Micromixers based on chaotic advection - Micromixers Fundamentals Design and Fabrication - page 197

(a)

(b)

(c)

(d)

(e)

(f)

FIGURE 6.2

Concentration distribution at a dimensionless position of x ) ¼ 1.5: (a) Re ¼ 119; (b) Re ¼ 139; (c) Re ¼ 146;

(d) Re ¼ 153; (e) Re ¼ 159; and (f) Re ¼ 186 (after 2).

reactive ion etching. Sealing and optical access were made possible through anodic bonding to a glass
wafer. Mixing channels with depths less than 100 m were fabricated.

Kochmann et al. [6] presented further designs for mixing improvement at high Reynolds
numbers. Additional 90 turns are added after the T-junction. According to numerical simulation at
Re ¼ 270 [6] , a single 90 turn would reach a mixing efficiency (see Chapter 8) of 45%, while two
90 turns in the S-form and U-form ( Fig. 6.5 (a)) would allow the mixing efficiency to reach 65%
and 70%, respectively. In the tangential shear design depicted in Fig. 6.5 (b), the T-junction inlet is
replaced by a shearing design. Instead of a head-on collision, the two mixing fluids enter the shear
chamber at different sides and leave it perpendicularly at the bottom. The micromixers were
fabricated in two layers of silicon. Microchannels were etched using DRIE technique. Optical
access was achieved with pyrex glass cover bonded anodically on top of the channel. The drawback
of the additional mixing elements is the increase in applied pressure, which is already too high for
the conventional T-mixer.

m m and widths less than 200 m