Description Of Particle Size Distribution Research Articles

Monte Carlo simulations of homogeneous nucleation and particle growth in the presence of background particles

The application of the Monte Carlo (MC) simulation technique for the modelling of nucleation processes with an existing background particle concentration is presented in this paper. Next to the nucleation of novel particles, the coagulation of an existing particle population as well as the condensational growth and evaporation of unstable particles (whose diameter is smaller than the critical Kelvin diameter) are included into the simulation. The usage of statistically weighted MC particles allows the description of particle size distribution (PSD), whose concentrations differ in several orders of magnitude. It is shown, that this approach allows to model the complex interplay between freshly nucleated particles and an existing background particle population. In this work, the nucleation of novel particles is modelled by three different nucleation theories discussed by [Girshick, S. L. and C.-P. Chiu (1990), The Journal of Chemical Physics 93], which comprise of (1) the classical nucleation theory, (2) a mathematical correction to (1) and (3) a self-consistency correction of (2). For the chosen simulation conditions, the resulting PSDs are independent of the used nucleation theory for longer simulation times, in which the simulations are described by the coagulation mechanism only. The time-frame is identified for which relevant discrepancies of the PSDs have to be taken into account.

New Theoretical and Methodological Approaches to the Study of Heat Transfer in Coal Dust Combustion

The existing theories of heat transfer in combustion chambers of boiler units fail to take into account a number of important factors that affect the reliability of results, and the methodological approaches to optimizing combustion processes can be revised in view of the spatial and temporal parameters of flame. Hence, the research aimed to improve the fundamental theoretical and methodological principles of studying heat transfer in coal dust combustion in the combustion chambers of industrial steam generators. The authors proposed to extend the theory of heat transfer with the mathematical description of particle size distribution of coal dust. In addition, the authors used the developed mathematical model of coal dust combustion based on a continuous curve of the particle size distribution in the ensemble. The mathematical model is consistent with the aeromechanical and thermal characteristics of flame. This work introduced a concept of flame continuum as a continuous medium, where the processes of combustion and heat transfer are studied. To achieve the research aim, in this paper, the methods of combustion chamber zoning, the equations of stationary and non-stationary heat conduction, radiation, and convective heat transfer, were used. These methods were tested on a number of high-temperature units.

A modified model for estimating the full description of soil particle size distribution

Zhao, P., Shao, M-a., Omran, W. and She, D. 2013. A modified model for estimating the full description of soil particle size distribution. Can. J. Soil Sci. 93: 65-72. A full description of the particle size distribution (PSD) curve is widely used as a basis for estimating soil hydraulic properties. However, the incomplete experimental data of PSD sets (i.e., percent clay, silt, and sand) often limit its uses. In this study, an empirical model modified from the Weibull model was used to estimate the complete description PSD from clay, silt and sand fractions. Results show that the estimated distribution agrees reasonably well with the actual distribution for 168 soils samples studied within six different textures. The values of coefficients of determination, the average absolute deviation and the maximum absolute deviation were 98.6%, 3.3% and 12.6%, respectively. The modified model performed best for silt loam samples containing about 70% silt content. The estimation accuracy varied with radii interval. For the estimated PSD curve, a 0.05-0.1 mm size interval was most poorly estimated and had the maximum deviation (28.2%), while the 0.5-1 mm interval was estimated well by the modified model. The model is recommended to estimate complete soil PSD using only clay, silt and sand fractions, which can be well fitted by the Weibull model. Further studies are suggested to validate the PSD estimation by this model when applied to soils with greater variation in texture.

An improvement on the power law for the description of particle size distributions in potable water treatment

In potable water treatment, the use of the power law to describe particle size distributions (PSDs) in particle counting practice is common. The power law is popular because it allows the reduction of numerous data bits to two meaningful parameters that completely describe the size distribution characteristics of a particle suspension. The model is however flawed. This paper presents the further development of an improved model (the variable-beta model) first proposed by Lawler (1997). Both the power law model and variable-beta model are used to describe the PSDs of a large number of potable water treatment samples taken from full-scale plants and the resulting correlations are compared. The findings from the comparison of data reduction methodologies support the argument that the variable-beta model is fundamentally more correct than the power law model and consequently describes the PSDs better.

Preparation and characterization of ball‐milled Nafion® powders for membrane applications

AbstractA method for producing Nafion® powder from commercially available pellets, and using this powder to produce membranes, is described. A description of particle size distribution, chemical composition, and thermal properties of Nafion® powders prepared by high‐energy ball milling of pellets is given. Nafion® powders prepared in this manner exhibit thermal behavior similar to that of the precursor pellets; however, traces of iron from the milling materials are shown to be present through transmission electron microscopy analysis of the particles. The membranes prepared by hot pressing of the Nafion® powders also show thermal behavior similar to that of the precursor pellet materials. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2275–2281, 2004

Experimental Investigation of Particle Break-up during Cold Deformation of Non Heat Treatable Aluminium Alloys

In the present work, image analysis has been used for a quantitative description of particle size distributions in NHT-aluminium alloys. The influence of magnification on the experimental results has been investigated. The results demonstrate that more large particles are detected when the magnification is reduced. For the present investigation this is probably due to that a larger sample area is measured at the lowest magnification, thereby increasing the probability of finding large particles. The particle break-up during processing of NHT-alloys has been investigated after cold rolling and hot plane strain deformation. For cold rolling, there is an increased tendency for particle break-up with increasing strain for 1050 and 3003, with the 3003-alloy showing the strongest tendency for such a break-up. The 5005-alloy did not show any sign of break-up with increasing strain.

Experimental Investigation and Modeling of a Wet Flue Gas Desulfurization Pilot Plant

A detailed model for a wet flue gas desulfurization (FGD) pilot plant, based on the packed tower concept, has been developed. All important rate-determining steps, absorption of SO2, oxidation of HSO3-, dissolution of limestone, and crystallization of gypsum were included. Population balance equations, governing the description of particle size distributions of limestone in the plant, were derived. Model predictions were compared to experimental data such as gas-phase concentration profiles of SO2, slurry pH profiles, solids content of the slurry, liquid-phase concentrations, and residual limestone in the gypsum. Simulations were found to match experimental data for the two limestone types investigated. A parameter study of the model was conducted with the purpose of validating assumptions and extracting information on wet FGD systems. The modeling tools developed may be applicable to other wet FGD plants.

The XL-I analytical ultracentrifuge with Rayleigh interference optics

The Optima XL-I analytical ultracentrifuge with integrated Rayleigh interference and ultra-violet/ visible optics, and how it provides a modern, convenient platform for acquiring hydrodynamic data, is described. With a choice of optical systems that can be used either alone or in combination, together with an easy to use software control interface, its usefulness in simplifying the analysis of interacting molecular systems and description of particle size distributions is indicated.

A population balance approach for the description of particle size distribution in suspension polymerization reactors

There exist modelling and experimental methodologies to meet productivity (conversion and batch time) and product molecular weight distribution (MWD) quality specifications in suspension polymerization reactors. However, no counterpart exists to address the issue of particle size distribution (PSD), which is of fundamental importance in determining suspension stability and product quality attributes. In industrial practice, PSD considerations are guided by mean-size correlations from the Weber number theory. The setting up of an industrial reactor usually demands considerable scaling and testing efforts. In this work, we obtain a model to describe the evolution of the PSD in a suspension polymerization reactor. First, relevant phenomena are identified and modelled individually: suspension MWD, suspension viscoelasticity, interfacial tension, injection—dissipation of mechanical energy and drop breakage—coalescence mechanism. A central point is the derivation of analytic expressions for breakage and coalescence rate distributions. A drop population balance leads to an integrodifferential equation whose numerical solution yields the evolution of the PSD. Breakage—coalescence parameters are estimated from the reported experimental data. Modelling identifies the role of individual phenomena and their interplay.

Comminution of food by complete-denture wearers.

A method for quantifying the comminution of an artificial test food (Optosil) was evaluated with respect to its suitability for measurements of masticatory performance in complete-denture wearers. Reference was made to subjects with natural dentitions. The description of particle size distributions generated by complete-denture wearers by a Rosin-Rammler equation was subject to limitations, due to the presence of large proportions of almost-intact particles, which had hardly been damaged or broken during chewing. This finding might be explained by: (i) the relatively high fracture strength of Optosil as compared with natural foods; and (ii) the limitations of complete-denture wearers in exerting bite forces. The particle size distributions obtained after repeated measurements and described by linear interpolation of data points were reproducible. In comparison with young adults with natural dentitions, the denture-wearers needed approximately seven times more chewing strokes to achieve an equivalent reduction in particle size.