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Experimental Study of a Single Bubble Formation and Its Deformation in Shear-thinning Fluids

Esfidani, Mohammad Taghi | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 47852 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Afshin, Hossein; Firoozabadi, Bahar
  7. Abstract:
  8. Bubble formation and bubble rising are widely used in many industrial processes such as bubble columns, extraction, fermentation, foaming and polymerization. Although many of these processes are faced with a series of bubbles, this study may help us better understand the hydrodynamics of single bubble formation and bubble rising and provides a deep insight into the modeling of a series of bubbles. Bubble velocity and drag coefficient in various fluids are the major parameters for designing the liquid-gas systems. These parameters are a function of the bubble size. In this study, single bubble formation is theoretically modelled in order to predict the size of the bubble at the moment of separation under different operating conditions. This mathematical modelling is based on the balance of forces acting on the bubble. The buoyancy, pressure and gas momentum forces are considered as driving forces and the surface tension, drag and inertia forces are regarded as resisting forces. In order to verify the results of the proposed model, a high-speed camera is used to observe the bubble formation in a wide range of operating conditions and physical properties of the Newtonian fluids. Various bubble parameters, such as bubble volume, are measured using an image processing code. To extend the presented model for shear thinning fluids, the effective shear rate for bubble growth is calculated using the results of experiments with three different CMC solutions and the viscosity is modified for non-Newtonian fluids. The proposed model estimates the size of the bubbles very well for a wide range of operating conditions. By examining the effect of fluid properties and system conditions on the bubble sizes, it was observed that increasing the fluid viscosity, surface tension, gas flow rate and needle diameter increases the size of the bubbles. However, increasing the fluid density reduces the size of the bubbles
  9. Keywords:
  10. Image Processing ; Bubble Formation ; Bubble Size ; Mathematical Modeling ; Non-Newtonian Fluids

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