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Spinnability of PEO solutions with respect to their aging
Zelenková, Jana; Peer, Petra; Filip, Petr
2013 - English
Non - negligible portion of pol ymer commodity suffers from ageing that participates in sometimes significant changes of products attributes. Rheology represents a useful tool for a description of this process. The aim of this contribution is to evaluate possible ageing of PEO solution ( polyethylen e oxide ( M w =300,000 g/mol) dissolved in water at 10 wt.% concentration) based both on rheological characterization and on quality of electrospun fibres. Rheological measurements in steady shear and oscillatory modes were carried out using a rota tional rheometer MCR 501 (Anton Paar, Austria) equipped with the concentric cylinders geometry. The electrospinning measurements were executed with the help of a proposed laboratory device. The tip - to - collector distance attained 20 cm, applied voltage rang ed from 20 to 30 kV. The obtained electrospun fibres were analysed using a scanning electron microscope (VEGA 3, Tescan, Czech Republic). Both types of measurements were carried out in the period of several months during which the solution studied was plac ed in a dark and tempered box (25°C). The measurements indicate no ageing impact on rheological characteristics or quality of electrospun fibres. This guarantees more or less the identical quality of non - woven textiles prepared from PEO solutions regardles s of time period during which the solutions are deposited.
Keywords:
polyethylene oxide (PEO); ageing; electrospinning; rheological properties
Fulltext is available at external website.
Spinnability of PEO solutions with respect to their aging
Non - negligible portion of pol ymer commodity suffers from ageing that participates in sometimes significant changes of products attributes. Rheology represents a useful tool for a description of ...
Influence of the spheroid prolongation on the drag force
Lukerchenko, Nikolay; Keita, Ibrahima; Kvurt, Y.; Miles, Jiří
2011 - English
The drag force acting on a spheroid moving perpendicularly to its axis of rotation in water was studied experimentally. Along the spheroid axis, which is normal to its axis of rotation, a round narrow hole was bored. The spheroid moved along a thin vertical thread stretched in water. A video system recorded the spheroid motion and the spheroid velocity was determined from the record. The drag force coefficient was calculated from the balance of forces acting on the spheroid. Two oblate, two prolate spheroids and one sphere with ratio of the axes 0.67; 0.81; 1.33; 2 and I (sphere), respectively, with approximately the same volumes, were used. The friction coefficient between the thread and spheroid was determined from the comparison of the experimental and calculated motions of the sphere, for which the drag force coefficient is known. The dependence of the drag force coefficient of the spheroid on the ratio of its semi-axes was obtained.
Keywords:
spheroid; drag force coefficient
Available in digital repository of the ASCR
Influence of the spheroid prolongation on the drag force
The drag force acting on a spheroid moving perpendicularly to its axis of rotation in water was studied experimentally. Along the spheroid axis, which is normal to its axis of rotation, a round narrow ...
Modelling of bed in process of particle saltation in channel
Kharlamova, Irina; Kharlamov, Alexander A.; Chára, Zdeněk; Vlasák, Pavel
2011 - English
For numerical modelling particle saltation in channel with rough bed is important to define a bed configuration. The paper deals with the bed consisting of spherical particles of the different size then the saltating particle. In horizontal x-z plane the particles are arranged hexagonally. In vertical direction the particles are distributed according to Gaussian distribution. Before each collision of the saltating particle with bed the bed is shifted on a random distance and it is rotated by a random angle, so there is uniform probability to find a bed particle in any point of the x-z plane. The bed structure is chosen with aim to represent the natural bed as much as possible, thus the known information about distribution of the bed particles along y-direction is used and the location of bed particles in the x-z plane is controlled by principles of equal probability and minimal dense packing.
Keywords:
bed structure; normal distribution; hexagonal packing
Available in digital repository of the ASCR
Modelling of bed in process of particle saltation in channel
For numerical modelling particle saltation in channel with rough bed is important to define a bed configuration. The paper deals with the bed consisting of spherical particles of the different size ...
Coarse-particles conveying in pipes
Vlasák, Pavel; Kysela, Bohuš; Chára, Zdeněk
2011 - English
Flow behavior of coarse-grained slurry depends generally on particle size, shape, density and concentration. The present paper describes the results of experimental investigation of the model coarse-grained slurries on the pipe loop of inner diameter 36 mm with smooth pipes. Graded pebble gravel and glass balls conveyed in water were studied. Research was focused on evaluation of the effect of slurry velocity and concentration on hydraulic gradient versus slurry velocity relationship and the slurry flow behavior. Particle distribution in the pipe vertical cross section and motion of particles along the pipe bottom were studied in a transparent pipe section.
Keywords:
coarse-grained slurry; gravel-water mixture; pressure drops; flow structure
Available in digital repository of the ASCR
Coarse-particles conveying in pipes
Flow behavior of coarse-grained slurry depends generally on particle size, shape, density and concentration. The present paper describes the results of experimental investigation of the model ...
Simulation of water and heat transport considering preferential flow. Experimental site Na Lizu
Votrubová, J.; Dohnal, M.; Vogel, T.; Tesař, Miroslav
2011 - English
Coupled water and heat transport in soil profile at the experimental site Na Lizu (Volynka headwater catchment, Sumava Mountains, southern Bohemia) is studied. The site is located on a mild slope cov-ered with grass. The soil is Cambisol developed upon biotite paragneiss bedrock. One-dimensional dual-continuum model with semi-separate flow domains representing the soil matrix and the network of preferential pathways (S1D) is employed. Hydraulic parameters of the model are set based on labo-ratory retention curve measurements and in-situ measurements of hydraulic conductivity. Thermal pa-rameters are estimated using methodology of Cote and Konrad (2005). Simulation is conducted for the summer season of 2009. The in-situ monitored precipitation and soil surface temperatures are used as the model upper boundary condition. Model performance was evaluated through comparison with soil water pressure and soil temperatures monitored in situ.
Keywords:
soil heat transport; advective heat flux; preferential flow; dual-continuum approach
Available in digital repository of the ASCR
Simulation of water and heat transport considering preferential flow. Experimental site Na Lizu
Coupled water and heat transport in soil profile at the experimental site Na Lizu (Volynka headwater catchment, Sumava Mountains, southern Bohemia) is studied. The site is located on a mild slope ...
Experimental investigation of drag force, Magnus force and drag torque acting on rough sphere moving in calm water
Lukerchenko, Nikolay; Keita, Ibrahima; Chára, Zdeněk; Vlasák, Pavel
2010 - English
The paper describes the results of experiments with a rotating golf ball moving quasi-steadily in calm water. The motion of the ball was recorded on a digital video camera. The dimensionless drag force, Magnus force, and drag torque coefficients were determined from the comparison of the calculated translational and angular velocities and trajectory with experimental ones for the rough particle. The proper value of the correction coefficients were established from condition of the best fitting of the experimental trajectory by the calculated one.
Keywords:
drag force; Magnus force; particle trajectory
Available in digital repository of the ASCR
Experimental investigation of drag force, Magnus force and drag torque acting on rough sphere moving in calm water
The paper describes the results of experiments with a rotating golf ball moving quasi-steadily in calm water. The motion of the ball was recorded on a digital video camera. The dimensionless drag ...
Choice of polymer samples geometry for measurement of elongational viscosity using ser universal testing platform
Filip, Petr; Švrčinová, Petra
2010 - English
Generation of purely uniaxial elongational flow of polymer melts is very uneasy problem. It seems that each hitherto developed device for measurement of uniaxial elongational viscosity also produces - to some extent - a planar flow. During the last period there has been questioned - based on this reasoning - the applicability of a SER Universal Testing Platform and was recommended the range of rectangular dimensions of polymer samples for which measurements of uniaxial elongational viscosity is possible to take into account. The aim of this contribution consists in verification of invariantness of uniaxial elongational measurements using the SER Universal Testing Platform with respect to the dimensions of polymer samples applied. There is shown that for sufficiently broad region of admissible widths and thicknesses the results are identical. For these measurements there was used LDPE Escorene (Exxon, U.S.A.).
Keywords:
uniaxial elongational flow; planar flow; polymer melts; uniaxial elongational viscosity; SER Universal Testing Platform; LDPE
Available in digital repository of the ASCR
Choice of polymer samples geometry for measurement of elongational viscosity using ser universal testing platform
Generation of purely uniaxial elongational flow of polymer melts is very uneasy problem. It seems that each hitherto developed device for measurement of uniaxial elongational viscosity also produces - ...
Approximation of velocity distribution in open channel flow
Ivanova, Irina; Vlasák, Pavel; Chára, Zdeněk; Kysela, Bohuš
2010 - English
The paper deals with approximation of spatial distribution of mean downstream velocity of sub-critical turbulent flow in an open rectangular channel with rough bed. New formulae of the local downstream velocity component Vx(y, z) dependence on the vertical coordinate y and lateral coordinate z were introduced. The vertical velocity profile was approximated by log-law and the power law was used to describe the effect of channel walls on the horizontal velocity profile. The suggested formulae of spatial downstream velocity component distribution were calibrated and verified using the experimental data obtained by PIV method. The proposed approximation is in good agreement with experimental data, the difference between experimental and calculated data is in range of 5 - 10% except the area near the channel’s corners and water level, where the maximal difference reaches 60% and 30% of experimental values, respectively.
Keywords:
spatial velocity profile; channel flow; vertical profile; lateral profile; power law; logarithmic law
Available in digital repository of the ASCR
Approximation of velocity distribution in open channel flow
The paper deals with approximation of spatial distribution of mean downstream velocity of sub-critical turbulent flow in an open rectangular channel with rough bed. New formulae of the local ...
A note to the simplification in description of some molecular-based polymer models
Kharlamov, Alexander; Filip, Petr
2010 - English
One type of integral is frequently met in various description of behaviour of polymer materials through molecular-based models starting with the classical Doi-Edwards one. The integrand in this integral for which an integrated region represents a solid angle is formed by a product of a unit vector (pointed at an element of this region) with a deformation gradient tensor. This product is raised to an exponent that is not usually an integer. The aim of this contribution is to derive substantially simplified expression for this integral respecting high accuracy of an approximation.
Keywords:
polymer materials; Doi-Edwards model; integral
Available in digital repository of the ASCR
A note to the simplification in description of some molecular-based polymer models
One type of integral is frequently met in various description of behaviour of polymer materials through molecular-based models starting with the classical Doi-Edwards one. The integrand in this ...
Effect of dense slurry composition on its flow behaviour in horizontal pipe
Vlasák, Pavel; Chára, Zdeněk
2010 - English
The paper deals with experimental investigation of the dense fine-grained slurries focused on the slurry pressure drops versus average velocity relationship. The content of fine, especially colloidal solid particles evokes a complex non-Newtonian behaviour of the slurry. Flow behaviour of dense slurry depends on particle size distribution, shape, density and chemical composition of the solid phase as well as on concentration of solids and carrier liquid properties. The re-circulation pipe loop with horizontal hydraulically smooth stainless steel pipes was used for measuring the slurry flow parameters. Different slurries containing kaolin, stony dust or sand conveyed in water were measured to document effect of the size distribution and chemical composition on the slurry flow behaviour.
Keywords:
dense slurry; flow behaviour; pressure drop; particle size distribution effect; concentration effect
Available in digital repository of the ASCR
Effect of dense slurry composition on its flow behaviour in horizontal pipe
The paper deals with experimental investigation of the dense fine-grained slurries focused on the slurry pressure drops versus average velocity relationship. The content of fine, especially ...
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