Numerical Investigation of Instabilities of Flow in Micro-fluid

Yazdi, Hossein | 2013

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 44744 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Moosavi, Ali
  7. Abstract:
  8. This research concerns investigating the behavior of two-phase flow in the inlet and outlet of the microchannels.Both the droplet based and the continuous microfluidics are considered. For the continuous system whenthe minor fluid enters the microchannel, due to ratio of viscosity of two fluids, viscous folding occurs.Viscous folding phenomena is similar to the buckling phenomena in solids.This means that the viscosity of the fluid, which is applied to two sides of the fluid layer, causes folding the fluid layer and changing the shape of it. For the study we employ a VOF based numerical routine. In order to verify numerical results, the grid and the time step independenciesare checked. In addition the numerical results are compared with someavailable experimental results and very good agreement is observed. A significant characteristic of our study compared to others is considering non-Newtonian fluids. 3D simulation results have shown that the studied phenomenacan be considered 2D. Therefore, the research is conducted in two dimensions.By changing the flow and fluid viscosity rate, possibility of viscous folding phenomenon is investigated. The results has revealed that if the viscosity ratio increases, the wavelength of the instability increases proportionally to the power 1/3. And with increasing flow rate, the wave height increasesproportionally to the power 1/2. For non-Newtonian fluidsemploying a power model it is shown that by increasing the exponent, because of the shear force, the flow becomesmore unstable.The wavelength and the height decrease with increasing the exponent. For non-Newtonian cases, the effects of increasing the flow rate are also studied. In order to study the effect of the inlet geometry on the droplet based microfluidics, four geometriesareconsidered. The resultshave shownthat if the extension rate is constant, droplets just deform and breakup of the droplets does not occur
  9. Keywords:
  10. Microchannel ; Drop Deformation ; Fluent Software ; Viscous Folding ; Nonnewtonian Liquid Drops ; Non-Newtonian Flow

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