General Approach to Problem Solving
•
Sketch the process.
Define your system.
Label all
known and unknown quantities.
•
Choose a model for the working substance.
•
Write down the mass balance equation.
•
Write down the energy balance equation.
•
Write down the entropy balance equation.
•
Use specialized or combined forms as needed.
Control
volume
or system
Mass
entering (1)
Mass
leaving (2)
Q
W

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Models of Working Substances
Solid/
liquid
Table A-3
C
p
= C
v
= C
Gases
Phase-change
fluids
(water &
refrigerants)
Tables A-2 to 8
& A-11 to 13
Mixtures
(advanced)
Perfect gas
Pv = RT
C
p
= constant
C
v
= C
p
– R
Table A-2a for C
p
.
u = C
v
T,
h = C
p
T
.
P and T are absolute.
Ideal gas
Pv = RT
C
p
= f(T) Table A-2b,c.
C
v
= C
p
– R
Table A-17 to 25
for u and h.
P and T are absolute.
Real gas
Figures A-15
RT
Pv
Z
v
v
)
P
,
T
(
f
Z
actual
ideal
actual
R
R
=
=
=
c
R
c
R
P
P
P
T
T
T
=
=
P and T are absolute.
∫
∫
=
=
T
0
v
T
0
p
dT
C
u
dT
C
h
This chart was inspired by Subrata Bhattacharjee,
The Expert System for Thermodynamics
,