a. 8.96 2.30 lb m 15.0 wt% H 2 SO 4
@ 77 F H1 = 10 Btu / lb m
o
U
|
|
| m ( lb
V
|
|
|
W
adiabatic mixing
3
m2 (lb m ) 80.0 wt% H 2 SO 4
@ 60o F H 2 = 120 Btu / lb m
60.0 wt% H 2 SO 4 @ T o F, H 3
U |m
|R
VS
mass balance: 2.30b0.150g + m b0.800g = m (0.600) W |m
|T
Total mass balance:
H 2 SO 4
m)
2
2
3
= 517 lb m (80%)
.
3
2.30 + m2 = m3
= 7.47 lb m (60%)
b. Adiabatic mixing Q = H = 0
.
b7.47gH b2.30gb10g b517gb120g = 0 H
3
3
= 861 Btu / lb m
.
E Figure 8.5 - 1
T = 140 o F
c.
d
i
H 60 wt%, 77 o F = 130 Btu / lb m
d
i
b
gb
g
Q = m3 H 60 wt%, 77 o F H 3 = 7.475 130 + 861 = 328 Btu
.
d. Add the concentrated solution the to dilute solution . The rate of temperature rise is
much lower (isotherms are crossed at a lower rate) when moving from left to right on
Figure 8.5-1.
8.97 a.
b.
x NH 3 = 0.30
Fig. 8.5-2
y NH 3 = 0.96 lb m NH 3 lb m vapor , T = 80 F
Basis: 1 lb m system mass
0.90 lb m liquid
010 lb m vapor
.
Mass fractions: zNH 3 =
b0.27 + 0.096glb
m
NH 3
1 lb m
x NH 3 = 0.30
0.27 lb m NH 3
0.63 lb m H 2 O
x NH 3 = 0.96
0.096 lb m NH 3
0.004 lb m H 2 O
= 0.37 lb m NH 3 lb m
1 0.37 = 0.63 lb m H 2 O lb m
Enthalpy: H =
0.90 lb m liquid
0.10 lb m vapor
670 Btu
25 Btu
+
= 44 Btu lb m
1 lb m
1 lb m
1 lb m liquid
1 lb m vapor
8-72