Copyright 2010 D.B. Dadyburjor and J. A. Shaeiwitz
Unsteady State
Mass and Energy Balances
ChE 202
Spring 2010

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Copyright 2010 D.B. Dadyburjor and J. A. Shaeiwitz
Retrospective –
Sub-processes considered
9
Change in pressure at constant temperature
9
Change in temperature at constant pressure
9
Change in T or P at constant volume
9
Change in phase at constant P and T
9
Mixing of pure components to multicomponent system at constant T
and P (and reverse)
9
Pure components in stoichiometric amounts reacting to form pure
products(s)
9
Combine to deal with more-complicated processes;
9
Use
algebraic
MB, EB balance equations --
Difference equations for closed systems (no input/output terms)
∆
(v
sys
2
)/2 + g
∆
z
sys
+
∆
= Q
(in)
/m
sys
– W
s
(by)
/m
sys
– P
ext
∆
Steady-state equations for open systems (no accumulation term)
-- to solve for needed quantities
)
(
)
(
,
,
,
,
)
ˆ
ˆ
ˆ
(
)
ˆ
ˆ
ˆ
(
0
by
s
in
out
i
i
p
i
k
i
in
i
i
p
i
k
i
W
Q
m
E
E
H
m
E
E
H
&
&
&
&
−
+
+
+
−
+
+
=
∑
∑
sys
U
ˆ
sys
V
ˆ