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National Repository of Grey Literature 3 records found  Search took 0.00 seconds. 
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.
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Určení objemového průtoku vazkoplastických kapalin mezikružím za pomoci aditivní metody
 Filip, Petr ; David, Jiří
An additive method enabling a direct determination of axial flow rate for viscous (power-law model) and viscoplastic (Vočadlo model) fluids in concentric annuli is presented. Flow rate through the actual concentric annulus is possible to express as a sum of axial flow rates through individual partial concentric annuli forming the whole annulus. The resulting relation for axial flow rate is possible to express in analytical forms without necessity of otherwise complicated derivations. The only numerical calculation consists in a determination of location of a zero shear stress for the original whole concentric annulus.
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K výběru odpovídajícího fenomenologického modelu pro vazkoplastické kapaliny
 David, Jiří ; Filip, Petr
At present a series of phenomenological models are used for the description of flow curves of viscoplastic materials. Their application for the given materials hitherto subjects to the two following factors: number of entering parameters and agreement with the experimental data. However, for the case of viscoplastic fluids there is still one point playing a crucial role: determination whether a mutual ratio of ciscous and plastic effects generated by the proposed model corresponds to the physical characteristics of the material studied. This contribution aims to analyse partially this topic and to provide a hint for a choice of a corresponding model
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