Hyeung Seok Heo

Numerical and Experimental Study on a Channel Mixer with a Periodic Array of Cross Baffles

In this study we show an enhanced mixing effect with a simple channel having a periodic array of cross baffles. We performed numerical compulation to obtain the steady flow field within the channel at low Reynolds numbers by using a commercial code, ANSYS CFX 10.0. A visualization experiment was also conducted to validate our numerical results qualitatively. In evaluating the mixing performance, we employed the Lyapunov exponent. It was shown that the visualized mixing pattern was in a good agreement with that numerically given. Our Liapunov exponent distribution in the space also demonstrates that the proposed channel design indeed exhibits a chaotic stirring at low Reynolds numbers. Our design is thus assumed to be applicable to designing a microchannel mixer with enhanced mixing effect

Enhancement of Stirring in a Straight Channel at Low Reynolds-Numbers with various Block-Arrangement

In this study a newly designed microchannel as an efficient fluid-mixer is proposed. This design is comprised of a channel and a series of blocks periodically attached on the bottom surface of the channel. In this configuration, the stirring is greatly enhanced at a certain range of parametric values. To characterize the flow field and the stirring effect, both numerical and experimental methods were employed. To obtain the velocity field, three-dimensional numerical computation to the Navier Stokes equations was performed by using a commercial code, FLUENT 6.0. The fluid-flow solutions were then cast into studying the characteristics of stirring with the aid of Lyapunov exponent. In this study, the Lyapunov exponents were computed manually because the commercial code does not provide the corresponding tool. In the experiment, flow visualization was performed by using pure glycerin in a tank and glycerin mixed with small amount of a fluorescent dye in the other tank. The numerical results show that the pattern of the particles’ trajectories in the microchannel heavily depends on the block arrangement. It was shown that the stirring is significantly enhanced by a larger block-height and reaches maximum when the height is 0.8 times the channel width. We also studied the effect of the block stagger angle. It was found that stirring performance is the best at the block stagger angle of 45°.

An experimental study on the AC electroosmotic flow around a pair of electrodes in a microchannel

This paper presents an experimental study on the AC electroosmotic flow in a microchannel having a pair of rectangular electrodes on the bottom wall with narrow gap. The microchannel was made of PDMS (Polydimethylsiloxane) and the electrodes of ITO (Indium Tin Oxide). The electrodes were arranged such that the electric field is mainly perpendicular to the channel’s longitudinal direction, thus creating a transversal secondary flow. The primary flow was driven by a pressure force through the fluid-level difference on both reservoirs of the channel. To measure the velocity distributions around the electrodes, we used a micro-PTV (particle tracking velocimetry) technique. We find that on the surface of the electrodes the flow velocity caused by the AC electroosmosis is directed from the electrode edge toward the side wall of the channel, and the maximum crosswise velocity occurs at the frequency 120Hz. A smooth profile of the crosswise velocity component along a vertical line was successfully obtained from the present experimental technique, and it shows a flow reversal due to the mass conservation principle.

A Study on Characteristics of Fluid Flow and Mixing in a Microchannel With a Controlled Local Electric Field

In this study a newly designed microchannel is proposed. This design is comprised of a channel and a series of metal electrodes periodically attached on the both side’s surfaces of the channel. In this configuration, the mixing effect is greatly enhanced at a certain parameter values. To characterize the flow field and the mixing effect, both numerical and experimental methods were employed. To obtain the potential field, electric field, and velocity vectors three-dimensional numerical computation was performed by using a commercial code, CFD-ACE+. The fluid-flow solutions were then cast into studying the characteristics of stirring with the aid of mixing index. In this study the mixing index were computed manually because the commercial code does not provide the corresponding tool. In the experiment, flow visualization was performed by using water with fluorescent particles. The numerical results show that the velocity pattern in the microchannel heavily depends on the metal electrodes arrangement on both sides. It was shown that the rotational flow is significantly enhanced by a higher voltage of metal electrode.

Study on the Mixing Performance Inside a Micromixer by Using Rapid-Prototyping Technology and Micro-LIF System

In this study a newly fabricated micromixer is proposed. This design comprises periodically arranged simple blocks. In this configuration, the stirring is greatly enhanced at a certain parameter set. This device is fabricated by rapid prototyping technology, stereolithography method, so that we can reduce the R&D time and cost. To characterize the flow field and the stirring effect both the numerical and experimental methods were employed. To obtain the material deformation, three-dimensional numerical computation to the Navier Stokes equations are performed by using a commercial code, FLUENT 6.0. Numerical results show that materials are deformed by the counter clockwise spiral motion of the secondary flows. In the experiment, flow visualization for the stirring effect is performed by using pure water in one reservoir and water mixed with a fluorescent dye in the other, so that we can see the flow motion inside the microchannel. The numerical and experiment results show that the stirring is significantly enhanced at larger block-height. We assert that we can apply the rapid-prototyping technology in the micro fabrication.Copyright

A Study on Stirring Characteristics in a Microchannel With Various Arrangement of Blocks

In this study a newly designed microchannel is proposed. This design comprises periodically arranged simple blocks. In this configuration, the stirring is greatly enhanced at a certain parameter set. To characterize the flow field and the stirring effect both the numerical and experimental methods were employed. To obtain the velocity field, three-dimensional numerical computation to the Navier Stokes equations are performed by using a commercial code, FLUENT 6.0. The fluid-flow solutions are then cast into studying the characteristics of stirring with the aid of Lyapunov exponent. In this study the Lyapunov exponents are computed manually because the commercial code does not provide the corresponding option. In the experiment, flow visualization for the stirring effect is performed by using pure glycerin in one tank and glycerin mixed with a fluorescent dye in the other. The numerical results show that the particles’ trajectories in the microchannel heavily depend on the block arrangement. It was shown that the stirring is significantly enhanced at larger block-height and it reaches maximum when the height is 0.8 times the channel width. We also studied the effect of the block stagger angle, and it turns out that the stirring performance is the best at the block angle 45°.Copyright