bluuebunny/crossref_metadata_2025 huggingface dataset:
4,4′‐Isophthaloyidiphthalic anhydride polyimides
Authors: Pratt J. R. , Blackwell D. A. , St. Clair T. L. , Allphin N. L.
Published: December 2004

A series of polyimides based on 4.,4′‐isophthaloyldiphthalic anhydride (IDPA) was prepared and characterized by inherent viscosity, differential scanning calorimetry (DSC), solubility, wide‐angle X‐ray scattering (WAXS), and isothermal thermogravimetric analysis (ITGA). Film forming, tough, insoluble polyimides were obtained with most of the 11 diamines used for evaluation. Two materials were semicrystalline. Several compositions showed excellent thermooxidative stability by ITGA at 300 and 350°C in air, as compared to Kapton‐H (Du Pont) film. The IDPA‐m‐phenylenediamine (m‐PDA) composition, for example, gave a flexible, amorphous film having a Tg of 259°C (identical with LARC‐TPI) and insoluble in a wide range of solvents. It is based on a potentially low‐cost dianhydride (IDPA) and, unlike LARC‐TPI, a low‐cost, domestically available diamine which gives a negative Ames test.
Effect of crosslinking density on the diffusion of antioxidant in XLPE matrices
Authors: Sheu Kueiying , Huang Samuel J. , Johnson Julian F.
Published: December 2004

A Fourier Transform Infrared spectrometer equipped with a microbeam accessary and a linear translation stage with a pinhole mask was used to monitor the diffusion of antioxidant in crosslinked polyethylene (XLPE) matrices crosslinked with controlled amounts of crosslinking agent. Integration of the peak area for a characteristic peak of the antioxidant at different positions along the sample indicated the changing concentration due to diffusion within 30 days. This technique allowed us to study an antioxidant with a molecular weight in the thousand range. The diffusion coefficients calculated were in the order of 10−11 – 10−10 cm2·s−1. It was observed that the diffusion constants dramatically changed with the crosslinking density.
Shear and nonisothermal elongational characterization of a liquid crystalline polymer
Authors: La mantia F. P. , Valenza A.
Published: December 2004

A commercial liquid crystalline polymer (LCP) sample was characterized both in shear and in nonisothermal elongational flow over a wide range of temperatures (240–350°C). The LCP sample employed was a copolyesteramide of 2,6 hydroxynaphthoic acid, terephthalic acid, and aminophenol manufactured by Celanese and commercially known as Vectra B950. The viscosity decreases dramatically at temperatures above the crystal‐nematic transition of the polymer. At lower temperatures, the extrusion of the sample is mainly due to plastic flow. Die‐swell values are very small and contraction of the extrudate is also revealed, but the sample shows high elasticity. The polymer is not spinnable at very low temperatures, and the melt strength rapidly decreases with increasing temperature.
Gas transport in multilayer packaging structures
Authors: Alger M. M. , Stanley T. J. , Day J.
Published: December 2004

Calculation of gas permeation in food packaging structures can be done using a steady‐state analysis employing the permeability coefficient. While this approach is adequate for some applications, for many others a time‐dependent transport analysis must be considered to make quantitative predictions of shelf life. The limitation of the simple permeability analysis for multilayer structures is illustrated for Saran‐coated polycarbonate and poly(ethylene terephthalate) soda cans. These more detailed calculations on package structures can be done using standard computer library routines to include both the effect of gas sorption and diffusion.
Morphology of polyamide and polyether block amide blends
Authors: Boublil H. , Okoroafor E. , Belhoucine M. , Rault J. , Atochem M. Glotin
Published: December 2004

The morphology of polyamide 12 and polyether block amide blends was investigated by electron microscopy and dynamic mechanical techniques. The blends are not miscible, and phase segregation is observed. In each phase, the lamellar structure of the pure components is observed. The stability of these micro phases is pointed out. When the mass ratio of the hard and soft sequences in the block copolymer is about 4, a partial miscibility takes place.
Cure analysis of sheet molding compound in molds with substructures
Authors: Fan Jyh‐Dar , Lee L. James , Kim Junil , Im Yong‐Taek
Published: December 2004

The effects of material flow, heat transfer, part geometry, and curing agents on the cure of sheet molding compounds (SMC) in molds with substructures were analyzed both experimentally and numerically. It was found that heat transfer during mold filling has a profound effect on the cure pattern, especially for fastcure resins molded for parts with thin dimensions.
Speculation on interfacial adhesion and mechanical properties of blends of PET and thermotropic polyester with flexible spacer groups
Authors: Shin Boo Young , Chung In Jae
Published: December 2004

A thermotropic liquid crystalline polyester (LCP) with a long flexible spacer group in the main chain was prepared by melt polymerization and mixed with poly(ethylene terephthalate) (PET). Differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) studies revealed that the crystallization of PET was accelerated by the addition of LCP in the matrix. Interfacial adhesion between PET and LCP was much improved by introduction of a long flexible spacer in the main chain. Fibers of the blend with 30 wt percent of LCP had fine microfibrillar structure with a large aspect ratio formed in the matrix. Initial modulus and ultimate strength were highly elevated by the addition of LCP due to good interfacial adhesion and microfibrillar structure of LCP in the blend.
Helical flow of curing highly viscous liquids
Authors: Jepsen C. , Mewes D.
Published: December 2004

For profile extrusion of rubber, a shear head is frequently placed at the outlet of the extruder. In the shear head, the rubber compound is heated to its cure temperature by means of internal friction between two coaxially rotating cylinders (annulus). The aim of this examination is to find suitable operating parameters for all rubber compounds. The highest possible temperatures and an even cure profile are the characteristics of suitable operations. The degree of cure should be as close as possible to the maximum cure permitted. For examination of the processes in the annulus, a coupled system of differential equations is set up and solved numerically. The cure profiles established along the annulus are of special interest. The effects of the geometry, the rotational speed of the inner cylinder, the volumetric flow, the operating temperatures, and the viscosity as a function of the shear rate and the temperature are examined. The results of the calculations show that the viscosity, which increases with increasing cure, has a strong effect on the velocity and dissipation profiles. The results of the experimental investigations on a shear head coincide well with theoretical prediction.
An experimental study of multiobjective dynamic optimization of a semibatch copolymerization process
Authors: Choi K. Y. , Butala D. N.
Published: December 2004

Optimal open loop control strategies are developed for a semibatch free radical copolymerization of methyl methacrylate and vinyl acetate using the multiobjective dynamic optimization method. A detailed kinetic model is validated through experimentation and used for the design of optimal controls. Both monomer feed rate and reactor temperature are varied to produce the copolymer of desired composition and molecular weight. The open loop control policies are implemented in a process control computer and tested on an experimental stirred tank polymerization system. Excellent agreement between the model predictions and the experimental data have been obtained.
Effects of thermal modification on the structural properties of thermotropic liquid crystalline copolyester and phenoxy resin blends
Authors: Kodama Minekazu
Published: December 2004

The effects of thermal modification on the structural properties were studied for a poly(ethylene terephthalate‐co‐p‐hydroxybenzoic acid) liquid crystal bended with phenoxy resin. Poor miscibility and phase separation between the blend components are observed by the temperature dependence of dynamic mechanical properties of sample molded at 260°C, over the composition range studied. The miscibility of the blends is increased by molding at 280°C, and the blends molded by increasing the processing time show a dynamic mechanical transition to a homogeneous blend. These changes are the result of an interchange reaction between the blend components. A rubbery modulus has been observed for such blends. This implies the formation of cross‐linked structures that accompany the interchange reactions.
Relationships in a bismaleimide resin system. Part I: Cure mechanisms
Authors: Donnellan Thomas M. , Roylance David
Published: December 2004

A series of bismaleimide resin systems has been examined in order to identify the molecular features responsible for the mechanical response of these materials. A range of network structures was produced both by formulation of resins with different ratios of N,N′‐bismaleimido‐4,4′‐diphenylmethane (BMI) and methylene dianiline (MDA), and by the use of different thermal processing cycles. Spectrographic and chromatographic techniques were used to study the reactions that occurred during the cure. Two principal reactions were confirmed: a Michael addition reaction which provides linear chain growth, and an addition reaction which produces crosslinking through the double bonds of the maleimide group. In general, curing at a lower temperature or increasing the MDA content served to favor chain extension over crosslinking, which might be expected to increase molecular mobility in the resin.
Static shear strength and adhesion friction of some thermoplastics
Authors: Benabdallah S. H.
Published: December 2004

The static shear strength and static friction of three thermoplastics have been investigated for the case of contact between a bulk plastic sample and a very smooth metallic plate. The minimum tangential force required to shear the interfacial adhesion bonds between the two surfaces was measured and defined as the adhesion component of friction Fa. Experimental results showed that Fa is large when the surface energy is high or the interfacial energy is small and that a correlation may exist between this force and the work of adhesion evaluated from Dupré equation. The real area of contact Ar was also measured using an optical device designed to handle samples and experimental conditions similar to the static friction tests. It was found that Ar is proportional to Pa0.9 where Pa is the apparent pressure of contact and an increase of Fa with Pr was observed. The static shear strength τ has been evaluated as the ratio Fa/Ar, and its relationships with the real contact pressure P approximated by linear functions. It was concluded that τ increases at high P, although it has not been verified for ultra‐high‐molecular‐weight polyethylene. An attempt has been made to explain the observed break in the data. The results indicated that (τ/τb) = κ′(τa/Pa) where b refers to bulk, a to apparent values, and κ′ is a proportionality constant that depends on the plastic material.
Electrical degradation of homo‐ and copolymers of styrenes and of styrene/2‐vinylnaphthalene
Authors: Gustafsson A. , Wiberg G. , Gedde U. W.
Published: December 2004

A variety of different styrene monomers [styrene (S), p‐fluorostyrene (p‐FS), pentafluorostyrene (PFS), p‐chlorostyrene (p‐ClS), p‐bromostyrene (p‐BrS), p‐methylstyrene (p‐MS), p‐tert‐butylstyrene (p‐tBS), p‐methoxystyrene (p‐MOS), p‐ethoxystyrene (p‐EOS), and p‐propoxystyrene (p‐POS)] have been polymerized by radical and cationic mechanisms. Copolymers of S/PFS, S/p‐ClS, S/2‐vinyl‐naphthalene (2‐VN), and S/p‐phenylstyrene (p‐PhS) were prepared by radical polymerization. All polymers were fully amorphous and transparent and exhibited only one glass transition temperature in the temperature range 77 to 141°C. Thin films of the polymers were subjected to external electrical partial discharges (PD). Typically, 20 PD experiments were conducted for each polymer and the data for the time to breakdown were adapted to the two‐parameter Weibull distribution function. The resistance towards PD of the various polymers was found to depend strongly on the monomeric structure. Complementary PD experiments on a series of narrow molecular mass polystyrenes confirmed that the minor variation in molecular mass between the different styrene polymers is of no importance for the PD resistance. The PD resistance of the homopolymers decreased in the following order: PS ≈︁ P(p‐MS) > P(p‐tBS) ≈︁ P(p‐BrS) > P(p‐POS) > P(p‐ClS) ≈︁ P(p‐MOS) > P(p‐EOS) ≈︁ P(p‐FS) > P(PFS). The time to breakdown for copolymers of S and PFS decreased monotonously with increasing PFS content. Styrene copolymers with low molar contents of 2‐ VN and p‐PhS exhibited a higher resistance towards PD than PS. The results are discussed with reference to various properties of the studied polymers, such as segmental mobility, ionization potential, resonance stabilization, and reactivity of the radicals formed.
Electrical noise characteristics of carbon black–filled linear low density polyethylene near the percolation threshold
Authors: Bengtsson Per , Kubát Josef , Klason Carl , McQueen Douglas H.
Published: December 2004

Electrical noise measurements have been used to study electrical conduction in carbon black‐filled linear low density polyethylene. Measurements of the resistivity, real part of the relative permittivity, thermal noise, and current noise have been carried out for carbon black contents and temperatures below, near, and above the percolation threshold for electrical conduction. The current noise shows a 1 /fα frequency dependence, with α near unity close to the percolation threshold, but increasing to 1.5 at higher resistivities or temperatures.
Investigation of the three region flow curve of polymeric liquid crystals by rheo‐optical methods
Authors: Asada Tadahiro
Published: December 2004

Steady flow behavior of bulk liquid crystals and polymeric liquid crystals are summarized into a three region flow curve. Changes in the internal structure during deformation and flow were investigated by rheo‐optical methods. Two different optical geometries were used. In one method, a light beam passed through perpendicular to the shear plate, and in the other method a light beam passed perpendicular to the edge of the lamina flow. The results indicate that the details of the internal texture do not necessarily appear in the rheological properties, such as viscosity, and that the molecular orientation mechanism under shear force is fundamentally different in a liquid crystal of rod‐like molecules and a suspended solution of rod‐like molecules. In the isotropic solution, the rod‐like molecules float or are suspended in a solvent and are oriented by the flow field of the solvent fluid. However, in a liquid crystal, the torque propagates directly on the individual rod‐like molecules, affecting their orientation. They flow as if it were a plastic solid.
Interfacial stress concentration and the effect of residual microstress on tensile fracture in filled epoxy resins
Authors: Wang Hong‐Bing , Li Shan‐Jun , Yu Tong‐Yin
Published: December 2004

Interfacial stress concentrations in rubber‐filled epoxy resin and glass bead–filled epoxy resin systems were studied by a photoelastic method. We found that the stress concentration is independent of the applied stress and the particle size, but decreases with increasing chemical bonding at the interface between rubber and matrix. For the rubber‐filled system, stress concentration is present at the equator of particles, while for either the untreated or treated glass bead‐filled system, it is on the two poles. The effect of interfacial residual microstress on tensile fracture was studied, and results showed that the function of residual microstress is limited as tensile elongation increases.
Analysis of polymer membrane formation through spinodal decomposition. III: Two‐dimensional simulations of early‐stage behavior
Authors: Chen Yuh‐Ling , Solc Karel , Caneba Gerard T.
Published: December 2004

A nonlinear diffusion equation is used to study early‐stage spinodal decomposition of polymer solutions, in relation to the membrane formation, in two dimensions. The effects of overall polymer composition and composition‐dependent mobility and diffusivity are included in our simulations. Our results show a kinetically stable structure is established during the early stages, which corresponds to a circular range of peaks in the two‐dimensional frequency spectrum. Such a spectrum is found to result in an interconnected cell structure in the two‐dimensional real space. A decrease in the level of polymer interdomain interconnectedness is obtained as time increases, which indicates the influence of interfacial tension. As the overall polymer composition is increased, an increase in interdomain distances is observed, although the same early stage morphological structure is obtained. Finally, calculated interdomain distances from the two‐dimensional simulation are larger than those obtained in equivalent one‐dimensional model systems.
Injection molding using a generalized eulerian lagrangian formulation
Authors: Alexandrou Andreas N. , Armed Alauddin
Published: December 2004

A mathematical and a numerical approach to model the injection mold filling stage is presented. The approach is based on a Generalized Eulerian Lagrangian (GEL) formulation. In purely Lagrangian formulations the solution is obtained at mesh points which follow the local fluid velocity. On the other hand, in Eulerian formulations the mesh is fixed and the solution is obtained at fixed spatial locations. In injection molding different parts of the flow domain are best analyzed by one but not both formulation methods. The Generalized Eulerian Lagrangian formulation combines the advantages of both formulations: In the same flow problem but different regions the GEL formulation allows the selective application of an Eulerian, Lagrangian, or a mixture of the two formulations. In this work the melt is described using the White‐Metzner constitutive relation and results are shown and discussed for the filling of a cavity from a single gate and from a fully open end under different process conditions.
The recirculating screw mixer: A new small‐volume mixer for the polymer laboratory
Authors: Scott Chris E. , Macosko Christopher W.
Published: December 2004

The recirculating screw mixer (RSM), a new small‐volume intensive mixer for the polymer laboratory, is designed, built, modeled, and tested. This type of batch mixer is intended for the mixing of 1 to 30 cm3 of viscous material at high shear rates. A material element in the mixer experiences alternating screw pump and tubular flows with reorientation between these flows. A mixer with a 10 cm3 sample capacity is built for testing and evaluation. Flow visualization experiments are used to investigate the quality of the distributive mixing achieved. The flows in the mixer are modeled for the cases of a Newtonian fluid and a power law fluid. The Newtonian model accurately predicts the recirculation time for particles suspended in Newtonian silicone oils. The power law model accurately predicts the screw torque obtained with a polystyrene and polyethylene. A method for the measurement of fluid rheology from the operating conditions of the RSM is proposed and tested. The mixing achieved by the RSM is compared to that obtained by a batch mixer with roller blades. Both mixers are used to prepare blends of ethylene‐propylene rubber in polystyrene. The morphologies of the resultant blends are compared and differences in the mixing action are discussed. The mixers are also used to prepare composites of fumed silica in polyethylene. The quality of mixing obtained in the RSM compares quite favorably with that obtained in the batch mixer with roller blades for polystyrene/ethylene‐propylene rubber reactive blends and polyethylene/silica composites.
Refinement of the converging flow method of measuring extensional viscosity in polymers
Authors: Bersted B. H.
Published: December 2004

A critical evaluation of assumptions made in the converging flow analysis of Cogswell is made, and a refined analysis is given by relaxing two of these assumptions. This reexamination of the Cogswell method was motivated by some recent encouraging comparative studies by Laun and Schuch of conventional extensional results and converging flow data. Of the two assumptions relaxed in the analysis, the relaxation of the assumption of a constant extensional viscosity above the orifice, into which the converging flow takes place, is shown to be primarily responsible for the substantially improved agreement with conventional extensional viscosity measurements. Because the variation of the extensional viscosity above the orifice is not known, solution of the equations is not given in closed form, and their solution is solved by an iterative procedure. The good agreement of the results of the modified converging flow analysis given here with conventional extensional measurements over a large range of rates demonstrates that converging flow methods can provide an accurate and relatively routine method of measuring extensional viscosity in molten polymers.
Morphology and mechanical properties of virgin and recycled polyethylene/polyvinyl chloride blends
Authors: Ajji A.
Published: December 2004

In this study, blends of virgin and recycled polyethylene (PE) and poly(vinyl chloride) (PVC), with a methylmethacrylate‐ethylacrylate copolymer as a processing aid, were prepared in the molten state. Different additives such as ethylenevinylacetate copolymers, ethylene‐methacrylic acid ionomer, and two peroxides (dibenzoyl and dicumyl), in the presence of a coupling agent, were used to compatibilize the blend or possibly induce graft structures. The blends' morphologies, tensile properties, and impact properties were studied. For blends with low copolymer concentration (below 3 wt%) the mechanical test data indicated a good performance. In the case of blends with ethylene methacrylic acid ionomer, improvements in the mechanical properties were obtained also at higher additive concentrations. Of the two peroxides, better results were obtained using the dibenzoyl one. The morphological studies indicated that the blends that showed good mechanical properties were better dispersed and had improved interphase adhesion.
Application of statistical experimental strategies to the process optimization of waterborne polyurethane
Authors: Yang Chien‐Hsin , Lin Shih‐Min , Wen Ten‐Chin
Published: December 2004

A modified acetone process for the preparation of aqueous polyurethane (PU) dispersion is investigated. PU dispersions were prepared by polyaddition of isophorone diisocyanate (IPDI) to poly(tetramethylene ether glycol) (PTMG) and dimethylolpropionic acid (DMPA), followed by neutralization of pendant COOH groups with triethylamine (TEA). The resulting prepolymer chain was then extended through reaction with an ethylenediamine (EDA) derivative bearing sulfonate groups. The effect of such preparation conditions as catalyst (dibutyltin dilaurate, DBTDL) concentration, the acetone/PU ratio, phase‐inversion temperature, agitation rate, and water‐addition rate on the average particle size of aqueous PU anionomer dispersions is systematically studied using fractional factorial design and response surface methodology. Fractional factorial analysis indicates that the effects of the acetone/PU ratio, phase‐inversion temperature, water‐addition rate as well as the two factor interactions of DBTDL concentration and phase‐inversion temperature, of the acetone/PU ratio and phase‐inversion temperature, and of acetone/PU ratio and agitation rate are the key variables influencing average particle size of PU dispersions. Empirical models for average particle size are fitted and plotted using central composite experimental design as contour diagrams in order to facilitate examination of the average particle size results. The results show that for a 100 g PU anionomer containing 0.311 wt % COOH and 1.51 wt % SO3H groups, a minimum number‐average particle size of the dispersion ∼ 25 nm can be obtained under an acetone/PU ratio, water‐addition rate, phase‐inversion temperature, catalyst concentration, and agitation rate of 3.65, 2 mL/min, 50°C, 150 ppm and 350 rpm, respectively.
Challenge of synthetic cellulose
Authors: Kobayashi Shiro
Published: December 2004

This article focuses on why and how the chemical synthesis of cellulose was accomplished. The synthesis of cellulose was an important, challenging problem for half a century in polymer chemistry. For the synthesis, a new method of enzymatic polymerization was developed. A monomer of β‐D‐cellobiosyl fluoride (β‐CF) was designed and subjected to cellulase catalysis, which led to synthetic cellulose for the first time. Cellulase is a hydrolysis enzyme of cellulose; cellulase, inherently catalyzing the bond cleavage of cellulose in vivo, catalyzes the bond formation via the polycondensation of β‐CF in vitro. It is thought that the polymerization and hydrolysis involve a common intermediate (transition state). This view led us to a new concept, a transition‐state analogue substrate, for the design of the monomer. The preparation of cellulase proteins with biotechnology revealed the enzymatic catalytic functions in the hydrolysis and polymerization to cellulose. High‐order molecular structures were in situ formed and observed as fibrils (cellulose I) and spherulites (cellulose II). In situ small‐angle neutron scattering measurements suggested a fractal surface formation of a synthetic cellulose assembly. The principle of cellulose synthesis was extended to the synthesis of other natural polysaccharides, such as xylan and amylose, and unnatural polysaccharides. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 693–710, 2005
Latex Particle Size Distributions from Multiwavelength Turbidity Spectra
Authors: Gulari Esin , Bazzi Ghassan , Gulari Erdogan , Annapragada A.
Published: December 2004

Accuracy, range, noise tolerance and resolution of turbitidy spectra analysis as a particle sizing method are discussed with respect to simulated data and data on latex spheres. The fine structure in the turbidity spectra is used to measure multimodal distributions with no apriori assumptions about the distribution.
Comparison of the Size Distribution of Boron Powders as Measured by Malvern Diffractometer and Coulter Counter
Authors: Davies J. Alwyn , Collins Dilys L.
Published: December 2004

Aspects of measuring the particle size distribution and median diameters of fine boron powders have been investigated. It has been demonstrated that high concentrations, typically 20 w/o, of wetting agent are necessary in a predispersion stage, especially if the material has a wide range of particle size. Measurements were made with both Coulter counting and a light scattering technique from which it has been demonstrated that for particles of median diameter in the range 10–30 μm, the latter oversizes with respect to the former by as much as 30%.
Regeneration of Form by Fourier Technique and its Application in Powder Characterization
Authors: Paramanand  , Ramakrishnan P.
Published: December 2004

Conventional shape parameters have serious limitations because of their inability to capture finer surface morphology as well as to regenerate the particle form. This problem has been successfully circumvented by applying Fourier analysis technique to the projected image of the particle profile to obtain Fourier coefficients which have been shown to be size inveriant and insensitive to starting point for digitization. Synthesis technique to regenerate the particle profile from Fourier coefficients has revealed that gradual addition of higher order harmonics brings the regenerated form very close to its original counterpart. The regeneration of the form of particles of different shapes as well as application of few strategy to harmonic amplitudes have amply demonstrated the capability of the technique as a potential tool for characterization of powders.
Variations in, and Relationships of Surface Area, internal angle of friction and compact diametral fracture strength with degree of compaction
Authors: Stanley‐Wood Nayland , Sarrafi Majid
Published: December 2004

The progress of the compaction process to produce from an assembly of particles a coherent mass can be achieved by the application of shear and normal stress. The achievement of a densified coherent mass necessitates, together with the yielding of material, the movement of particles over and between each other. In uniaxial compaction the angle of internal friction, δE, is a projection of the unique critical state line which divides a three dimensional relationship between volume change (V), shear stress (ϕ) and normal stress (σ) into yield domains and surfaces. There is one region for failure and flow (the Hvorslev surface) and another region for failure and consolidation (the Roscoe surface).

In this paper the concepts of the Roscoe and Hvorslev surfaces together with the Coulomb yield criterion have been applied to the uniaxial compaction, over a range of compactable stresses, of titanium dioxide (20–2000 kPa). The characteristics of applied and shear stress, angle of internal friction (δE), angle of shearing resistance (ϕ) and surface area (SBET) were measured and correlated with the compaction stress (σc) and diametral strength (σf) of the compacts to investigate the phenomena of uniaxial compaction.
Computation of the Frequency Distributions of Distances Between Particles Randomly Dispersed in a Fluid Flow
Authors: Raasch Jürgen , Umhauer Heinz
Published: December 2004

Pulse holography can be used as a method for the experimental investigation of transport processes that occur in flows of dispersed phases. Since a complete evaluation of a hologram involves the measurement and recording of the position of every individual particle, it delivers all the information about the spatial distribution of particles at the instant of exposure.

An exact knowledge of the spatial distribution of the dispersed phase is particularly important for those chemical engineering processes which require the spatial distribution of particles to be as homogeneous as possible. Maximum homogeneity is achieved when the particles are distributed purely randomly. For this case, the distributions of distances between neighbouring particles are calculated. They represent a standard which can be adopted as the basis for the assessment of real particle distributions, such as exist momentarily in flows of dispersed phases and are determined by the evaluation of pulse holograms.
Applications of Prism‐Cell Light‐Scattering Spectrometer to Particle Sizing in Polymer Solutions
Authors: Chu Benjamin , Xu Renliang , Nyeo Sulong
Published: December 2004

A prism‐cell light‐scattering spectrometer has been modified to accept both a diode‐array detector for measurements of angular distribution of scattered intensity and a photomultiplier tube for measurements of time‐dependent intensity‐intensity correlation function. This spectrometer permits the practice of light scattering at small scattering angles down to a few degrees. Here we make a brief study of the reliability of characteristic linewidth distributions obtained by several methods of analysis on the correlation data, which correspond to a reasonably broad unimodal distribution. Then the prism‐cell light‐scattering spectrometer is used to characterize a polymer solution consisting of two different molecular weights. To obtain characteristic linewidth distribution, the correlation data are analyzed by both the constrained regularization method (CONTIN) and the maximum‐entropy method (MEM).
Removal of Adhering Particles of Polystyrene Latex and iron oxide on a wall by shear flow in water
Authors: Niida Tohru , Kousaka Yasuo , Furukawa Teiji
Published: December 2004

The velocity for removal of particles adhering on a wall has been measured for polystyrene latex (PSL) and iron oxide particles at laminar and turbulent flow in a glass cell. The results indicate that larger particles detache at lower flow velocities and the width of the velocity range for removing adhering particles is wider when the particle size is smaller in the laminar flow regime. Both the viscous drag force for removing particles determined experimentally and the adhesive force obtained theoretically are proportional to the particle diameter, and the coefficients of friction were estimated to be 0.01–0.08 and 0.01–0.02 for PSL and iron oxide particles, respectively. The ranges of the viscous force, the adhesive force and the coefficient of friction are not so far from the values given by Kanaoka et al. [2].
A Sampler for Total Suspended Particulates with Size Resolution and high sampling efficiency for large particles
Authors: Holländer Werner , Dunkhorst Wilhelm , Pohlmann Gerhard
Published: December 2004

For a field intercomparison of various widely used dust samplers, a reference instrument was needed. Based on a Wide Range Aerosol Classifier (WRAC), several improvements were introduced compared with the original design including mass flow control of the samplers and the plenum air, brushless threephase blowers, hyperbolic inlets and generally a more compact design, allowing for more comfortable operation. In addition, for measurement of small particle size distributions, a Hauke high‐volume, low‐pressure impactor (LPI 150/0.15) was included, so that size distribution information with cuts at 0.12, 0.30, 1.19, 3.14, 10.2, 20.4, 37.4 and 60 μm could be obtained. In addition, the aspiration efficiency was measured under in situconditions and parallel measurements were performed with the two reference samplers built so that the performance was well characterized.
Report Joint Meeting of GVC Committees on “Particle Characterization” and “Crystallization”, Winterthur 1988
Authors: Schäfer Michael
Published: December 2004

This Committee stood under the banner of joint meetings with the Crystallization Committee. Further it was characterized by two aspects, namely technological innovation in connection with measurement methods and their (on‐line) application in engineering processes, whether for the sake of model formation or for process control or quality assurance in industry.
Improved Resolution and Accuracy in Electrical Sensing Zone particle counters through hydrodynamic focussing
Authors: Merkus Henk G. , Liu Houyuan , Scarlett Brain
Published: December 2004

The electrical sensing zone technique is long established, well researched and widely used. It is often used as a reference method against which others are compared or calibrated. This position should not be allowed to disguise the potential which exists for still greater accuracy and versatility. In this paper the use of the hydrodynamic focussing technique is evaluated and an experimental comparison is made with a normal Coulter stand for several samples. It is clearly shown that hydrodynamic focussing enables higher resolution and accuracy to be obtained for materials with narrow or unusual particle size distributions.
Particle Size Analysis by Interaction of Charged Particles with an Alternating Electric Field
Authors: Vanck Rainer M. , Bernigau Norbert G.
Published: December 2004

A theoretical model for the interaction of charged particles with an alternating current field is developed. This model permits the determination of the particle size distribution by a numerical nonlinear iterative method. Results of numerical simulations are presented and discussed. Restrictions on the applicability of the model as an on‐line measuring system are pointed out.
Evaluation of a Commercial Instrument of Sedimentation Field Flow Fractionation
Authors: Mori Yasushige , Merkus Henk G. , Scarlett Brian
Published: December 2004

The analysis of particles in the sub‐micron range by sedimentation field flow fractionation (SFFF) is not new, but its commercial exploitation is recent. This inevitably will lead to a rigorous evaluation of the technique by many laboratories, for many applications, as well as to rapid development.

This paper describes first an evaluation of the new commercial instrument using both ideal and real materials. These experiments lead to a discussion of the software package and of the influence of experimental conditions. A particular study is described of the combination of the SFFF technique with that of quasi‐elastic light scattering. The paper concludes that SFFF now offers the technology for realistically measuring particle size distributions at high resolution in the submicron size range. The analysis time is in the order of one hour, but can be reduced at the expense of resolution.
Constraints On The Size And Shape Of The Receiving Aperture in a phase/doppler system
Authors: Naqwi Amir A. , Durst Franz
Published: December 2004

Using computations based on Mie scattering theory, the influence of the size and shape of the receiving aperture on the signal properties of a phase/Doppler system is examined. For circular apertures exceeding a certain size limit, it is shown that the signal phase is non‐monotonic with respect to the particle diameter and exhibits abrupt changes of 180° at certain values of the diameter. This difficulty may be overcome by using rectangular apertures with appropriate aspect ratios.
Dispersion of Monosized Heavy Particles in Grid Turbulence Effects of Body Forces
Authors: Maquet Cecille , Trinite Michel , Ledoux Michel
Published: December 2004

Dispersion of monosized drops downstream a point injection in a grid‐generated turbulence is studied. Influence of extra bodyforces is also investigated by use of ferrofluid drops and magnetic field. Datas are obtained through LDV and given for fluid and particles mean and fluctuant velocities. Presence probability repartition for particles downstream the injection is obtained by LDV counting.
Velocity and Drop Size Measurements in Fuel Sprays in a direct injection diesel engine
Authors: Pitcher Graham , Wigley Graham , Saffman Mark
Published: December 2004

High‐pressure injection fuel sprays have been investigated in a single‐cylinder research Diesel engine using the laser and phase Doppler anemometry techniques to measure fuel droplet velocities and sizes and their spatial and temporal distributions within the spray. The measurements relate to the determination of the droplets' axial velocity component and diameter on the spray centre line between 75 and 100 nozzle diameters downstream from a single‐hole injector nozzle. The experimental program covered the use of both Diesel and a non‐combusting alcohol fuel. Measurements at radial locations in the spray and at different fuel loads were also taken for the alcohol fuel. Temporally resolved measurements of droplet velocity and size are presented together with time — averaged values in such a way as to isolate the contributions from the leading and trailing regions of each spray and identify two different break — up mechanisms occurring as suggested by a conceptual model of the spray behaviour.
Prediction of Gas‐Particle Turbulent Free or Confined Jet Flows
Authors: de Azevedo Jaão Luis Toste , Pereira José Carlos Fernandes
Published: December 2004

Numerical predictions of two‐phase turbulent gas‐particle flows are reported for two test cases: for a plane jet and for an axisymmetric free jet. The numerical algorithm uses an Eulerian approach for the fluid phase and the particulate phase is described by using a Lagrangian stochastic model. The k‐ε turbulence model was used to characterize the length and time scales of the fluid. In the plane confined jet the influence of the restitution coefficient on the statistical distribution of velocities was analysed. Particular attention was dedicated to the ε equation corrections regarding the problem of the free jet spreading rate overprediction. The influence of the particle tangential momentum equation on the prediction of particle concentration near the centre line in axisymmetric free jets was also analysed. Comparisons between predictions and experimental data are presented and shown to be satisfactory regarding the incomplete knowledge of turbulent multiphase flows.
A Statistically Conditioned Averaging Formalism for Deriving Two‐Phase Flow Equations
Authors: Aliod Ricardo , Dopazo C.
Published: December 2004

A statistical formalism overcoming some conceptual and practical difficulties arising in existing two‐phase flow (2 PHF) formulations and modelling techniques is introduced. Basic theorems for the case of dispersed 2 PHF are presented. Phase interaction terms with a clear physical meaning enter the equations and this formalism provides some guidelines to avoid closure assumptions or to close those terms rationally. Continuous phase averaged continuity, momentum, turbulent kinetic energy and turbulence dissipation rate equations can be rigorously and systematically obtained with this methodology in a single step. These equations display a structure similar to that for single‐phase flows. It is also assumed that the dispersed phase is well described by a "Boltzmann‐type" equation and Eulerian "continuity", momentum and fluctuating kinetic energy equations for the dispersed phase are obtained. A k‐ε turbulence model for the continuous phase is used. A gradient transport model is adopted for the dispersed phase fluctuating fluxes of momentum and kinetic energy. Closure assumptions are proposed for the phase interaction terms. This model is then used to predict the behaviour of an axisymmetric turbulent jet of air laden with solid particles varying in sizes and concentrations. Numerical results compare reasonably well with available experimental data.
The Origin of Turbulence Acquired by Heavy Particles in a round, turbulent jet
Authors: Mastorakos Epaminondas , McGuirk James J. , Taylor Alexander M. K. P.
Published: December 2004

The paper describes the application of a stochastic separated flow model for the dispersed phase to the prediction of a particle‐laden turbulent air jet discharging at 13 m/s from a 15 mm nozzle into stagnant surroundings. Emphasis is placed on the stochastic element of the Lagrangian particle tracking part of the model and on the importance of particle initial conditions over the first 20 jet diameters. Calculations are presented for 80 m̈m sized glass particles which clarify how particles with turbulent Stokes number less than unity acquire axial turbulence much larger than radial. Far from being only a response to the gas‐phase turbulence as implied by the model, the axial turbulence is shown to be also produced by an interaction between particle radial turbulence fluctuations and cross‐stream spatial gradients in particle mean velocity, here referred to as "fanspreading". In addition, initial particle turbulence levels remain identifiable for about 10 jet diameters; the initial radial turbulence reinforces the fan‐spreading contribution and leads to extra generation of axial turbulence farther downstream. In general, the results agree well with experimental measurements.
On‐Line Characterization of the Shape and Size of Particles
Authors: Castellini Carlo , Francini Franco , Longobardi Giuseppe , Pampaloni Enrico
Published: December 2004

An image analysis system for extracting on‐line quantitative geometric and densitometric information from images of ore samples is described. The apparatus employs a pulsed semiconductor laser as the light source for illuminating of a flowing stream of particles and a non‐interlaced solid‐state TV camera as size measurement device in a shadowgraph imaging system. The problem of the sampling volume is discussed and several size distributions of solid particulates are presented. The particle size measurement range is 2–400 μm.
Fly Ash Size Distributions: Use of coulter multisizer and fitting to truncated lognormal distributions
Authors: Ghosal Sarbajit , Ebert Jon L. , Self Sidney A.
Published: December 2004

Accurate information on the size distribution of fly ash is needed to determine its role in the radiation transfer process in pulverized coal combustors. The Coulter Multisizer was used to determine the size distribution in the particle diameter range 1–200 μm. To size over such large diameter ranges, data must be obtained using several orifices, and then combined. In order to use the smaller orifices, the larger particles have to be removed from the sample. A wet‐sieving apparatus, designed for accurate separation of the particles by size, is described. A scheme for combining data obtained using orifices of different diameters is presented. It appears from this study that the lower limit of size measurement using an orifice is set by sensitivity, rather than by signal/noise. A lognormal distribution function, truncated outside the measurement limits, fits the size distribution data well. This function allows detailed size information to be stored compactly using four parameters. Size parameters for six fly ashes representative of U. S. coals are presented.
The Angular Polarization Ratio for the Characterization of Small Droplets in Oil Sprays
Authors: Ossler Frederik , Beretta Federico , D'Alessio Antonio , Tregrossi Antonio
Published: December 2004

The angular patterns of the polarization ratio were calculated for droplets with diameters between 0.020 and 50 μm at 500 nm wavelength. It was observed that the patterns for droplets slightly smaller than 1 μm were dominated by a backward peak belonging to the glory. The peak was successfully used to characterize aerosols of light and heavy oils with a Junge‐like size distribution. Experiments conducted with heavy oil sprays produced by air‐assisted atomization presented the same feature. A quantitative comparison of the experimental results with the Lorenz‐Mie theory showed that the size distribution of these sprays was bimodal.
Sampling of Autocorrelating Powder Flows
Authors: Heiskanen Kari , Niemelä Oili
Published: December 2004

Sampling powder flows in industrial grinding circuits are discussed. Work was done with different types of sampler and with different minerals and sampling objectives. It was found that all the samplers showed marked autocorrelation in sample mass for all the minerals ground. Typical autocorrelation could be found at both high (1 · 10−3–15 · 10−3 Hz) and low (1 · 10−4 – 4 · 10−4 Hz) frequencies. Higher frequencies were attributed to powder transport and low frequencies to mill circuit variations. The effects of the found autocorrelation on systematic errors and on industrial sampling schemes are discussed. Systematic sampling produced large errors if operated at sampling intervals that were high‐frequency autocorrelation frequencies or small multiples of these. Low‐frequency autocorrelation was less detrimental to the sampling results.
Flow Characteristics of Granular Bulk Materials
Authors: Luong Minh Phong
Published: December 2004

The paper discusses the interest in conventional triaxial tests widely used in soil mechanics for a better understanding of both the mechanical behaviour and flow characteristics of granular bulk materials. It proposes a rheological characterization of granular foodstuffs on diverse types of stress path using a conventional triaxial cell. The characteristic state concept, defining the disaggregation threshold of the granular structure, is found to be suitable and even indispensible for examining the mechanical behaviour and the flowability of stored bulk materials. The experimental results readily suggest, as an indicator of the arching effect, a rheological index that characterizes the particle interlocking breakdown and hence the flowability of the stored materials. In addition, this study offers a realistic physical meaning for parameters in use in constitutive models (yield conditions and flow rules) when describing granular flow in various hopper geometries. The case of silos equipped with vibrating hoppers necessitates additionally the study of the rheological behaviour of materials under cyclic and vibratory loadings in order to analyse the processes of densification or disaggregation conditioning the flowability of the stored materials during emptying operations.