Design a Microfludic Platform to Study the Influence of Flow Fluctuation and Nutrient Gradient in Plankton Ｅcology
Date Issued
2014
Date
2014
Author(s)
Hsiao, Po-Jen
Abstract
This study aims at designing a microfluidic platform to study the influences of flow fluctuation and nutrient gradient in plankton ecology. This microfluidic platform has three different layers. The bottom layer is a turbulent channel which serves to generate turbulence in a cavity, the middle layer is a 3 mm thick agarose gel and the top layer is a concentration-gradient channel. The turbulent channel consists of a round cavity which attaches to a straight main channel. Two geometrical parameters are varied herein: the cavity radius (R = 250 μm, 500 μm, 750 μm, 1000 μm, 1500 μm, 5000 μm) and the design of the cavity mouth. The throatless design is the cavity connected to main channel directly and the throat design is the cavity and main channel connected to main channel with a pair of semicircle. The concentration-gradient channel consists of two symmetric channels which are fed with water and dye. The two solutions diffuse through the agarose gel into the turbulent channel, creating concentration gradient in the cavity.
From the μPIV results, we find that both the size and the mouth design affect the velocity field significantly. At the same Re, velocity decreases as the size of cavity grows. Moreover, throatless design leads to faster velocity than the throat design. Viewing from the streamline, the occurrence of vortices take place at radius of the cavity reaches 500 μm, whereas the number of vortex remains 1 from Reynolds number 1 to 5. As the radius of the cavity reaches 750 μm, the number of vortices remains 2 from Reynolds number 1 to 10, When the radius of the cavity exceeds 1000 μm, no vortex occurs in the cavity under the same Reynolds number. For Reynolds number larger than 50, there is only one vortex in the cavity regardless of cavity size . Under the same Reynolds number, turbulence intensity of the throat design is larger than of the throatless design. We also find that the turbulent intensity decreases as Reynolds number increases. Comparing to throatless design, throat design tends to increase the Kolmogorov length scale. In addition, the Kolmogorov length scale increase with cavity size, but decrease with Reynolds number.
In our microfluidic platform, we create a flow-free environment in the cavity with constant-concentration boundary condition. The agarose gel permits the passage of molecules by diffusion, but completely blocks advection. This advantage allowing as to study plankton ecology just by turbulent flow field and flow-free concentration gradient.
Subjects
流場紊變
營養鹽梯度
微流元件
Type
thesis
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