Wyniki wyszukiwania - Biblioteka Nauki

1

The choice of two-phase flow structure model in refrigerant's throttling process

100%

Królicki Z. , Białko B.

Zeszyty Naukowe Politechniki Świętokrzyskiej. Mechanika

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1999

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tom Z. 67

359--366

EN

The choice of flow structure model is a key point in cognitive analysis and mathematical modeling of two-phase flows. The problem is particularly difficult in the case of flows with large thermodynamic parameters gradients of two-phase refrigerant. Two-phase refrigerant throttling process, occurring in cryogenics and refrigerating engineering, is a good example of this problem. Both, introductory analysis and theoretical calculations results are often displayed on diagrams called "flow maps". This paper presents flow maps for two-phase refrigerant throttling process in capillary throttling elements. Additionally representation of throttling process progress is proposed. Results of theoretical analysis were confirmed by a set of experiments conducted on test bed allowing full throttling process visualization. The experiments were performed for exemplary flow cases. The experiment results were compared with results obtained by other authors.

2

Cavitation phenomena in the injection nozzle: theoretical and numerical analysis

100%

Volmajer M. , Kegl B.

Journal of KONES

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2004

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tom Vol. 11, No. 3-4

295-303

3

Numerical study of a polydisperse two-phase jet

100%

Barata J. , Perestrelo N.

Archiwum Motoryzacji

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2000

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tom Nr 2

113-125

EN

Low emissions gas turbine combustors will demand fuel injection systems that are efficient in the accomplishment of the mixing of fuel and air in the shortest possible residence time. This paper describes a computational study of a polydisperse two-phase turbulent jet, which is the basic configuration to analyze how the various parameters influence the size distribution and the dispersion of the droplets in the injection process. An Eulerian frame for the for the gas phase was used in conjunction with a Lagrangian approach to describe both interphase slip and turbulence on particle motion. Good agreement of the computations with the experimental data is obtained for both the gas and the particles turbulence modulation and anisotropy effects were introduced and were found to be very important to the successful performance of the computational method. The exchange of monumentum and turbulence energy between the two phases was shown to play a decisive role on the flow development. The predictions confirmed the measurements and showed that the particles do not follow the turbulent gas flow, but they affect it significantly. Considerably high values of the radial velocity were detected around the centerline far from the jet exit where the velocity of the particles lags that of the fluid, that seems to be associated with the effect of shear induced lift forces.

PL

Przedstawiono studium komputerowe polidyspersyjnej dwufazowej strugi turbulentnej, które jest bazą wyjściową do oceny wpływu różnych parametrów na rozkład średnicy kropel podczas wtrysku do ośrodka gazowego. Wykorzystano Eulerowską analizę do fazy gazowej oraz analizę Lagrange'a do obliczania drogi cząstek. Uzyskane wyniki obliczeniowe są zgodne z eksperymentalnymi. Turbulencja i niejednorodność średnic kropel mają istotny wpływ na rozwój strumienia. Stwierdzono także, że składowe promieniowe prędkości z daleka od otworu rozpylacza uzyskują wysokie wartości.

4

Recent progress in ultra fast electron beam X-ray computed tomography

100%

Hampel U. , Fischer F. , Bieberle M. , Schleicher E.

Zeszyty Naukowe. Elektryka / Politechnika Łódzka

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2009

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tom z. 114

145-148

EN

A new ultra fast electron beam X-ray CT scanner has been developed, implemented and tested in different applications. It consists, amongst other components, of an electron beam unit with 10 kHz scanning capability and 1 mm focal spot size and a 240 element circular CZT detector arc. The system is capable to produce slice images at up to 7 kHz frame rate of moderately absorbing objects with maximum 120 mm diameter. The paper introduces the scanner and first results for two-phase flow measurements in a bubble column and a fluidized bed.

5

Velocity and gas-void fraction in two-phase liquid-gas flow in narrow mini-channels

80%

Sowiński J. , Dziubiński M. , Fidos H.

Archives of Mechanics

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2009

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tom Vol. 61, nr 1

29-40

EN

In the study, the values of velocity and gas void fraction in two-phase gas-liquid flow in narrow vertical mini-channels were experimentally determined. The influence of the physicochemical properties of liquid, the channel gap width and the superficial velocity of gas and liquid, on gas void fraction arid gas bubble flow velocities in the flowing two-phase1 mixture in narrow, vertical mini-channels was investigated. The value of gas phase velocity was defined by means of a drift model, determining the values of distribution parameter Co. The relation describing the value of gas void fraction depended on the Bankoff coefficient and gas input volume fraction.

6

Fractal analysis in two phase flow

80%

Mosdorf R. , Poniewski M. , Ulbrich R.

Zeszyty Naukowe Politechniki Świętokrzyskiej. Mechanika

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1999

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tom Z. 67

303--312

EN

The paper presents principles of fractal analysis of measurement signals. The application of such indicators as autocorrelation function. Hurst exponent, the largest Lapunow exponent, correlation dimension. Kołmogorow entropy for the measuring signal analysis are discussed. The fractal analysis of experimental data was used to analyse the results of registration of local changes of gas void fraction in the flow of water-air mixture crosswise to the tube bundle in the shell-side space. The occurrence of low dimensional attractors of correlation dimensions close to D2=1.1 and D2=3.9 was found.

7

Hydraulic characteristics of the airlift pump

80%

Kujawiak S. , Makowska M. , Matz R.

Acta Scientiarum Polonorum. Formatio Circumiectus

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2018

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tom 17

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nr 4

8

Spatial distribution and settling velocity of heavy particles in synthetic turbulent ﬁelds

80%

Łuniewski M. , Pozorski J.

Transactions of the Institute of Fluid-Flow Machinery

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2017

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tom nr 135

87--100

EN

We analyse numerically the motion of small inertial particles, subject to gravity, in two simple velocity ﬁelds: two-dimensional cellular ﬂow, and a three-dimensional ﬂow being the superposition of random Fourier velocity modes. The latter, also known as the kinematic simulation or synthetic turbulence, has often been applied in various studies, including those aiming to predict particle dispersion. The interplay of the particle inertia and the acceleration of gravity has non-trivial consequences for trajectories of particles and their spatial distribution, known as a preferential concentration. Also, we compute the average settling velocity of particles in function of their inertia and the number of ﬂuid velocity modes used in simulations. The present paper aims to study these efects, as the synthetic turbulence represents an interesting option for subﬁlter modeling in particle-laden large-eddy simulation.

9

CFD simulation as a tool for the identification of the manifold element reaction to pressure pulsations excitation (one- and two-phase flow)

80%

Cyklis P. , Kantor R.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2003

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tom Vol. 7, No 3

363-374

EN

The periodicity of compressor operation is a source of pressure pulsations in volumetric compressor manifolds. An analysis of pressure pulsations is important for several reasons. The Helmholtz model, applied in all commercial programs offered by the companies professionally dealing with damping pressure pulsations, contains numerous simplifying assumptions; a straight pipe segment, with an ideal gas isentropic flow assumption, substitutes each element of the piping system. In many cases this model is insufficient. The existing experimental methods could not be used in the design of a muffler. The aim of this paper is to show a new method to identify an arbitrary fragment of a manifold, i.e. a method of identification of the appropriate complex transmittance matrix elements using CFD simulation. This method allows the liquid phase dispersed in the compressed gas and non ideal gas as a working medium to also be considered. The most important conclusion of this work is that identification of acoustic element parameters in the manifold, based on multi-dimensional simulation model, is feasible. The author obtained much better results from the developed method than those yielded by the classic Helmholtz model. A comparison between pure gas and gas with oil contamination is also shown in the paper.

10

Podobieństwa i różnice w ruchu ciepła podczas przepływu dwufazowego gaz - ciecz i ciecz - ciecz

80%

Dybek B.

Inżynieria i Aparatura Chemiczna

|

2009

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tom Nr 6

45-46

PL

Praca dotyczy sposobu obliczania wartości współczynnika wnikania ciepła w warunkach przepływu dwufazowego. Scharakteryzowano w niej równania proponowane w literaturze przedmiotu dla układów dwuskładnikowych. Na podstawie danych eksperymentalnych dokonano oceny skuteczności- metod słusznych dla układów gaz - ciecz w odniesieniu do układów ciecz - ciecz.

EN

The paper describes methods for heat transfer coefficient calculation in two-phase flow. The literature equations for predicting heat transfer in two-component systems are presented. On basis of experimental data the effectiveness of calculation methods for heat transfer in liquid — liquid systems originally used for calculations of heat transfer in gas - liquid systems was evaluated.

11

Turbulent mixing of a cloud wit h the enviranment: two-phase evaporating flow. Numerical simulations, laboratory experiments and field measurements

80%

Malinowski S. P.

Journal of Theoretical and Applied Mechanics

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2007

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tom Vol. 45 nr 3

587-601

EN

A brief overview of numerical simulations, laboratory experiments and in-situ measurements aimed at investigation of the cloud-clear air interfacial-mixing, conducted in recent years at the Institute of Geophysics, University of Warsaw is presented. The most interesting finding from these studies is that the evaporative cooling at the interface separating cloudy and clear filaments results in density differences in scale of centimeters. This effect influences smallest scales of turbulent motions through production of TKE by buoyancy forces and makes the small-scale turbulence anisotropic.

PL

W artykule zawarto zwarty przegląd symulacji numerycznych, eksperymentów prowadzonych w laboratorium oraz pomiarów in situ, których celem było badanie mieszania turbulencyjnego na granicy chmury z nienasyconym otoczeniem. Badania te prowadzono w Instytucie Geofizyki Uniwersytetu Warszawskiego. Najciekawszym wynikiem tych prac jest pokazanie wpływu, jaki ma parowanie wody chmurowej na granicy chmury na dynamikę turbulencji w małych skalach. Parowanie powoduje powstanie lokalnych różnic gęstości o skali przestrzennej rzędu centymetrów. Działanie sił wyporu prowadzi do produkcji drobnoskalowej turbulencji. Ponieważ wyróżniony jest kierunek pionowy, turbulencja ta jest anizotropowa.

12

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

80%

Mosdorf R. , Rafałko G. , Zaborowska I. , Dzienis P. , Grzybowski H.

Archives of Thermodynamics

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2024

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tom 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.

13

Diffusive-inertial droplet separation model from two-phase flow

80%

Mikielewicz J. , Dolna O. , Kwidziński R.

Archives of Thermodynamics

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2021

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tom Vol. 42, no 3

141--158

EN

This paper concerns analytical considerations on a complex phenomenon which is diffusive-inertial droplet separation from the two-phase vapour-liquid flow which occurs in many devices in the power industry (e.g. heat pumps, steam turbines, organic Rankine cycles, etc.). The new mathematical model is mostly devoted to the analysis of the mechanisms of diffusion and inertia influencing the distance at which a droplet separates from the two-phase flow and falls on a channel wall. The analytical model was validated based on experimental data. The results obtained through the analytical computations stay in a satisfactory agreement with available literature data.

14

Weryfikacja metod obliczania udziału objętościowego gazu

80%

Czernek K. , Okoń P.

Inżynieria i Aparatura Chemiczna

|

2018

|

tom Nr 3

51--52

PL

Przedstawiono wyniki obliczeń wpływu parametrów hydrodynamicznych na udział objętościowy faz podczas przepływu w rurach pionowych mieszaniny dwufazowej gazu i cieczy. Dokonano oceny dokładności wybranych metod obliczeniowych uwzględniających parametry hydrodynamiczne i określono przydatność metod w obliczeniach procesowych aparatów wykorzystujących tę formę przepływu.

EN

The calculation results of hydrodynamic parameters’ impact on a volume fraction in gas-liquid two-phase flow in vertical pipes are presented in the paper. The accuracy of selected calculation methods cited in literature was evaluated for various hydrodynamic parameters. The usefulness and accuracy of these methods in process calculations of apparatus in which this type of flow exist were determined.

15

Określenie grubości filmu cieczy otaczającego pęcherz gazowy w przepływie rzutowym mieszaniny dwufazowej ciecz nienewtonowska - gaz

80%

Fidos H.

Inżynieria i Aparatura Chemiczna

|

2004

|

tom Nr 3s

37-38

EN

A method for determination of the thickness of liquid film surrounding a gas bubble in the slug flow in a two-phase non-Newtonian liquid-gas system in vertical pipes was presented. A simple method of film thickness determination was proposed on the basis of measured slug flow parameters. The film thicknesses determined by discussed methods were compared.

16

Two-phase gas-liquid flow in conditions of expansion and contraction of channel

80%

Witczak S. , Wiśniowska J.

Journal of Energy Science

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2012

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tom Vol. 1, nr 2

135--143

EN

The paper presents the results of studies concerning the effects of sudden change of cross-sectional area on the flow patterns and local pressure losses in the horizontal flow of two-phase mixture. The scope of research include the observation of flow patterns of flowing mixture and their disturbances caused sudden change in cross-section of the pipeline. In addition, flow resistance affecting pressure change before and after the local obstacle were measured. The experiment was conducted in a horizontal flow through the measuring channel with a local obstacle in the form of a sudden change in channel cross-sectional area. Measurement channel was a system of two interconnected tubes with internal diameters of 40 and 22 mm and a total length of 7 m. The air, water and oil were used in the experiments. Analysis of the experimental data leads to the conclusion that the mathematical model for calculating the two-phase flow pattern disturbance areas and their impact on the value of the pressure drop in the pipe with a sudden expansion and contraction should take into account both the parameters of the liquid phase and gas phase.

17

Non-Invasive Evaluation of Wavy Liquid Film

80%

Czernek K. , Witczak S.

Chemical and Process Engineering

|

2013

|

tom 34

|

nr 2

241-252

EN

The study presents the possible use of optoelectronic system for the measurement of values specific for hydrodynamics of two-phase gas very-high-viscosity liquid flow in vertical pipes. An experimental method was provided, and the findings were presented and analysed for selected values which characterise the two-phase flow.

18

Absorption radiometric system

80%

Lech M.

Prace Naukowe Instytutu Techniki Cieplnej i Mechaniki Płynów Politechniki Wrocławskiej. Monografie

|

1998

|

tom Vol. 52, nr 29

66-66

EN

There are various uses for radioisotope devices, also in metrology, broadly conceived. Most often, absorption systems are used. Such systems, though familiar and used for many years, lacked theoretical and methodical descriptions. The monograph aims at filling this gap. The work presents the results of the studies on the absorption system with the use of betaradiation sources, which are often used in measurements of two-phase gas-solid flows. The influence of the radiation beam collimation on the radiation attenuation coefficient as well as the measurement error related to changing location of the absorbent in the measurement have been measured, the interaction of the beta-particle beam with the homogeneous and heterogeneous absorbents and the optimum parameters of such systems have been provided. The model of the radiometric system has been described and the results of the experimental tests of this model have been presented. An original method for calculating the coefficients of radiation attenuation in dispersed absorbents as well as the results of the experiments have been given. The monograph is addressed to both metrology experts and practising constructors who deal with the application of ionising radiation.

19

Evolution of flow patterns, gas fraction profiles and bubble size distributions in gas-liquid flows in vertical tubes

80%

Lucas D. , Krepper E. , Prasser H. M.

Transactions of the Institute of Fluid-Flow Machinery

|

2003

|

tom nr 112

37-46

EN

Air-water flow at ambient conditions in a vertical pipe an inner diameter of 51.2 mm is investigated. An electrode wire-mesh sensor enables the measurement of the phase distribution with a very high resolution in space and in time. Local bubble size distributions are calculated from the data. The measurements were done in distances from the gas injection device. As a result, the development of bubble size distributions as well as the development of the radial gas fraction profiles can be studiet. It was found, that the bubble size distribution as well as local effects determine the transistion from bubble flow. The data are used for the development of a model, which predicts the development of the bubble size distribution and the transition from bubble flow in the case of stationary flow in a vertical pipe.

20

Obliczenia zmian ciśnienia statycznego gazu w strefie nieustalonego ruchu cząstek poziomego transportu pneumatycznego

80%

Dzido G. , Raczek J. , Thullie J.

Inżynieria i Aparatura Chemiczna

|

2003

|

tom Nr 4

20-22

PL

W pracy przedstawiono porównanie profili ciśnienia statycznego gazu określonych eksperymentalnie z obliczonymi na drodze numerycznego rozwiązania modelu przepływu jednorodnego. Na podstawie uzyskanych wyników dobrano równanie opisujące współczynnik tarcia cząstek o ścianę pozwalające na możliwie najdokładniejszy opis zmian ciśnienia statycznego gazu na drodze poziomego transportu materiałów sypkich.

EN

The paper presents comparison of the static pressure profiles determined experimentally with computed by numerical solution of the uniform flow model. Based on results obtained the equation for particle friction factor was selected, that gives possibility of accurate static gas profile description in the horizontal pneumatic conveying of powders.