Page 229 - Chemical engineering design

PIPING AND INSTRUMENTATION
2
3
s, density 998 kg/m .
The properties of the fluid are: viscosity 0.99 mNM
Calculate the total pressure drop due to friction when the flow rate is 3500 kg/h. 205
Solution
3 2 3 2
Cross-sectional area of pipe D 25 ð 10 D 0.491 ð 10 m
4
3500 1 1
Fluid velocity,u D ð ð D 1.98 m/s
3600 0.491 ð 10 3 998
3
Reynolds number,Re D 998 ð 1.98 ð 25 ð 10 /0.99 ð 10 3
4
D 49,900 D 5 ð 10 5.4
Absolute roughness commercial steel pipe, Table 5.2 D 0.046 mm
3
Relative roughness D 0.046/ 25 ð 10 D 0.0018, round to 0.002
From friction factor chart, Figure 5.7, f D 0.0032
Miscellaneous losses

fitting/valve number of velocity equivalent pipe
heads, K diameters

entry 0.5 25
elbows 0.8 ð 4 40 ð 4
globe valve, open 6.0 300
gate valve, 1/2 open 4.0 200
exit 1.0 50
Total 14.7 735

Method 1, velocity heads

2
2
A velocity head D u /2g D 1.98 / 2 ð 9.8 D 0.20 m of liquid.
Head loss D 0.20 ð 14.7 D 2.94 m
as pressure D 2.94 ð 998 ð 9.8 D 28,754 N/m 2
120 1.98 2
Friction loss in pipe,P f D 8 ð 0.0032 998 ð
3
25 ð 10 2
D 240,388 N/m 2 5.3
2
Total pressure D 28,754 C 240,388 D 269,142 N/m D 270 kN/m 2

Method 2, equivalent pipe diameters
Extra length of pipe to allow for miscellaneous losses
D 735 ð 25 ð 10 3 D 18.4m