26
2 Active and Passive Micromixers
M1
M2
(a) Unbalanced split and collision
(b) SAR micromixers with sinusoidal walls
Fig. 2.15 Micromixers based on SAR mechanism [49]
passive micromixing concept using a sigma micromixer shown in Fig. 2.17. Diffusive mass flux between two miscible streams, flowing laminar in the microchannel,
was enhanced when the velocity at the diffusion interface was increased. Microparticle image velocimetry was utilized for visualization of the flow. The result showed
the effectiveness of the proposed passive micromixing concept and improvement of
mixing performance compared to existing designs.
Using conventional UV-lithography, Hong et al. [54] designed, fabricated and
successfully characterized a passive micromixer with modified Tesla structure shown
in Fig. 2.18. At low flow rates, the mixing is primarily by diffusion, but at high
flow rates both convection and diffusion contributes to mixing. Excellent mixing
performance over a wide range of flow conditions at micro scale was observed using
simulation and experiment. Chung et al. [55] proposed a passive micromixer design
that utilizes the self-circulation of the fluids in the mixing chamber as shown in
Fig. 2.19. The micromixer consisted of an inlet port, a circular mixing chamber and
an outlet port. The micromixer was constructed with two-layers PMMA. The upper
PMMA layer was blank. Using a CNC high-speed engraving and milling machine,
the micromixer structures were built on the lower PMMA layer. The self-circulation
phenomenon in the micromixer was studied using numerical simulation. At Re =
10, no circulation zone was observed, and the flow was similar to the symmetrical
creeping flow. However, at Re = 300, a large self-circulation area was seen in the
mixing chamber, which promotes mixing.
2 Active and Passive Micromixers
M1
M2
(a) Unbalanced split and collision
(b) SAR micromixers with sinusoidal walls
Fig. 2.15 Micromixers based on SAR mechanism [49]
passive micromixing concept using a sigma micromixer shown in Fig. 2.17. Diffusive mass flux between two miscible streams, flowing laminar in the microchannel,
was enhanced when the velocity at the diffusion interface was increased. Microparticle image velocimetry was utilized for visualization of the flow. The result showed
the effectiveness of the proposed passive micromixing concept and improvement of
mixing performance compared to existing designs.
Using conventional UV-lithography, Hong et al. [54] designed, fabricated and
successfully characterized a passive micromixer with modified Tesla structure shown
in Fig. 2.18. At low flow rates, the mixing is primarily by diffusion, but at high
flow rates both convection and diffusion contributes to mixing. Excellent mixing
performance over a wide range of flow conditions at micro scale was observed using
simulation and experiment. Chung et al. [55] proposed a passive micromixer design
that utilizes the self-circulation of the fluids in the mixing chamber as shown in
Fig. 2.19. The micromixer consisted of an inlet port, a circular mixing chamber and
an outlet port. The micromixer was constructed with two-layers PMMA. The upper
PMMA layer was blank. Using a CNC high-speed engraving and milling machine,
the micromixer structures were built on the lower PMMA layer. The self-circulation
phenomenon in the micromixer was studied using numerical simulation. At Re =
10, no circulation zone was observed, and the flow was similar to the symmetrical
creeping flow. However, at Re = 300, a large self-circulation area was seen in the
mixing chamber, which promotes mixing.