6-67
6-90 An adiabatic open feedwater heater mixes steam with feedwater. The outlet mass flow rate and the
outlet velocity are to be determined.
Assumptions Steady operating conditions exist.
Properties From a mass balance
m 3
m 1 m 2
0.2 10 10.2 kg/s
The specific volume at the exit is (Table A-4)
P3
T3
100 kPa ½
¾ v 3 # v f @ 60qC
60qC
¿
m 3v 3
A3
2
0.001017 m 3 /kg
The exit velocity is then
V3
Water
100 kPa
50qC
10 kg/s
4m 3v 3
3
Steam
100 kPa
160qC
0.2 kg/s
1
100 kPa
60qC
SD 2
4(10.2 kg/s)(0.001017 m 3 /kg)
S (0.03 m) 2
14.68 m/s
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