ECH 152A, Fall 2011, Roland Faller
Solutions for Homework 4, October 19, 2011
Problem 1
(From Midterm 2010)
(a) What is the deﬁnition of enthalpy?
(b) What is the diﬀerence between steady state and equilibrium?.
(c) Which of these are state functions: Heat, Pressure, Enthalpy, Temperature?
(d) Deﬁne ”ideal gas”.
Solution
(a)
H
=
U
+
pV
(b) In equilibrium there are now ﬂows, no time dependencies and no driving
forces. In steady state driving forces and ﬂows are constant.
(c)
p,H,T
(d) A gas fulﬁlling the equation
pV
=
NRT
Problem 2
(From 2010)
We have a ﬂow system with three inlets and one outlet. The gases we are using
have
c
P
(
A
) = 1
.
78
kJ
kg K
and
c
P
(
B
) = 2
.
38
kJ
kg K
. Use steady state in all cases
below.
In inlets 1 and 2 gas A enters with 1 kg/min each, in inlet 3 gas B enters with
2 kg/min.
(a) What is the ﬂow rate in the outlet.
(b) Assume only inlets 1 and 2 are open and the gases enter with 340 K in inlet
1 and 360 K in inlet 2 what is the outlet temperature?
(c) Inlet 3 is opened and the gas enters with 333 K (rest as in part b), what is
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 Fall '09
 Faller
 Thermodynamics, Steady State, Roland Faller

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