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Drag Reduction Using Geometrically Structured Surfaces for Non-newtonian Multi-phase Fluids

Javaherchian, Javaneh | 2019

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 51701 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Moosavi, Ali
  7. Abstract:
  8. With the advancement of the industry, microscale devices use due to its unique characteristics. On the other hand, it is essential to find ways to reduce drag inside microchannels because of The importance of energy. One of the methods is to optimize the contact surface using structured geometric surfaces. These hydrophobic surfaces reduce drag by trapping the air in roughness and creating a two-phase flow. The purpose of this project is to reduce the drag within the microchannel using structured geometric surfaces for non-Newtonian and multiphase flows. In most previous studies, with simplification, Newtonian and two-phase flows have been investigated. While most industrial fluids show non-Newtonian behavior, in industrial processes,the non-Newtonian flow behavior can't be defined by Newtonian one.On the other hand, it is usually possible that the input flow is a multi-phase. In the present work, the results of drag reduction are first validated using a numerical method of phase field for water on a hydrophobic surface with a previous experimental study. To investigate the non-Newtonian properties of materials, considering the T-junction microchannel and non-Newtonian fluid as a continuous phase, the simulations of droplet formation are done and validated with the results of the previous study. After investigating the non-Newtonian fluid in the microchannel of the Newtonian paper and specifying the optimum size of the rectangular hydrophobic microstructure, the rate of reduction in the pressure drop for different non-Newtonian fluids, whose viscosity was defined with a power-model, in an optimized hydrophobic microchannel is investigated with two-dimensional simulations. The results showed that the hydrophobic surfaces are sufficient not only to reduce the pressure drop in non-Newtonian fluids but also in some cases, such as shear-thickening fluids, reduce the pressure drop more than the Newtonian ones. The highest reduction in pressure drop is for a non-Newtonian fluid with the flow behavior index of 1.2 in Reynolds number of 140 and equals to 48.6%. The optimum microstructure dimensions in the microchannel to having the minimum pressure drop for the Newtonian and non-Newtonian fluids have been the same. In this case,the depth-to-width ratio and the width-to-pitch ratio of the microstructure are obtained 0.3 and 12.5, respectively. After that, The performance of Newtonian and non-Newtonian fluids for the hydrophobic microchannel with the non-parallel wall (convergent and divergent) in terms of the contact angle is studied. In the end, the efficiency of hydrophobic surfaces is analyzed for some different two-phase input flows. The results demonstrated a positive effect of hydrophobicity on different two-phase regimes and reduced pressure drop to 41% in some cases
  9. Keywords:
  10. Hydrophobic Materical ; Pressure Drop ; Non-Newtonian Fluids ; Two Phase Flow ; Microchannel ; Microstructure

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