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A Study on the Flow Instability Generation of Viscoelastic Fluid in Microchannels with Side Wells and Its Applications to Microreactor
- Alternative Title
- 측면 골이 있는 미세유체채널에서 점탄성 유체의 유동 불안정성 연구와 이를 활용한 미세반응기 개발
- Author(s)
- 홍선옥
- Advisor
- 김주민
- Department
- 일반대학원 에너지시스템학과
- Publisher
- The Graduate School, Ajou University
- Publication Year
- 2021-02
- Language
- eng
- Alternative Abstract
- Mixing in micro-scale flows is a core technique for a wide range of microfluidic applications. However, there remain many challenging issues to overcome low efficient mixing in microchannels since the turbulent flow cannot be practically achieved in microfluidic environments due to their inherent small length scales. Many different mixing schemes have been proposed based on the active and passive methods which are categorized by requiring external forces or not. One of the passive methods, convective mixing using the lateral fluid motion induced in complicated multi-layered microchannels, has been employed to enhance the mixing performance by enlarging the interfacial area between fluid streams. However, both complicated process for channel fabrication and insufficient mixing based on steady state flow condition are still problematic, which demands significant improvements. In this dissertation, an efficient mixing scheme is proposed based on the inertio-elastic flow instability in a viscoelastic dilute polymer solution occurring in the microchannels with side wells. First, the flow instability was investigated in dilute polymer solutions in a straight microchannel with side wells. The time-dependent and irregular vortex dynamics was observed in cavities placed at the sides of the channel. In addition, the effects of polymer concentration, molecular weight, and channel geometry on the inertio-elastic instability have been studied. The notable changes of the flow instability according to the dimensionless parameters such as Reynolds and Weissenberg numbers were analyzed with fluorescence microscopy, imaging processing, and numerical simulation. Second, a highly efficient mixing method in a serpentine channel combined with side wells was proposed to achieve a significantly wider range of flow rates than in a conventional serpentine channel. For comparison purpose, the flow dynamics in Newtonian fluid, where the inertial effect is significant, was also investigated using fluorescence microscopy and numerical simulation. Although Dean vortex is developed as flow rate increased, the strength of the secondary flow was too weak to enhance the mixing in the Newtonian flow. In this study, we demonstrated that the efficient mixing can be achieved in the viscoelastic polymer solution by the synergistic combination of the flow instabilities generated both in the side wells and along the serpentine channels. Onset of the chaotic fluid motion was also studied by observing the abrupt increase of the pressure drop between the channel inlet and outlet. Finally, this mixing scheme was applied to the continuous synthesis of silica nanoparticles with more uniform size distribution and regular shape in a viscoelastic medium. In addition, the agglomerator of product on the channel walls was significantly reduced by the flow instability generated in the viscoelastic dilute polymer solution in the gear-shaped microchannel, as compared to those in Newtonian solution. We expect that the current studies contribute to the understanding of microscale viscoelastic flow dynamics and pave a novel route to the development of efficient micromixers based on the nonlinear dynamics of dilute polymer solutions.
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- Graduate School of Ajou University > Department of Energy Systems > 4. Theses(Ph.D)
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