|
| |
|
|
Breaking of Rod-shaped Model Material during Compression.
Kulaviak, Lukáš ; Pěnkavová, Věra ; Růžička, Marek ; Punčochář, Miroslav ; Zámostný, P. ; Grof, Z. ; Štěpánek, F. ; Schöngut, M. ; Havlica, Jaromír
The breakage of a model anisometric dry granular material caused by uniaxial compression was studied. The bed of uniform rod-like pasta particles (8 mm long, aspect ratio 1:8) was compressed (Gamlen Tablet Press) and their size distribution was measured after each run (Dynamic Image Analysing). The compression dynamics was recorded and the effect of several parameters was tested (rate of compression, volume of granular bed, pressure magnitude and mode of application). Besides the experiments, numerical modelling of the compressed breakable material was performed as well, employing the DEM approach (Discrete Element Method). The comparison between the data and the model looks promising.
Fulltext: content.csg -  PDF
Plný tet: SKMBT_C22018011012170 - PDF
|
|
|
Powder Rheology of Nanocrystalic Particles.
Kulaviak, Lukáš ; Pěnkavová, Věra ; Růžička, Marek ; Punčochář, Miroslav ; Zámostný, P. ; Grof, Z. ; Štěpánek, F. ; Schöngut, M. ; Havlica, Jaromír
Pigments are mostly nanometric powder of anisometric particles providing complex rheological behaviour. The interparticle forces of grains (> 100 μm) are based on direct contact, which is mainly influenced by the particle size and shape. On the other hand powder (< 4 μm) and especialy nanometric powder (< 100 nm) is influenced mainly by electrostatic charges and by moisture (respectively by the liquid and solid bridges forming). However the morphology affects the surface area and thus the distribution of surface charge and\nthe moisture content on/in single particle. Last but not least, it is also good to know the history of the powder, i.e. the effect of aging and the memory of the powder on the strength of the material. The nanometric powder TiO2 was chosen as a demonstration material and measuring device was FT4 powder rheometer.
Fulltext: content.csg - PDF
Plný tet: SKMBT_C22018011012520 - PDF
|
|
| |
|
| |
|
|
Detection of Apparent Wall Slip in Microdispersion Liquids
Pěnkavová, Věra ; Tihon, Jaroslav ; Wein, Ondřej
Zdánlivý přístěnný skluz je možno detekovat přímo různými vizualizačními technikami, pokud je mikrodisperzní kapalina dostatečně transparentní, nebo nepřímo pomocí viskozimetrie, kdy je měření prováděno v minimálně dvou různých geometriích senzoru. Z rozdílných tokových křivek naměřených v různých geometriích je možno pomocí statistického zpracování vyhodnotit jak viskozitu v objemu disperze, tak skluzový příspěvek podél stěny.
Fulltext: content.csg - PDF
Plný tet: Penkavova at al_CHISA 2015 - PDF
|
|
|
Models of AWS Material Functions
Wein, Ondřej ; Pěnkavová, Věra
New classes of 4-parameter models of fluidity for the shear-thinning non-Newtonian liquids are introduced, including their local pseudosimilarity representation. The models cover both purely-viscous (PV) and visco-plastic (VP) flow behavior. New 4-parameter model of slipidity (Navier slip coefficient) is introduced, as well as its modification for retarded AWS (slipidity decreasing with rising shear stress) and wall dilatancy (negative slipidity). Their asymptotic behavior, as well as their asymptotic sub-models are identified and prepared for implementation in the software AWSWork.
|
|
|
The Deflocculation of Kaolin Suspensions – the Effect of Various Electrolytes
Pěnkavová, Věra ; Guerreiro, M. ; Tihon, Jaroslav
The deflocculation effect of conventional additives to kaolin suspensions is evaluated from the results standard rheological measurements. Several widely used electrolytes (NaOH, Na2CO3, Na2SiO3, SHMP = sodium hexametaphosphate, and CMC = sodium salts of carboxymethylcellulose) have been tested. The optimal concentrations of these deffloculants, in respect to reaching the maximum reduction of initial suspension viscosity, are found. The stability of deflocculated kaolin suspensions against sedimentation is evaluated and different aspects of the observed flow enhancement discussed. Inorganic electrolytes are found to be more effective in viscosity reduction, but on the other hand, low-molecular organic CMC additives produce more stable final suspensions.
Fulltext: content.csg - PDF
Plný tet: SKMBT_C22013102415150 - PDF
|
|
|
Rheology of Colloidal Dispersions: Deflocculation of Kaolin Dispersions
Guerreiro, M.I.A. ; Růžička, Marek ; Pěnkavová, Věra
All inorganic additives in their optimal concentrations proved to be effective at reducing the initial viscosity to 1%. In the case of NaOH two different trends were observed: firstly this additive behaved as a deflocculant agent where, at its optimal range of concentrations, the viscosity of kaolin dispersion reduced to its minimal value, secondly when used at concentrations above its optimal range, sodium hydroxide behaved like a flocculant agent increasing strongly the viscosity of kaolin dispersions. The possible cause was attributed to an excess of Na+ and OH- species in bulk media that promoted the reversible effect. Similar effect was also reported for NaCMC at high and medium molar weight, were the viscosity firstly decreased to a certain concentration of additive and then above that concentration started to increase. Thus low molar weight NaCMC was the most effective among the organic additives since it decreased the viscosity to 10% of initial viscosity. Qualitative evaluation showed that organic additives promoted more stable dispersions, in contrast to poor stability offered by the inorganic additives, with exception of NaOH that provided dispersions with good stability inside of its optimal range.
|
|
|
Wall Shear Stress Induced by Taylor Bubbles in Inclined Flow Channels
Tihon, Jaroslav ; Pěnkavová, Věra ; Vejražka, Jiří
The motion of single air bubbles in flat channels is experimentally investigated. The electrodiffusion technique of near-wall flow diagnostics is applied to measure the wall shear stress distribution under large rising bubbles. The measurements are synchronized with the visual observation of bubble movement by a high-speed camera. The analysis of video records provides information on the bubble shape and terminal velocity. The experiments are carried out for three different channel configuration (with heights of 1.5, 4, and 8 mm), cover a wide range of channel inclination angles (from horizontal to vertical position), and dealing with both the bubbles in stagnant and in co-flowing water.
Fulltext: content.csg - PDF
Plný tet: SKMBT_C22012112614030 - PDF
|
guest ::
RSS feed.