Page 125 - DJJ20063- Thermodynamics 1
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DJJ20063- Thermodynamics 1
Figure 3.2.6-2 illustrates some thermodynamic system into which is flowing a fluid with
pressure P1, specific volume v1, specific internal energy u1 and velocity C1. The entry is at
height Z1 above some datum level. In its passage through the system, external work W
may be done on or by the fluid and also heat energy Q may be received or rejected by the
fluid from or to the surroundings.
The fluid then leaves the system with pressure P2, specific volume v2, specific internal
energy u2 and velocity C2. The exit is at height Z2 above some datum level.
W
P1 v1
U1C1
SYSTEM
ENTRY
(OR CONTROL VOLUME)
Z1 P2
v2
EXIT Z2
Q
Figure 3.2.6-2 Thermodynamic system
The application of the principle of energy conservation to the system is,
Total energy entering the system = Total energy leaving the system
or, for unit mass of substance,
C 2 C 2
gZ + u + P v + 1 + Q = gZ + u + P v + 2 + W (3.25)
1
1
1
1
2 2 2 2 2 2
This is called the steady flow energy equation.
This equation is not applicable to all energy forms. In such cases, the energy forms
concerned are omitted from the energy equation.
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