2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
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Fig. 8. Effect of air flow rate on moisture removal
(Conditions: V
s
= 0.01 l.s
-1
, T
w
= 80
○
C, T
wb
= 28
○
C, T
db
= 36
○
C).
As shown, the concentrations were practically
unchanged at 0.022 kg.kg
-1
for water flow rate of 200
kg.hr
-1
and 0.032 kg.kg
-1
for water flow rate of 300
kg.hr
-1
. However, the figure again demonstrates that
higher water flow rate results in higher concentration
change.
B. Moisture Removal
In the regenerator, the desiccant solution is regenerated
with the help of heat from the hot water and the moisture
released is removed by the flowing air. The following is
the mathematical explanation of how the gain and loss of
moisture in the air and the solution are evaluated.
The increased moisture in the air or moisture gain
should be equal to the decreased moisture or moisture
loss from the desiccant solution. However, from this
experiment, they often do not match. The following is the
comparison of moisture gain in the air and loss in
solution.
1) Effect of desiccant solution flow rate on moisture
removal
Fig. 9 shows the difference in the rate of moisture loss
in solution and the rate of moisture gain in the air is
affected by desiccant solution flow rate.
The result shows that increase in desiccant flow rate
leads to increase in the rate of moisture loss and increase
in the rate of moisture gain. This is because higher
desiccant flow rate has a higher capacity for desiccant
solution to evaporate moisture. However, moisture
movement affected by desiccant flow rate is in reverse
direction compared with the concentration change
affected by desiccant flow rate (see Fig. 4).
The loss and gain of moisture in solution and in the air
should be equal because they are tested in the same unit
and under the same conditions. However, this
experiment shows some discrepancy.
a.
b
.
Fig. 9. Effect of desiccant flow on moisture gain in the air and
moisture loss in solution a. water flow rate at 200 kg.hr
-1
b. water flow
rate at 300 kg.hr
-1
(Conditions: m
a
=765 kg.hr
-1
, T
w
=80
○
C, T
wb
=28
○
C,
T
db
=36
○
C).
As seen in Fig. 9a, the moisture gain line is above the
moisture loss line at around 0.1g.s
-1
. This means some
moisture was added to the system. In this experiment, this
may be attributed to a small hot water leakage in the
system. This can explain why the moisture gain is higher
than moisture loss.
Fig. 9b shows the effect of desiccant solution on
moisture movement at 300 kg.hr
-1
of water flow rate. The
result is similar to Fig.9a. However, Fig. 9b has a higher
moisture movement for both the loss and gain because of
a higher water flow rate. The Figure also shows the
margin of error associated with the measurements in the
test. In many cases the results fall within the error
margin.
2) Effect of water temperature on moisture removal
Fig. 10 shows the moisture removal rate as function of
water temperature. The results show that higher water
temperature results in higher moisture removal. This
agrees with the concentration change (Fig. 5) affected by
the similar conditions. According to the effect of water
temperature (see Fig. 10a), at lower water temperature,
moisture gain takes place. This similar to the effect found
in Fig. 5 at 200 kg.hr
-1
water flow rate. Moisture removal
increases when the water flow rate is higher as seen in
Fig. 10b.
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.20
0.25
0.30
0.35
0.40
Concentration increase
kg.kg
-1
Air flow rate kg.s
-1
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0.000
0.005
0.010
0.015
Moistureremoval rate
g.s
-1
Desiccant flow rate l.s
-1
Moisturegain
Moisture loss
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0.000
0.005
0.010
0.015
Moisture removal rate
g.s
-1
Desiccant flow rate l.s
-1
Moisture gain
Moisture loss
Water flow 200 kg.hr
-1
water flow 300 kg.hr
-1
