Chapter 8
Internal Forced Convection
835
The flow rate through a specified water pipe is given. The pressure drop and the pumping power
requirements are to be determined.
Assumptions
1
The flow is steady and incompressible.
2
The entrance effects are negligible, and thus the
flow is fully developed.
3
The pipe involves no components such as bends, valves, and connectors.
4
The
piping section involves no work devices such as pumps and turbines.
Properties
The density and dynamic viscosity of water are given to be
ρ
= 999.1 kg/m
3
and
μ
= 1.138
×
10
3
kg/m
⋅
s, respectively. The roughness of stainless steel is 0.002 mm (Table 83).
Analysis
First we calculate the mean velocity and the Reynolds number to determine the flow regime:
5
3
3
2
3
2
10
40
.
1
s
kg/m
10
138
.
1
m)
m/s)(0.04
98
.
3
)(
kg/m
1
.
999
(
Re
/
m
98
.
3
4
/
m)
(0.04
/
m
0.005
4
/
×
=
⋅
×
=
=
=
=
=
=
−
μ
ρ
ππ
D
s
s
D
V
A
V
m
c
m
V
V
L
= 30 m
D
= 4 cm
Water
5 L/s
which is greater than 10,000. Therefore, the flow is turbulent. The
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 Fall '10
 Dr.DanielArenas
 Fluid Dynamics, Thermodynamics, Convection, Force, Mass, Power, power input, friction factor

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