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Evaluation of methods for determination of surfactants
Soukupová, Alena ; Doležalová Weissmannová, Helena (referee) ; Vávrová, Milada (advisor)
This bachelor thesis deals with the evaluation of the methods used for the determination of surfactants. On the base of literature search the review of possible methods applicable for the determination of detergents in the surface waters and wastewaters was set up. The theoretical part presents the definitions of the surface water and wastewater, possible sources of pollution are discussed and methods of water cleaning are listed. The definition and classification of various classes of surfactants is also included. This work is theoretical; therefore the evaluation was made on the basis of the information obtained from accessible literature. The evaluation of the discussed methods is given in the conclusion.
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Experimental Study of Bubble Interactions with the Solid Surface
Zedníková, Mária ; Vobecká, Lucie ; Vejražka, Jiří ; Růžička, Marek
The experiments were carried out in a rectangular vessel equipped with a device generating the bubbles of defined size ranging from 0.4 to 2.0 mm (Vejrazka et al., 2008). Cleaned glass was used as a hydrophilic surface and polypropylene, polyethylene and Teflon were used as hydrophobic surfaces. Deionised water with addition of sodium dodecyl sulphate was used as liquid. The collision and attachment process was observed by means of high speed camera. The following quantities were evaluated from the image sequences: impact and rebound velocities of a bubble, maximal bubble deformation during the contact with the surface and the time required for three-phase contact line formation. The experimental results were compared with our previous investigations (Fujasova-Zednikova et al., 2009).
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Vliv viskoelastických vlastností mezifázového rozhraní na oscilace bubliny
Vejražka, Jiří ; Vobecká, Lucie ; Zedníková, Mária ; Orvalho, Sandra ; Tihon, Jaroslav
Shape oscillations of bubbles in surfactant solutions are investigated by means of high-speed imaging. Two cases are studied: bubbles attached to a capillary tip, and bubbles freely rising after detachment. The frequency f and the decay time τ of shape oscillations are evaluated, and their dependence on the surfactant concentration and on the bubble size is investigated. If the surfactant is present, τ shortens and a minimum is found for a certain concentration. This observation demonstrates that in the surfactant solutions, the energy dissipation linked to interfacial effects can be much more important than the dissipation due to liquid viscosity. The frequency f increases with increasing concentration of the surfactant first, and then it drops rapidly at concentration, at which τ is minimal. The initial increase of the oscillation frequency suggests that the interfacial elasticity can play an important role in surfactant solutions.
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Effect of surfactants ageing on drag reduction
Mík, Václav ; Myška, Jiří
Four different surfactants were investigated in a closed hydraulic loop in order to find the influence of age of the solution on drag reducing effectiveness and on decrease of critical shear stress. It shows that ageing of a particular surfactant is dependent on its concentration. Different sensitivity of solutions to flow disturbances indicates an individualism of single surfactants with worm-like micelles.
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