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Wyszukujesz frazę "thermodynamic nonequilibrium" wg kryterium: Wszystkie pola


Wyświetlanie 1-3 z 3
Tytuł:
Gradient theory for the description of interfacial phenomena in flashing water flows
Autorzy:
Banaszkiewicz, M.
Badur, J.
Powiązania:
https://bibliotekanauki.pl/articles/1953939.pdf
Data publikacji:
2000
Wydawca:
Politechnika Gdańska
Tematy:
capillarity
flashing flow
thermodynamic nonequilibrium
Opis:
The present work concerns the description of phenomena taking place within interfacial regions during a flow of water, which is accompanied by heterogeneous flashing. The main aim of the work is to present a unified approach to first order phase transitions with the inclusion of capillary effects and to built on this basis a mathematical model describing nonequilibrium two-phase flows, in which the properties of the mixture include capillary components. The analysis of the problem was started with a discussion of physical aspects of flashing, which are the contents of Chapter 2. On the basis of the experimental data analysis a physical model of the phenomenon was formulated. In Chapter 3 a gradient description of first order heterogeneous phase transitions was given. The analysis was begun with a discussion of the properties and structure of interfacial areas. On the basis of the analysis constitutive equations for reversible stress tensor and free energy of a two-phase system treated as a homogeneous medium were formulated. The constitutive equations include capillary components modelled by means of the dryness fraction gradients and resulting from the nonuniformity of the system caused by the existence of two phases and interfacial surfaces. On the basis of the proposed theory a homogeneous model of two-phase flow with capillary effects was derived, which is a subject of Chapter 4. Taking into consideration the assumptions of the homogeneous model, one-dimensional balance equations for mass, momentum and energy of the mixture and mass of vapour were derived. A constitutive equation for the source term appearing in the last equation was obtained on the basis of the theory of internal parameters with the usage of the proposed form of free energy including a gradient term known from the second gradient theory. The remaining constitutive equations for the density of the two-phase system, wall shearing stresses and capillary pressure were also given. The proposed mathematical model was investigated from the point of view of wave properties, which were discussed in Chapter 5. The analysis of small disturbations was conducted, as a result of which a dispersion equation was obtained giving a relation between the velocity of disturbations, attenuation coefficient and frequency. This dispersive model was then applied for the prediction of critical mass flux in a channel flow using PIF method. On the basis of the comparison of the model predictions with experimental measurements a reasonably good agreement was found. In Chapter 6 the results of numerical calculations of flashing flow in channel were presented. Since the proposed mathematical model contains several phenomenological coefficients, a parametric analysis was performed in order to determine their value and the influence on solutions. For the sake of the analysis the classical benchmark experiment known as the Moby Dick was used. After fitting the solution of the model into the experimental measurements new calculations for other runs and other experiments were carried out. As a result of the analysis a good agreement of the model with reality was found, as well as its usefulness for the calculations of pressure and void fraction distributions in channels and for the determination of mass flow rate of two-phase systems. It constitutes a confirmation of the correctness of the proposed model as well as the theory on the basis of which it was built.
Źródło:
TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk; 2000, 4, 2; 213-290
1428-6394
Pojawia się w:
TASK Quarterly. Scientific Bulletin of Academic Computer Centre in Gdansk
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Control-volume-based model of the steam-water injector flow
Autorzy:
Kwidziński, R.
Powiązania:
https://bibliotekanauki.pl/articles/240854.pdf
Data publikacji:
2010
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
kondensacja
nadkrytyczny dozownik wodno-gazowy
nierównowaga termiczna
równanie bilansowe
straty nieodwracalne
balance equations
condensation
irreversible losses
supercritical steam-water injector
thermodynamic nonequilibrium
Opis:
The paper presents equations of a mathematical model to calculate flow parameters in characteristic cross-sections in the steam-water injector. In the model, component parts of the injector (steam nozzle, water nozzle, mixing chamber, condensation wave region, diffuser) are treated as a series of connected control volumes. At first, equations for the steam nozzle and water nozzle are written and solved for known flow parameters at the injector inlet. Next, the flow properties in two-phase flow comprising mixing chamber and condensation wave region are determined from mass, momentum and energy balance equations. Then, water compression in diffuser is taken into account to evaluate the flow parameters at the injector outlet. Irreversible losses due to friction, condensation and shock wave formation are taken into account for the flow in the steam nozzle. In two-phase flow domain, thermal and mechanical nonequilibrium between vapour and liquid is modelled. For diffuser, frictional pressure loss is considered. Comparison of the model predictions with experimental data shows good agreement, with an error not exceeding 15% for discharge (outlet) pressure and 1 K for outlet temperature.
Źródło:
Archives of Thermodynamics; 2010, 31, 1; 45-59
1231-0956
2083-6023
Pojawia się w:
Archives of Thermodynamics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Nonequilibrium state of engineering systems
Autorzy:
Dolinskii, A.
Draganov, B.
Kozirskii, V.
Powiązania:
https://bibliotekanauki.pl/articles/410714.pdf
Data publikacji:
2012
Wydawca:
Polska Akademia Nauk. Oddział w Lublinie PAN
Tematy:
stan nierównowagi
systemy niestabilne
termodynamika
nonequilibrium state
unstable system
thermodynamic
Opis:
We present a characteristic of nonequilibrium phenomena and describe a method of determining the interdependence of thermodynamic forces and irreversible processes caused by them.
Źródło:
ECONTECHMOD : An International Quarterly Journal on Economics of Technology and Modelling Processes; 2012, 1, 1; 33-34
2084-5715
Pojawia się w:
ECONTECHMOD : An International Quarterly Journal on Economics of Technology and Modelling Processes
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-3 z 3

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