Biomedical Engineering Reference
In-Depth Information
Figure 4.60
Striation thickness.
In the process of folding and stretching, the striation thickness is the distance
between the filets of the diffusing species (Figure 4.60); the diffusion time is then
given by Fourier's law
2
s
(4.88)
t
»
2
D
Ottino [67] has shown that the striation thickness is reduced after each folding
of the filet according to
σ
-
n
(4.89)
s n
( )
=
s
(0)
t
t
We analyze two types of channels: straight channels and channel with turns
(Figure 4.61). We show that the mixing process is much more efficient in channels
with turns.
Suppose first that the microchannel is straight. Because the walls are fixed and
the plug is moving, two recirculation patterns form inside the plug [Figure 4.62(a)].
Striation thickness in the plug is given by [67]
L
(4.90)
s
=
(0)
s
t
t
d
Figure 4.61
Two different types of microchannels; the channel with turns is much more efficient
for mixing the components inside the droplets.
