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1

New gas-liquid two-phase flow pattern maps based on the energy ratio of pressure fluctuation through a Venturi tube

Sun Zhiqiang, Chen Luyang, Yao Fengyan

Metrology and Measurement Systems

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2019

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Vol. 26, nr 2

241--252

EN

To find effective and practical methods to distinguish gas-liquid two-phase flow patterns, new flow pattern maps are established using the differential pressure through a classical Venturi tube. The differential pressure signal was first decomposed adaptively into a series of intrinsic mode functions (IMFs) by the ensemble empirical mode decomposition. Hilbert marginal spectra of the IMFs showed that the flow patterns are related to the amplitude of the pressure fluctuation. The cross-correlation method was employed to sift the characteristic IMF, and then the energy ratio of the characteristic IMF to the raw signal was proposed to construct flow pattern maps with the volumetric void fraction and with the two-phase Reynolds number, respectively. The identification rates of these two maps are verified to be 91.18% and 92.65%. This approach provides a cost-effective solution to the difficult problem of identifying gas-liquid flow patterns in the industrial field.

2

Low-frequency pressure fluctuation damper based on hydropneumatic spring with constant stiffness

Figiel A., Kudźma Z., Stosiak M.

Journal of Theoretical and Applied Mechanics

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2018

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Vol. 56 nr 3

841—855

EN

A wide spectrum of pressure fluctuation frequencies occurs in hydraulic systems. Particularly hazardous and difficult to eliminate are pressure fluctuations in the range up to 50 Hz, resulting in the generation of infrasounds by machines equipped with a hydrostatic drive. The best protection against the harmful effect of ultrasounds is to suppress them at the very source, i.e. to eliminate the causes of the generation of this noise. This paper presents a concept of reducing pressure fluctuation in the range of low excitation frequencies by means of a low-frequency damper of special design. The basis for designing pressure fluctuation dampers effective in reducing pressure fluctuation amplitudes in the range of low frequencies (< 50 Hz), which also function as acoustic filters of the generated infrasounds, is provided. The effectiveness of the low-frequency damper in reducing pressure fluctuation amplitudes has been experimentally tested. The damper was found to be most effective when its eigenfrequency coincided with the excitation frequency to be reduced.

3

Budowa stanowiska oraz wstępne badania wpływu drgań mechanicznych na mikrozawory hydrauliczne

Stosiak M., Towarnicki K., Lubecki A.

Interdisciplinary Journal of Engineering Sciences

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2018

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Vol. 6, no. 1

48--52

PL

W artykule przedstawiono wymagania stawiane układom mikrohydraulicznym. Zwrócono uwagę na występujące zakłócenia pracy. Podano przykłady oraz źródła powodujące zaburzenia pracy układu hydraulicznego. Omówione zostało wstępne stanowisko badawcze do identyfikacji wpływu zewnętrznych drgań mechanicznych na elementy mikrohydrauliczne. Przedstawiono zarówno schemat hydraulicznego układu pomiarowego, jak również blokowy układ aparatury pomiarowej. Jako reprezentatywny element mikrohydrauliczny który został poddany drganiom mechanicznym użyto mikrozaworu maksymalnego. Zawarto przekrój jego budowy oraz elementów składowych.

EN

Fluid pressure fluctuations in a microhydraulic system can be caused by fluctuations in the rate of fluid delivery, due to the operational kinematics of the micropump’s displacement elements, as well as by external excitations. This paper presents the requirements for microhydraulic systems and indicates the disturbances that can occur during operation. A test stand was designed to identify the impact of external mechanical vibrations on microhydraulic elements. Test stand was equipped with a measuring system to generate and record vibrations and examine their effect on the operation of microhydraulic components. Set parameters and operating conditions of the system during measurements were given. A relief microvalve was chosen, as a representative microhydraulic component. Based on the measurements, additional component derived from external vibrations was identified in frequency spectrum of pressure pulsations.

4

Regional features analysis of plugged holes of dense phase gas-solid separation fluidized bed

Zhang B., Zhao Y., Luo Z., Song S., Duan C., Dong L.

Physicochemical Problems of Mineral Processing

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2014

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Vol. 50, iss. 2

667--679

EN

In contrast to traditional coal separation, dry separation does not require water and does not cause water pollution. Dense phase gas–solid fluidized beds are used for dry separation. The plugged holes in the air distributor should be tested to ensure the stability of these beds for particle separation. The pressure fluctuation is sensitive to these plugged holes. This sensitivity can be tested and diagnosed by determining the standard deviation of the pressure fluctuation. In areas with partial blockage, that is the areas with weak fluidization, a decrease in the volume fraction of the particles and in the pressure differences in the transverse of the bed results in an increase of the standard deviation of the pressure fluctuation, thereby stimulating the lateral mixing of medium-sized particles. The standard deviation and the mixing intensity decrease axially. The value of sensitivity of the plugged holes in the air distributor decreases as the height of the bed increases. The features of air distributors affect the surrounding areas. The distribution law determining the influence of plugged holes on the beds is symmetrical. As the blockage of the fluidized bed distributor region increases, the mean square error of the pressure fluctuation in the related regions increases. The intensity of the effect is proportional to the distance to the plugged holes.

5

Reduction of infrasounds in machines with hydrostatic drive

Kudźma Z., Stosiak M.

Acta of Bioengineering and Biomechanics

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2013

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Vol. 15, no. 2

51--64

EN

Some hazards posed by the operation of hydraulic systems, connected with low-frequency vibrations and noise are presented. Special attention is focused on infrasounds. The sources of low-frequency vibrations and noise and ways of reducing them are indicated. An original solution ensuring the effective reduction of vibrations and noise in a wide frequency range, i.e., a wide-band damper of pressure fluctuations, also performing the function of an acoustic filter, is proposed. The effectiveness of the damper was confirmed by the results of laboratory tests and tests carried out on engineering machines working in real conditions.

6

Energy of intrinsic mode function for gas-liquid flow pattern identification

Sun Z., Gong H.

Metrology and Measurement Systems

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2012

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Vol. 19, nr 4

759-766

EN

Gas-liquid flows abound in a great variety of industrial processes. Correct recognition of the regimes of a gas-liquid flow is one of the most formidable challenges in multiphase flow measurement. Here we put forward a novel approach to the classification of gas-liquid flow patterns. In this method a flow-pattern map is constructed based on the average energy of intrinsic mode function and the volumetric void fraction of gas-liquid mixture. The intrinsic mode function is extracted from the pressure fluctuation across a bluff body using the empirical mode decomposition technique. Experiments adopting air and water as the working fluids are conducted in the bubble, plug, slug, and annular flow patterns at ambient temperature and atmospheric pressure. Verification tests indicate that the identification rate of the flow-pattern map developed exceeds 90%. This approach is appropriate for the gas-liquid flow pattern identification in practical applications.

7

Właściwości dynamiczne linii hydraulicznych lotniczych napędów hydraulicznych

Ułanowicz L.

Prace Naukowe Instytutu Technicznego Wojsk Lotniczych

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2008

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nr 23

89-116

PL

W artykule zaprezentowano wyniki analiz własności dynamicznych linii hydraulicznej uwzględniających efekt bezwładności cieczy płynącej w przewodzie sztywnym, jak i gięt-kim, efekt ściśliwości tej cieczy i efekt tarcia lepkiego. W rozważaniach potraktowano linię hydrauliczną jako czwórnik o dwóch wejściach i dwóch wyjściach, charakteryzujący się określoną macierzą transmitancji. Główne rozważania przeprowadzono dla modelu o zmiennej rezystancji. Podano rozwiązanie ogólne w funkcji operatora Laplace'a oraz adaptację modelu linii hydraulicznej dla przepływu turbulentnego i przepływu przez przewód o sprężystych ściankach. Wprowadzając odpowiednie uproszczenia do modelu o zmiennej rezystancji otrzymano kolejno model o stałej rezystancji i model linii bez strat.

EN

This paper presents the results of a hydraulic line dynamic properties analysis taking into account inertia of the fluid flowing in rigid and flexible lines, the compressibility effect for this fluid and the viscous friction effect. The following are described and analyzed: solution of the wave equation in the form binding four variables: pressure and flow rate at the line input, and pressure and flow rate and the line output; two of the above-mentioned variables should be regarded as independent (input) and the other two as dependent (output), the accuracy comparison of distributed parameters model to lumped parameters model with regard to applicability range in hydraulic systems analysis, pressure value at given installa-tion points as a response to rapid valve closing (transient response) or to valve opening (fluid hammer effect). In these considerations the hydraulic line is regarded as a two-port with two inputs and two outputs with a definite transmittance matrix. Main considerations concern the variable resistance model. A general solution is given as a function of the Laplace operator. Adaptation of the hydraulic line model to the turbulent flow and to the flow through a line with elastic boundaries is given. Introducing appropriate simplifications into the variable resistance model, the constant resistance model and lossless line model is obtained. Also, general solutions for three different lump parameter models are presented. Accuracy of individual methods are compared with examples for selected systems.

8

Experimental investigations of the flow phenomena in the rotor blades of the axial flow low speed compressor stage at the unstable part of the overall performance characteristic

Witkowski A., Ziach M., Majkut M., Strozik M.

Archive of Mechanical Engineering

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2008

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Vol. LV, nr 4

313-330

EN

The paper presents experimental investigations of pressure fluctuations near the tip clearance region of the rotor blades of the axial-flow low-speed compressor stage in stable and unstable parts of the overall performance characteristic. In this investigation, unsteady pressure was measured with the use of high frequency pressure transducers mounted on the casing wall of rotor passage. The pressure signals and their frequency characteristics were analyzed during the steady-state processes, before the rotating stall, during the transition from the steady-state process to the rotating stall, and during a stabilized phenomenon of low-frequency rotating stall. As the operating point moves to the unstable region of flow characteristic, an inception of the rotating stall can be observed, which rotates with a speed of about 41.4% of the rotor speed. The results of this study confirm that in the low-speed axial compressor stage operating in a rotating stall regime there appears one stall cell that spreads over to adjacent rotor blade channels. As the flow rate is reduced further, the frequency of the rotating stall decreased to 34.8% of the rotor speed and the number of blade channels with the stall cell increases.

PL

W pracy przedstawiono eksperymentalne badania pulsacji ciśnienia w obszarze szczeliny nadłopatkowej łopatek koła wirnikowego, w osiowym, niskoobrotowym stopniu sprężającym, w statecznym i niestatecznym obszarze charakterystyki aerodynamicznej. Nieustalone impulsy ciśnienia próbkowane były za pomocą wysokoczęstotliwościowych przetworników ciśnienia zamontowanych na osłonie zewnętrznej koła wirnikowego. Przeanalizowano impulsy ciśnieniowe oraz ich charakterystyki częstotliwościowe zarówno w obszarze statecznej pracy koła wirnikowego, w obszarze przejścia, jak i w obszarze ustabilizowanego zjawiska niskoczęstotliwościowego oderwania wirującego. W miarę jak punkt pracy przemieszcza się do obszaru niestatecznej części charakterystyki pojawia się oderwanie wirujące z częstotliwością wynoszącą 41.4% częstotliwości obrotów wirnika. W wyniku przeprowadzonych badań stwierdzono, że w badanym niskoobrotowym stopniu sprężającym, występuje w kanałach międzyłopatkowych kota wirnikowego, jedna komórka oderwania, która obejmuje swym zasięgiem kilka sąsiednich kanałów. Dalsze zmniejszanie strumienia przepływu powoduje spadek częstotliwości wirującego oderwania do 34.8% częstotliwości obrotów wirnika oraz wzrost liczby kanałów łopatkowych, w których to oderwanie występuje.

9

Komputerowe wspomaganie procesu nawęglania i hartowania

Górecki M.

Zeszyty Naukowe Politechniki Świętokrzyskiej. Mechanika

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2005

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Z. 82

59-71

PL

W artykule przedstawiono wyniki badań grubości warstw nawęglonych oparte na rzeczywistych procesach przeprowadzonych na stanowisku do nawęglania próżniowego oraz symulacji komputerowej przy pomocy programu ANSYS. Wykonana została symulacja dla warunków rzeczywistych, w celu późniejszego przeprowadzenia optymalizacji zakresu ciśnień w procesie nawęglania próżniowego.

EN

The results of case depth masurements of carburized layers based both on the real processes carried out at carburizing stand and ANSYS simulation are shown in this paper. The simulation was carried out for actual conditions in order to optimize the pressure ranges in carburizing process.

10

Identification of steam-water two-phase flow regimes in vertical upward tube

Bai B., Guo L., Zhao L.

Zeszyty Naukowe Politechniki Świętokrzyskiej. Mechanika

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1999

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Z. 67

173--183

EN

Both the fluctuating static pressures on the tube wall and the differential pressure fluctuation were measured to obtain the objective identification of steam-water two-phase flow regimes in a vertical upward tube of 20.0-mm interior diameter. The test pressures were 1.0MPa, 2.0MPa and 3.0MPa and the mass flux ranged from 100 to 900kg/m2s. The fluctuating mechanisms were studied by the statistical theory. The root mean square (RMS) of the pressure fluctuation can not be used to discriminate the flow regime transition under the condition of the high pressure, which was used successfully by Wambsganss in air-liquid loop. The frequency of differential pressure fluctuation ranged from 0 to 5 Hertz, and the shapes of the PDF and PSD concerned the various flow regimes. The flow regimes can be identified based on the RMS of the differential pressure fluctuation. The results by the method agreed well with the flow regimes provided by McQuillan and Whalley.