The Reynolds number is:
is conventionally considered the inner diameter.
The velocity averaged over a cross-section of the tube is:
Where Q is the flow rate and R
i
is the radius of the inside of the tube.
The flow rate, Q, is described as:
In case of a parabolic velocity profile, the axial velocity is:
We cannot assume that the flow of the fluid as it enters the 1425A system is laminar. Therefore, the
entrance length can only be estimated to be some value between the value found by the above equa-
tion, and the value from the equation of the entrance length for turbulent flow, which is described as:
20
Re =
l x V xȡ
ȝ
V
avg
=
Q
ʌ5
i
2
Q =
ʌ5
i
4
p
ȝO
V
max
= 2 x V
avg
L = 4.4 x D x Re
1/6
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