theoretical studies of liquid desiccant columns for hybrid air conditioner
TRANSCRIPT
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1
Theoretical studies ofliquid desiccant columns
for hybrid air conditioner
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Introduction
Application of low humidityEssential forarchives, museums,etc.
Desirable for human comfort
Vapor compression systemDehumidification by vapor condensation
High COP but deep dehumidification notpossible
Desiccant cooling systemDehumidification by absorption of vapor
Deep dehumidification but low COP
Proposed hybrid systemDehumidification by both condensation and
absorption
High COP and more dehumidification 2
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Analysis of three circuits
a) Solution circuit
b) Vapor compression circuit
c) Air circuits Simulation of the system
Fabrication and testing of a 0.8 TR capacity LDVC hybrid
system
Objectives
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LITERATURE SURVEY
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Yadav, 1995Conducted experiments in conventional vapour compression
system and liquid desiccant cycle. It has an energy saving of 80% at
90% latent heat load.
Khalid et al., 1997Simulated an open cycle vapour absorption and liquid desiccantsystem using LiBr for the process of absorption and
dehumidification found suited for hot and humid climate
Kessling et al., 1998Liquid desiccant cooling systems enable efficient energy storage for
air dehumidification and air-cooling using low temperature heat.
Meunier, 1998Shows that solid sorption is very effective low grade cooling not
only for air conditioning but for deep-freezingalso.
Fanger, 1999 The perceived indoor air quality (IAQ) increases with a decrease inrelative humidity, as long as it Is kept between 30 to 70%
Techajunta et al.,
1999
Conducted experiments in a solar simulator on solid desiccant
regeneration and air dehumidification for air conditioning in a
tropical humid climate, and found that regeneration rate is strongly
dependent on insolation, and slightly affected by air flow rate.
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Armando et al., 2000 Used lithium bromide as the liquid desiccant, modeled an opensystem and observed the system to be more efficient in colder and
drier climates and that system efficiency can be improved by
employing indoor air re-circulation
Jain, 2001 The temperature required for regenerating the liquid desiccant islow; therefore solar energy can be utilized effectively.
Dieng and Wang2001
Conducted review on solar adsorption technologies and emphasizedthe possibility of using non-polluting materials and energy saving
(more than 50%) as the important characteristics .
Goktun and Deha Er,
2001
Conducted theoretical evaluation of the maximum overall
performance of a hybrid air conditioning system which consists of a
conventional vapour compression system (VCS) cascaded withsolar assisted vapour absorption system.
Ahmed, 2003Studied the desorption characteristics of liquid desiccant bed for
solar dehumidification for air conditioning systems. Air stream at a
low grade temperature is applied in the desorption process
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R2
Evaporator
Expn.
Valve
Condenser
R1
R3R4
Compressor
VAPOUR COMPRESSION SYSTEM
conditioned space ( Supply air )
A4A5A4
A1
Ar
A2
Pump2
D2
A6
Pump1
A3
Dehumidifier
D2
D3
Regenerator
D4
D1
WITH AIR CIRCUIT
AND DESICCANT LOOP
Block diagram of the proposed hybrid system
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dry bulb temperature
humidityratio
A2
A4
Ar
A1
A5
R3R2
Compressor
R1
R4
Evaporator
Expn.
Valve
Condenser
A1
A4
conditioned space
( Supply air )
A4A5A2
VAPOR COMPRESSION SYSTEM WITH AIR CIRCUIT
D1
D3Pump2
D2
A6
D2Pump1
D4
D4
A3
Regenerator
Dehumidifier
AND DESICCANT LOOP
A3
A6
h
Process diagram
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dZ
air out
maha+dha
Wa+dWat
a
+dta
mahaWata
solution in
air in solution out
Z
mshsxt
s
ms+dmhs+ dhsx+dxts+dts
9
Computational Model Counter flow
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Algorithm
1. Calculate the enthalpy of inlet air: ha= f(ta, Wa)
2. Calculate heat transfer coefficient:hc= f(v)
3. Estimate Lewis number: Le = (/D)2/3
4. Estimate mass transfer coefficient: hm= hc/CpLe
5. Estimate interface vapor pressure, humidity ratio and enthalpy:
pi= ps= f(xs, ts); Wi= 0.622 pi/(ptpi); hi= f(ts, Wi)
6. Estimate the moisture absorbed and total heat transfer:
dm= hmdA(Wi-Wa); dq = hcdA (hi-ha)/cpm
7. Estimate air properties at exit of the element:
Wa* = Wa+ dWa; ha* = ha+dha; ta* = f(ha* ,Wa* )
8. Estimate solution flow rate, concentration, enthalpy and temperature at exit of the
element:
ms* = ms+ dm = ms+dWa; xs* = 1-[((1-xs) ms-(madWa))/ms* ] ; hs* = hs+ (dq/ms* );
ta* = f(hs* ,xs* )10
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Parameter Range Mean value
Inlet air temperature,
taa1,oC
6-22 14
Inlet air specific
humidity, Waa1, g/kg6-10 8
Inlet air temperature,
tar1,o
C (reg)
30-50 45
Inlet air specific
humidity, War1, g/kg15-30 20
S/A flow ratio (%) 0.05 - 150 Varied
Table 1: Performance parameters Table 2: Fixed/operating parameters
11
Parameter value
Inlet solution concentration, xsa1,% 45
Inlet solution concentration, xsr1,% (reg) 30
Inlet solution temperature, tsa1,oC 20
Inlet solution temperature, tsr1,oC (reg) 20
Height of absorber and regenerator, cm 40
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Parameter Variation Influence Result
Air temperature increasesolution T
solution VP
dehumidification suppressed
solution concentration
Solution temperature
Air specific humidity increase air VP
dehumidification enhanced
solution concentration
Solution temperature
S/A ratio increase capacity
dehumidification enhanced
solution concentration
Absorber
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Parameter Variation Influence Result
Air temperature increasesolution T
solution VP
desorption increased
solution concentration
Solution temperature
Air specific humidity increase air VP
desorption suppressed
solution concentration
S/A ratio increase capacitydesorption enhanced
solution concentration
Regenerator
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COUNTER FLOW
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6 7 8 9 100.0
0.5
1.0
1.5
2.0
2.5
3.0
S/A=0.05% S/A=0.2% S/A=0.8% S/A=1.6% S/A=3.2% S/A=6.4%
Changeinsp.humidity,
Waa,g
/kg
Inlet air sp.humidity,Waa1
,g/kg
6 7 8 9 100
1
2
3
4
5
6
7
8 S/A=0.05% S/A=0.2% S/A=0.8% S/A=1.6% S/A=3.2% S/A=6.4%
Changeinairte
mperature,
taa,o
C
Inlet air sp.humidity,Waa1
,g/kg
4 6 8 10 12 14 16 18 20 22 24
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5 S/A=0.05%S/A=0.2%S/A=0.8%S/A=1.6%S/A=3.2%S/A=6.4%
Changeinsp.h
umidity,
Waa,g
/kg
Inlet air temperature,taa1
,oC
4 6 8 10 12 14 16 18 20 22 24
0
1
2
3
4
5
6
7
8
9
Changeinairtemperature,
taa,o
C
Inlet air temperature,taa1
,oC
S/A=0.05%S/A=0.2%S/A=0.8%S/A=1.6%S/A=3.2%S/A=6.4%
EFFECT OF INLET AIR SPECIFIC HUMIDITY (ABSORBER)
EFFECT OF INLET AIR TEMPERATURE (ABSORBER) 15
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6 7 8 9 10
15
20
25
30
35
40
45
S/A=0.05% S/A=0.2% S/A=0.8% S/A=1.6% S/A=3.2% S/A=6.4%Outletsolution
concentration,xsa2,%
Inlet air sp.humidity,Waa1
,g/kg
6 7 8 9 10
14
15
16
17
18
19
20
21
22 S/A=0.05% S/A=0.2% S/A=0.8% S/A=1.6% S/A=3.2% S/A=6.4%
Outletsolutiontemperature,tsa2,o
C
Inlet air sp.humidity,Waa1
,g/kg
4 6 8 10 12 14 16 18 20 22 245
10
15
20
25
30
35
40
45
S/A=0.05%S/A=0.2%S/A=0.8%S/A=1.6%S/A=3.2%S/A=6.4%
Outletsolution
concentration,xsa2,%
Inlet air temperature,taa1
,oC
4 6 8 10 12 14 16 18 20 22 248
10
12
14
16
18
20
22
24
S/A=0.05%S/A=0.2%S/A=0.8%S/A=1.6%S/A=3.2%S/A=6.4%Outletsolutiont
emperature,tsa2,o
C
Inlet air temperature,taa1
,oC
EFFECT OF INLET AIR SPECIFIC HUMIDITY (ABSORBER)
EFFECT OF INLET AIR TEMPERATURE (ABSORBER) 16
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14 16 18 20 22 24 26 28 30 32
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Changeinsp.humidity,War,
g/kg
Inlet air sp. humidity, War1
,g/kg
S/A=0.2%S/A=0.4%S/A=0.8%S/A=1.6%S/A=3.2%S/A=6.4%
14 16 18 20 22 24 26 28 30 320
2
4
6
8
10
12S/A=0.2%S/A=0.4%S/A=0.8%S/A=1.6%S/A=3.2%S/A=6.4%
Changeinairtemperature,tar,
oC
Inlet air sp. humidity, War1
,g/kg
34 36 38 40 42 44 46 48 50 520.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Changeinsp.h
umidity,War,
g/kg
Inlet air temperature, tar1
,oC
S/A=0.05%S/A=0.2%S/A=0.8%S/A=1.6%S/A=3.2%S/A=6.4%
34 36 38 40 42 44 46 48 50 52-1
0
1
2
3
4
5
6
7
8
9
10
11
12
13 S/A=0.05%S/A=0.2%S/A=0.8%S/A=1.6%S/A=3.2%S/A=6.4%
Changeinairtemperature,tar,
oC
Inlet air temperature, tar1
,oC
EFFECT OF INLET AIR SPECIFIC HUMIDITY (REGENERATOR)
EFFECT OF INLET AIR TEMPERATURE (REGENERATOR) 17
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14 16 18 20 22 24 26 28 30 3230
32
34
36
38
40
42
44
46
48
50
52
54 S/A=0.2%S/A=0.4%S/A=0.8%S/A=1.6%S/A=3.2%S/A=6.4%
Outletsolutionconcentration,
xsr2,%
Inlet air sp. humidity, War1
,g/kg
14 16 18 20 22 24 26 28 30 3231
32
33
34
35
36
37
38
39
40
41
42
43
44
45
S/A=0.2%S/A=0.4%S/A=0.8%S/A=1.6%S/A=3.2%S/A=6.4%
Outletsolutiontemperature,
tsr2,o
C
Inlet air sp. humidity, War1
,g/kg
34 36 38 40 42 44 46 48 50 5230
32
34
36
38
40
42
44
46
48
50
52
54 S/A=0.05%S/A=0.2%S/A=0.8%S/A=1.6%S/A=3.2%S/A=6.4%
Outletsolutionc
oncentration,
xsr2,%
Inlet air temperature, tar1
,oC
34 36 38 40 42 44 46 48 50 52
32
34
36
38
40
42
44
46
48
50
52
S/A=0.05%S/A=0.2%S/A=0.8%S/A=1.6%S/A=3.2%S/A=6.4%
Outletsolutiontemperature,
tsr2,o
C
Inlet air temperature, tar1
,oC
EFFECT OF INLET AIR SPECIFIC HUMIDITY (REGENERATOR)
EFFECT OF INLET AIR TEMPERATURE (REGENERATOR) 18
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ABSORBER
REGENERATOR
19
0 1 2 3 4 5 6 7
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
Changeinsp.h
umidity,
W,g
/kg
S/A ratio,%
ts1
=12oC
ts1=18oCt
s1=24
oC
ts1
=30oC
ts1
=40oC
ts1
=50oC
0 1 2 3 4 5 6 7
0
1
2
3
4
5
Changeinsp.
humidity,Wr,
g/kg
S/A ratio,%
tsr1
=10oC
tsr1
=15oC
tsr1
=20oC
tsr1
=25oC
tsr1
=30oC
tsr1
=40oC
tsr1
=50oC
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COUPLED COLUMNS
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Block diagram of coupled columns
21
C i l d l C l d l
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Computational Model- Coupled columns
msahsaxstsa
msa+dmhsa+ dhsa
xs+dx
tsa+dtsa
dZ
marhar
Wartar
marhar+dhar
War+dWartar+dtar
Z
Regenerator
air in
Weak
solution out
msr+dmhsr+ dhsr
xw+dx
tsr+dtsr
msrhsrxwtsr
dZ
Strong
solution out
Weak
solution in
Strong
solution in
maahaa+dhaa
Waa+dWaataa+dtaa
maahaa
Waataa
Process
air in
Absorber Regenerator
Dehumdified
air out Humidified
air out
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Table 3. Operating parameters
Parameter Range Mean value
Process air temperature, taa1,oC 10-18 14
Process air specific humidity, Waa1, g/kg 6-10 8
Regeneration air temperature, tar1
, oC 35-50 45
Regenerator air specific humidity, War1
, g/kg 15-30 20
S/A flow ratio (%)
Absorber
Regenerator
0.3-1.6
0.3-1.6
0.8
0.8
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10 12 14 16 180.5
1.0
1.5
2.0
2.5
3.0
Decreaseofspecifichumidity
inabsorber,
Waa,g
/kg
Process air temperature , taa1
,oC
(S/A)r=0.4%
(S/A)r=0.6%
(S/A)r=0.8%
(S/A)r=1.0%
(S/A)a=0.8%
10 12 14 16 181
2
3
4
5
6
7 (S/A)a=0.8% (S/A)r=0.4% (S/A)
r=0.6%
(S/A)r=0.8%
(S/A)r=1.0%
Increaseofairtemperature
inabsorber,taa,o
C
Process air temperature, taa1
,oC
10 12 14 16 18
0.5
1.0
1.5
2.0
2.5(S/A)
a=0.8% (S/A)
r=0.4%
(S/A)r=0.6%
(S/A)r=0.8%
(S/A)r=1.0%
Increaseofspecifichumidity
inregenerator,War,g
/kg
Process air temperature, taa1
,oC
10 12 14 16 180
1
2
3
4
5
6
(S/A)a=0.8% (S/A)
r=0.4%
(S/A)r=0.6%
(S/A)r=0.8%
(S/A)r=1.0%
Decreaseofa
irtemperature
inregenerator,tar,
oC
Process air temperature, taa1
,oC
EFFECT OF PROCESS AIR TEMPERATURE (ABSORBER)
EFFECT OF PROCESS AIR TEMPERATURE (REGENERATOR)24
3 0 6
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6 7 8 9 100.0
0.5
1.0
1.5
2.0
2.5
3.0
Specific humidity of process air, Waa1
, g/kg
Decreaseo
fspecifichumidity
intheab
sorber,
Waa
g/kg
(S/A)a=0.2%
(S/A)a=0.4%
(S/A)a=0.8%
(S/A)a=1.6%
6 7 8 9 100
1
2
3
4
5
6
Increaseofairtemperature
intheabsorber,taa
oC
(S/A)a=0.2%
(S/A)a=0.4%
(S/A)a=0.8%
(S/A)a=1.6%
Specific humidity of process air, Waa1
, g/kg
6 7 8 9 100.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
(S/A)a=0.2%
(S/A)a=0.4%
(S/A)a=0.8%
(S/A)a=1.6%
Increaseofspecifichumidity
intheregen
erator,Waa
g/kg
Specific humidity of process air, Waa1
, g/kg
6 7 8 9 101
2
3
4
5
6
7
8
9
10
11
(S/A)a=0.2%
(S/A)a=0.4%
(S/A)a=0.8%
(S/A)a=1.6%
Decreaseofairtemperature
inther
egenerator,tar
oC
Specific humidity of process air, Waa1
, g/kg
EFFECT OF PROCESS AIR SPECIFIC HUMIDITY (ABSORBER)
EFFECT OF PROCESS AIR SPECIFIC HUMIDITY (REGENERATOR)25
3.0 6
(S/A) 0 2%
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14 16 18 20 22 24 26 28 30 320.0
0.5
1.0
1.5
2.0
2.5
(S/A)a=0.2%
(S/A)a=0.4%
(S/A)a=0.8%
(S/A)a=1.0%
(S/A)a=1.6%
Decreaseofspecifichumidity
intheabsorber,
Waa
g/kg
Specific humidity of regenerator air, War1
, g/kg
14 16 18 20 22 24 26 28 30 320
1
2
3
4
5
Increaseofairtemperature
in
theabsorber,taa
oC
(S/A)a=0.2%
(S/A)a=0.4%
(S/A)a=0.8%
(S/A)a=1.0%
(S/A)a=1.6%
Specific humidity of regenerator air, War1
, g/kg
14 16 18 20 22 24 26 28 30 32
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Increaseofspecifichumidity
intheregenerator,War
g/kg
Specific humidity of regenerator air, War1, g/kg
(S/A)a=0.2%
(S/A)a=0.4%
(S/A)a=0.8%
(S/A)a=1.0%
(S/A)a=1.6%
14 16 18 20 22 24 26 28 30 32
1
2
3
4
5
6
7
8
9
10
Specific humidity of regenerator air, W
ar1, g/kg
(S/A)a=0.2%
(S/A)a=0.4%
(S/A)a=0.8%
(S/A)a=1.0%
(S/A)a=1.6%
Decreaseof
temperature
intheregen
erator,taro
C
EFFECT OF REGENERATOR AIR SPECIFIC HUMIDITY (ABSORBER)
EFFECT OF REGENERATOR AIR SPECIFIC HUMIDITY (REGENERATOR)26
(S/A) =0 3%(S/A) 0 8% 6
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35 40 45 50
0.0
0.5
1.0
1.5
2.0
2.5
Decrea
seofspecifichumidity
inth
eabsorber,
Waa
g/kg
Temperature of regenerator air, tar1
oC
(S/A)r=0.3%
(S/A)r=0.4%
(S/A)r=0.6%
(S/A)r=0.8%
(S/A)a=0.8%
35 40 45 500
1
2
3
4
5
6(S/A)
a=0.8% (S/A)
r=0.3%
(S/A)r=0.4%
(S/A)r=0.6%
(S/A)r=0.8%
Increaseofairtemperature
inthe
absorber,taa
oC
Temperature of regenerator air, tar1
oC
35 40 45 50
0.0
0.5
1.0
1.5
(S/A)r=0.3%
(S/A)r=0.4%
(S/A)r=0.6%
(S/A)r=0.8%
(S/A)a=0.8%
Temperature of regenerator air, tar1
oC
Increaseof
secifichumidity
intheregen
erator,War
g/kg
35 40 45 50
0
1
2
3
4(S/A)
a=0.8% (S/A)r=0.3%(S/A)
r=0.4%
(S/A)r=0.6%
(S/A)r=0.8%
decreaseofairtemperature
intheregen
erator,tar
oC
Temperature of regenerator air, tar1
oC
EFFECT OF REGENERATOR AIR TEMPERATURE (ABSORBER)
EFFECT OF REGENERATOR AIR TEMPERATURE (REGENERATOR)27
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28
EFFECT OF PROCESS AIR TEMPERATURE ON SOLUTION CONCENTRATION
10 12 14 16 18
27
30
33
36
39
42
45
48
51
tar1=35o
C
tar1
=40oC
tar1
=45oC
tar1
=50oC
tar1
=35oC
tar1
=40oC
tar1
=45oC
Absorberexit
Solutionconcentration%
Process air temperature,taa1
oC
Regeneratorexit
(S/A)a
=(S/A)r
= 0.3tar1=50oC
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Conclusions
At high range of S/A ratio
Solution has to be necessarily pre-cooled.Cooling of air will only complement the dehumidification.
Change in humidity increases with increase in air specific
humidity, solution concentration and decrease in air
temperature at the inlet.
At low range of S/A ratio
Air has to be pre-cooled for the sustained
dehumidification of air.
Solution temperature has negligible influence ondehumidification.
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Desiccant to assist only in dehumidification
Entire cooling supported by compression system
Regeneration achieved by warm condenser air
Air properties decide the process whether it is absorption
or regeneration
Regeneration is possible at temperatures above 30oC
Thus the proposed hybrid system is feasible
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Conclusions
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Thank You