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Experimental and Theoretical Investigation of Ascending Accelerated Motion of Single Bubble in Quiescent Newtonian and Non-newtonian Liquids

Shahsavari, Mona | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 49738 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Firoozabadi, Bahar; Afshin, Hossein
  7. Abstract:
  8. The gas-liquid interaction is one of the most important and common phenomenons in chemical, biochemical and mineral industries which is generally observed as liquid in a gas stream (droplet) or gas in a liquid stream (bubble). Although bubbles produced in the industrial applications are in the form of a group of bubbles, understanding the hydrodynamics of a single bubble in a quiescent liquid provides a starting point for studying bubble groups. It should be noted that changes in the velocity and drag coefficient of the bubbles in various fluids are essential parameters for designing gas-liquid systems. In the present research, in order to examine the effect of system parameters and thermophysical properties of liquids on the bubble velocity, bubble motion has been examined by analyzing all of the recorded video frames from the moment of detachment to the time at which the terminal velocity is reached in Newtonian and non-Newtonian liquids. Experiments were carried out using water, glycerin and 80%, 85%, 90%, and 95% aqueous glycerin solutions, which cover a wide range of viscosities, and also by using 0.25%, 0.5%, 0.75%, 1%, and 1.5% aqueous solutions of CMC. Investigation of the effect of various parameters on the dynamics of the bubble motion indicates that the difference between the initial velocity of the bubble (just after the detachment from the needle tip) and the terminal velocity, and the time required for the bubble to reach its terminal velocity increase with increasing bubble equivalent diameter and with decreasing ambient fluid viscosity. In addition, when the bubble reaches its terminal velocity, empirical relations have been proposed for distance between the mass center of the bubble and needle tip in Newtonian and non-Newtonian liquids. In this study, dynamics of the accelerated motion and uniform motion of a single spherical bubble in a quiescent high-viscosity Newtonian liquid has been modeled theoretically. The proposed mathematical model is based on the Newton's law of motion and the balance of buoyancy, drag, history and added-mass forces. To achieve nearly true results, an empirical relation has been proposed for the initial velocity of the bubble (just after the detachment) and it has been used as an initial condition for solving the equations. Due to the presence of non-linear terms in the equation of motion, HPM method has been used as a powerful analytical method to analytically calculate the velocity. Comparison between the analytical and numerical results and also experimental data for Reynolds number between 0.154 and 20.378 shows good agreement. Moreover, an analytical relation has been presented for drag coefficient of the bubble that covers both accelerated and uniform motion of the bubble in Newtonian liquid
  9. Keywords:
  10. Drag Coefficient ; Homotopy Perturbation ; Non-Newtonian Fluids ; Gas-Liquid Interactions ; Acceleration Rising Bubble

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