
406 Heat Transfer: Thermal Management of Electronics
where ρ
b
and V
b
are density and volume of the oating object, respectively. The sec-
ond term on the left side of Equation 15.7 is the buoyancy force applied on the object.
Substituting for F
D
from Equation 15.6 and solving for U
m
gives
(15.8)
The values of C
D
is determined such that U
m
in Equation 15.6 is the average uid
velocity in the annular space between the object and the tube. If A is the annular ow
cross section area around the oating object, the ow rate is
V
V
== −
AU A
g
CA
m
b
DF
b
2
1
ρ
ρ
.
(15.9)
The annular cross section area in a rotameter is usually related ...