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Particle Radius (particle + radius)

Distribution by Scientific Domains

Polymers and Materials Science	50%

Selected Abstracts

Computationally efficient expressions for the collision efficiency between electrically charged aerosol particles and cloud droplets

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 618 2006
S. N. Tripathi
Abstract A multiple factor parametrization is described to permit the efficient calculation of collision efficiency (E) between electrically charged aerosol particles and neutral cloud droplets in numerical models of cloud and climate. The four-parameter representation summarizes the results obtained from a detailed microphysical model ofE, which accounts for the different forces acting on the aerosol in the path of falling cloud droplets. The parametrization's range of validity is for aerosol particle radii of 0.4 to 10 ,m, aerosol particle densities of 1 to 2.0 g cm,3, aerosol particle charges from neutral to 100 elementary charges and drop radii from 18.55 to 142 , m. The parametrization yields values ofE well within an order of magnitude of the detailed model's values, from a dataset of 3978E values. Of these values 95% have modelled to parametrized ratios between 0.5 and 1.5 for aerosol particle sizes ranging between 0.4 and 2.0 , m, and about 96% in the second size range. This parametrization speeds up the calculation ofE by a factor of ,103 compared with the original microphysical model, permitting the inclusion of electric charge effects in numerical cloud and climate models. Copyright © 2006 Royal Meteorological Society [source]

Size-Dependent Endocytosis of Nanoparticles

ADVANCED MATERIALS, Issue 4 2009
Sulin Zhang
The cellular uptake of nanoparticles by living cells is predicted to be strongly size-dependent, according the thermodynamic analysis, and an optimal particle radius of , 25,30 nm at which the cellular uptake reaches a maximum of several thousand is shown to exist. The theoretical prediction provides valuable guidance for the rational design of nanoparticle-based drug-delivery systems. [source]

Modeling and experimental studies on combustion characteristics of porous coal char: Volume reaction model

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 5 2010
Anup Kumar Sadhukhan
A generalized single-particle model for the prediction of combustion dynamics of a porous coal char in a fluidized bed is analyzed in the present work using a volume reaction model (VRM). A fully transient nonisothermal model involving both heterogeneous and homogeneous chemical reactions, multicomponent mass transfer, heat transfer with intraparticle resistances, as well as char structure evolution is developed. The model takes into account convection and diffusion inside the particle pores, as well as in the boundary layer. By addressing the Stefan flow originated due to nonequimolar mass transfer and chemical reactions, this work enables a more realistic analysis of the combustion process. The model, characterized by a set of partial differential equations coupled with nonlinear boundary conditions, is solved numerically using the implicit finite volume method (FVM) with a FORTRAN code developed in-house. The use of a FVM for solving such an elaborate char combustion model, based on the VRM, was not reported earlier. Experiments consisting of fluidized-bed combustion of a single char particle were carried out to determine the internal surface area of a partially burned char particle and to enable model validation. Predicted results are found to compare well with the reported experimental results for porous coal char combustion. The effects of various parameters (i.e., bulk temperature and initial particle radius) are examined on the dynamics of combustion of coal char. The phenomena of ignition and extinction are also investigated. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 299,315, 2010 [source]

Sorption and Diffusion of Propylene and Ethylene in Heterophasic Polypropylene Copolymers

MACROMOLECULAR SYMPOSIA, Issue 1 2007
Michael Bartke
Abstract Summary: Sorption experiments of ethylene and propylene in different polypropylene powder samples, both homopolymer and heterophasic copolymers with different rubber content, have been carried out in a high-pressure magnetic suspension balance at 10 bars pressure and 70,°C. The gross solubilities measured can be well correlated with the rubber content of the polymer samples. Solubility of ethylene and propylene in the rubber phase differ from solubility in the amorphous fraction of the homopolymer, especially the concentration ratio of propylene to ethylene differs significantly between rubber phase and amorphous fraction of the homopolymer. From the slope of monomer uptake, information on kinetics of mass-transfer can be gained. No significant differences were observed in terms of mass-transfer for ethylene and propylene. With increasing rubber content, effective diffusion coefficients increased slightly. By combined sorption studies with powder samples and compressed films, information about both effective diffusion coefficients and the effective length scale of diffusion could be gained. It could be shown, that the particle radius is not the characteristic length of diffusion in the studied powder samples. Mass transfer of nearly all samples could be described by a constant diffusion length of 120 to 130 µm, independently on particle size. This indicates that the effective scale of diffusion in polymer particles is in between microparticle and macroparticle scale used in classical particle modeling. [source]