Biomedical Engineering Reference
In-Depth Information
Figure 6.57
Different types of single-phase flow focusing.
Equation (6.107) is an implicit equation relating the relative width
e
=
w
1
/
w
to
the flow rate ratio
Q
1
/(
Q
1
+
Q
2
). An efficient focusing is obtained for
Q
1
<<
Q
2
and
a first-order approximation of
w
1
is
w
1
2
Q
1
1
»
(6.108)
w
Q
6.5.1.2 Single-Phase 3D Focusing
More sophisticated flow focusing may be obtained by a 3D geometry. In particular,
focusing in a small defined region inside a channel can be achieved by using the
principle of FFDs described in Chapter 4 (see also Figure 6.61).
The designs and shapes must be compatible with the principles of microfabrica-
tion. Devices such as that of Figure 6.61 can realize interesting flow focusing [23,
24]. Two successive FFDs are used, the first one placed below the incoming flow
and the next one placed above it.
The evolution of the focusing of the flow is shown in Figure 6.61. After the first
focusing, the flow is confined to a triangle at the upper part of the channel. After
Figure 6.58
2D flow focusing. (Courtesy of COMSOL.)
