Biomedical Engineering Reference
In-Depth Information
An oil with viscosity of approximately 200 cP is used for hydraulic motors in
conventional mechanics. Many other liquids, such as ethanol, kerosene, and water,
have viscosity of approximately 1 cP. If, for example, a motor or conventional
hydraulic cylinder has a diameter of 100 mm and uses oil, it is possible to make a
motor or hydraulic cylinder with a diameter of 500
m using kerosene or ethanol. In
order to decrease the size further, it is possible to use pneumatic motors. Gases have
viscosity of approximately 0.02 cP, which allows for micromotors with a diameter
of 10
m
m. So, using hydraulic or pneumatic micromotors, it is possible to develop
micromachine tools and micromanipulators in the range needed for micromecha-
nical devices.
m
8.3.6.2 Forces of surface tension (capillary forces)
A round bar with diameter
d
touches a base (Fig.
8.10
). The water steam is
condensed in the contact area. The superficial tension produces the capillary force
F
that tightens the bar to the base:
F
¼ s p
d
:
(8.61)
This force scaling is:
F
A
¼ s
A
p
d
A
¼ s
B
p
S
d
B
¼
S
F
B
:
(8.62)
Fig. 8.10 Capillary forces
