2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
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parallel. The regenerating fluid (i.e. water) flows through
these channels and transfers heat thought the plate wall to
the desiccant solution which is in direct contact with the
air. The desiccant solution flows downwards and is
spread over a thin porous medium, while the air flows
upwards in the passages between the plates. Some of
water contained in the desiccant solution evaporates and
is absorbed by the air flowing upwards.
Fig. 2. Schematic diagram of the regenerator.
The moisture in the desiccant solution is released to
the air stream as a result of heating the solution. In the
regenerator under investigation, the hot water used to heat
the solution can be heated either by solar energy or waste
heat from another process.
B. Experimental Setup
The regenerator is tested in a specially designed
experimental rig as shown in Fig. 3. The liquid desiccant
stored in the weak solution tank flows to the solution
distributor and then passes through to the upper part of
the regenerator. The concentrated solution leaves the
regenerator at the bottom part and is stored in a second
tank. The regeneration air, after being brought to the
desired temperature and humidity, flows from the lower
part through the upper part of regenerator then exits the
system. Hot water is pumped through the internal
channels of the regenerator in a cross flow direction with
respect to the flows of the desiccant solution and the air.
Fig. 3. Schematic diagram of the experimental setup.
Dry and wet bulb temperature sensors are placed at a
number of locations, i.e. at the inlets and outlets of the
air, hot water and desiccant solution. The experimental
data is collected using a data logger at 10 second
intervals. The concentration at the inlet is checked before
every experiment and randomly checked every 10 minute
interval while the concentration at the outlet is measured
every 2 minute.
Temperatures were measured using thermocouples
type K calibrated with an accuracy of +0.2
○
C. Water flow
was measured by TRIMEC
®
inline flow meter with an
accuracy of +0.0013 kg.s
-1
while a capture hood air flow
meter having 5% tolerance was employed. Desiccant
flow rate was measured using a rotameter with an
accuracy of +0.0002 l.s
-1
. The concentration was
measured with a refractometer with in accuracy of
+0.0013 kg.kg
-1
.All three meters, water, air and desiccant
solution flow meters, were placed at the inlet streams.
The desiccant solution used was Lithium Chloride
with initial concentration varying between 0.27 to 0.33
kg.kg
-1
and flow rate from 0.003 to 0.014 l.s
-1
at ambient
temperature. Water temperatures ranged from 50 to 83
○
C.
Air flow rates ranged from 765 to 1310 kg.hr
-1
and fixed
at the Bangkok design conditions (wet bulb temperature
28.0
○
C and dry bulb temperature 36.4
○
C [15].
IV. R
ESULTS AND
D
ISCUSSIONS
This section presents the results of a parametric study
to examine the effects of desiccant flow rate, water
temperature, the air wet bulb temperature, dry bulb
temperature and flow rate on (1) the concentration
increase (∆
X) of the desiccant solution between the inlet
and outlet of the regenerator and (2) moisture loss from
the desiccant solution and moisture gain in the air. The
effect of each of these parameters was examined at two
water flow rates, 200 and 300 kg.hr
-1
.
A. Concentration Increase
1) Effect of desiccant flow rate
Fig. 4 shows the effect of desiccant flow rate at
following conditions
1
: dry bulb temperature of 36
○
C and
wet bulb temperature of 28
○
C while the air flow rate was
kept at 765 kg.hr
-1
and water temperature at 80
○
C.
Fig. 4. Effect of desiccant flow rate on moisture removal
(Conditions: m
a
= 765 kg.hr
-1
, T
w
= 80
○
C, T
wb
= 28
○
C, T
db
= 36
○
C).
As seen, the higher the desiccant flow rate the lower
the concentration change. This is because the high
desiccant flow rate restricts the time for solution to
release moisture into the flowing air.
1
These represent the summer design ambient condition of the hot
and humid city of Bangkok
Desiccant solution in
Air out
Desiccant solution out
Air in
Water out
Water in
Regenerator
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.000
0.005
0.010
0.015
Concentration increase
kg.kg
-1
Desiccant flow rate l.s
-1
Water flow 200 kg.hr
-1
water flow 300 kg.hr
-1
