The Numerical Simulation of Droplet Generation and its Control Using Electrowetting Method in Microfluidic Devices

Merdasi, Arshia | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: English
  3. Document No: 52899 (58)
  4. University: Sharif University of Technology, International Campus, Kish Island
  5. Department: Science and Engineering
  6. Advisor(s): Moosavi, Ali; Shafii, Mohammad Behshad
  7. Abstract:
  8. In this research, two important mechanisms were discussed including droplet generation and jumping mechanisms using electro wetting-on-dielectric. For these purposes, the finite element method (FEM) was used to solve the unsteady Naiver-Stokes equation. In addition, the level set method was applied to capture the interface between two phases. In the current study, first, droplet generation in a T-junction fluidic channel device was studied through using electro wetting actuation. The efficacy of electro wetting on the droplet generation frequency as well as droplet diameter is visible in a T-junction fluidic channel since after applying voltages, specified with non-dimensional electro wetting numbers of η=0.5 and 1.2, dispersed phase is pulled out into the oil phase. For controlling the droplet, it was aimed to numerically investigate the electro wetting-induced droplet spreading and jumping over a system consisting of a flat surface and a surface with topographical bumps. It was shown that for the case of flat surface, there was a good agreement between obtained data and experimental observation during the process of droplet spreading. The results also demonstrate that droplet jumping is boosted over the bumps and the droplet jumps to larger heights in comparison with the flat substrate. It has been shown that between the considered shapes, the triangular bump leads to larger dynamic and therefore, droplet can jump with a larger velocity. In addition, the droplet jumping process is significantly affected by electro wetting number, droplet-ambient liquid viscosity and the Ohnesorge number. The mechanism of electro wetting-induced droplet jumping was also studied over a substrate with a geometric heterogeneity in the form of a conical bump and then the results were compared with those of a flat substrate under different hydrophilicities (θ_Y=120°, 144°). Obtained results divulged that the droplet jumping process can be enhanced through applying a topographic heterogeneity as well as larger surface wettability (θ_Y=144°). Moreover, it was demonstrated that increasing the cone height does not necessarily provide a better condition for the jumping. This means that there is an optimum value for the height of conical bump (h*=0.8) which results in larger droplet jumping height
  9. Keywords:
  10. Droplet Jumping ; Electrowetting ; Level Set Method ; Droplet Generation ; Microfluidic System

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