Biomedical Engineering Reference
In-Depth Information
Figure 1.11
Change of contact angle when increasing the electric potential (electrowetting
number).
evaporated,
V
a
is the evaporated volume and
∆ρ
sat
is the density change from the
liquid to vapor phase. Figure 1.10 shows the evaporation amount as a function of
temperature and number of sacrificial droplets in a closed petri dish. The evapora-
tion number is closely related to the evaporated mass of liquid.
1.4.6
Multiphysics
Biotechnological microsystems most of the time combine the use of different physi-
cal phenomena, like hydrodynamics, electrics, magnetics, thermics, and chemical
reactions. In this section, we present some dimensionless numbers useful for micro-
systems incorporating multiphysics, and we recall some others that are well known
from the macroscale.
The electrowetting number is used for electrowetting applications [10]. It is the
ratio of the electric force acting on a droplet to the capillary force
2
η
ew
C U
=
γ
(1.22)
Figure 1.12
Schematic view of Marangoni convective motion in a droplet sitting on a heated
plate.
