21-1
Chapter 21
21.1 A pump curve shows the relationship between pressure head and volumetric flowrate
through a pump
21.2 All depends on the system curve, so the statement is false since parallel or series
21.3 For the pump and system curve (Figure a) the intersection represents the maximum flow
21.4 The film heat transfer coefficient, for turbulent flow inside a tube, increases with flowrate
21.5 The only way to fix the cavitation problem for this case is to raise the NPSHA curve.
Therefore, by running the pumps in parallel, the flow is split between the pumps and the
For a centrifugal pump
21-2
21.6 For laminar flow, the flow of liquid is governed by the Hagen-Poiseuille equation given
as:
4
128 p
f
p
VL
PD
21.7 The relative change in pressure and hence vapor specific volume in the two columns will
21.8 (a) An increase in column pressure increases the vapor density and decreases the
superficial vapor velocity in the tower. Hence the column will have a reduced tendency to
flood.
21.9 From Equation (18.21), the NPSHA is given by
21-3
21.10 Assuming turbulent flow, we can write:
21.11 (a) Only the 2-pumps in parallel set up will give you the desired flow. The desired
operating point lies to the right of the single and 2-pumps in series set up and hence is not
21-4
21.12
21-5
21.13
21-6
21.14
21-7
21.15
21-8
21.16
21-9
21.17
21-10
21.18
21-11
21.19
21-12
21-13
21.20 At 208ºC, P* = 78.96 kPa
kPa 04.0kPa 9678kPa 79
*.–PPNPSH inletA
m/s 4
s/h 3600m 001313.0kg/m 6.978
kg/h 500,18
23
u
21-14
21.21 (a) 1.25 in sch 80 Di = 0.03246 m
*
2
tan
2P
D
ufL
ghPNPSH eq
kA
(b) T = 40ºC
K
6.4203
97.10ln
*
T
P
1
1.2
1.4
21-15
21.22 (a) at 125 Mg/h and 3500 rpm
Pin = 2 bar
Pout = ?
(b) at 125 Mg/h and 2200 rpm
Pin = 4 bar
Pout = 9 bar
(c) at 125 Mg/h
Pin = 2 bar
Pout = 24 bar
12
in
out
P
P
At 3500 rpm: 6.3
out
P
Puse 2 stages
Use 3500 rpm with 2 stages
21-16
21.23 NtOG = 20
G = 80 kmol/h
L = 20 kmol/h
25.0
L
21-17
21.24
18-17
21-18
21.25
18-18
21-19
21.26 – See Section 24.2 and Example 24.1
21.27 Increase capacity by 25%
T
LM 37
C
Cooling Water
15
30
25.1
15
30
1
2
1
2
1
2T
M
T
M
T
T
m
m
Q
Q
Solve equations (1) and (2) simultaneously
75 C 75 C
45 C 30 C
21-20
21.28