ME 326H: THERMODYNAMICS I
Test 1, Feb. 23, 1996
1) (28%)
A substance is inside a piston/cylinder system.
Initially, the substance is at T
1
=150°C
and P
1
=10 kPa. The piston is moved to compress the substance isothermally until P
2
=100 kPa.
a) If the substance is argon, what is the change in the specific internal energy of the argon, u
2
u
1
(kJ/kg)?
b) If the substance is argon, how much heat transfer
1
q
2
(kJ/kg) occurred?
c) If the substance is steam, what is the change in the specific internal energy of the steam, u
2
u
1
(kJ/kg)?
d) If the substance is steam, describe in a few sentences how you could calculate how much heat
transfer
1
q
2
(kJ/kg) occurred.
SOLUTION:
a): Argon acts as an ideal gas, for which u=u(T only), so for an isothermal process, D
u=0
.
b): First Law for CM is
1
q
2

1
w
2
=u
2
u
1
=0, so
1
q
2
=
1
w
2
so
=202.7 kJ/kg
c): From Table D.12, u
1
=2587.4 kJ/kg; u
2
=2582.4 kJ/kg,
so u
2
 u
1
=5 kJ/kg
d):
1
q
2
=u
2
u
1
+
1
w
2
=5 kJ/kg +
; However, since steam tables should be used for Pv data,
should get data for various P values for v between v
1
and v
2
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 Spring '07
 Dr.Kinne
 Thermodynamics, Energy, Heat, Heat Transfer

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