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Diffusion Battery – The Renewed Aerosol Spectrometer for Nanoparticles
Holubová Šmejkalová, A. ; Ondráček, Jakub ; Zíková, Naděžda ; Ždímal, Vladimír
The aim of the experiments was to develop new control software for the diffusion battery model DB 3040, in order to optimize measurements with this device. The software allows for larger variability of key control parameters of the diffusion battery and re-opens its application beyond determination of activity size distributions. In comparison with the most widely used method of aerosol spectrometry based on electrical mobility of particles, the method of diffusion battery can be advantageous in situations where we need to measure aerosols of relatively low concentrations with size distributions peaking bellow 20 nanometers.
Fulltext: content.csg -  PDF
Plný tet: SKMBT_C22013010916340 - 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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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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Boiling two phase flow in a coil-shaped duct combined with heat conduction in solid body
Novák, Aleš ; Hrubý, Jan ; Kozel, Karel
Forced-convection boiling in a coil-shaped duct heated from the outer side has an advantage of enhancing the heat transfer and reducing the risk of boiling crisis by pushing the liquid against the outer wall due to centrifugal force. Because of the large heat fluxes, the heat conduction in the solid walls is taken into account. The model is based on differential equations of mass, momentum and energy conservation. In the resulting quasi-1D model, the liquid and vapor phases are allowed to flow at different velocities. The model simulates a laboratory steam generator built in Institute of Thermomechanics AS CR.
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Measurement of heat transfer on an experimental exchanger with a specially-shaped capillary tube
Peukert, Pavel ; Hrubý, Jan
First results were evaluated from tests with a new experimental condensation heat exchanger with a corrugated capillary tube. Several measurements were performed at different inlett steam pressure levels (from 2.3 to 7.4 bar) and different flow velocities on the cooling side of the tube. One of the goals is to observe the effective length of the corrugated tube. The second objective is determining the dependence on the flow velocity of the cooling water. Klíčová slova: condensation heat exchanger, minichanel tube heat
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Nonequilibrium condensation processes in steam turbines in the light of new measurements of heterogeneous particles
Hrubý, Jan ; Kolovratník, M. ; Ždímal, Vladimír ; Bartoš, Ondřej ; Moravec, Pavel ; Jiříček, I.
In a steam turbine, droplets are formed either homogeneously or via heterogeneous nucleation on pre-existing heterogeneous particles. In a pioneering work, the present team developed a system to measure the number and size of heterogeneous particles down to diameter of 3 nm. This work reports on measurements at Power Plant Prunéřov II. For the first time, the data is at higher parameters (0.27 MPa, 250°C), and the diffusion battery was used to determine the size distribuition of the particles, showing count-mean diameter of about 13 nm.
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