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Particle Diameter (particle + diameter)
Kinds of Particle Diameter Selected AbstractsThe Nanocrystalline Nickel with Catalytic Properties on Methanol Oxidation in Alkaline MediumFUEL CELLS, Issue 5 2009R. M. A. Tehrani Abstract The hexagonal closed packed (hcp) nanocrystalline nickel (Ni), with an average diameter of 9.7,±,2.27,nm was deposited uniformly on composite graphite (CG) by the rapid scanning (6,500,mVs,1) voltammetry technique. The hcp-nano Ni-modified CG electrode was investigated for the catalytic oxidation of methanol in alkaline medium through the formation of NiOOH. A high anodic current was obtained at peak potential of +570,mV vs Ag/AgCl. Both the scan rate and the methanol concentration affected the oxidation of methanol. The results showed that catalytic activity had increased with decrease in Ni particle diameter. It was also shown that the hcp-nano Ni/CG modified electrode was the most efficient catalyst in the oxidation of methanol. [source] An investigation on thermal-recycling of recycled plastic resin (spherically symmetric analysis of abrupt heating processes of a micro plastic-resin particle)HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 4 2006Ryuji Yamakita Abstract A fundamental understanding of the physical properties of a micro plastic-resin particle subjected suddenly to hot combustion gas, such as the temperature history in the micro particle and its lifetime, is necessary for effectively realizing thermal recycling of recycled plastic resin. However, micro plastic particles have such small diameters, ranging from 100 µm to 200 µm, that the measurement of temperature histories within them is extremely difficult. In this paper, therefore, a spherically symmetric one-dimensional analysis is applied to the abrupt heating process of a micro plastic resin particle in a high temperature inert atmosphere. Variations of the temperature history and the lifetime with the ambient gas temperature and the initial particle diameter are numerically analyzed, by dividing the entire heating process into four independent periods; the solid heating period, the melting period, the liquid heating period, and the vaporization period. Effects of the Nusselt number on the particle lifetime are also discussed. It is found that, by suitably taking account of the influences of heat transfer properties, the proposed simplified analysis is useful for estimating the fundamental and overall temperature characteristics of a micro plastic resin particle under abrupt heating. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(4): 279,293, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20113 [source] Radio-tracking gravel particles in a large braided river in New Zealand: a field test of the stochastic theory of bed load transport proposed by EinsteinHYDROLOGICAL PROCESSES, Issue 3 2001H. M. Habersack Abstract Hans A. Einstein initiated a probabilistic approach to modelling sediment transport in rivers. His formulae were based on theory and were stimulated by laboratory investigations. The theory assumes that bed load movement occurs in individual steps of rolling, sliding or saltation and rest periods. So far very few attempts have been made to measure stochastic elements in nature. For the first time this paper presents results of radio-tracing the travel path of individual particles in a large braided gravel bed river: the Waimakariri River of New Zealand. As proposed by Einstein, it was found that rest periods can be modelled by an exponential distribution, but particle step lengths are better represented by a gamma distribution. Einstein assumed an average travel distance of 100 grain-diameters for any bed load particle between consecutive points of deposition, but larger values of 6·7 m or 150 grain-diameters and 6·1 m or 120 grain-diameters were measured for two test particle sizes. Together with other available large scale field data, a dependence of the mean step length on particle diameter relative to the D50 of the bed surface was found. During small floods the time used for movement represents only 2·7% of the total time from erosion to deposition. The increase in percentage of time being used for transport means that it then has to be regarded in stochastic transport models. Tracing the flow path of bed load particles between erosion and deposition sites is a step towards explaining the interactions between sediment transport and river morphology. Copyright © 2001 John Wiley & Sons, Ltd. [source] Numerical studies on the reaction of carbon particles in a vacuum residue,air flameINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 9 2006Ho Young Park Abstract A computational work was carried out for the study of one-dimensional, laminar, premixed, flat, atomized vacuum residue (VR) particle,air flames. The mathematical model includes the specified pyrolysis scheme, soot and char oxidation scheme. With some experimental works, the product composition and kinetic parameters of VR pyrolysis were determined and used for the present computational work. The computed results show that the oxidation of VR carbon char and soot occurs mainly in the reaction zone and the oxidation rate of soot is much higher than that of VR carbon char. The oxidation rates of carbon char and soot can be increased with the decrease in particle diameter, and it might be accomplished by the more effective atomization and mixing of solid particles with combustion air. Copyright © 2005 John Wiley & Sons, Ltd. [source] A mathematical model of powder components oxidation during thermal spray processISRAEL JOURNAL OF CHEMISTRY, Issue 3-4 2007Alexey Kossenko A model developed on the basis of kinetic principles of mass transfer allows performing computer simulation of the oxidation of powder materials during the thermal spray process. Such simulation enables one to determine the oxidation degree of the powder. The calculation is based on determining quasi-stationary oxygen diffusion flow on a flying particle. Calculations performed for various spray powders and various flammable gases demonstrate a significant decrease of the oxidation degree with the growth of the particle diameter and density of a spray powder. The calculation results were confirmed by experiments. [source] Effects of diatomite on extrudate swell behavior of polypropylene composite meltsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2010J. Z. Liang Abstract Extrudate swell (i.e., die swell) is an important parameter for characterization of melt elasticity during extrusion of polymeric melts, and die swell ratio (B) is usually used to describe quantitatively the melt swell degree. The B of the polypropylene (PP) composites filled with diatomite particles was measured by means of a melt flow rate instrument to investigate the effects of the filler content and size on the die swell behavior of the composite system melts under the experimental conditions with temperature from 210 to 230°C and load varying from 1.2 to 7.5 kg. The particle diameters were 5, 7, and 13 ,m, and the filler volume fractions were 5, 10, and 15%, respectively. The results showed that the B of the composites decreased nonlinearly with an increase of the filler volume fraction, whereas it increased as a quadratic function with an increase of the particle diameter when the load and temperature were fixed. It might be attributed to the interaction between the inclusions and the matrix, leading to blocking the recovery of the elastic deformation as the composite melts left from the die exit. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Effect of the carboxylic acid monomer type on the emulsifier-free emulsion copolymerization of styrene and butadieneJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2007Mahdi Abdollahi Abstract Carboxylated styrene,butadiene rubber latexes were prepared through the emulsifier-free emulsion copolymerization of styrene and butadiene with various carboxylic acid monomers. The effects of various carboxylic acid monomers on the particle formation process were investigated. The type of carboxylic acid monomer strongly affected the particle nucleation. The number of particles and thus the polymerization rate increased with the increasing hydrophobicity of the carboxylic acid monomers. There was a significant difference in the polymerization rate per particle. The results showed that particle nucleation and growth were dependent on the hydrophilic nature of the carboxylic acid monomers. The average particle diameter of the carboxylated styrene,butadiene rubber latexes in the dry state was obtained through some calculations using direct measurements of the average particle diameter in the monomer-swollen state by a dynamic light scattering technique. Several parameters, such as the polymerization rate, number of latex particles per unit of volume of the aqueous phase, and polymerization rate per particle, were calculated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [source] Supercritical CO2 extraction of accumulated capsidiol from biotic elicitor-activated Capsicum annuum L fruit tissuesJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2 2005ur Salg Abstract This work investigates the supercritical CO2 extraction of capsidiol from pepper fruit tissues activated with Alternaria alternate (Fr) Keissler suspension culture as a biotic elicitor. Capsidiol production in the fruit tissue was markedly increased by the treatment with a biotic elicitor and reached its maximum level after 4 days of elicitation. The effects of separation parameters such as temperature, pressure, supercritical solvent flow rate, particle diameter and also initial capsidiol concentration were investigated on solubility, initial extraction rate and extraction yield. The optimal extraction conditions were obtained at the temperature of 40 °C, the pressure of 400 bar, the supercritical CO2 flow rate of 2 cm3 min,1, and the average particle diameter of 116 µm. The results showed that the ratio of the supercritical CO2 extraction yield to the organic solvent extraction yield was changed from 84 to 97 wt-% depending on the initial capsidiol concentration. Copyright © 2004 Society of Chemical Industry [source] Fabrication by three-phase emulsification of pellicular adsorbents customised for liquid fluidised bed adsorption of bioproductsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 11 2003Mohsen Jahanshahi Abstract A novel dense pellicular adsorbent, custom-designed for liquid fluidised bed adsorption of protein bioproducts, has been fabricated by coating zirconia,silica particles with agarose gel in a three-phase emulsification process. A slurry feedstock comprising solid zirconia,silica particles (120 µm average diameter) suspended in an aqueous solution of agarose was emulsified in an oil,surfactant mixture in a stirred vessel to yield composite droplets. These were subsequently stabilised by cooling to form spherical pellicular particles characterised by a porous, pellicular coat cast upon a solid core. The impact of agitation speed, surfactant concentration, oil viscosity and slurry composition upon the pellicle depth and overall particle diameter was investigated. Pellicle depth decreased with increasing impeller speed and decreased oil viscosity, whilst increased slurry viscosity enhanced that parameter. Initial increases from low concentrations of Span 80 surfactant (0.1% w/v oil) reduced the depth of the agarose pellicle, but the highest values investigated (1.5% w/v oil) promoted particle aggregation. The fluidisation behaviour of particles fabricated under various conditions was characterised by the measurement of expansion coefficients and axial dispersion coefficients for the liquid phase when operated in a standard fluidised bed contactor. Both parameters were found to be comparable or superior to those reported for conventional, composite fluidised bed adsorbents. The controlled coating of porous agarose upon a solid core to yield specific pellicular geometries is discussed in the context of the fabrication of adsorbents customised for the recovery of a variety of bioproducts (macromolecules, nanoparticulates) from complex particulate feedstocks (whole broths, cell disruptates and unclarified bio-extracts). Given the agreement between the size of the pellicular particles and the trends expected from theory, the large-scale manufacture of such particles for customised industrial use is recommended. Copyright © 2003 Society of Chemical Industry [source] SUPERHEATED STEAM-DRYING OF MATE LEAVES AND EFFECT OF DRYING CONDITIONS ON THE PHENOL CONTENTJOURNAL OF FOOD PROCESS ENGINEERING, Issue 3 2006EVERTON FERNANDO ZANOELO ABSTRACT Four drying experiments of mate leaves (Ilex paraguariensis St. Hilaire) were carried out in a packed bed superheated steam dryer by varying outlet steam temperature from 120 to 140C and equivalent particle diameter from 4.7 × 10,3 to 6.95 × 10,3 m. The influence of these variables on the drying coefficient calculated by assuming a simplified drying kinetic model was investigated. A classical statistical approach revealed the significant effect of both factors on this parameter. Two additional drying runs were performed at identical conditions with conventional hot air and low pressure superheated steam, respectively. The influence of drying atmosphere on the total content of phenols was evaluated. A conventional process of extraction by using an aqueous methanol solution was adopted. Analyses for total phenols were performed by spectrophotometry at 715 nm by applying Folin-Denis assay. The leaves dried with superheated steam had approximately 47% higher retention of these compounds. [source] Effects of Calcium Chloride and Sodium Hexametaphosphate on Certain Chemical and Physical Properties of SoymilkJOURNAL OF FOOD SCIENCE, Issue 8 2007P. Pathomrungsiyounggul ABSTRACT:, Soymilks with sodium hexametaphosphate (SHMP) (0% to 1.2%) and calcium chloride (12.50, 18.75, and 25.00 mM Ca) were analyzed for total Ca, Ca ion concentration, pH, kinematic viscosity, particle diameter, and sediment after pasteurization. Higher added Ca led to significant (P, 0.05) increases in Ca ion concentration and significant (P, 0.05) decreases in pH. At certain levels of SHMP, higher concentrations of added Ca significantly increased (P, 0.05) kinematic viscosity, particle diameter, and sediment. Increasing SHMP concentration reduced Ca ion concentration, particle diameter, and dry sediment content, but reduced kinematic viscosity of samples (P, 0.05). Adding SHMP up to 0.7% influenced pH of soymilk in different ways, depending on the level of Ca addition. When the pH of Ca-fortified soymilk was adjusted to a higher level, ionic Ca decreased as pH increased. There was a negative linear relationship between the logarithm of ionic Ca concentration and the adjusted pH of the soymilk. Ionic Ca appeared to be a good indicator of thermally induced sediment formation, with little sediment being produced if ionic Ca was maintained below 0.4 mM. [source] The effect of mixer properties and fill level on granular flow in a bladed mixerAICHE JOURNAL, Issue 2 2010Brenda Remy Abstract The discrete element method was used to study the effect of mixer properties and fill level on the granular flow of monodisperse, cohesionless spheres in a bladed mixer. For fill levels just covering the span of the blades, a three-dimensional (3-D) recirculation zone develops in front of the blades, which promotes vertical and radial mixing. Increasing fill level reduces the size of the recirculation zone, decreases bed dilation and hinders particle diffusivities. However, above a critical fill level, the behavior of the particles within the span of the blade is found to be invariant of fill level. At low-fill levels, the pressure within the particle bed varies linearly with bed height and can be approximated by hydrostatics. At higher fill levels, a constant pressure region develops within the span of the blades due to the angled pitch of the blades. Cylinder wall friction is shown to significantly influence granular behavior in bladed mixers. At low-wall friction, the 3-D recirculation zone observed for high-wall friction conditions does not develop. High-wall friction leads to an increase in convective and diffusive particle mixing. Shear stresses are shown to be a function of wall friction. Blade position along the vertical axis is shown to influence flow patterns, granular temperature and stress. The effect of increasing the mixer diameter at a constant particle diameter was also studied. When the mixer diameter is larger than a critical size such that wall effects are minimized, the observed granular behavior follows simple scaling relations. Particle velocities and diffusivities scale linearly with mixer size and blade speed. Normal and shear stress profiles are found to scale linearly with the total weight of the particle bed. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Design of a two-step pulsed pressure-swing adsorption-based oxygen concentratorAICHE JOURNAL, Issue 2 2010V. Rama Rao Abstract A two-step pulsed pressure-swing adsorption (PPSA) process has been modeled to assess the extent to which an oxygen concentrator might be miniaturized for medical applications. The process consists of a single bed of packed adsorbent particles that is alternately pressurized and depressurized at the feed end. An enriched oxygen product is withdrawn at ambient pressure from the product end when the bed is pressurized at the feed end. The product end remains closed during depressurization. The model development addresses the manner in which axial dispersion enters into the describing equations and the formulation of proper boundary conditions, both of which have not been handled rigorously in some prior modeling studies. The describing equations are solved using COMSOL® Multiphysics software. The effect on the performance of the adsorption time, desorption time, bed length, particle diameter, and imposed pressure drop across the bed have been investigated. An interesting novel result is that for a chosen particle size, bed length, and applied pressure drop, there is an optimum combination of adsorption and desorption times that maximizes the product purity. The results suggest that there are operating windows for both 5A and partially Ag-exchanged Li-substituted 13X zeolite adsorbents wherein the product oxygen purity is greater than 90%. At a given product flow rate within this operating window, the extent of miniaturization is limited by the (maximum) cycling frequency that is practically achievable. Sizing of an oxygen concentrator for personal medical applications is also discussed. A principal conclusion is that a compact oxygen concentrator capable of producing a highly oxygen-enriched product is possible using commercially available adsorbents and implementable operating conditions. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Particle-scale simulation of the flow and heat transfer behaviors in fluidized bed with immersed tubeAICHE JOURNAL, Issue 12 2009Yongzhi Zhao Abstract A kind of new modified computational fluid dynamics-discrete element method (CFD-DEM) method was founded by combining CFD based on unstructured mesh and DEM. The turbulent dense gas,solid two phase flow and the heat transfer in the equipment with complex geometry can be simulated by the programs based on the new method when the k-, turbulence model and the multiway coupling heat transfer model among particles, walls and gas were employed. The new CFD-DEM coupling method that combining k-, turbulence model and heat transfer model, was employed to simulate the flow and the heat transfer behaviors in the fluidized bed with an immersed tube. The microscale mechanism of heat transfer in the fluidized bed was explored by the simulation results and the critical factors that influence the heat transfer between the tube and the bed were discussed. The profiles of average solids fraction and heat transfer coefficient between gas-tube and particle-tube around the tube were obtained and the influences of fluidization parameters such as gas velocity and particle diameter on the transfer coefficient were explored by simulations. The computational results agree well with the experiment, which shows that the new CFD-DEM method is feasible and accurate for the simulation of complex gas,solid flow with heat transfer. And this will improve the farther simulation study of the gas,solid two phase flow with chemical reactions in the fluidized bed. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Dynamics of particles suspended in a yield stress fluid flowing in a pipeAICHE JOURNAL, Issue 5 2008Othmane Merkak Abstract This study seeks to understand the basic mechanisms governing the dynamics of a solid particle in a Poiseuille flow field of a viscoplastic fluid. An experimental set-up to create flows with a prescribed flow rate and enable the particles to be visualized in three dimensions was designed and validated. The absence of slip at the interfaces between flows and particles was characterized. The Reynolds numbers are low, gravity effects negligible and plastic effects significant. The ratio of pipe diameter to particle diameter is 8. The dynamics of a particle in a velocity field depends strongly on its position in the sheared wall zone or in the moving rigid zone. The effect of rigid and sheared zones on particle behavior was examined. Changes in particle translation and rotation velocities were quantified. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source] Flocculation of biological cells: Experiment vs. theoryAICHE JOURNAL, Issue 7 2003Binbing Han Flocculation of biological cells is important in the biotechnology industry, as it could lead to improved efficiencies for bioreactor harvesting operations such as microfiltration. Experimental studies for flocculation of yeast and CHO cells using cationic polyelectrolytes suggest the existence of a steady-state, self-similar floc size distribution. The experimentally determined floc size distributions were modeled using a population balance approach. For flocculated yeast suspensions, the variation of the floc volume fraction with dimensionless particle diameter is predicted by the population balance model assuming a binary breakage distribution function. However, the variation of floc number fraction with dimensionless particle diameter is better predicted assuming a log normal fragment distribution function probably due to the presence of submicron-sized yeast cell debris. For CHO cell flocs, the floc volume and number fractions are predicted using a log normal fragment distribution function. CHO cells are far more fragile than yeast cells. Thus, individual CHO cells in a CHO cell floc can lyse leading to the formation of a number of small particles. [source] Small-molecule release from poly(D,L -lactide)/poly(D,L -lactide-co-glycolide) composite microparticlesJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2005Emily J. Pollauf Abstract Addition of biodegradable polymer shells surrounding polymeric, drug-loaded microparticles offers the opportunity to control drug release rates. A novel fabrication method was used to produce microparticles with precise control of particle diameter and the thickness of the polymer shell. The effect of shell thickness on release of a model drug, piroxicam, has been clearly shown for 2- to 15-µm thick shells of poly(D,L -lactide) (PDLL) surrounding a poly(D,L -lactide-co-glycolide) (PLG) core and compared to pure PLG microspheres loaded with piroxicam. Furthermore, the core-shell microparticles are compared to microspheres containing blended polymers in the same mass ratios to demonstrate the importance of the core-shell morphology. Combining PDLL(PLG) microcapsules of different shell thicknesses allows nearly constant release rates to be attained for a period of 6 weeks. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:2013,2022, 2005 [source] The production of high polymer to surfactant microlatexesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2010Raul P. Moraes Abstract Starved-feed microemulsion polymerization of styrene was investigated. The influence of the type (SDS or Dowfax 2A1) and concentration of anionic surfactant on the final particle size of latex made by the polymerization of microemulsions of styrene was studied. In addition, the influence of 1-pentanol and acrylic acid as cosurfactants was examined. Latexes with 20% solids content and polymer to surfactant ratio of 22 were produced, with a particle diameter of 42 nm and very low polydispersity indexes. Smaller particles are produced using SDS than Dowfax 2A1 for the same weight fraction of surfactant; however, similar particle sizes were obtained with the same molar concentrations of SDS and Dowfax 2A1. Further shot additions of monomer increased solids level as high as 40% and polymer to surfactant ratios greater than 40, with particles remaining monodisperse with average diameter smaller than 60 nm. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 48,54, 2010 [source] Kinetics of the batch cationic emulsion polymerization of styrene: A comparative study with the anionic caseJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2006Jose Ramos Abstract An in-depth study on the kinetics of the cationic emulsion polymerization of styrene in a batch reactor is presented. This study is focused on the effect of the amount of the cationic surfactant dodecyltrimethylammonium bromide (DTAB), using two different cationic initiators: 2,2,-azobisisobutyramidine dihydrochloride (AIBA), 2,2,-azobis (N,N,-dimethyleneisobutyramidine) dihydrochloride (ADIBA), on kinetics and colloidal features such as conversion, number of particles, number average of radicals per particle, mean particle diameter, and particle size distribution (PSD) of the polystyrene latices obtained by emulsion polymerization in a batch reactor. Furthermore, the results of the cationic emulsion polymerization were compared with its homologous anionic case. Using DTAB as cationic surfactant an expected increase in the total rate of polymerization was observed when the DTAB concentration increased. However, the total number of particles increased much more than in the anionic system. On the other hand, a dependence on the particle size of the rate of polymerization per particle together with the average number of radicals per particle was found. These differences between cationic and anionic emulsion polymerizations were explained taking into account the limited particle coagulation observed with cationic surfactants, and the high rate of radical formation of cationic initiators. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4461,4478, 2006 [source] Role of grafting in the emulsion polymerization of vinyl acetate with poly(vinyl alcohol) as an emulsifier.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2001Abstract The role of grafting in particle nucleation during the emulsion polymerization of vinyl acetate with partially hydrolyzed poly(vinyl alcohol) (PVA) as an emulsifier and potassium persulfate as an initiator was investigated. The polymerizations were carried out in batch with a low solids (10%) recipe. An automated reaction calorimeter (Mettler RC1) was used for the direct monitoring of the kinetics of emulsion polymerizations with three medium molecular weight PVAs differing in their degrees of blockiness (Poval 217EE > 217E > 217). Smith,Ewart case 1 kinetics (average number of free radicals per particle < 0.5) were followed in all cases, and no constant rate in interval II was observed. Contrary to what was expected, a nonlinear relationship was observed between the rate of polymerization (Rp) and the number of particles (Np). At Rp max,Np (217E) > Np (217EE) > Np (217), and the final Np was independent of the degree of blockiness of PVA. The particle size distributions were broad (particle diameter = 20,100 nm) and bimodal. On the basis of these data, we concluded that particle nucleation was continuous and was accompanied by extensive limited aggregation during the particle growth stages. The evolution of the amounts of grafted PVA and poly(vinyl acetate) (PVAc) were determined in polymerizations employing the two PVAs differing the most in blockiness (Poval 217EE and 217). The grafted PVAc followed similar profiles, increasing with conversion, particularly near the end of the two reactions. The amounts of grafted PVAc were about the same in the final latexes (37,39%). In contrast, the grafting of PVA was nearly complete by the time monomer droplets had disappeared in each reaction (25% conversion). However, the extent of grafting differed significantly, with the blockier PVA having about one-third the grafting of the more random PVA (,10% vs ,30%). In these low solids recipes, grafting appeared to be primarily a solution event, occurring predominantly in the aqueous phase and not at the particle/water interface, as was previously speculated. The PVAc grafts grew until the molecules became water-insoluble and precipitated, forming polymer particles. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3633,3654, 2001 [source] Alkylated poly(styrene-divinylbenzene) monolithic columns for ,-HPLC and CEC separation of phenolic acidsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 17 2007Zdenka Ku, erová Abstract Macroporous poly(styrene-divinylbenzene) monolithic columns were prepared in fused silica capillaries of 100 ,m id by in-situ copolymerization of styrene with divinylbenzene in the presence of propan-1-ol and formamide as the porogen system. The monoliths were subsequently alkylated with linear alkyl C-18 groups via Friedel-Crafts reaction to improve the retention and chromatographic resolution of strongly polar phenolic acids. A new thermally initiated grafting procedure was developed in order to shorten the time of the alkylation process. The grafting procedure was optimized with respect to the reaction temperature, time, the grafting reactant concentration, and the solvent used. The type of solvent and the grafting temperature are the most significant factors affecting the hydrodynamic properties, porosity, and efficiency of the columns. While the equivalent particle diameter of the grafted column increased, the capillary-like flow-through pore diameter decreased in comparison to non-alkylated monoliths. The hydrodynamic permeability of the monolith decreased, but the monolithic column still permitted fast ,-HPLC separations. [source] Yodel: A Yield Stress Model for SuspensionsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2006Robert J. Flatt A model for the yield stress of particulate suspensions is presented that incorporates microstructural parameters taking into account volume fraction of solids, particle size, particle size distribution, maximum packing, percolation threshold, and interparticle forces. The model relates the interparticle forces between particles of dissimilar size and the statistical distribution of particle pairs expected for measured or log-normal size distributions. The model is tested on published data of sub-micron ceramic suspensions and represents the measured data very well, over a wide range of volume fractions of solids. The model shows the variation of the yield stress of particulate suspensions to be inversely proportional to the particle diameter. Not all the parameters in the model could be directly evaluated; thus, two were used as adjustable variables: the maximum packing fraction and the minimum interparticle separation distance. The values for these two adjustable variables provided by the model are in good agreement with separate determinations of these parameters. This indicates that the model and the approximations used in its derivation capture the main parameters that influence the yield stress of particulate suspensions and should help us to better predict changes in the rheological properties of complex suspensions. The model predicts the variation of the yield stress of particulate suspensions to be inversely proportional to the particle diameter, but the experimental results do not show a clear dependence on diameter. This result is consistent with previous evaluations, which have shown significant variations in this dependence, and the reasons behind the yield stress dependence on particle size are discussed in the context of the radius of curvature of particles at contact. [source] Calcium- and Lanthanum-Modified Lead Titanate (PCLT) Ceramic and PCLT/Vinylidene Fluoride-Trifluoroethylene 0-3 NanocompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2000Q. Q. Zhang Calcium- and lanthanum-modified lead titanate (PCLT) powders with size in the nanometer range were prepared by a sol,gel process. The PCLT gel was annealed at 850°C to produce powder with an average particle diameter of 80 nm. A dense and fine-grained PCLT ceramic, with grain size of ,0.7 ,m, was prepared by sintering the sol,gel-derived powder at 1150°C. The piezoelectric and pyroelectric properties of the PCLT ceramic varied linearly with the degree of poling in the ceramic. PCLT/vinylidene fluoride-trifluoroethylene (P(VDF-TrFE)) 0-3 nanocomposites with PCLT volume fractions of 0.1,0.5 were fabricated, using PCLT powders imbedded in a P(VDF-TrFE) matrix. The ceramic data were used to model the piezoelectric and pyroelectric properties of the PCLT/P(VDF-TrFE) composites, and good agreements were obtained. [source] Bed Stability and Sedimentation Associated With Human Disturbances in Pacific Northwest Streams,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 2 2009Philip R. Kaufmann Abstract:, To evaluate anthropogenic sedimentation in United States (U.S.) Pacific Northwest coastal streams, we applied an index of relative bed stability (LRBS*) to summer low flow survey data collected using the U.S. Environmental Protection Agency's Environmental Monitoring and Assessment Program field methods in a probability sample of 101 wadeable stream reaches. LRBS* is the log of the ratio of bed surface geometric mean particle diameter (Dgm) to critical diameter (D*cbf) at bankfull flow, based on a modified Shield's criterion for incipient motion. We used a formulation of LRBS* that explicitly accounts for reductions in bed shear stress that result from channel form roughness due to pools and wood. LRBS* ranged from ,1.9 to +0.5 in streams within the lower quartile of human riparian and basin disturbance, and was substantially lower (,4.2 to ,1.1) in streams within the upper quartile of human disturbance. Modeling results suggest that the expected range of LRBS* in streams without human disturbances in this region might be generally between ,0.7 and +0.5 in either sedimentary or volcanic lithology. However, streams draining relatively soft, erodible sedimentary lithology showed greater reductions in LRBS* associated with disturbance than did those having harder, more resistant volcanic (basalt) lithology with similar levels of basin and riparian disturbance. At any given level of disturbance, smaller streams had lower LRBS* than those with larger drainages. In sedimentary lithology (sandstone and siltstone), high-gradient streams had higher LRBS* than did low-gradient streams of the same size and level of human disturbance. High gradient streams in volcanic lithology, in contrast, had lower LRBS* than low-gradient streams of similar size and disturbance. Correlations between Dgm and land disturbance were stronger than those observed between D*cbf and land disturbance. This pattern suggests that land use has augmented sediment supplies and increased streambed fine sediments in the most disturbed streams. However, we also show evidence that some of the apparent reductions in LRBS*, particularly in steep streams draining small volcanic drainages, may have resulted in part from anthropogenic increases in bed shear stress. The synoptic survey methods and designs we use appear adequate to evaluate regional patterns in bed stability and sedimentation and their general relationship to human disturbances. More precise field measurements of channel slope, cross-section geometry, and bed surface particle size would be required to use LRBS* in applications requiring a higher degree of accuracy and precision, such as site-specific assessments at individual streams. [source] Compartmentalization in Atom Transfer Radical Polymerization (ATRP) in Dispersed Systems,MACROMOLECULAR THEORY AND SIMULATIONS, Issue 8 2006Yasuyuki Kagawa Abstract Summary: Compartmentalization in atom transfer radical polymerization (ATRP) in dispersed systems at low conversion (<10%) has been investigated by means of a modified Smith,Ewart equation focusing on the system n -butyl acrylate/CuBr/4,4,-dinonyl-2,2,-dipyridyl at 110,°C. Compartmentalization of both propagating radicals and deactivator was accounted for in the simulations. As the particle diameter (d) decreases below 70 nm, the polymerization rate (Rp) at 10% conversion increases relative to the corresponding bulk system, goes through a maximum at 60 nm, and thereafter decreases dramatically as d decreases further. This behavior is caused by the separate effects of compartmentalization (segregation and confined space effects) on bimolecular termination and deactivation. The very low Rp for small particles (d,<,30 nm) is due to the pseudo first-order deactivation rate coefficient being proportional to d,3. Simulated propagating radical concentration ([P,]) as a function of particle diameter (d) at 10% conversion for ATRP of n -butyl acrylate ([nBA]0,=,7.1 M, [PBr]0,=,[CuBr/dNbpy]0,=,35.5 mM) in a dispersed system at 110,°C. The dotted line indicates the simulated [P,] in bulk at 10% conversion. [source] Particle Size of Pneumatically Conveyed Powders Measured Using Impact DurationPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 6 2007Peter J. Coghill Abstract CSIRO Minerals has developed a technique for measuring particle size in pneumatically conveyed powders [1] by measurement of the acoustic waves produced by particle impacts upon a specially designed transducer. Previous work has focused on using the peak acoustic wave amplitude to determine particle size. This produces a spectrum that is hard to determine the particle size from, as the peak amplitude is a non-linear function of particle diameter, and is strongly affected by angle of incidence and velocity of the impacting particle. In this paper impact duration measurements are used to overcome these difficulties while retaining the advantages of being able to measure in high solids loadings of up to at least 0.5,kg/m3 of powder. In laboratory tests the impact size monitor's (ISM) results have been correlated with optical diffraction measurements of the mean (by number) powder size with a correlation coefficient of 0.985 and a relative error of 5.5,%. The ISM operated successfully in the laboratory at a loading of 0.5,kg/m3 of powder and measured particles down to 50,microns in size. [source] Gas-solid Two-phase Mixtures Flowing Upward through a Confined Packed Bed,PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 3-4 2006Yurong 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] Electrostatic Charge Measurement and Charge Neutralization of Fine Aerosol Particles during the Generation ProcessPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 5 2005Chuen-Jinn Tsai Abstract An aerosol charge analyzer has been constructed to measure the charge distribution of NaCl particles generated in the laboratory. A radioactive electrostatic charge neutralizer utilizing Po-210 was used to neutralize the electrostatic charge of the particles. The atomization technique was used to generate NaCl particles with diameters of 0.2 to 0.8 ,m, while the evaporation and condensation method was adopted to generate particles of 0.01 to 0.2 ,m in diameter. The experimental data demonstrates that the absolute average particle charge depends on the particle diameter, and is higher than that calculated by the Boltzmann charge equilibrium for particles within the range of 0.2 to 0.8 ,m. The charge increases with decreasing NaCl concentration. When these particles are neutralized using the Po-210 neutralizer, it is found that the electrostatic charge reaches the Boltzmann charge equilibrium. For 0.01 to 0.2 ,m NaCl particles generated using the evaporation and condensation method, test results show that the absolute average particle charge is higher than that calculated by the Boltzmann charge equilibrium for particles larger than 0.03 to 0.05 ,m in diameter, while it is lower than that predicted by the Fuchs theory [1], for particles smaller than 0.03 to 0.05 ,m. However, after charge neutralization, particles with diameter above 0.05 ,m reach the Boltzmann charge equilibrium condition, and the charges for particles with diameters of 0.010 to 0.05 ,m, agree well with Fuchs' theory. [source] Size Measurement of Very Small Spherical Particles by Mie Scattering Imaging (MSI)PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 5 2004Arne Graßmann Abstract The Mie Scattering Imaging method (MSI) gathers out-of-focus images of dispersed spherical particles present in a laser light sheet and extracts the individual particle diameter from these images. The general idea of the method has been around for more than a decade and a number of papers has dealt with it over recent years. Our work focuses on small particle sizes from 20 ,m down to 2 ,m, a range which has not been tackled so far although it is of great importance in particle systems. We present an optical set-up with a special arrangement of camera lenses that allows to work in this range. An evaluation algorithm based on correlation of the experimental optical information with theoretical Mie scattering was found to give the most accurate results for particle sizing. Besides accuracy measurements on solid spheres the versatility of the method is demonstrated by an example of transient droplet growth between 2,7,,m. [source] Clustering behaviour in gas,liquid,solid circulating fluidized beds with low solid holdups of resin particlesTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2010Jianhua Liu Abstract The flow in a gas,liquid,solid circulating fluidized bed is self-organised and manifests itself with clustering of particles and bubbles. The clustering behaviour in the fluidized bed at low solid holdups of resin particles was experimentally investigated with a high-speed image measurement and treatment technique of complementary metal oxide semiconductor to enhance the fundamental understanding on such a flow. Several new physical quantities were suggested to characterise such ordered flow structures. The main findings are as follows. The clusters of solid particles largely exist as doublets and triplets, the mixed groups of particles and bubbles mostly exist as one bubble carrying two to four particles. Increasing superficial liquid velocity, particle diameter or density weakens the aggregation degrees of both particle and mixed clusters in the riser and downer, except that the increase of superficial liquid velocity enhances the mixed clustering behaviour in the riser. The climbing of the auxiliary liquid velocity or liquid phase viscosity intensifies the aggregation behaviour, except that the increase of liquid phase viscosity reduces the mixed clustering degree in the riser. The influences of superficial gas velocity and surface tension of liquid phase on the clustering behaviour seem to be a little complex and the trends are not simply increasing or decreasing. The life cycle of solid particle clusters in the GLS riser is not sensitive to the operation conditions, being around 0.07,s. The mixed clusters' life cycle is more sensitive to the conditions and physical properties of phases, changing from 0.02 to 0.07,s. L'écoulement dans un lit fluidisé de circulation gaz-liquide-solide s'organise souvent de lui même et se manifeste avec l'agrégation des particules et des bulles. Le comportement de l'agrégation dans le lit fluidisé à faible retenue de particules de résine solide a été étudié expérimentalement en utilisant une technique d'imagerie ultra-rapide de mesure et de traitement à base de semi-conducteur complémentaire à l'oxyde de métal afin d'approfondir la compréhension fondamentale d'un tel écoulement. Plusieurs nouvelles quantités physiques ont été suggérées pour caractériser une telle structure d'écoulement auto-organisé. Les principaux résultats sont comme suit. Les agrégations de particules solides existent principalement en tant que doublets et triplets, les groupes mixtes de particules et de bulles existent pour la plupart sous la forme d'une bulle comportant deux à quatre particules. Une augmentation de la vitesse superficielle du liquide, du diamètre des particules ou de la densité affaiblit à la fois les degrés d'agrégation des particules et des agrégats mixtes dans la colonne montante et dans la colonne descendante, sauf que l'augmentation de la vitesse superficielle du liquide intensifie le comportement d'agrégation mixte dans la colonne montante. L'accroissement de la vitesse auxiliaire du liquide ou de la viscosité de la phase liquide intensifie le comportement d'agrégation, sauf que l'augmentation de la viscosité de la phase liquide réduit le degré d'agrégation mixte dans la colonne montante. Les influences de la vitesse superficielle du gaz et de la tension de surface de la phase liquide sur le comportement de l'agrégation semblent être quelque peu complexes et les tendances ne sont pas simplement croissantes ou décroissantes. Le cycle de vie des agrégats de particules solides dans la colonne gaz-liquide-solide montante n'est pas sensible aux facteurs, tournant autour de 0.07,s. Le cycle de vie des agrégats mixtes est plus sensible aux conditions de fonctionnement et aux caractéristiques physiques des phases, évoluant de 0.02 à 0.07,s. [source] | ||||||||||||||||||||||||||||||||||