Browsing by Author "Chen, J. J."

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Analysis of filling of an oval disk-shaped chamber with microfluidic flows
(2006-11-20)
Chen, J. J.
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Liu, W. Z.
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Lin, J. D.
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Wu, J. W.
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機械工程學系
The filling of an oval disk-shaped micro-chamber by liquid is analyzed with reference to micro-systems with inlets and outlets of various widths, which are fabricated using MEMS technology. The results concern the motion of the gas-liquid interface. The flow fields during the filling of the micro-chambers are also studied. During the filling, the front shape is determined by the competition among inertia, adhesion and surface tension. The effects of non-dimensional parameters, such as the Reynolds number and the Weber number, both determine by the inlet velocity, as well as the wall adhesive conditions, on the flow characteristics are examined. The effects of the widths of channels in a circular chamber and the lengths of the semi-major and semi-minor axes of an oval chamber on the filling process are also investigated. Geometric changes alter the angle between the microchannels and the micro-chamber at their intersection and significantly affect the filling of the micro-chamber with the liquid. The location of bubble entrapment is plotted parametrically against the Weber number, the liquid/substrate contact angle and the change in the angle between the microchannels and the micro-chamber at intersection. Evidently, air is entrapped when the inertia is high, large changes in the angle between the channels and the chamber at the intersection are made, and a hydrophobic property is observed inside the chamber wall. The numerical results are also compared with experimental measurements; they indicate similar filling processes. (c) 2006 Elsevier B.V. All rights reserved.
Chaotic passive micromixers with microstructures placed on the top and bottom floors of channel
(2008-01-01)
Chen, J. J.
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Lai, Y. R.
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Lin, J. D.
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機械工程學系
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Department of Mechanical Engineering
The objective of this study is to present chaotic micromixers in which a series of microstructures are placed on the top and bottom floors of channels. Passive micromixers fabricated by MEMS technologies with crosswise grooves and ridges are considered. Numerical simulations using the commercial software CFD-ACE(U) are employed to predict the effects of various patterns of microstructures on mixing efficiency with the range of Reynolds number from 0.05 to 50. The influences of non-dimensional parameters such as the Reynolds number as well as the geometrical parameters on the mixing performance are presented in terms of the mixing index. Micromixers which are made of PDMS are used to investigate the mixing characteristics influenced by the different kinds of microstructures. A significant amount of stirring resulting from chaotic mixing can be seen due to the fluids flowing through the crosswise ridges embedded on the top and bottom floors of channels. While Re is greater than 1, the mixing index of the micromixer with crosswise ridges starts to increase as Re increases. This means that the flow field in this micromixer results in efficient chaotic mixing. Simulation results are presented to compare with the experimental data, and a very good agreement can be achieved. Finally, various numbers of the crosswise ridges with the same orientation in one cycle of the channels are investigated to present to the mixing performance in the microchannels. An optimal design can be found in our works.