Analyzing the performance of an active diverging-type micromixer

• Main Authors: Jing-yang Sie, 謝景揚
• Other Authors: Chen-li Sun
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/22485727413008315533

碩士 === 國立臺灣科技大學 === 機械工程系 === 96 === In this study, mixing performance of an active micromixer is investigated by numerical simulation and experiments. An active micromixer is comsisted of three sections: the T junction, the mixing section, and the outlet. Two parameters are explored: half angle of the mixing section and phase difference of the two sinusoidal pressure actuations. A diverging-type micromixer with a half angle of 25° is used in the numerical simulation. At the two inlets, time-varying sinusoidal pressures (amplitude 500 Pa, frequency 100 Hz) superimposed by a constant shift of 250 Pa are applied. From the numerical results, best mixing is achieved with a MI (mixing index) of 0.66 when the actuating pressures are anti-phase (phase difference π). On the contrary, in-phase actuation (phase difference 0) leads to poorest mixing. The evolutions of concentration profiles and flow fields reveal that fluid is stretched by a pair of circulations in the diverging region to enhance local mixing. Furthermore, fluid tends to flow from one inlet directly into the other when the actuating pressures are not inphase. The residual fluid in the opposite inlet is then pushed to the other side of the diverging region. This phenomenon helps to increase the contact area between the two fluids and mixing is improved significantly. At a phase difference of π, the unique circulation in the confluence region leads to three-dimensional helical flow so that best mixing is achieved. During the experiments, both flow visualization and mixing quantification are conducted. For the diverging-type micromixers, minimum CV (0.04) is accomplished at θ = 20° with a phase difference of 0.75π. For the converging-type micromixers, minimum CV (0.09) is accomplished at θ = -30° with a phase difference of 0.75π. Under dynamic pressure actuations, flow instability is observed for both straight and diverging-type micromixers. Since flow instability tends to enhance the fluid stretching and folding effects,mixing performance can be easily improved by alternating the geometry of the mixing section.