M.Sc Student | Holenberg Yulia |
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Subject | Multiphase Dynamics of Visco-Plastic Media Interfacing Newtonian Fluids |

Department | Department of Chemical Engineering |

Supervisors | Dr. Olga Lavrentev |

Professor Emeritus Avinoam Nir | |

Full Thesis text - in Hebrew |

Multiphase dynamics of viscoplastic media interfacing Newtonian fluids have been experimentally and analytically studied. Established shapes and velocities of Tetrachloroethylene drops and air bubbles of various volumes passing through the tubes under the forces of gravity and buoyancy were analyzed. The experiments have demonstrated that for every set of physical and geometrical parameters of the system, there exists a critical volume of a fluid particle below which gravity induced stresses are not high enough to yield the Carbopol or Gelatin solution adjacent to the interface. For larger particles, after an initial transient period, a steady state is established with the terminal velocity depending solely upon the physical parameters of the system. An established shape is assumed as the particle reaches terminal velocity. The yielded region thickness was determined by measuring the velocity of drops and bubbles of the same radius moving in tubes of varying radii. For example, the velocity of small drops and bubbles increases proportionally with the radius of the drop, and is generally independent of the tube radius.

The collision and interaction of equal-size fluid particles was analysed with focus on the dynamics of their deformation and coalescence into a single particle. The interaction proved to be substantially non-stationary. It was observed that, if two equal drops are initially placed on the axis of a cylindrical tube, the trailing particle moves substantially faster than the leading particle due to the influence of the disturbance flow behind the leading drop. For relatively small separations the velocity ratio decreases quickly with the initial separation. For moderate separations the velocity ratio maintains at almost constant value. For larger separations the velocity ratio decreases quickly again until the ratio reaches unity value. Above this separation, both drops attain the same velocity as would a single dropand no interaction is observed. It is believed that the yielded regions associated with each drop do not intersect in this case.

Exact analytical solutions describing natural and thermocapillary convection in a double layer system have been studied. The system consisted of Newtonian and Hershel-Bulkey fluids subjected to longitudinal temperature and concentration gradients. Horizontal orientation of the system and linear Soret effect were taken into account. The dependence of the flow patterns (including the appearance and position of unyielded regions), velocity profile, mass and heat transfer rate on the governing parameters have all been studied.