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Penetration of Commercial Filter Materials in Detailed Study
Ondráček, Jakub ; Zíková, Naděžda ; Ždímal, Vladimír
Testing of various filter materials proved the functionality, good precision and reproducibility of a home-made filter tester. The measurements of penetration for standard commercial filter materials might be useful for many scientists and other users working with these materials. The comparison of penetration for different types of filtration materials showed wide variety of penetration curves, MPPS and the maximum penetration. This study also confirmed our initial doubts about the standard filter efficiency testing method, regarding the used testing material, setting of MPPS and measuring only the total penetration of a polydisperse aerosol. Therefore, such a study could serve also as a basis for improvements in the filter efficiency standard method, which seems to give insufficient and in some perspectives limited or even misleading information.
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Plný tet: SKMBT_C22012102615351 - PDF
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Size Dependence of Reactive Uptake Coefficient in Chemical Reactions on Aerosol Nanoparticles
Levdansky, Valerij Vladimirovič ; Smolík, Jiří ; Ždímal, Vladimír ; Moravec, Pavel
Chemical reactions in aerosol systems play a significant role in formation of new aerosol particles and their growth in the atmosphere and in various areas of nanotechnology. In the case of nanoscale aerosol particle the size effects can sufficiently affect the rate of chemical reactions both inside the particle and on its surface. The size dependence of a chemical reaction occurring on the nanoparticle surface can be related to the size dependence of the intrinsic activation energy for a chemical reaction and the adsorption kinetics of reactant molecules. Here we consider some aspects of the possible influence of the mentioned effects on the reactive uptake coefficient in the Eley-Rideal mechanism of a chemical reaction.
Fulltext: content.csg - PDF
Plný tet: SKMBT_C22012102615344 - PDF
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Mass Accomodation Coefficient for Nanoscale Aerosol Particles
Levdansky, Valerij Vladimirovič ; Smolík, Jiří ; Ždímal, Vladimír ; Moravec, Pavel
The influence of size effects on physicochemical transformations and transfer processes in the heterogeneous systems with nanoobjects attracts increasing attention of researchers. These problems are of interest for nanotechnology and atmospheric physics. Size effects can influence the cohesive energy as well as the activation energies of vacancy formation and diffusion of atoms in the nanoscale particles (Vanithakumari and Nanda, 2008). Phase transitions (including nucleation) in aerosol systems with nanoscale particles (clusters) also depend on the nanoparticle size (Levdansky et al., 2010). Hear we discuss the size dependence of the mass accommodation coefficient gama in the gas–nanoparticle system.
Fulltext: content.csg - PDF
Plný tet: SKMBT_C22012102615343 - PDF
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Growth of Sulfuric Acid Nanoparticles at Wet and Dry Conditions
Škrabalová, Lenka ; Brus, D. ; Ždímal, Vladimír ; Lihavainen, H.
Aerosol particles influence global radiative balance and climate directly through scattering and absorbing solar radiation and indirectly by acting as condensation cloud nuclei. The atmospheric nucleation is often followed by a rapid growth of freshly formed particles. The initial growth of aerosol is the crucial process determining the fraction of nucleated particles growing into cloud condensation nuclei sizes (~ 50 nm and larger). Many recent studies have suggested that the sulfuric acid plays a key role in the atmospheric nucleation and subsequent growth of newly formed particles. (Sipilä et al., 2010). The subject of this experimental study is growth behaviour of sulfuric acid nanoparticles produced by homogenous nucleation at wet and dry conditions.
Fulltext: content.csg - PDF
Plný tet: SKMBT_C22012102615341 - PDF
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Aerosol Dynamics – Mathematical Formulation, Numerical Solution
Pušman, Jan ; Ždímal, Vladimír
Mathematical and computer modeling of aerosols is used in a wide range of applications including atmospheric physics and chemistry, environmental protection, nuclear safety and industrial applications such as the production of nanomaterials. The aim of this work is twofold. We present a closer look at some aspects of mathematical modeling of aerosols as sub-discipline of continuum mechanics. We provide an overview of common methods and we discuss limitations on their applicability. The long-term goal of authors is to create a new solver of aerosol dynamics based on OpenFOAM platform. A mathematical formulation of the problem is given in terms of Navier-Stokes- Fourier system coupled with evolutionary equation governing aerosol size distribution. Trial numerical simulations in a 2D channel were performed under physically simplified conditions.
Fulltext: content.csg - PDF
Plný tet: SKMBT_C22012102615340 - PDF
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Statistical Evaluation of New Particles Formation Events at Košetice Station
Zíková, Naděžda ; Ždímal, Vladimír
In this work, we present a basic statistical evaluation of NPF at Košetice background station in the region of middle Europe.Variability between the two years is not high, especially ratio of NPF events to all classifiable days varies only by several percents between the two years. Results from Košetice station are very similar to those from Hyytiala station (Finland), despite different geographical location and different time periods.
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Plný tet: SKMBT_C22012102615331 - PDF
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Processes of Nanoparticle Formation in Low Temperature Plasma
Brožek, V. ; Mastný, L. ; Moravec, Pavel ; Neufuss, Karel ; Ondráček, Jakub ; Ždímal, Vladimír
This work describes the synthesis of nanoparticles during interaction of several different metals (Ag) or their respective oxides (TiO2, Cr2O3) with oxygen-hydrogen plasma having temperatures above 25000 K. Resulting nanoparticles and/or their aggregates in the size range of 25-300 nm were deposited on metallic targets and/or trapped in the water filters and separated using ultra-centrifugal apparatus. The aerosol spectrometer SMPS 3936 (scanning mobility particle sizer) was used to study the particle size distribution of generated nanoparticles in the size range 14 – 700 nm. In order to extend the measured particle size range towards larger sizes, the APS 3321 spectrometer (aerodynamic particle sizer) with the size range 500-20000 nm was used simultaneously. Both spectrometers were set-up to sample with three minute time resolution. Process conditions and production of inorganic nanoparticles of defined composition are discussed in this work.
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Influence of Size Effects on Homogeneous Nucleation Inside Nanoparticles
Levdansky, V.V. ; Smolík, Jiří ; Ždímal, Vladimír ; Moravec, Pavel
It is known that many physicochemical processes in aerosol systems with nanoscale particles and in nanoparticles themselves depend on the particle size. The influence of size dependence of the condensation coefficient on gas-phase nucleation was discussed in (Levdansky et al., 2010). Some problems related to nucleation in confined space, in particular the depletion effect of the ambient phase, were considered in (Kožíšek et al., 2011; Schmelzer and Abyzov, 2011). Here we study the size effects in homogeneous nucleation inside nanoparticles related to size dependence of the effective rate constant for the attachment of monomers to the critical cluster.
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