National Repository of Grey Literature 159 records found  1 - 10nextend  jump to record: Search took 0.01 seconds. 
The measurement of the heterogeneous particles in the steam
Bartoš, Ondřej ; Hrubý, Jan ; Ždímal, Vladimír ; Kolovratník, Michal ; Jiříček, I. ; Moravec, Pavel ; Zíková, Naděžda
The aim of this extended abstract is to reveal the work done as cooperation between several institutions which was presented and published in recent years (Kolovratník, 2014). The formation of droplets in low-pressure steam turbines has a significant impact on the efficiency of energy conversion due to the strongly nonequilibrium nature of this process . The condensed water also erodes the turbine blades. A very important question is to what extent heterogeneous nucleation contributes to the phase transition process . In the case of heterogeneous nucleation , the number of droplets depends only on the number of h eterogeneous particles in the system, whereas in the case of homogeneous nucleation, the number of created droplets is determined rather by the expansion rate - in a faster expansion, greater supersaturation and more droplets are formed until the released condensation enthalpy quenches the nucleation.\nThe specific number of droplets (number of droplets per unit mass of steam) formed in the turbine can be determined by optical probes, developed first by Walters and later in the Czech Republic improved by Petr and Kolovratník. Until recently, no information was available on the relative importance of heterogeneous nucleation in forming these droplets.
Experimental Methods to Study Aerosol Nanoparticles.
Ždímal, Vladimír ; Schwarz, Jaroslav ; Ondráčková, Lucie ; Ondráček, Jakub
During the last few decades, the experimental possibilities of studying aerosol particles have grown enormously. Not only is it possible to determine the particle size distribution in different metrics, not only can the chemical composition of the size-resolved aerosol be determined, but methods have been developed over the last two decades that allow all of these tasks to be handled in real time. These methods stem from several basic physical principles: molecular diffusion based on Brownian motion, electrostatic separation of particles with predictable charge, condensational growth of particles, gravitational settling, acceleration of particles in nozzles, inertial impaction, and light scattering on particles.\nHowever, if we are specifically interested in separating particles smaller than 100 nanometers in diameter, the choice of experimental methods would be substantially reduced. In fact, we have only four physical principles that can be utilized in this size range with reasonable degree of uncertainty: Brownian motion, electrostatics, impaction and condensation. For the determination of the chemical composition in a given size range, the most commonly used is a combination of physical / chemical ionization with mass detection, however, the range of quantifiable substances is greatly limited.\nRecently, exposure monitoring of workers in the production of engineered nanoparticles has become increasingly important. Here, the task is further complicated by the fact that it is necessary to sample directly from the vicinity of the worker's mouth to determine personal exposure. As far as the collection of nanoparticles in the respiratory zone is concerned, there is not yet a great choice of options, and experimental methods are still being developed and tested. A promising alternative is a stationary measurement, where state-of-the-art aerosol spectrometers are located close to the working space of the personnel, so that the actual exposure of the worker can be estimated. In this case, however, it is necessary to calibrate the on-line instruments by comparison with simultaneous personal collection.\n
The origin of air pollution on the basis of one year measurements of PM2.5 and PM10 at two urban background stations in Prague
Schwarz, Jaroslav ; Pokorná, Petra ; Rychlík, Š. ; Škáchová, H. ; Smolík, Jiří ; Ždímal, Vladimír ; Vlček, O. ; Hůnová, I.
The particulate matter (PM) mass concentration in cities corresponds to the sum of the concentrations measured at the background stations and the difference between the city and background stations. For this reason, at high background concentrations of PM, the result of emission reduction measures is low. Most of the reported episodes of increased PM concentrations in winter in central European cities are caused by sources of local or regional origin from the combustion of coal and / or biomass for heating purposes. Improvement of air quality in cities is possible provided that causality is understood, especially when it comes to atmospheric aerosol and its concentration, sources and origin.\nThe aim of the work was to determine the origin of air pollution in Prague on the basis of one year parallel measurements of atmospheric aerosol at two urban background stations.\n\n
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Comparison of chemical composition and sources at rural background station between 1993/1994/1995 and 2009/2010: Effect of legislative measures and economic transformation on air quality.
Pokorná, Petra ; Schwarz, Jaroslav ; Krejčí, R. ; Swietlicki, E. ; Havránek, Vladimír ; Ždímal, Vladimír
Presented data of the chemical composition of PM2.5 from the first half of the 1990s are the basis for evaluation of legislative measures and economic development on air quality in the Czech Republic during the last two decades. The aim of this work is to compare the chemical composition and sources of PM2.5 at the rural background station, determined in 2009/2010, with the situation in 1993/1994/1995.
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Dependence of activated aerosol on horizontal hydrometeor type.
Zíková, Naděžda ; Pokorná, Petra ; Pešice, Petr ; Sedlák, Pavel ; Ždímal, Vladimír
Atmospheric aerosol (AA) affects not only cloud formation, but also other cloud properties such as droplet size distribution, chemical composition, etc. The interaction between AA and cloud does not have to be investigated only by aerial measurements, but the same processes can be observed in fog and low clouds. An example of a station suitable for such research is Milešovka station, where the fog (or low clouds) is 55% of the time. Here, measurements were made to describe the effect of fog on the number size distributions of AA and activated nucleation nuclei.
ACTRIS IMP – participation of the Czech republic in the national research infrastructures and ACTRIS Central facilities.
Ondráček, Jakub ; Váňa, M. ; Klánová, J. ; Holoubek, Ivan ; Ždímal, Vladimír
ACTRIS (The Aerosol, Clouds and Trace Gases Research Infrastructure) is pan-european research infrastructure, having the main goals in provision of high quality scientific data and provision of information about short-lived atmospheric components and processes leading to changes in these components in natural and controlled laboratory environment. ACTRIS is a logical continuation of 15-years development of large research infrastructures being funded by member states and European Commission through the Research Infrastructure Programme (including e.g. EARLINET, EUSAAR, CREATE and CLOUDNET).
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NMR Aerosolomics as a Tool to Distinguish Various Types of Aerosol Samples.
Horník, Štěpán ; Schwarz, Jaroslav ; Ždímal, Vladimír ; Sýkora, Jan
In the recent study, the summer and winter aerosol samples were analyzed using NMR aerosolomics approach. The samples were collected in Prague-Suchdol during summer 2008 and winter 2009 in two different particle size fractions - PM2.5 and PM 10. Around 50 compounds were identified in each aerosol spectrum owing to the comprehensive library. The profile of 86 identified compounds, which were identified in the samples altogether, served as an input data for statistical analysis. Multivariate statistical analysis clearly discriminates the two groups studied. Furthermore, it is possible to determine the most significant compounds.
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GROWTH RATES OF ATMOSPHERIC AEROSOL PARTICLES AT FOUR BACKGROUND STATIONS IN THE CZECH REPUBLIC
Holubová, Adéla ; Zíková, Naděžda ; Ždímal, Vladimír ; Plachá, H. ; Bitter, M.
Differences or similarities of growth rates and condensation sinks - characteristics represanting New Particle Formation events were investigated at four background stations located in different types of enviroments, influenced by a different mixture of emissions sources. We found out that the median growth rate is very similar at all stations and the most grequent length of growth lasted between 2 and 4 hours. On the contrary, differences were found in variables affecting growth rates.
Application of Cross-Section Filtration to Detect and Correct Errors Caused by Technical Problems in SMPS.
Wagner, Zdeněk ; Kovanic, P. ; Zíková, Naděžda ; Ondráček, Jakub ; Schwarz, Jaroslav ; Ždímal, Vladimír
The aim of the work is thus development of a robust algorithm for detection of such errors and their fully automatic correction. The algorithm should be fast so that it could be applied in real time.
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Nanoparticles Personal Exposure Measurement Using a Novel Active Personal Nanoparticle Sampler During Machining and Weldind of Nanomaterials.
Ondráčková, Lucie ; Vlčková, Lucia ; Ondráček, Jakub ; Schwarz, Jaroslav ; Ždímal, Vladimír
Development of nanotechnology has grown very rapidly in past decades. Therefore, it has become increasingly important to monitor the exposure of workers in nanoparticle-based manufacturing operations. In order to determine real personal exposure, it is advisable to take a sample within the worker’s breathing zone. To perform this task, there is not much of a choice yet, since experimental methods are still under development. Recently, a novel active personal nanoparticle sampler (PENS) has been developed, collecting both respirable mass fraction (RPM) and nanoparticles (NPs) simultaneously.
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2 Ždímal, V.
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1 Ždímal, Václav
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