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Homogenní nukleace vody v difúzní komoře s laminárním tokem
Manka, A. ; Brus, David ; Hyvärinen, A.-P. ; Lihavainen, H. ; Wölk, J. ; Strey, R.
Homogeneous nucleation rates of water at temperature between 240 and 270 K were measured in a laminar flow diffusion chamber at ambient pressure and Helium as carrier gas. The experimental results extend the nucleation rate data from literature substantially. Using the macroscopic vapor pressure, density and surface tension of water we calculate the nucleation rates predicted by classic theory and by the empirical correction function of CNT by Völk and Strey. As in the case of other systems, CNT predicts a stronger temperature dependence than experimentally observed, whereas the agreement with empirical correction function is good. Furthermore, the isothermal nucleation rates curves allow us to determine the experimental critical cluster sizes by use of the nucleation theorem. A comparison with the critical cluster sizes calculated by use of the Gibbs-Thomson equation is remarkably good.
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Kavitace a nukleace bublin ve vodě s příměsemi
Zima, Patrik ; Maršík, František ; Sedlář, M.
The latest advances in modeling of cavitation in water flows and experimental investigation of bubble nucleation in a cavitation nozzle will be presented. The emphasis will be put on presenting the results of the recent measurements with cavitation nozzle and the critical assessment of the applicability of the cavitation nozzle principle for determining the size of critical bubble radii. Some results of numerical modeling of cavitation in pumps will be summarized.
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Model determination of the chemical forms of iron and nickel in the surface waters
Kubínová, Petra
The paper is focused on the evaluation of the possible chemical forms of occurrence of the elements iron and nickel in the surface waters in the experimental catchment Lesní potok (Černokostelecko region). The program PhreeqC (version 2.4.2.) was used for the speciation calculations. There is used the time period from November 2005 to May 2006 as the input data in the evaluation. The redox conditions markedly influence the content of the individual chemical forms of studied elements. Studied elements are present mainly in their mobile (divalent) state during the year. In the extreme case, i.e. during the snow melt, the values of redox potential are considerably higher and the concentration of trivalent state of iron (and nickel) is increasing.
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Natural flooding in Lužnice floodplain - an holistic approach
Pithart, David ; Montagová, Martina ; Hartvich, P. ; Černý, R. ; Prach, K.
Natural flooding was analysed in the Lužnice River floodplain in a holistic approach. Benefits of natural flooding can be summarised as folows: 1. Water retention is increased due to the soil absorption, evapotranspiration, filling of oxbows, pools and natural depressions and finally the space between the river terreces. Real flood event are analysed here in terms of water distribution among these processes. 2. Natural flooding reduces the loss of ionts from the watershed by flowing the river outflouw and loss of carbon loss by slowing the decomposition processes. 3. Flooding creates and maintains floodplain geobiodiversity by re-forming of floodplain subsystems and differentation of its impact on these subsystems. For these reasons, maintaining and enchenging of natural flooding seems to be a prerequisite of sustainable management of riverine landscape.
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