Yes (77)
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Rheological characterisation of LDPE materials by means of differential constitutive equations
Pivokonský, Radek; Zatloukal, M.; Filip, Petr
2007 - English
For rheological description of branched LDPE melts (Escorene LD165BW1 a Bralen RB0323) the following differential constitutive equations were used: eXtended Pom-Pom, Phan Thien-Tanner-XPP, and modified Leonov models. There was carried out quantitative and qualitative comparison of efficiency of the predictions determined by these models with the experimental data measured at 200oC. For both materials there were measured linear viscoelastic properties, shear and uniaxial extensional viscosities. Pro reologický popis rozvětvených LDPE materiálů (Escorene LD165BW1 a Bralen RB0323) byly vybrány následující modely: eXtended Pom-Pom, Phan Thien-Tanner-XPP a modifikovaný Leonovův model. U obou materiálů byly proměřeny lineární viskoelastické vlastnosti, smyková a elongační viskozita.
Keywords:
constitutive equations; polymer melts; shear flow; elongational flow
Available in digital repository of the ASCR
Rheological characterisation of LDPE materials by means of differential constitutive equations
For rheological description of branched LDPE melts (Escorene LD165BW1 a Bralen RB0323) the following differential constitutive equations were used: eXtended Pom-Pom, Phan Thien-Tanner-XPP, and ...
High order geometrical and functional discretization for the Navier-Stokes equations
Hoření, Bohumír; Chára, Zdeněk
2007 - English
The paper deals with an applicability of high order methods for geometrical as well as functional approximations. Usefulness of this approach is demonstrated on selected examples. Příspěvek se zabývá použitelností metod vyšších řádů pro geometrické a funkcionální aproximace pro řešení Navier-Stokosových rovnic. Vhodnost navržených postupů je ukázána na vybraných příkladech.
Keywords:
Navier-Stokes equations
Available in digital repository of the ASCR
High order geometrical and functional discretization for the Navier-Stokes equations
The paper deals with an applicability of high order methods for geometrical as well as functional approximations. Usefulness of this approach is demonstrated on selected examples....
Numerical simulation and experimental investigation of pulsating flow
Chára, Zdeněk; Hoření, Bohumír
2007 - English
The contribution presents numerical as well as experimental investigations of laminar and turbulent pulsating flow in an initial part of a rigid pipe. The simulations were performed with help of Fluent 6.3. Measurements of velocity profiles were done by an ultrasound velocity monitor UVP. Příspěvek prezentuje výsledky numerických simulací pulzačního proudění ve vstupním úseku potrubí. Numerické simulace byly prováděny v prostředí Fluent 6.3. Simulace jsou doplněny měřeními pomocí ultrazvukové metody UVP.
Keywords:
pulsating flow
Available in digital repository of the ASCR
Numerical simulation and experimental investigation of pulsating flow
The contribution presents numerical as well as experimental investigations of laminar and turbulent pulsating flow in an initial part of a rigid pipe. The simulations were performed with help of ...
Empirical model respecting a local extreme of a course of the viscosity function
Filip, Petr; David, Jiří; Pivokonský, Radek
2007 - English
Almost all empirical models dealing with the flow curves of non- Newtonian fluids can be applied only in the case of monotonous course of these curves. Exceptionally it is possible to model viscosity behaviour of rheologically more complex materials if there appears, in the course of a flow curve, a global extreme. The 8-parameter model proposed enables a description of viscosity behaviour in dependence on shear rate or shear stress also for the case when an extreme (maximum or minimum) is only local. Prakticky všechny empirické modely jsou použitelné pouze pro případ monotónního průběhu viskozity. Výjimečně je možné modelovat reologicky složitější kapalinu vykazující globální extrém průběhu viskozity. Navržený 8-parametrický model umožňuje modelovat průběh viskozity i při výskytu pouze lokálního extrému.
Keywords:
Viscosity; Empirical model
Available in digital repository of the ASCR
Empirical model respecting a local extreme of a course of the viscosity function
Almost all empirical models dealing with the flow curves of non- Newtonian fluids can be applied only in the case of monotonous course of these curves. Exceptionally it is possible to model ...
Investigation of drag force and drag moment of rotating translationally moving sphere in calm water
Kharlamov, Alexander; Kvurt, Y.; Chára, Zdeněk; Vlasák, Pavel
2007 - English
The paper describes results of experiments with rotating spherical particles moving quasi-steadily in the calm water. The motion of the particles was recorded by a digital video camera. The Cartesian coordinates and the angle of rotation of the particles were determined from the record of the particles motion. The dimensionless drag coefficient, drag moment coefficient and translational and rotational Reynolds numbers were calculated from the time series of the particles coordinates and angle of rotation for each recorded frame. The effect of the particles translational motion on the drag moment and the effect of the particles rotation on the drag force were evaluated from the experimental data. Článek popisuje výsledky experimentů s rotujícími sférickými částicemi pohybujícími se kvazi stabilně v klidné vodě. Pohyb částic byl zaznamenán digitální videokamerou a ze záznamu trajektorie částic byly určeny souřadnice a úhel rotace částic. Z časových řad souřadnic a úhlu rotace částic byly stanoveny bezrozměrné součinitele odporové síly a rotačního momentu i translační a rotační Reynoldsova čísla částice. Byl vyhodnocen vliv translačního pohybu částic na rotační moment a vliv rotace částic na odporovou sílu.
Keywords:
spherical particle; drag force; drag moment; particle rotation
Available in digital repository of the ASCR
Investigation of drag force and drag moment of rotating translationally moving sphere in calm water
The paper describes results of experiments with rotating spherical particles moving quasi-steadily in the calm water. The motion of the particles was recorded by a digital video camera. The Cartesian ...
Calculation of the Saltation Characteristics as Functions of the Initial Parameters
Piatsevich, Siarhei; Lukerchenko, Nikolay; Chára, Zdeněk; Vlasák, Pavel
2006 - English
The results of the 3D simulation of the solid spherical particles saltation in an open channel with rough bed are presented. The dependences of mean saltation length, mean saltation height, mean saltation velocity and mean deviation of angle of particle trajectories with respect to the downstream direction were studied and determined as the functions of the saltation process parameters, such as the flow shear velocity and the particle diameter. Příspěvek popisuje výsledky 3D numerické simulace saltačního pohybu pevné kulovité částice v otevřeném kanále s drsným dnem. Závislost střední délky, střední výšky, střední rychlosti saltace a střední úhlové odchylky trajektorie částice od osy proudění byly studovány a určeny jako funkce parametrů saltačního procesu, tj. smykové rychlosti proudu a průměru částice.
Keywords:
spherical particle saltation; mean saltation length; mean saltation height; mean saltation velocity; deviation of particle trajectories
Available in digital repository of the ASCR
Calculation of the Saltation Characteristics as Functions of the Initial Parameters
The results of the 3D simulation of the solid spherical particles saltation in an open channel with rough bed are presented. The dependences of mean saltation length, mean saltation height, mean ...
Wing airfoil rime ice accretion prediction
Horák, V.; Hoření, Bohumír
2006 - English
The paper presents the rime ice accretion prediction code. Model includes the calculation of a velocity distribution, droplet motion equations and detetrmination of a water mass flux impacting on the wing airfoil surface. Changing the airfoil shape is illustrated in compare of experimental results. Příspěvek popisuje modelovéní klasické námrazy. Model zahrnuje výpočet rychlostního pole, rovnice pohybu kapek a stanovení toku vody dopadající na profil křídla. Změna tvaru profilu křídla je srovnána s výsledky experimentu
Keywords:
rime ice accretion; numerical methods
Available in digital repository of the ASCR
Wing airfoil rime ice accretion prediction
The paper presents the rime ice accretion prediction code. Model includes the calculation of a velocity distribution, droplet motion equations and detetrmination of a water mass flux impacting on the ...
Flow behaviour of Vočadlo-type fluids during back extrusion
Filip, Petr; David, Jiří; Pivokonský, Radek
2006 - English
The aim of this contribution is to present semi-analytical form describing a velocity profile for Vočadlo-type fluids including a location of the plug flow region in an annular passage. Cílem příspěvku je presentace semianalytického tvaru rychlostního profilu kapaliny Vočadlova typu včetně určení polohy oblasti pístového toku v koncentrickém mezikruží.
Keywords:
back extrusion; Vočadlo model; viscoplastic flow
Available in digital repository of the ASCR
Flow behaviour of Vočadlo-type fluids during back extrusion
The aim of this contribution is to present semi-analytical form describing a velocity profile for Vočadlo-type fluids including a location of the plug flow region in an annular passage....
Comparison of heat transfer in a straight and helical tube and influence of preset singularities on heat transfer in straight tube at the flow of surfactant solutions
Mík, Václav; Mihálka, L.; Kořenář, Josef; Myška, Jiří
2006 - English
Experiments were made on a hydraulic facility with closed loop. The influence of a preset valve and circular bend 180° on the heat transfer along the 16 mm tube was investigated. Three different concentrations of cationic surfactant Arquad S 50 (oleyltrimethylammonium chloride) in mixture with NaSal (sodium salicylate) were experimented with. The range of Reynolds numbers was 8.000-100.000 and the heat flux through the tube wall was 22 and 40 kW/m2. Experimentálně byl na hydraulické trase s uzavřeným okruhem sledován vliv předřazeného ventilu a kruhového oblouku 180° na přestup tepla podél přímé kruhové trubky o průměru 16 mm. Použity byly 3 koncentrace kationaktivního surfaktantu s obchodním názvem Arquad 50 (oleyltrimethylamonium chlorid) s přísadou NaSal (salicylan sodný). Rozsah Reynoldsových čísel byl 8 000 – 100 000 a tepelný tok stěnou trubky 22 a 40 kW/m2.
Keywords:
drag reduction; heat transfer
Available in digital repository of the ASCR
Comparison of heat transfer in a straight and helical tube and influence of preset singularities on heat transfer in straight tube at the flow of surfactant solutions
Experiments were made on a hydraulic facility with closed loop. The influence of a preset valve and circular bend 180° on the heat transfer along the 16 mm tube was investigated. Three different ...
Local resistance of surface mounted obstacles
Chára, Zdeněk; Hoření, Bohumír
2006 - English
The influence of surface mounted obstacles on free level of channel flow is discussed. The obstacles of square cross section are placed sequentially along a hydraulic flume and perpendicularly to the flow direction across the whole channel width. Three various spacing between the obstacles - 5H, 11H and 23H (H is height of the obstacle) were tested for different flow discharges. The surface levels were recorded and the results were compared with numerical simulations. Based on the experimental data and numerical simulations the resistance coefficients of the individual obstacles were determined. V článku je diskutován vliv na stěně položených překážek na proudění s volnou hladinou. Překážky o čtvercovém příčném profilu jsou umístěný kolmo na proudění přes celou šířku kanálu. Tři různé vzdálenosti – 5H, 11H a 23H byly testovány (H je výška překážky) pro různé průtoky. Experimentálně získané výsledky průběhu hladin jsou porovnány s numerickými výpočty a jsou určeny lokální odporové koeficienty.
Keywords:
free surface flow
Available in digital repository of the ASCR
Local resistance of surface mounted obstacles
The influence of surface mounted obstacles on free level of channel flow is discussed. The obstacles of square cross section are placed sequentially along a hydraulic flume and perpendicularly to the ...
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