2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
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The above figure also shows that the concentration
change for water flow rate of 300 kg.hr
-1
is considerably
higher than that for 200 kg.hr
-1
at the low desiccant flow
rates. This is because at higher water flow rate, there is
higher heat transfer rate from the hot water to desiccant
solution. The effect of water flow rate diminishes at
higher desiccant flow rates.
2) Effect of water temperature
Fig. 5 shows the effect of hot water temperature on the
concentration change.
Fig. 5. Effect of water temperature on moisture removal
(Conditions: V
s
= 0.01 l.s
-1
, m
a
= 765 kg.hr
-1
, T
wb
= 28
○
C, T
db
= 36
○
C).
At water flow rate o f 200 kg.hr
-1
and low
temperatures, there was a slight drop in the desiccant
concentration. However, increases of concentration were
observed at the higher water temperature and flow rate.
The concentration reduction at lower water flow rate
of 200 kg.hr
-1
demonstrates the reverse effect of
regeneration process due to insufficient driving force; that
is, the difference between partial pressure at surface of
desiccant solution and the flowing air. In general, the
partial pressure of the desiccant solution at the surface is
higher than at flowing air. In this case, the partial
pressure of moisture at the surface of desiccant solution is
lower than the partial pressure of moisture in the flowing
air. Therefore, moisture in air transfers to the desiccant
solution. This phenomenon demonstrates the need for
higher water temperature and flow rate in order to
achieve the desired desiccant concentration increase.
3) Effect of air dry bulb temperature, wet bulb
temperature and flow rate
The effect of dry bulb temperature on the
concentration change keeping the other parameters
constant is shown in Fig. 6. The results show that the
higher the dry bulb temperature of the regeneration air,
the higher the concentration increase for both the water
flow rates of 200 kg.hr
-1
and 300 kg.hr
-1
. This is to be
expected because higher temperature air with fixed wet
bulb temperature is dryer and thus has higher capacity to
absorb moisture. The results show a near linear
relationship for both water flow cases.
Fig. 6. Effect of dry bulb temperature on moisture removal
(Conditions: V
s
= 0.01 l.s
-1
, m
a
= 765 kg.hr
-1
, T
w
= 80
○
C, T
wb
= 28
○
C).
Conversely, the effect of wet bulb temperature while
maintaining the dry bulb temperature at 36
○
C is shown in
Fig. 7. As shown, higher wet bulb temperatures result in
lower concentration increase. This is because air with
higher bulb temperature but kept at constant dry bulb
temperature contains more moisture.
Fig. 7. Effect of wet bulb temperature on moisture removal
(Conditions: V
s
= 0.01 l.s
-1
, m
s
= 765 kg.hr
-1
, T
w
= 80
○
C, T
db
= 36
○
C).
At the same conditions of air dry and wet bulb
temperature, a higher water flow rate results in high heat
transfer from hot water to the desiccant solution which in
turn results in high capability to release moisture to air.
For this reason, the curve of concentration change of 300
kg.hr
-1
water flow rate (solid line) lies above the curve for
200 kg.hr
-1
water flow rate (dotted line).
The effect of air flow rate on the concentration change
is shown in Fig. 8.
-0.01
0.00
0.01
0.02
0.03
0.04
0.05
0.06
45
55
65
75
85
Concentration increase
kg.kg
-1
Water temperature
○
C
0.00
0.01
0.02
0.03
0.04
0.05
0.06
30
35
40
45
50
55
Concentration increase
kg.kg
-1
Dry bulb temperature
○
C
0.00
0.01
0.02
0.03
0.04
0.05
0.06
18
20
22
24
26
28
30
Concentrationincrease
kg.kg
-1
Wet bulb temperature
○
C
Water flow 200 kg.hr
-1
water flow 300 kg.hr
-1
Water flow 200 kg.hr
-1
water flow 300 kg.hr
-1
Water flow 200 kg.hr
-1
water flow 300 kg.hr
-1
