Number of found documents: 527
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The role of solvents in the preparation of hydrophobic nanofibrous membrane containing fumed silica
Peer, Petra; Polášková, M.; Musilová, I.; Filip, Petr
2018 - English
It is well-known that a type of used fumed silica nanoparticles plays a dominant role in wettability of the corresponding nanofibrous mats. As a result, the desired contact angle can be approximately achieved by a choice of adequate fumed silica nanoparticles. However, less attention has been hitherto paid to an active role of solvents in connection with the tailoring this contact angle. For analysis we used poly(vinyl butyral) representing electrospun-friendly material, various types of fumed silica nanoparticles and two solvents - methanol and ethanol. It is demonstrated that a choice of polymer solvents plays a significant role in contact angle changes. Hence, in combination of the type of fumed silica nanoparticles and the type of solvent it is possible to achieve a finer partition of the required contact angles. Keywords: PVB solution; solvents; fumed silica; electrospinning; rheology Available at various institutes of the ASCR
The role of solvents in the preparation of hydrophobic nanofibrous membrane containing fumed silica

It is well-known that a type of used fumed silica nanoparticles plays a dominant role in wettability of the corresponding nanofibrous mats. As a result, the desired contact angle can be approximately ...

Peer, Petra; Polášková, M.; Musilová, I.; Filip, Petr
Ústav pro hydrodynamiku, 2018

Thermal induced morphological changes of poly(ethylene oxide) nanofibrous webs
Polášková, M.; Peer, Petra; Ponížil, P.; Čermák, R.
2018 - English
The crystallinity of fibres prepared by electrospinning shows lower level in comparison with samples processed by common technologies such as moulding or film casting. Thus, the attempts to improve the structure of electrospun fibres in order to increase physical and mechanical properties of nonwoven webs are obvious. Post-process thermal treatment is one of the possibilities of the crystallinity enhancement that can be easily included to the finishing operation of final products. For the experiment we used poly(ethylene oxide) representing electrospun-friendly material and two solvents - methanol and water, both ensuring good electrospinnability. It is demonstrated that a choice of polymer solvents plays a significant role in fibre diameter and their capabilities to resist applied heat. However, in all cases the enhancement of crystallinity is detected at the short time of thermal exposure. Keywords: PEO nanofibres; degree of crystallinity; electrospinning Available at various institutes of the ASCR
Thermal induced morphological changes of poly(ethylene oxide) nanofibrous webs

The crystallinity of fibres prepared by electrospinning shows lower level in comparison with samples processed by common technologies such as moulding or film casting. Thus, the attempts to improve ...

Polášková, M.; Peer, Petra; Ponížil, P.; Čermák, R.
Ústav pro hydrodynamiku, 2018

Experimental investigation of settling slurry flow in inclined pipe sections
Vlasák, Pavel; Chára, Zdeněk; Matoušek, Václav; Kesely, Mikoláš; Konfršt, Jiří
2018 - English
Narrow particle size distribution glass beads-water slurry flow in the pipe sections of different inclination were investigated on an experimental pipe loop of inner diameter D = 100 mm. The study refers to the effect of pipe inclination and slurry velicity on local concentration distribution, pressure drop-velocity relationship, and deposition limit. The study revealed that the glass beads-water mixtures in the inclined pipe sections were significantly stratified: the solid particles moved principally close to the pipe invert, and for flow velocities close to the deposition limit sliding bed or stationary deposit is created even in inclined pipe sections. Keywords: settling slurry; inclined pipe; pressure drops; concentration distribution; radiometry Available at various institutes of the ASCR
Experimental investigation of settling slurry flow in inclined pipe sections

Narrow particle size distribution glass beads-water slurry flow in the pipe sections of different inclination were investigated on an experimental pipe loop of inner diameter D = 100 mm. The study ...

Vlasák, Pavel; Chára, Zdeněk; Matoušek, Václav; Kesely, Mikoláš; Konfršt, Jiří
Ústav pro hydrodynamiku, 2018

Formování kapek v systému dvou nemísitelných kapalin
Kysela, Bohuš; Konfršt, Jiří; Chára, Zdeněk; Šulc, R.; Jašíková, D.
2017 - Czech
Velikost kapek při míchání dvou vzájemně nemísitelných kapalin závisí především na působení vnějších sil. Smyková napětí působící na částici v závislosti na fyzikálních parametrech (povrchové napětí, hustota, viskozita) ovlivňují konečnou distribuci velikostí tvořených kapek. V první fázi jsme se pokusili modelovat dvě reálné nemísitelné kapaliny voda-silikonový olej, které jsou dány svými vlastnostmi. A to na jednoduchém případě výtoku z kapiláry, kde jsme se snažili ověřit, zda a jak moc přesně lze modelovat chování tohoto systému s různými odchylkami fyzikálních parametrů. Dále jsme se snažili určit rovnovážné a mezní stavy v závislosti na zadaných fyzikálních vlastnostech. The CFD simulation of simple two phase system using VOF model was verified by the real measurements. The system of two immiscible liquids silicone oil and water was tested on simple task with droplet formation from immersed jet. The setup of physical properties in CFD simulations was corrected by the experimental results. Keywords: VOF; liquid; multiphase Available at various institutes of the ASCR
Formování kapek v systému dvou nemísitelných kapalin

Velikost kapek při míchání dvou vzájemně nemísitelných kapalin závisí především na působení vnějších sil. Smyková napětí působící na částici v závislosti na fyzikálních parametrech (povrchové napětí, ...

Kysela, Bohuš; Konfršt, Jiří; Chára, Zdeněk; Šulc, R.; Jašíková, D.
Ústav pro hydrodynamiku, 2017

Evaluation of the turbulent kinetic dissipation rate in an agitated vessel
Kysela, Bohuš; Konfršt, Jiří; Chára, Zdeněk; Sulc, R.; Jašíková, D.
2017 - English
The design of agitated tanks depends on operating conditions and processes for that are used for. An important parameter for the scale-up modelling is the dissipation rate of the turbulent kinetic energy. The dissipation rate is commonly assumed to be a function of the impeller power input. But this approach gives no information about distribution of the dissipation rate inside the agitated volume. In this paper the distributions of the dissipation rate inside the agitated vessels are estimated by evaluations of the CFD (Computational Fluid Dynamics). The results obtained from RANS (Reynolds Averaged Navier-Stokes equations) k-epsilon turbulent model and LES (Large Eddy Simulations) with Smagorinsky SGS (Sub Grid Scale) model are compared. The agitated vessels with standard geometry equipped with four baffles and stirred by either a standard Rushton turbine or a high shear impeller were investigated. The results are compared with mean dissipation rate estimated from the total impeller power input. Keywords: flow; large-eddy simulation Fulltext is available at external website.
Evaluation of the turbulent kinetic dissipation rate in an agitated vessel

The design of agitated tanks depends on operating conditions and processes for that are used for. An important parameter for the scale-up modelling is the dissipation rate of the turbulent kinetic ...

Kysela, Bohuš; Konfršt, Jiří; Chára, Zdeněk; Sulc, R.; Jašíková, D.
Ústav pro hydrodynamiku, 2017

Local velocity scaling in T400 vessel agitated by Rushton turbine in a fully turbulent region
Šulc, R.; Ditl, P.; Fořt, I.; Jašíková, D.; Kotek, M.; Kopecký, V.; Kysela, Bohuš
2017 - English
The hydrodynamics and flow field were measured in an agitated vessel using 2-D Time Resolved Particle Image Velocimetry (2-D TR PIV). The experiments were carried out in a fully baffled cylindrical flat bottom vessel 400 mm in inner diameter agitated by a Rushton turbine 133 mm in diameter. The velocity fields were measured in the zone in upward flow to the impeller for impeller rotation speeds from 300 rpm to 850 rpm and three liquids of different viscosities (i.e. (i) distilled water, ii) a 28% vol. aqueous solution of glycol, and iii) a 43% vol. aqueous solution of glycol), corresponding to the impeller Reynolds number in the range 50 000 < Re < 189 000. This Re range secures the fully-developed turbulent flow of agitated liquid. In accordance with the theory of mixing, the dimensionless mean and fluctuation velocities in the measured directions were found to be constant and independent of the impeller Reynolds number. On the basis of the test results the spatial distributions of dimensionless velocities were calculated. The axial turbulence intensity was found to be in the majority in the range from 0.388 to 0.540, which corresponds to the high level of turbulence intensity. Keywords: agitated vessel; Rushton turbine; PIV Fulltext is available at external website.
Local velocity scaling in T400 vessel agitated by Rushton turbine in a fully turbulent region

The hydrodynamics and flow field were measured in an agitated vessel using 2-D Time Resolved Particle Image Velocimetry (2-D TR PIV). The experiments were carried out in a fully baffled cylindrical ...

Šulc, R.; Ditl, P.; Fořt, I.; Jašíková, D.; Kotek, M.; Kopecký, V.; Kysela, Bohuš
Ústav pro hydrodynamiku, 2017

Simulation of collagen solution flow in rectangular capillary
Kysela, Bohuš; Skočilas, J.; Zitny, R.; Stancl, J.; Houska, M.; Landfeld, A.
2017 - English
The viscoelastic properties of foods and polymers can be evaluated from flow of the material in capillary with specified dimension and shape. The extrusion rheometer equipped by capillary with rectangular cross-section was used for determination of the rheological behaviour of water collagen solution. The measurements of the axial profiles in longitudinal direction of the total stresses at capillary wall were performed for various shear rates. The linear viscoelastic model of Oldroyd B type: White-Metzner model was used for simulation of fluid flow in OpenFOAM software package. The simulations describe the effect of relaxation time on wall total stress in convergent-divergent capillary. Keywords: collagen; viscoelastic model; convergent-divergent capillary Fulltext is available at external website.
Simulation of collagen solution flow in rectangular capillary

The viscoelastic properties of foods and polymers can be evaluated from flow of the material in capillary with specified dimension and shape. The extrusion rheometer equipped by capillary with ...

Kysela, Bohuš; Skočilas, J.; Zitny, R.; Stancl, J.; Houska, M.; Landfeld, A.
Ústav pro hydrodynamiku, 2017

Řízený pohyb kulové částice v kanále s volnou hladinou
Chára, Zdeněk; Kysela, Bohuš; Konfršt, Jiří
2017 - Czech
V příspěvku jsou prezentovány experimentální výsledky proudění kolem kulovité částice, kdy částice je umístěna na tenké tyčce a její pohyb je řízen asynchronním motorkem. Pro určení rychlostních polí kolem pohybující se částice byla použita metoda 2D PIV. Měření se uskutečnila v kanále s volnou hladinou, jehož dno bylo pokryto jednou vrstvou skleněných tyček o průměru 6mm. The paper presents experimental results of the flow around the spherical particle, where the particles are placed on a thin rod and its movement is controlled by a step motor. To determine the velocity fields around the moving particle, the 2D PIV method was used. The measurement was carried out in the open channel, the bottom of which was covered with one layer of 6 mm diameter glass bars. Keywords: open channel; PIV; turbulence Available at various institutes of the ASCR
Řízený pohyb kulové částice v kanále s volnou hladinou

V příspěvku jsou prezentovány experimentální výsledky proudění kolem kulovité částice, kdy částice je umístěna na tenké tyčce a její pohyb je řízen asynchronním motorkem. Pro určení rychlostních polí ...

Chára, Zdeněk; Kysela, Bohuš; Konfršt, Jiří
Ústav pro hydrodynamiku, 2017

Flow behaviour and structure of heterogeneous particles-water mixture in horizontal and inclined pipes
Vlasák, Pavel; Chára, Zdeněk; Konfršt, Jiří
2017 - English
Available at various institutes of the ASCR
Flow behaviour and structure of heterogeneous particles-water mixture in horizontal and inclined pipes

Vlasák, Pavel; Chára, Zdeněk; Konfršt, Jiří
Ústav pro hydrodynamiku, 2017

Simulace pohybu částic v nakloněném potrubí pomocí kombinace CFD a DEM
Mildner, Michael; Konfršt, Jiří; Kysela, Bohuš; Chára, Zdeněk; Vlasák, Pavel
2017 - Czech
Numerická simulace proudění rozplavených hrubozrnných suspenzí (hydrotransport, odlučovače atp.) vyžaduje použití výpočtů pro vícefázové proudění. Za předpokladu toku suspenze (např. vody a pevných částic) v uzavřených profilech bez přístupu vzduchu můžeme úlohu zjednodušit na dvoufázové proudění (voda-pevné částice). Vhodným nástrojem pro výpočet takovéhoto dvoufázového proudění je kombinace metody konečných objemů FVM s metodou diskrétních elementů DEM. Metoda diskrétních elementů je použita na řešení kolizí mezi jednotlivými částicemi, což je nezbytnou podmínkou pro reálné řešení proudění více- koncentrovaných suspenzí. Numerická simulace byla provedena na jednoduché geometrii nakloněného potrubí, kde jsou získané výsledky porovnávány s výsledky získanými na experimentální trase pro transport suspenzí opatřené sklopnou částí. Numerical flow simulation of scattered coarse-grained suspensions (hydrotransport, separators, etc.) requires the use of calculations for multiphase flow. Assuming the suspension flow (eg. water and solid particles) in closed profiles without air access, the task can be simplified to a two-phase flow (water-solid particles). A suitable tool for calculating such two-phase flow is the combination of the finite volume method FVM, with the discrete element method DEM. The discrete element method is used to solve collisions between individual particles, which is a prerequisite for a real solution of more concentrated suspension flow. Numerical simulation was performed on a simple geometry of inclined pipeline, where the obtained results were compared with the results obtained on the experimental slurry transport route equipped with a foldable part. Keywords: CFD; FVM; DEM; transport of suspension Available on request at various institutes of the ASCR
Simulace pohybu částic v nakloněném potrubí pomocí kombinace CFD a DEM

Numerická simulace proudění rozplavených hrubozrnných suspenzí (hydrotransport, odlučovače atp.) vyžaduje použití výpočtů pro vícefázové proudění. Za předpokladu toku suspenze (např. vody a pevných ...

Mildner, Michael; Konfršt, Jiří; Kysela, Bohuš; Chára, Zdeněk; Vlasák, Pavel
Ústav pro hydrodynamiku, 2017

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