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Consistency of empirical corrections of the classical nucleation theory for nucleation in steam with nucleation experiments and molecular simulations
Hrubý, Jan ; Duška, Michal ; Němec, Tomáš ; Kolovratník, M.
We compare experimental nucleation rates for water vapour in various carrier gases, nucleation rates deduced from empirical adjustments of the classical nucleation theory (CNT) earlier developed to reproduce pressure and optical data for condensing steam flows in converging-diverging nozzles and turbine stages, and ucleation rates obtained from molecular simulations. Results of original molecular dynamic simulations for TIP4P/2005 force field in the NVE conditions are provided. New experimental nucleation rate data sets are generated based on empirical CNT corrections by Valha and Nedbal (1980) and by Petr and Kolovratník (2011). Correction of the CNT for non-isothermal nucleation conditions is applied to experimental, simulated and the derived experimental data. The derived experimental\nnucleation rate data follow a similar temperature trend as the nucleation rate data for water vapour in carrier gases at lower temperatures. The ratio of observed nucleation rates to CNT predictions decreases more steeply with temperature than the empirical correction by Wölk et al. (2002). Ratios of nucleation rates computed from molecular simulations to CNT predictions do not show a significant temperature trend.
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Molecular Simulations of the Vapor–Liquid Phase Interfaces of Pure Water Modeled with the SPC/E and the TIP4P/2005 Molecular Models
Vinš, Václav ; Celný, David ; Planková, Barbora ; Němec, Tomáš ; Duška, Michal ; Hrubý, Jan
In our previous study [Planková et al., EPJWeb. Conf. 92, 02071 (2015)], several molecular simulations of vapor-liquid phase interfaces for pure water were performed using the DL POLY Classic software. The TIP4P/2005 molecular model was successfully used for the modeling of the density profile and the thickness of phase interfaces together with the temperature dependence of the surface tension. In the current study, the extended simple point charge (SPC/E) model for water together with TIP4P/2005 were employed for the investigation of vapor-liquid phase interfaces over a wide temperature range from 250 K to 600 K. Results of the new simulations are in a good agreement with most of the literature data. TIP4P/2005 provides better results for the saturated liquid density with its maximum close to 275 K, while SPC/E predicts slightly better saturated vapor density. Both models give qualitatively correct representation for the surface tension of water.
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Tepelné výpočty pro zařízení pro ukládání tepla s využitím materiálů se změnou skupenství
Duška, Michal ; Hrubý, Jan
Výzkumná zpráva popisuje výsledky dosažené v rámci řešení projektu dle hospodářské smlouvy se zadavatelem JABLOTRON ALARMS a.s. Matematické modely pro body smlouvy "Tepelný výpočet akumulační nádoby, obsahující PCM zapouzdřený v přibližně kulových kapslích…“ a "Tepelný výpočet topné tyče pro ohřev vody při nucené cirkulaci" (později upřesněné na přirozenou konvekci) jsou popsány v kapitole 1. Vyvinuté matematické modely byly implementovány v prostředí Excel s využitím procedur VBA v podobě výpočetních programů popsaných v kapitole 2. Výpočetní programy byly dodány zadavateli v požadovaných termínech. Alternativní materiály pro ukládání tepla s fázovou změnou, zejména materiály na bázi parafínových vosků a aditiva zlepšující tepelnou vodivost a jiné vlastnosti jsou diskutovány v kapitole 3.
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