Wyniki wyszukiwania - BazTech

1

Complexity of two-phase flow dynamics using the recurrence and high speed video analysis

Mosdorf Romuald, Rafałko Gabriela, Zaborowska Iwona, Dzienis Paweł, Grzybowski Hubert

Archives of Thermodynamics

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2024

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Vol. 45, no 2

73--81

EN

During flow boiling in a system with small (mini/micro) channels, several instabilities may occur at the same time, which overlap each other  such a phenomenon complicates the analysis of boiling dynamics. The above mentioned processes cause that the fluctuation of recorded signals occur on various time scales. Although many criteria for the stability of two-phase flows are available, their practical application is limited (they need many recorded parameter of two phase flow). Methods which we are looking for should allow flow pattern identification based on a small number (or single) recorded signals. The paper presents a new approach to the recurrence plot method combined with Principal Component Analysis and Self-Organizing Map analysis. The single signal of pressure drop oscillations has been analyzed and used for flow pattern identification. New method of correlation analysis of flow patterns on video frames has been presented and used for flow pattern identification. The obtained results show that pressure drop oscillations and high speed video contain enough information about flow pattern for flow pattern identification.

2

Possible Suppression of Magnetorotational Instability by Rapid Radial Flow

Abramowicz M. A., Horák J., Kluźniak W.

Acta Astronomica

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2013

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Vol. 63, No. 2

267--273

EN

By investigating the magnetorotational instability (MRI) in a region of rapidly varying accretion-disk thickness, e.g., in the ISCO region, we find a limit to the applicability of a recent finding by Balbus (2012) that the MRI is present also in the region of Rayleigh-unstable flow.

3

Wyznaczanie prędkości przemieszczania się zaburzeń w skraplającym się czynniku chłodniczym

Bohdal T.

Pomiary Automatyka Kontrola

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2012

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R. 58, nr 5

439-442

PL

W artykule przedstawiono wyniki badań prędkości przemieszczania się zaburzeń w dwufazowym czynniku chłodniczym. Podczas badań na stanowisku pomiarowym w skraplającym się czynniku chłodniczym R404A wywoływano skokową zmianę ciśnienia. Wprowadzone zaburzenie przemieszczało się ze skończoną prędko-ścią, zależną od parametrów ośrodka, a głównie od wartości stopnia zapełnienia. Uzyskane wyniki pomiarów porównano z wynikami obliczeń według zależności innych autorów.

EN

A theoretical and experimental analysis of disturbances propagation and determination of propagation velocity in a two-phase refrigerant was made. During investigations at an experimental facility, a step change of the pressure in a refrigerant R404A flow was induced. The introduced disturbance propagated with a finite velocity depending on the parameters of the medium and on the void fraction especially. The obtained experimental data were compared with the results of calculations based on formulas proposed by other authors.

4

Modelling of Pressure-Drop Instability in Single and Multi Microchannels System

Grzybowski H., Mosdorf R.

Acta Mechanica et Automatica

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2012

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Vol. 6, no. 3

45-51

EN

In the paper the model of pressure-drop oscillations has been proposed. The model was based on the iterative solution to equations. The dynamics of pressure-drop oscillations in a single channel and in two neighbouring channels have been analyzed. There has been assumed that the pressure-drop oscillations in the system are caused by interactions between the heat supply system and liquid supply system. These interactions influence the heat and mass transfer inside the microchannel. Obtained results indicate that the shape of pressure drop curve has a significant influence on the system stability. When the slope of curve ? = () in the region between function extremes increases then the pressure oscillations become chaotic. In case of multichannel system the thermal interactions (occurring through the channel walls) and hydrodynamic interactions (occurring inside the common channels outlet) have been considered. Four types of two-phase flow behaviours in parallel channels have been observed depending on the intensity of interactions: alternate oscillations, consistent oscillations, periodic oscillations and completely synchronized oscillations. Obtained qualitative results have been compared with conclusions of experimental results reported by other researches. The good qualitative agreement with experimental results has been obtained.

5

Badanie rozwoju i zaniku wrzenia czynnika chłodniczego w kanale

Bohdal T.

Pomiary Automatyka Kontrola

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2010

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R. 56, nr 4

337-343

PL

Przeprowadzono badania eksperymentalne rozwoju i zaniku wrzenia pęcherzykowego proekologicznych czynników chłodniczych w kanale rurowym. Procesom tym towarzyszy zjawisko zerowego kryzysu wrzenia związane z histerezą aktywizacji zarodków. Potwierdzono, że rozwój i zanik wrzenia wykazuje własności falowe. Rozwój wrzenia następuje w postaci tzw. frontu wrzenia, który przemieszcza się przeciwnie do kierunku przepływu z prędkością zależną od przegrzania cieczy przy ogrzewanej ściance. Analogicznie zanik wrzenia sukcesywnie postępuje zgodnie z kierunkiem przepływu czynnika. Badania potwierdziły występowanie histerezy rozwoju i zaniku wrzenia pęcherzykowego w kanale.

EN

Experimental investigations of development and decay of bubbly boiling of environment-friendly refrigerants in a tubular channel were performed. These processes are accompanied by the zero boiling crisis phenomenon connected with the nuclei activation hysteresis. It was confirmed that the development and decay of boiling have wave properties. The development of boiling occurs in the form of the so-called boiling front which shifts in the direction opposite to the flow direction with the speed dependent on the wall superheat. The decay of boiling progresses successively in compliance with the refrigerant flow direction. The tests confirmed the occurrence of development and decay hysteresis of bubbly boiling in the channel. In the description including the wave effect, there was taken into account the pressure change impulse vp and boiling front vt translocation velocity. These velocities depend on the refrigerant spore filling ? in a channel . Besides, bubble boiling in flow has a very important employment aspect. Such phenomena occur not only in evaporators of cooling devices, but also in other energy systems. Under dynamic conditions some changes of parameters can cause negative exploitation qualities characterised by instability of machines and motors.

6

Badanie przemieszczania się zaburzeń w skraplającym się czynniku chłodniczym

Bohdal T.

Pomiary Automatyka Kontrola

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2009

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R. 55, nr 4

236-242

PL

Przeprowadzono badania eksperymentalne przemieszczania się zaburzeń w skraplającym się czynniku chłodniczym R404A. Podczas badań na stanowisku pomiarowym w skraplaczu chłodzonym powietrzem wywoływano skokową zmianę ciśnienia. Wzrost ciśnienia w kanale rurowym skraplacza powodował rozwój skraplania czynnika chłodniczego a spadek ciśnienia jego zanik. Stwierdzono, że zjawisko ma charakter falowy. Wprowadzone zaburzenie przemieszczało się ze skończoną prędkością zależną od parametrów ośrodka dwufazowego w postaci fali ciśnieniowej i temperaturowej.

EN

Experimental investigations concerning the displacement of disturbances in the condensing R404A refrigeration medium were conducted. During the investigations, abrupt pressure changes were triggered off on the measuring facility in a condenser chilled with air. A pressure increase in the pipe channel of the condenser caused an expansion of the condensation of the refrigeration medium, while a pressure drop resulted in its fading. It was found that this phenomenon is of a wavy nature. The disturbances introduced were displaced with a finite velocity, which depended on the parameters of the two-phase medium in the form of pressure and temperature waves.

7

Condensation of refrigerant R404A under external disturbances

Bohdal T., Łomiak M.

Archives of Thermodynamics

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2009

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Vol. 30, no. 2

37-57

EN

The paper describes results of experimental investigations of condensation of the refrigerant R404A in the flow through a coiled tube under conditions of external disturbances that occur in refrigeration units. The development and decay of condensation is induced by impulse changes of parameters of the two-phase system, such as pressure and mass flux density in the tubular channel. It is confirmed that the two-phase systems exhibit wave properties and that the disturbances propagate with finite velocities. Experiment-based correlations are obtained to describe the propagation of disturbances during development and decay of condensation of the refrigeration medium in the tubular channel.

8

Analysis of propagation of disturbances in a two-phase refrigeration medium

Bohdal T., Czapp M.

Transactions of the Institute of Fluid-Flow Machinery

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2008

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nr 121

3-16

EN

A theoretical and experimental analysis of propagation of disturbances and determination of propagation velocity in a two-phase refrigeration medium has been made. During investigations on the experimental facility, a step change of the pressure in flow of a refrigerant R404A was induced. The introduced disturbance propagated with a finite velocity depending on the parameters of the medium and, more markedly, on the void fraction. The obtained experimental data were compared with results of calculations based on formulas of other investigators.

9

On the Mass Ratio of TU Men

Smak J. I.

Acta Astronomica

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2006

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Vol. 56, No. 3

277--282

EN

Radial velocities of TU Men measured from peaks of the emission lines are re-analyzed within the three-body approximation. The resulting crude estimate of the mass ratio is q=M₂/M₁=0.5±0.2. Using the mass of the secondary estimated from the M₂-P relation we obtain an independent lower limit q>0.41±0.08. These estimates exclude the possibility of superhumps being due to the tidal instability involving the 3:1 resonance which requires qcrit=0.25. The common belief that q_crit could be as high as q=0.33 is critically re-examined. It is shown that the results of numerical simulations, which form the basis of this belief, do not apply to situations encountered in the case of the observed superhumps.

10

A new experimental technique to identify the frequency of macro-instabilities in stirred vessels

Paglianti A., Montante G., Magelli F.

Inżynieria Chemiczna i Procesowa

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2005

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T. 26, z. 3

451-460

EN

A new experimental technique for detecting the macro-instabilities (i.e., low frequency fluctuations of flow) that take place in a stirred vessel is presented. It is based on the use of a pressure transducer and it is cheap and of simple operation. By comparison with data taken from the literature, this technique and the related method for time series analysis are shown to provide reliable information.

PL

Przedstawiono nową technikę doświadczalną wyznaczania makroskopowych niestabilności, które występują w mieszalnikach. Jej podstawą jest wykorzystanie przetwornika ciśnienia. Metoda jest tania i prosta w zastosowaniu. Przez porównanie z danymi literaturowymi pokazano, że metoda ta dostarcza równie wiarygodnych informacji jak inne, droższe techniki.

11

On the Nature of Regular Pulsation in Two LBV Stars of NGC 300

Dziembowski W. A., Sławińska J.

Acta Astronomica

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2005

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Vol. 55, No. 2

195--204

EN

Two A-type supergiants in NGC 300 exhibit periodic light variations. The measured periods are 72.5 and 96.1 days. We show that the variability may be explained by the excitation of strange mode driven by the opacity mechanism acting in the layer of the iron opacity bump. The explanation requires that the two stars are significantly undermassive. In sequences of stellar models with decreasing luminosity-to-mass ratio, the unstable strange modes represent continuations of strictly aperiodic thermal modes.

12

Formowanie się atmosferycznych frontów głównych jako wynik procesu samoorganizacji

Rymarz C.

Biuletyn Wojskowej Akademii Technicznej

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2000

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Vol. 49, nr 3

51-74

PL

W pracy przedstawiono genezę i budowę atmosferycznego frontu, który oddziela masy o istnieniu różnym stopniu nagrzania. W dotychczasowych rozważaniach uwzględnia się jedynie warunek konieczny powstania i zaniku frontu. Sformułowano nowy warunek dostateczny, który ma związek z wystąpieniem zjawiska samo-organizacji w strukturach dysypatywnych. Zbadano ogólne i asymptotyczne kryteria spełnienia.

EN

Genesis and construction are presented of atmospheric main front, which separates the masses heated to significantly different degrees. In the to date studies the necessary condition for the front creation and decay is only considered. A new sufficient condition is given, which is connected with ocurring of self-organization effect in the dissipate structures. The general and asymptotic criteria of fulfillness are investigated.

13

Absolute instability of compressible three-dimensional flow

Tuliszka-Sznitko E.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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1999

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Vol. 3, No 1

5-16

EN

In the present paper the instability character (absolute/convective) of compressible viscous flow around geometries rotating in uniform flow is analysed. The linear local stability theory is used to investigate the boundary layer stability. Following the works of Briggs and Bers in the field of plasma physics, the absolute instability region is identified by singularities of dispersion relation called pinch - points. Calculations have been made for different Mach numbers and wall temperatures.

14

Pulsational Instability Domains in the Upper Main Sequence

Pamyatnykh A. A.

Acta Astronomica

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1999

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Vol. 49, No. 2

119--148

EN

Updated theoretical instability domains in the Hertzsprung-Russell and in the log g-log Teff diagrams for the β Cep, the SPB and the δ Sct star models are presented. The position of the instability domains is very sensitive to the chemical composition parameters (X,Z) and to the extent (dover) of the convective overshooting, due to influence of these effects on the evolution, in particular, on the location of the Zero-Age Main Sequence (ZAMS) and the Terminal-Age Main Sequence (TAMS). Also, the heavy element abundance, Z, is of critical importance on the instability itself for the β Cep and the SPB models. The comparison of theoretical and observational domains may be used to constrain these parameters.

15

Stability of Taylor-Dean flow of fiber suspensions

Nsom B.

Applied Mechanics and Engineering

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1998

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Vol. 3, no 2

185-204

EN

We present a theoretical study of the stability of the Taylor-Dean flow of dilute and semi concentrated suspensions of stiff fibers. To this end, we consider a wide-gap Couette-Taylor configuration with pressure gradient acting in the transverse direction. The Ericksen anisotropic fluid equation of state is used to describe the suspension rheological behavior. The marginal stability states are computed with respect to three parameters: the gap-width, the ratio of representative pumping and rotation velocities and the rheological parameter h2 (h2 being an explicit function of the fiber aspect ratio (dilute suspension), concentration and number density (semi concentrated suspension)).