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Thermodynamic Relations
Perfect Liquids
/Solids:
Incompressible:
d
v
≈
0
Small Specific Volume:
P
v
<<
u
h
≈
u
Heat Capacities
:
Internal Energy
:
d
u
=
C
v
d
T
+
∂
u
∂
v
|
T
d
v
⟶
d
u
≈
d
h
≈
C
d
T
Entropy
:
From
Internal Energy
...
d
u
=
T
d
s
−
P
d
v
⟶
d
s
=
d
u
T
+
P
T
d
v
⟶
d
s
=
C
d
T
T
⟶
Δ
s
=
s
2
−
s
1
=
C
ln
(
T
2
T
1
)
Ideal Gas
:
Fully compressible:
P
v
=
R
T
W
Internal Energy
/
Enthalpy
:
u
=
u
(
t
)
h
=
u
+
P
v
=
h
(
t
)
Heat Capacities
:
Internal Energy
:
d
u
=
C
v
d
T
+
∂
u
∂
v
|
T
d
v
=
C
v
d
T
Enthalpy
:
d
h
=
C
p
d
T
+
∂
h
∂
P
|
T
d
P
=
C
p
d
T
Entropy
:
From
Internal Energy
in terms of
Specific Volume
...
d
s
=
d
u
T
+
P
T
d
v
⟶
d
s
=
C
v
d
T
T
+
R
W
d
v
v
⟶
Δ
s
=
C
v
ln
(
T
2
T
1
)
+
R
W
ln
(
v
2
v
1
)
From
Enthalpy
in terms of
Pressure
...
d
s
=
d
h
T
−
v
T
d
P
⟶
d
s
=
C
p
d
T
T
−
R
W
d
P
P
⟶
Δ
s
=
C
p
ln
(
T
2
T
1
)
−
R
W
ln
(
P
2
P
1
)
Internal Energy
: