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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homogeneous and heterogeneous nucleation processes in steam, both in the laboratory and at power plants using the steam withdrawn from the steam turbine.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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Dual-system Magnetoresistive Sensor of Turbine Blades Vibration
Procházka, Pavel ; Vaněk, František ; Hodboď, Robert
The paper is focused on new methods of non-contact sensing vibrations and deflections of rotating machine parts, especially blades of steam turbines. Special attention is paid to the methods and magnetoresistive sensors developed in the Institute of Thermomechanics for non-contact measurements of characteristics of rotating blades inside steam turbines under operation. Principles of non-contact sensors based on measuring deflections are described and compared, including new types of magnetoresisitive sensors.
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Research of pressure pulsations and vibrations at the turbine 1000 MW
Procházka, Pavel ; Vaněk, František ; Sadílek, J. ; Hodboď, Robert
Experimental research of pressure pulsation with simultaneous measurements of stator and blade vibrations in the L – 1 stage was conducted at the turbine 1000 MW of the nuclear power plant Temelín in 2012. The aim of this work was to find out links and possible sources of increased vibrations of the blades of the 3rd rotor stage during the turbine start-up. The applied methods and used appliances are described in the paper. Observed phenomena are analyzed with focus on the causes of blade vibrations.
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Research of pressure pulsations and vibration in the turbine 1,000 MW
Procházka, Pavel ; Vaněk, František ; Sadílek, J.
The paper describes the methods and equipment used in experimental research of pressure pulsations with simultaneous measurement of vibration of the stator and blades of the third moving wheel in the turbine 1,000 MW at the nuclear power plant Temelín in 2012. The aim of this work was to find links and possible sources of blade vibration during the turbine start-up. The observed phenomena are analyzed, focusing on the causes of blade vibrations in the stage L-1.
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A computationally efficient and accurate numerical representation of thermodynamic properties of steam condensing steam flow in steam turbines
Hrubý, Jan
Mathematical modeling of the non-equilibrium condensing transonic steam flow in the complex 3D geometry of a steam turbine is a demanding problem both concerning the physical concepts and the required computational power. Available accurate formulations of steam properties IAPWS-95 and IAPWS-IF97 require much computation time. For this reason, the modelers often accept the unrealistic ideal-gas behavior. Here we present a computation scheme based on a piecewise, thermodynamically consistent representation of the IAPWS-95 formulation. Density and internal energy are chosen as independent variables to avoid variable transformations and iterations. On the contrary to the previous Tabular Taylor Series Expansion Method, the pressure and temperature are continuous functions of the independent variables, which is a desirable property for the solution of the differential equations of the mass, energy, and momentum conservation for both phases.
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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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