Ne (235)
Počet nalezených dokumentů:
235
Publikováno od
do
LDA measurements and turbulence spectral analysis in an agitated vessel
Kysela, Bohuš; Konfršt, Jiří; Chára, Zdeněk
2012 - anglický
During the last years considerable improvement of the derivation of turbulence power spectrum from Laser Doppler Anemometry (LDA) has been achieved. The irregularly sampled LDA data is proposed to approximate by several methods e.g. Lomb-Scargle method, which estimates amplitude and phase of spectral lines from missing data, methods based on the reconstruction of the auto-correlation function (referred to as correlation slotting technique), methods based on the reconstruction of the time series using interpolation between the uneven sampling and subsequent resampling etc. These different methods were used on the LDA data measured in an agitated vessel and the results of the power spectrum calculations were compared. The measurements were performed in the mixing vessel with flat bottom. The vessel was equipped with four baffles and agitated with a six-blade pitched blade impeller. Three values of the impeller speed (Reynolds number) were tested. Long time series of the axial velocity component were measured in selected points. In each point the time series were analyzed and evaluated in a form of power spectrum.
Klíčová slova:
LDA/LDV; turbulence; mixing
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
LDA measurements and turbulence spectral analysis in an agitated vessel
During the last years considerable improvement of the derivation of turbulence power spectrum from Laser Doppler Anemometry (LDA) has been achieved. The irregularly sampled LDA data is proposed to ...
Motion of rotating spherical particles touching a wall
Chára, Zdeněk; Vlasák, Pavel; Keita, Ibrahima
2012 - anglický
The paper deals with an analysis of motion of rotating spherical particle in calm water, when the particle is in contact with a smooth, horizontal wall. The motion was visualized by a fast digital camera at 1000 frames/second. Based on software analysis the particle trajectories as well as rotational velocities were determined. Values of vertical, horizontal and rotational velocities were used as input parameters for numerical model and the results are compared with experimental data. Experiments were performed with glass particle of diameter 25 mm, initial values of rotational speeds varied from 500 to 3000 revolution per minute.
Klíčová slova:
particle rotation; particle trajectory; Magnus force
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
Motion of rotating spherical particles touching a wall
The paper deals with an analysis of motion of rotating spherical particle in calm water, when the particle is in contact with a smooth, horizontal wall. The motion was visualized by a fast digital ...
Sedimentation of dilute suspension in intermediate region
Vlasák, Pavel; Chára, Zdeněk
2012 - anglický
The present paper describes the results of experimental investigation of the continuous sedimentation of a dilute model of fine-grained suspension in the intermediate region of settlement. The effects of particle size (glass beads of average diameter 150–850 μm), concentration, and inclination of the vessel axis on particle fall velocity were evaluated. It was confirmed that the local relative particle-liquid velocity has a practically constant value across the vessel cross-section. The settling pattern is strongly affected even by a very gentle slope of the vessel axis, which causes an asymmetrical absolute velocity profile and significant increase of the local concentration and absolute fall velocity of particles near the upward-facing wall of the vessel.
Klíčová slova:
sedimentation; intermediate settlement; particle size; concentration; vessel inclination
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
Sedimentation of dilute suspension in intermediate region
The present paper describes the results of experimental investigation of the continuous sedimentation of a dilute model of fine-grained suspension in the intermediate region of settlement. The ...
Motion of multiple cylinders in potential flow of ideal fluid
Kharlamov, Alexander A.; Filip, Petr
2011 - anglický
The flow field past multiple arbitrarily moving cylinders is calculated using a generalisation of the conventional images method. The flow is presented by a flow from an infinite set of dipoles. For calculation purposes the infinite series must be, however, truncated. The kinetic energy of fluid is presented as a sum over all modelling dipoles. A rather good convergence of the method is observed. However, if the distances between any cylinders tend to zero, the method fails in zones close to the contact point. Nevertheless, even for the case of touching cylinders the series for the kinetic energy remain convergent. In case of just two cylinders the method projects on the classical method of images. Method is validated by several comparisons with solutions known from the literature.
Klíčová slova:
generalised images method; potential flow; ideal fluid; circular cylinders
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
Motion of multiple cylinders in potential flow of ideal fluid
The flow field past multiple arbitrarily moving cylinders is calculated using a generalisation of the conventional images method. The flow is presented by a flow from an infinite set of dipoles. For ...
On the electrospinning of PVB solutions
Švrčinová, Petra; Filip, Petr; Lubasová, D.
2010 - anglický
Extension rheological characteristics belong to the principal description of polymer jet formation during a process of electrospinning. However, in spite of nearly absence of shear deformation of polymer solutions during the process of their spinnability, it seems that shear electrorheological characteristics can serve as an indicator of good or bad quality of an electrospun template. The experiments were carried out with four polyvinylbutyral (PVB) solutions in concentration of 10 wt%. Shear viscosities in absence (η0) and presence (η) of electric field were measured using a rotational rheometer equipped with an electrorheological cell. It was shown that the good solvents of PVB exhibit an almost constant curve of η/η0 vs. electric field strength, whereas the viscosity curves for the poor solvents exhibit enhancement. This enhancement corresponds to better quality of electrospun templates (obtained for polymer solutions of PVB with poor solvents).
Klíčová slova:
electrospinning; elongational viscosity; polyvinylbutyral (PVB)
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
On the electrospinning of PVB solutions
Extension rheological characteristics belong to the principal description of polymer jet formation during a process of electrospinning. However, in spite of nearly absence of shear deformation of ...
Experimental evaluation of the drag torque, drag force and Magnus force acting on a rotating prolate spheroid
Lukerchenko, Nikolay; Keita, Ibrahima; Kvurt, Y.; Miles, Jiří
2010 - anglický
The drag torque, drag force and Magnus force acting on a spheroid rotating around its axis of symmetry and moving perpendicularly to this axis in initially quiescent water were studied using experimental data and numerical simulation. The prolate spheroid with ratio of the axes 4/3 was speeded up in special device, which ensured the required rotational and translational velocity in the given plane. A video system was used to record the spheroid motion in water. Using the video records the spheroid translational and angular velocities and trajectory of its center were determined and compared with the results of the numerical simulation. The dependences of the coefficients of the drag torque, drag force and Magnus force on the Reynolds number and dimensionless angular velocity were obtained.
Klíčová slova:
prolate spheroid; drag torque; drag force; Magnus force
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
Experimental evaluation of the drag torque, drag force and Magnus force acting on a rotating prolate spheroid
The drag torque, drag force and Magnus force acting on a spheroid rotating around its axis of symmetry and moving perpendicularly to this axis in initially quiescent water were studied using ...
Multi-wall carbon nanotube networks prepared from pure MWCNT and their oxidised forms effect of compressive strain on electric resistence
Olejník, R.; Slobodian, P.; Říha, Pavel; Kimmer, D.; Sáha, P.
2010 - anglický
Multi-wall carbon nanotube networks were prepared by filtration of CNT aqueous dispersions. CNT dispersions were prepared with the help of surfactant system (sodium dodecyl sulfate with amylalcohol) by ultrasonication. Three types of MWCNT tubes were used. The first were pure CNT delivered by supplier. The others were oxidized CNT oxidized (1. acid solution of KMnO4; 2. the mixture of acids H2SO4 + HNO3). It was found that oxidization significantly changes properties of prepared carbon nanotube networks. There were observed differences in porous structures networks analyzed by SEM microscopy. Moreover, the apparent density of prepared MWCNT networks also changes according to the used CNT. The network electrical resistance is also affected by process of MWCNT oxidation as well as by compressive strain. It was found that the network resistance is sensitive to compressive strain both in the course of strain growth and when loading/unloading cycles are imposed.
Klíčová slova:
carbon nanotube network; compression; electrical resistence; stress sensor
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
Multi-wall carbon nanotube networks prepared from pure MWCNT and their oxidised forms effect of compressive strain on electric resistence
Multi-wall carbon nanotube networks were prepared by filtration of CNT aqueous dispersions. CNT dispersions were prepared with the help of surfactant system (sodium dodecyl sulfate with amylalcohol) ...
Powder injection moulding of a ceramic part
Hausnerová, B.; Marcaníková, L.; Filip, Petr
2009 - anglický
The aim of the study is to optimize the production of alumina ceramic parts via Powder Injection Moulding (PIM) technology. As a case study fabric with main demand on surface-roughness tolerances has been selected with the potential of high production quantities for textile machines industry. The process is searched in terms of material tailoring, part design and dimensions, and processing conditions of injection moulding, debinding and sintering steps. Rheological, thermal and pressure-volume-temperature characteristics were measured in order to provide the reliable data for the simulation of injection moulding as well as thermal and thermogravimetric analyses have been carried out to attain non-porous final sintered products.
Klíčová slova:
powder injection moulding; sintering; pressure-volume-temperature
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Powder injection moulding of a ceramic part
The aim of the study is to optimize the production of alumina ceramic parts via Powder Injection Moulding (PIM) technology. As a case study fabric with main demand on surface-roughness tolerances has ...
Polyvinyl chloride filled with bismuth oxychloride powder
Polášková, M.; Sedláček, T.; Kharlamov, Alexander; Pivokonský, Radek; Saha, P.
2009 - anglický
Mixing of polymers with radiopaque agents enables the polymers visibility on X-ray images and represents the easiest way to accurately locate the polymeric surgical device during a critical procedure. Medical-grade polyvinyl chloride was compounded with various amounts of bismuth oxychloride, chosen for its unique properties such as high radiopacity, non-toxicity, excellent chemical and physical stability and good dispersibility in the polymeric matrix. Micro-compounder Haake MiniLab II, consisting of a conical co-rotating twin-screw compounder with an integrated backflow channel, was used for melt mixing and simultaneously for rheological measurement. Rheological data received from micro-compounder were supplemented and correlated with the data obtained from Anton Paar rotational rheometer. Structure of prepared composites was studied by scanning electron microscopy, and their thermo-mechanical properties were tested using dynamic mechanical analysis.
Klíčová slova:
olyvinyl chloride; bismuth oxychloride; radiopaque agents
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Polyvinyl chloride filled with bismuth oxychloride powder
Mixing of polymers with radiopaque agents enables the polymers visibility on X-ray images and represents the easiest way to accurately locate the polymeric surgical device during a critical procedure. ...
A note to the tube theory
Kharlamov, Alexander; Filip, Petr; Švrčinová, Petra
2009 - anglický
The classical Doi-Edwards (DE) model represents a basic issue for tube theories. The model describes dynamics of polymer strands between entanglements and predicts stress in linear polymers. In this contribution there is considered the dynamics of the whole molecules within the same tube picture. When the molecule end-to-end vector is considered as a Hookean spring the damping function shows weaker thinning. The presented model describes one of the possible mechanisms leading to weaker damping exhibited by branched polymers.
Klíčová slova:
tube theory; damping function; branched polymers; Doi-Edwards model
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
A note to the tube theory
The classical Doi-Edwards (DE) model represents a basic issue for tube theories. The model describes dynamics of polymer strands between entanglements and predicts stress in linear polymers. In this ...
NUŠL poskytuje centrální přístup k informacím o šedé literatuře vznikající v ČR v oblastech vědy, výzkumu a vzdělávání. Více informací o šedé literatuře a NUŠL najdete na webu služby.
Vaše náměty a připomínky posílejte na email nusl@techlib.cz
Provozovatel
Zahraniční báze