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National Repository of Grey Literature 2 records found  Search took 0.00 seconds. 
Experimental research of heterogeneous nuclei in expansion chamber
 Bartoš, O. ; Hrubý, Jan ; Kolovratník, M.
An expansion chamber has been developed to investigate experimentally homogeneous and heterogeneous nucleation processes in steam. A chamber design allows to measure in the laboratory but also in power plants using the steam withdrawn from the steam turbine. The purpose of the device is to provide a new approach to study the physics of non-equilibrium wet steam formation, which is one of the factors limiting the efficiency and reliability of steam turbines. The expanded steam or a known mixture of steam with a non-condensable gas rapidly expands in the expansion chamber. Due to adiabatic cooling, the temperature drops below the actual dew point. When reaching a sufficiently high supersaturation, droplets are nucleated. By tuning the supersaturation in the so-called nucleation pulse, particles of various size ranges can be activated. This fact is used in the present study to measure the aerosol particles present in the air. Homogeneous nucleation was negligible in this case. The experiment demonstrates the functionality of the device, data acquisition system and data evaluation methods.
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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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