Biomedical Engineering Reference
In-Depth Information
Figure 3.35
Schematic of the capillary force on a triple line.
The velocity of the flow decreases like
t
. This decrease results from a balance
between the constant Laplace driving pressure and the increasing flow resistance in
the channel.
3.6.6 Force on a Triple Line
The analysis of capillary rise in tubes and capillary pumping has shown the expres-
sion of the capillary force on the triple contact line [20]. This expression can be
generalized to any triple contact line [21]. For a triple contact line W — as sketched
in Figure 3.35—the capillary force is
�
�
�
ò
ò
F
=
f dl
=
γ θ
cos
ndl
(3.51)
W
W
Suppose that we want to find the value of the resultant of the capillary forces in
a particular direction, say, the
x
-direction (Figure 3.36). The projection along the
x
-direction of (3.51) is
Figure 3.36
Capillary force on a triple contact line in the
x
-direction.
