Fluid Flow
CONTINUITY EQUATION
Example:
Continuity Equation - Centrifugal Pump
The inlet diameter of the reactor coolant pump shown in Figure 3 is 28 in. while the
outlet flow through the pump is 9200 lbm/sec. The density of the water is 49 lbm/ft3.
What is the velocity at the pump inlet?
Solution:
Ainlet
pr
2
(3.14)
14 in
1 ft
12 in
2
4.28 ft2
minlet
moutlet
9200lbm
sec
(rAv)inlet
9200lbm
sec
vinlet
9200lbm
sec
Ar
9200lbm
sec
(4.28 ft2)
49lbm
ft3
vinlet
43.9
ft
sec
The above example indicates that the flow rate into the system is the same as that out of the
system. The same concept is true even though more than one flow path may enter or leave the
system at the same time. The mass balance is simply adjusted to state that the sum of all flows
entering the system is equal to the sum of all the flows leaving the system if steady-state
conditions exist. An example of this physical case is included in the following example.
Rev. 0
Page 13
HT-03
