Page 265 - Chemical engineering design

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F
Friction factor
f Installed cost factor, piping CHEMICAL ENGINEERING
G Mass flow rate MT 1
g Gravitational acceleration LT 2
H Height of liquid above the pump suction L
h Pump head L
K Number of velocity heads
L Pipe length L
m Mass flow-rate MT 1
N Pump speed, revolutions per unit time T 1
N s Pump specific speed
n Index relating pipe cost to diameter
T
P Pressure ML 1 2
T
P f Pressure loss in suction piping ML 1 2
T
P s Safe working pressure ML 1 2
T
P v Vapour pressure of liquid ML 1 2
T
P Difference in system pressures (P 1 P 2 ) ML 1 2
† 1 2
P f Pressure drop ML T
p Cost of power, pumping
3 1
Q Volumetric flow rate L T
T
R Shear stress on surface, pipes ML 1 2
t Pipe wall thickness L
u Fluid velocity LT 1
2 2
W Work done L T
z Height above datum L
z Difference in elevation (z 1 z 2 ) L
Pump efficiency
Fluid density ML 3
T
Viscosity of fluid ML 1 1
T
d Design stress ML 1 2
T
s Safe working stress ML 1 2
Re Reynolds number
NPSH avail Net positive suction head available at the pump suction L
NPSH reqd Net positive suction head required at the pump suction L
† Note: In Volumes 1 and 2 this symbol is used for pressure difference, and pressure drop (negative pressure
gradient) indicated by a minus sign. In this chapter, as the symbol is only used for pressure drop, the minus
sign is omitted for convenience.
5.13. PROBLEMS
5.1. Select suitable valve types for the following applications:
1. Isolating a heat exchanger.
2. Manual control of the water flow into a tank used for making up batches of
sodium hydroxide solution.
3. The valves need to isolate a pump and provide emergency manual control on
a by-pass loop.
4. Isolation valves in the line from a vacuum column to the steam ejectors
producing the vacuum.
5. Valves in a line where cleanliness and hygiene are an essential requirement.
State the criterion used in the selection for each application.