles de gaz par l'introduction d'un facteur d'accélération dans le sillage dans la relation de Davies-Taylor-Collins (Collins, 1967), décrivant l'influence du diamètre de colonne sur la vitesse de montée d'une bulle à t,te sphérique isolée. [source]


Slot die coating of dilute suspensions

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2009
Yi-Tsun Lin
Abstract An experimental study was carried out to investigate slot die coating of dilute suspensions. Polymethyl methacrylate (PMMA) particles of different sizes were added to glycerol solutions as test fluids. The coating flow experiment was performed on a lab coater. The operating window, which is a domain in which only a stable and uniform coating solution is possible, was determined experimentally. It was found that adding particles has little effect on the physical properties of glycerol solutions, as only the fluid viscosity increases slightly. Two coating defects are commonly observed; ribbing which is caused by flow instability refers to lateral waves on the coated surface, and air entrainment which implies that air bubbles are trapped in the coating solution. Adding particles has little effect on the operating window if the coating defect is ribbing. However, the operating window can be expanded substantially if the coating defect is air entrainment. Higher the particle concentration, or the smaller the particle size, more significant is the expansion of the operating window. The maximum coating speed may increase to 80% for high suspension particle density number. A previous study reported that there exists an optimal particle size which has the largest operating window for a given pure solution; this was not found in the present work. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source]


Population balance modeling of the conidial aggregation of Aspergillus niger

BIOTECHNOLOGY & BIOENGINEERING, Issue 2 2008
P.-J. Lin
Abstract Numerous biotechnological production processes are based on the submerse cultivation of filamentous fungi. Process design, however, is often hampered by the complex growth pattern of these organisms. In the morphologic development of coagulating filamentous fungi, like Aspergillus niger, conidial aggregation is the first step of filamentous morphogenesis. For a proper description of this phenomenon it is necessary to characterize conidial populations. Kinetic studies performed with an in-line particle size analyzer suggested that two distinct aggregation steps have to be considered. The first step of conidial aggregation starts immediately after inoculation. Both the rate constants of formation and disintegration of aggregates have been determined by measuring the concentration of conidia at the beginning of the cultivation and the concentration of particles at steady state during the first hours of cultivation. In contrast to the first aggregation step, where the collision of conidia is presumed to be responsible for the process, the second aggregation step is thought to be initiated by germination of conidia. Growing hyphae provide additional surface for the attachment of non- germinated conidia, which leads to a strong decrease in particle concentration. The specific hyphal length growth rate and the ratio of particle concentration to the growing adhesion hyphal surface are decisive matters of the second aggregation step. Both aggregation steps can be described by population dynamics and simulated using the program package PARSIVAL (PARticle SIze eVALution) for the treatment of general particle population balances. Biotechnol. Bioeng. 2008;99: 341,350. © 2007 Wiley Periodicals, Inc. [source]


Influence of Crystallization Conditions on Rheology and Microstructure of Dense Suspensions of Crystals of Eflucimibe

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 2 2006
S. Teychene
Abstract The crystallization process of eflucimibe, a new ACAT inhibitor, was carried out in a mixture of two solvents, ethanol and n-heptane, by cooling. During the process, as the volume fraction of crystals was raised, the suspension went towards a very structured gel-like network. This phenomenon acts as a brake to the extrapolation of the process. Experiments were carried out in a glass double-jacketed 750,mL reactor in a LABMAX controlled system. At the end of the crystallization, rheological flow characteristics at constant ambient temperature were determined. The samples behave like a plastic fluid. The evolution of the elastic and viscous moduli as a function of the applied strain for a given oscillation frequency was measured. The results showed that the variation of the elastic modulus with particle concentration follows a power law. It was shown that for particle concentration higher than 2,% (volume fraction) needle-like growing crystals form a network in which solvent is trapped. [source]


A New Photothermal Therapeutic Agent: Core-Free Nanostructured AuxAg1,x Dendrites

CHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2008
Kuo-Wei Hu
Abstract A new class of AuxAg1,x nanostructures with dendrite morphology and a hollow interior were synthesized by using a replacement reaction between Ag dendrites and an aqueous solution of HAuCl4. The Ag nanostructured dendrites were generated by the reaction of AgNO3 with ascorbic acid in a methanol/water system. The dendrites resemble a coral shape and are built up of many stems with an asymmetric arrangement. Each stem is approximately 400,nm in length and 65,nm in diameter. The bimetallic composition of AuxAg1,x can be tuned by the addition of different amounts of HAuCl4 to the Ag dendritic solution. The hollowing process resulted in tubular structures with a wall thickness of 10.5,nm in Au0.3Ag0.7 dendrites. The UV/Vis spectra indicate that the strongest NIR absorption among the resulting hollow AuxAg1,x dendrites was in Au0.3Ag0.7. The MTT assay was conducted to evaluate the cytotoxicity of Ag dendrites, hollow Au0.06Ag0.94 and Au0.3Ag0.7 dendrites, and Au nanorods. It was found that hollow Au0.06Ag0.94 and Au0.3Ag0.7 dendrites exhibited good biocompatibility, while both Ag dendrites and Au nanorods showed dose-dependent toxicity. Because of absorption in the NIR region, hollow Au0.3Ag0.7 dendrites were used as photothermal absorbers for destroying A549 lung cancer cells. Their photothermal performance was compared to that of Au nanorod photothermal therapeutic agents. As a result, the particle concentration and laser power required for efficient cancer cell damage were significantly reduced for hollow Au0.3Ag0.7 dendrites relative to those used for Au nanorods. The hollow Au0.3Ag0.7 nanostructured dendrites show potential in photothermolysis for killing cancer cells. [source]


Effect of Solvation Film on the Viscosity of Colloidal Dispersions

CHINESE JOURNAL OF CHEMISTRY, Issue 5 2005
Peng Chang-Sheng
Abstract Viscosity is one of the most important properties of colloids in mixing, transportation, stabilization, energy consumption, and so on. According to Einstein's viscosity equation, the viscosity of a colloidal dispersion increases with the increase of particle concentration. And the equation can be applicable to all micro-particle dispersions, because the effect of solvation films coated on particles can be neglectable in that case. But with the decrease of particle size to nano-scale, the formation of solvation films on nano-particles can greatly affect the viscosity of a dispersion, and Einstein's equation may not be applicable to this case. In this work, one kind of micro-size silica particle and two kinds of nano-size silica particles were used to investigate the effect of solvation films on dispersion viscosity, dispersed in water and ethyl alcohol solvents, respectively. The results of theoretical calculation and experimental investigation show that the increase of viscosity is contributed from solvation films by more than 95 percent for nano-particle dispersions, while less than 10 percent for micro-particle dispersions. [source]


A non-linear and non-Gaussian state-space model for censored air pollution data

ENVIRONMETRICS, Issue 2 2005
Craig J. Johns
Abstract Lidar technology is used to quantify airborne particulate matter less than 10,,m in diameter (PM10). These spatio-temporal lidar data on PM10 are subject to censoring due to detection limits. A non-linear and non-Gaussian state-space model is modified to accommodate data subject to detection limits and outline strategies for Markov-chain Monte Carlo estimation and filtering. The methods are applied to spatio-temporal lidar measurements of dust particle concentrations. Copyright © 2004 John Wiley & Sons, Ltd. [source]