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.
An analysis of the liquid filling processes in an oval disk-shaped micro chamber is demonstrated while associated with the micro systems at various widths of inlet and outlet which are fabricated using MEMS technology. The results are presented in terms of the movement of the gas-liquid interface. During the filling processes the front shape results from the competition among the inertia, adhesion and surface tension. The influences of non-dimensional parameters such as the Reynolds number and Weber number, both based on the inlet velocity, as well as the wall adhesive conditions on flow characteristics are investigated. The effects of the change in channel widths of a circle chamber as well as the change in lengths of semimajor axis and the semiminor axis of an oval chamber on the filling process are also studied. The above-mentioned geometric changes result in a change in the angle between the microchannels and micro chamber at intersection and significantly affect the filling phenomenon of liquid in the micro chamber. It is evident that the air entrapment appears while the strong inertia is imposed and hydrophobic property inside the chamber wall occurs. The numerical results are also compared with experimental measurements and show similar filling processes.