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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 ...
On the electrospinning of PVB solutions
Švrčinová, Petra; Filip, Petr; Lubasová, D.
2010 - English
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).
Keywords:
electrospinning; elongational viscosity; polyvinylbutyral (PVB)
Available on request at various institutes of the ASCR
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 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 ...
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 - English
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.
Keywords:
prolate spheroid; drag torque; drag force; Magnus force
Available on request at various institutes of the ASCR
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 ...
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 ...
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 - English
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.
Keywords:
carbon nanotube network; compression; electrical resistence; stress sensor
Available on request at various institutes of the ASCR
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) ...
On behaviour of PVB solutions in electrospinning
Švrčinová, Petra; Lubasová, D.; Filip, Petr; Martinová, L.
2010 - English
Electrospinning produces nanofibre sheets from polymer solutions under high electric field. Rheological properties of these solutions play a substantial role in a nanofibre formation simultaneously with properties of polymers and solvents applied. This contribution aims at a determination of dependence of shear viscosity of polyvinylbuthyral (PVB) on the intensity of electric field to which PVB solutions are exposed. PVB was dissolved consecutively in a series of solvents as 10% wt. solution. It was found that the viscosity ratio (viscosity of a solution in presence of electric field/viscosity of a solution in absence of electric field) depends on the polarity of solvent. This pre-determines the possibility of application of the individual solvents for the process of electrospinning.
Keywords:
nanofibre; electrospinning; polymer solution; viscosity ratio; electric field
Available in digital repository of the ASCR
On behaviour of PVB solutions in electrospinning
Electrospinning produces nanofibre sheets from polymer solutions under high electric field. Rheological properties of these solutions play a substantial role in a nanofibre formation simultaneously ...
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