Steam
enters a system at 200 kPa and 350^{o}C and leaves the system at the same mass
flow rate at 180 kPa and 350^{o}C. 
Calculate the flow work in kJ/kg
for this process assuming the usual sign
convention in which work done by
the system is
considered to be positive. 


Read : 
This problem
reinforces the point that it takes energy to push
fluid into a system and it takes energy to push
a fluid out of a system into the surroundings. This energy is called flow work and it can be very significant. 











In this problem, we
apply the definition of flow work to evaluate the net amount of flow work in a simple flow system, perhaps a long pipe. 










Diagram: 











Given: 
P_{1} 
200 
kPa 



P_{2} 
180 
kPa 

T_{1} 
350 
°C 



T_{2} 
350 
°C 










Find: 
W_{flow} 
??? 
kJ/kg 
















Assumptions: 
None. 











Equations
/ Data / Solve: 


















The net amount of PV or flow
work in a flow process is the flow work done by
the system through exiting streams minus the flow work done on the system through entering streams. 















Eqn 1 











We know the inlet and outlet pressures, so now we need to determine the inlet and outlet specific volumes. We can get this information from the Steam Tables or the NIST Webbook. 











V_{1} 
1.4330 
m^{3}/kg 



V_{2} 
1.5927 
m^{3}/kg 











Now, we can plug
values into Eqn 1 to evaluate
the flow work. 











W_{flow,exit} 
286.69 
kJ/kg 







W_{flow,inlet} 
286.59 
kJ/kg 



W_{flow,net} 
0.1006 
kJ/kg 








100.6 
J/kg 










Verify: 
No assumptions. 










Answers : 
W_{flow,net} 
101 
J/kg 















