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Investigation of droplet nucleation in CCS relevant systems – design and testing of the expansion chamber
Čenský, Miroslav ; Hrubý, Jan ; Vinš, Václav ; Hykl, Jiří ; Šmíd, Bohuslav
A unique in-house designed experimental apparatus for investigation of nucleation of droplets in CCS relevant systems is being developed by the present team. The apparatus allows simulating various processes relevant to CCS technologies. Gaseous mixtures with CO2 are prepared in a Mixture Preparation\nDevice (MPD) based on accurate adjustment of flow rates of individual components [EPJ Web of Conferences 143, 02140 (2017)]. The mixture then flows into an expansion chamber, where it undergoes a rapid adiabatic expansion. As a consequence of adiabatic cooling, the mixture becomes supersaturated and nucleation and simultaneous growth of droplets occurs. In this study, we describe the design and testing of the expansion part of the experimental setup. The rapid expansion was realized using two valve systems, one for low pressures (up to 0.7 MPa) and the other for high pressures (up to 10 MPa). A challenge for a proper design of the expansion system is avoiding acoustic oscillations. These can occur either in the mode of Helmholtz resonator, where the compressible gas in the chamber acts as a spring and the rapidly moving\ngas in the valve system as a mass, or in the “flute” mode, where acoustic waves are generated in a long outlet tubing.\n
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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homogeneous and heterogeneous nucleation processes in steam, both in the laboratory and at power plants using the steam withdrawn from the steam turbine.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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EXPERIMENTAL APPARATUS FOR MEASUREMENT OF DENSITY OF SUPERCOOLED WATER AT HIGH PRESSURE
Hrubý, Jan ; Hykl, Jiří ; Peukert, Pavel ; Šmíd, Bohuslav
Thermodynamic behavior of supercooled water (metastable fluid water existing transiently below the equilibrium freezing point) at high pressures was subject to many recent theoretical studies. Some of them assume that a second critical point of water exists, related to two liquid phases of supercooled water: the low-density liquid and the high-density liquid. To test these theories, an original experimental cryogenic apparatus is being developed. The volume changes are measured optically in custom-treated fused-silica capillary tubes. The capillaries are placed in a metal vessel designed for pressures up to 200 MPa. The vessel is connected to a circulation thermostat enabling a rapid change of temperature to prevent freezing. A new high-vacuum device was developed for degassing of the ultrapure water sample and filling it into the measuring capillaries. The experiments will contribute to fundamental understanding of the anomalous behavior of water and to applications in meteorology, aerospace engineering, cryobiology etc.
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Experimentální studie o matematickém modelování velmi rychlého pneumatického systému
Hrubý, Jan ; Šmíd, Bohuslav ; Pavelka, Miroslav ; Krejčí, A. Petr
Podáváme obecné úvahy pro návrh, matematické modelování a experimentální testování pneumatických systémů s typickým přechodovým časem 1 ms. Tok plynu je typicky kritický nebo blízký kritickému s významným vlivem stlačitelnosti. Podáváme model se soustředěnými parametry, který zahrnuje bilance hmoty, energie a hybnosti. Ukazujeme, že setrvačnost plynu hraje významnou roli. Pro konkrétní systém, navržený pro aplikaci v základním výzkumu aerosolových částic, ukazujeme rozumnou shodu soustředěného modelu s experimentálními testy prototypu.
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