University of Babylon /College Of Engineering
Electrochemical Engineering Dept.
Second Stage /Thermodynamics
Steady-State Flow Processes
The term steady state implies that conditions at all points in apparatus are constant
with time.
The mass of system within the control volume is constant, or in other meaning
there is no change with time in the properties of fluid, the only work of the process
is shaft work which is means work done by or on the fluid flowing through a piece
of equipment and transmitted by a shaft which protrudes from the equipment and
which rotates or reciprocates. The general energy balance equation becomes:
U 
1 2
u  zg  Q  W
2
Note: "steady state" does not necessarily imply "steady flow,"
W1  P1 A1
V1
V
 P1V1 , and W2  P2 A2 2  P2V2
A1
A2
Since W represents all the work done by the unit mass of fluid, it is equal to
algebraic sum of shaft work
University of Babylon /College Of Engineering
Electrochemical Engineering Dept.
Second Stage /Thermodynamics
W  WS  P2V2  P1V1
U 
1
u 2  zg  Q  WS  P2V2  P1V1
2
U  ( PV ) 
H 
1
u 2  zg  Q  WS
2
u 2
 zg  Q  Ws
2
, because H  U  (PV )
But in many applications, kinetic- and potential-energy terms are omitted, because
they are negligible compared with other terms.
H  Q  Ws