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Dynamics and Heat transfer of Two-phase Non-Newtonian Fluids in Superhydrophobic Channels

Shahsavari, Arghavan | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 55558 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Moosavi, Ali
  7. Abstract:
  8. When the fluid passes through the microchannel, some energy is lost due to drag force and pressure drop. One of the methods used in the last few decades to optimize energy consumption is creating superhydrophobic surfaces in microchannels. These surfaces, with their features such as increasing the contact angle and reducing the contact angle hysteresis, can reduce energy loss, which is due to the presence of unevenness on the surface, and by trapping air and creating a two-phase flow, they reduce the drag force. On the other hand, the air trapped inside these irregularities will also affect the heat transfer of the passing fluid in the microchannel, which by creating resistance in the passing flow, will reduce its speed and, as a result, lose energy. Among the important applications of the use of superhydrophobic surfaces, we can mention the creation of self-cleaning surfaces, medical and sanitary fields, lab-on-chip technology, microfluidics, the oil and gas industry, and marine industries. Therefore, knowing the dynamics and heat transfer inside the microchannels will give a better view of the fluid behavior. On the other hand, most of the research in this field has been carried out with the assumption that the fluid is Newtonian and single-phase, while in the industry, most of the fluid used is non-Newtonian, which behaves differently than Newtonian fluid. For this reason, in the present study, the dynamic effects and heat transfer of two-phase non-Newtonian fluids with the Power law model are investigated in superhydrophobic channels using numerical simulation in Comsol Multiphysics software. In this study, the effect of heat transfer as a boundary condition on the upper and lower walls of the microchannel and as a constant temperature and constant heat flux was investigated and it was observed that when the heat transfer is carried out through the upper wall, its effect is greater than the boundary condition through the lower wall. Also, in certain conditions, non-Newtonian fluids with a fluid characteristic of 0.8 have a pressure drop of about 50.15% less than non-Newtonian fluids with a fluid characteristic of 1.2. Even when the constant temperature boundary condition is applied, the non-Newtonian fluid with the fluid characteristic of 0.8 has a lower pressure drop than the Newtonian fluid. The reduction of pressure drop for 0.8 fluid characteristic is about 30.40% better than that of a Newtonian fluid. Also, the dimensionless Nusselt number for Newtonian fluids is higher than other non-Newtonian fluids. Because the mixing of the main fluid is much better for the Newtonian fluid and correspondingly, the Nusselt number is higher. Compared to the Reynolds number, the Nusselt number increases as it increases
  9. Keywords:
  10. Superhydrophobicity ; Heat Transfer ; Non-Newtonian Fluids ; Two Phase Flow ; Superhydrophobic Surfaces ; Pressure Drop ; Microchannel

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