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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.
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Experimental research of heterogeneous nuclei in superheated steam
Bartoš, Ondřej ; Kolovratník, M. ; Šmíd, Bohuslav ; Hrubý, Jan
A mobile steam expansion chamber has been developed to investigate experimentally homogeneous and heterogeneous nucleation processes in steam, both in the laboratory and at power plants using the steam withdrawn from the steam turbine. The purpose of the device is to provide new insight into the physics of nonequilibrium wet steam formation, which is one of the factors limiting the efficiency and reliability of steam turbines. The expanded steam or a mixture of steam with a non-condensable gas rapidly expands in the expansion chamber. Due to adiabatic cooling, the temperature drops below the dew point of the steam at a given pressure. 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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A 19m Deep Well – a Downward Thermal Diffusion Cloud Chamber?
Holub, R.F. ; Hopke, P.K. ; Hovorka, J. ; Otahal, P. ; Ždímal, Vladimír
An unusual phenomenon, first observed on a clear summer day after several rainy days, were droplets constantly hitting the water surface in a 19 m deep and 2.4 m diameter water well. This droplet formation was occurring during the night as well. Since the droplet formation was near continuous, we called it “the eternal rain”. The water well is about 230 years old and located in the Benedictine monastery in Broumov, Czech Republic.
Fulltext: content.csg -  PDF
Plný tet: SKMBT_C22013091713150 - PDF
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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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Heterogenní částice v parních turbínách: měření na elektrárně Prunéřov II a další vývoj měřicích metod
Hrubý, Jan ; Kolovratník, M. ; Ždímal, Vladimír ; Jiříček, I. ; Bartoš, O. ; Moravec, P.
The form in which various impurities and admixtures are transported in steam circuits of power plants is a missing piece of knowledge needed to fully understand the processes of liquid phase formation in the low-pressure stages of steam turbines and, consequently, to model these processes and suggest modifications of turbine operation and design. The existence of heterogeneous particles in the superheated steam has been proven by the present team using an original sampling device, enabling using standard aerosol instrumentation to characterize the heterogeneous particles in superheated steam. We report measurements at power plant Prunéřov II, where 5.6E9 particles per kilogram of dry steam was found. The Sauter diameter of the particles d32=30nm was determined. The mass balance indicates, that substantial part of the mass of impurities is contained in particles <3nm, the current detection limit. For this reason an expansion chamber is being developed with a goal of detecting particles down to 1nm.
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