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Zedníková, Mária ; Vejražka, Jiří ; Stanovský, Petr
A model is developed for predicting the outcome of breakup of a fluid particle (bubble or drop), which is initially deformed (e.g. due to turbulence) and breaks into two daughter particles. An initially dumbbellshaped deformation of the particle is assumed. The evolution of sizes of particle subparts is calculated using RayleighPlesset equations, which consider the inertia of surrounding fluid, capillary action and viscous effects. The redistribution of internal fluid in the particle is calculated using Bernoulli equation. The model computes the sizes of daughter particles after the breakup. By assuming various initial conditions (various initial shapes and initial velocities of deformation), the size distribution of daughter particles is obtained. These size distributions are qualitatively compared with available experimental data and reasonable agreement is observed. Because of strong assumptions, this model cannot be used directly for accurate prediction of size distribution after a breakup. However, it provides an insight in the physics of the breakup, especially on the effect of inner phase properties.
Fulltext: content.csg  PDF Plný tet: SKMBT_C22017030713510  PDF


Experiments of Bubble and Drop Breakup in a Turbulent Flow.
Zedníková, Mária ; Vejražka, Jiří ; Stanovský, Petr
Bubble and drop breakage in a turbulent flow is studied experimentally. In an experimental cell, the turbulent flow (of distilled water) is generated by an array of coaxial nozzles, which allows adjusting independently the turbulence intensity and the mean velocity. Either air or cyclohexane is injected in order to produce bubbles or drops. Their breakage by the turbulent flow is observed using a highspeed camera. The image processing provides information about particles in each image. Tracking software is developed and it allows to identify and characterize the breakup events (their location, number and sizes of daughter particles and also trajectories prior the breakup) and to distinguish them from a simple overlap of multiple bubbles. The parameters characterizing the breakup are then studied in dependence on local flow conditions.
Fulltext: content.csg  PDF Plný tet: SKMBT_C22016120713101  PDF


Characterization of Turbulent Flow in a Breakup Cell.
Vejražka, Jiří ; Zedníková, Mária ; Stanovský, Petr
Our research focuses on breakup of bubbles and drops induced by a flow turbulence. In this contribution, we describe the experimental setup used for studying the breakup, and we characterize flow within it. The setup is a rectangular glass cell, in which a turbulent flow is generated by a set of coaxial nozzles. The flow within it is characterized by means of particle image velocimetry. From the velocity data, i) local dissipation rate (ε) is estimated using LargeEddy PIV method, and ii) statistics of velocity difference in two points is evaluated. Estimation of ε is validated by integrating the total dissipation in the setup, which reasonably agrees with the injected kinetic energy. The probability density function of velocity difference is nonGaussian and when properly normalized, it is universal within the setup.
Fulltext: content.csg  PDF Plný tet: SKMBT_C22016120713100  PDF


Dynamics of Shape Oscillations of a Bubble Attached to a Capillary Tip
Vobecká, Lucie ; Vejražka, Jiří ; Orvalho, Sandra ; Zedníková, Mária ; Tihon, Jaroslav
The shape oscillations of a bubble, which is attached to a tip of a capillary tube, are studied experimentally. It is observed that the attachment leads to an appearance of an additional lowfrequency mode (denoted as mode 1), when compared to standard theories of oscillations of free bubbles or drops. It is observed that the frequency of mode 1 scales with the bubble size as f ~ D^(2). The oscillation dynamics of a bubble is strongly influenced if some surface active agent is present in the liquid. Due to interfacial elasticity, the surfactants presence in low concentration increases the oscillation frequency. The decay of oscillations is also faster, probably due to an increase of energy dissipation by Marangoni stresses.


Oscillation of a Bubble in Surfactant Solution
Vobecká, Lucie ; Vejražka, Jiří ; Zedníková, Mária ; Orvalho, Sandra ; Tihon, Jaroslav
The decay of shape oscillations of a bubble in solutions of a soluble nonionic surfactant are studied by means of highspeed imaging. The oscillations are induced by a sudden motion of a capillary, to which the bubble is attached. The bubble then either detaches or remains attached at the capillary. In both cases, the observed bubble shape is decomposed into eigenmodes (Legendre polynomials). The frequency f and the decay time τ of the lowest oscillation mode are evaluated. Their dependences on the surfactant concentration c, on the bubble size and on the bubble age are studied.
