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The research and development of the key components for desiccant cooling system
WREC 1996
THE RESEARCH AND DEVELOPMENT OF THE KEY COMPONENTS FOR DESICCANT COOLING SYSTEM HE-FE1 ZHANG and JIN-DI W Institute of Air-Conditioning
and Solar Energy,
Northwestern Polytechnical University,
Xi’an, 710072, P. R. China zu-SHE Aeronautic
Industry
Civilian
LIU
Products Company,
Xi’an,
7 10075,
P. R. China
ABSTRACI An air conditioning option, that is, desiccant cooling system (DCS) in which alternative energy source, such as solar energy,
nature gas and rejected heat, can play their part for the benefit of environment and
saving energy is constructed by regenerative (recuperator)
dehumidification
component combined with heat exchanger
and evaporative cooler.
The mathematical model of an rotary desiccant wheel that can be used to calculate the performance of stationary or rotary bed and transient or steady state operation is founded by considering many terms. A computer program for this new model has been compiled and some results of computer simulation compared with experimental value, they are good in agreement. The performance of evaporator is estimated by computer. We developed some kinds of evaporator of which the COP is about lo-15
to decrease the room temperature and clean the air in drier climates. Using a new
kind of chemical refrigerant invented by Zu-She Liu , the air conditioner will be simple in construction and very efficient (COP>30).
KEY WORDS Desiccant cooling system; rotary desiccant wheel ; evaporator ; chemical refrigerant.
PERFORMANCE OF DESICCANT WHEEL Mathematical
Model of a Rotary Solid Desiccant Dehumidifier
The key component of a desiccant cooling system is the dehumidifier which is slowly rotated through the 653
WREX 1996 process air and regeneration air streams. The following set of governing equations are derived by considering the transient air humidity,
temperature and circumfurencial
convection terms, heat diffusion and mass
diffusion in solid desiccant. The air moisture balance equation
(1) The air enthalpy balance equation
(2) The desiccant moisture balance equation
gY+ =$$(Y
0 g
-
D,,(l
- f.)
21n(kg aw + e
azz 1
[ rlZj7 -
(3)
Y,).
Y)
The desiccant enthalpy balance equation
(4)
= CM,(C,u+
Ati)+m&l
[a.f.(t - L) + K,f,.(Y - Y&?l.
In addition to the governing equations the following boundary conditions are required, (Zn-@,&@
for regeneration air
Y Ill=Yr and Il,l=fZ.
For Prowss air (O<@
Y I&=Y, and ~l,=t,.
Cyclical B. C. are
Y(O,Z,z)= Y(Z?z,Z,T)
KO,Z,T)
W(O,Z,z)
L(O,Z,r)
= WV(Zn,Z,z)
= t(zn,Z,z) = t,(2n,z,z).
(5)
(I) =t,,. If flow is steady, the ini_ tial conditions of Y and t equal their inlet conditions. For regeneration air Y (0, Z , 0) =Y2 and t(@,Z, 0) = h. For process air Y(O,Z,O)=YI and t(@,Z,O)=t,. For transient problem initial conditions are W(O,Z,
0) =W,, and t,(@,Z,
Results of Simulation A computer program according to this new model- RDCS has been compiled.
The differential
equations
can be solved by relaxation and iteration method ; for space difference two kinds of schemes, one order up 654
WREC 1996 wind differencing
for convection and central differencing for diffusion,
are adapted; for time difference
many schemes can be choosed, that is ,fully implicit or semi-implicit and explicit schemes. The results of computer simulation from RDCS have been compared with theoretical and experimental values given by references. Both of them are good in agreement indicated in Fig. 1 and Fig. 2.
0.012
.
0.012
s 0.01 5 g 0.008 E 0.006 5: 3 0.004 X 0.002
REGEN
TEMP 95-c
REGEN
TFMP
95%
01
0
2
4 8
8 10 12 14 16 18 20
0 2
??Experimental
value, -Predicted
RH= l.235W+267.99Wz-3170. RH=O. Fig. 1.
??Experimental
value
Relative humidity expression :
+10087.16W’
RD, GEL
value ,-Predicted
value
Relative humidity expression :
RH=O. 0078-O.
7Ws
05759W+24.1655w2
- 124. 478W3+204.
W
3316+3.18W
10 12 14 16 18 ;O
TIME(MIN)
TIME(MN
ID, GEL.
8
4 6
226W’
W>O. 07 Fig. 2.
DAMIN Gel (Dynamic character)
SEIBU
GIKEN
Gel
(Dynamic Character)
EVAPORATIVE COOLER The primary component of a desiccant cooling system is the dehumidifier,
but without evaporative cooler
the system cannot be consisted. Although not directly solar, evaporative cooling for comfort control is extensively used in drier climates. We studied two kinds of evaporator made by ceramic and compound honeycomb which should have superior character such as the high absorptivity of water, ratio of surface area and wet intension.
In general,
the COP which is a measure of the energy required to meet the cooling load is
very high for evaporative cooler (between 10-15). sumed),
the COP will be infinity theoretically.
If it is natural evaporation (no mechanical work con-
Using the first law of thermodynamics for adiabatic evap
ration process, The energy balance eqation is 4 (h, - h,) = C,(T, - 2’1) + a&.
(6)
The inlet and outlet parameters of airflow can be obtained by solving equation (6) combined with continuous equation.
A program has been complied. From this code some typical results are given in Fig. 3 and
Fig. 4, one for small mass flow rate of air (0. 2M3/s>, another for 10000M3/h.
655
tWTtEC 1996 hzR RATE OF now
0.2(M1/S)
AIR RATE OF FLOW 1000O(Ms/H)
0 10 20 30 40 50 60 70 80 901;; 35- . I 9 . .-- , ' w * \ \ ; '\ b '\ 34 ;p.5 \ \ \ '\ \ \ ,34 , 5 11 \ 1, 33 : '$ & '1, '\ '\ ' ' 1 33 32: ;“' ' 'i '\ ' ' \ 32
\l. 5;
28 27 26 25
,
‘\
\
‘\ ‘\
I \ \ x-31 ',2.d[K6'&0/"3 '\ '\ 30 x \ :\ '',2* ;,, Y, '\ '\ ' 29
31:
p 130 c= 29
,
:,
', ' '\ '\ '\ 28 ; $3.o‘, s t '. 27 \ \ \ -z '\ '. '\ '\3.5', '\ '\ 26 1' '-.'*!*.1 0 10 20 30 40 50 60 70 80 9010i5
Relative humidity (RI&/%)
350 10 2030 4050 60.70 80 gOIO,o, 34 151 \ \ \ \ \ \ \34 3 \ \lO, \ \ \ \ 1 \ I33 3 \ \15\ \ \ \ \ \ \'32 32 \ \iO\ 1 \ \ \ 1 _31 31 \ \25\ \ \ \ \ \ 30 e30 I .a ' 30[KgH,O/h] \ ' 2g +29 28
\ \
' 35\
'
'
'
',28
'40' ' ' ' \.27 27 \ , 45' ' ' 26 ' ',50', '. '. 26 25- * ). . s . . . . 0 10 2030 4050 60 70 80 9010i5
ReIative humidity (RI&/%)
Fig. 3.
Fig. 4.
NEW CHEMICAL REFRIGERANT A new chemical refrigerant, chemical reaction,
which consists of thirty-six chemicals through many steps, for example, heat
composition,
combination,
decomposition and distillation etc. crossw&e to form cold
source, can be used to all kind of refrigeratory apparatus such as air conditioner, refrigerator and storage. There are some prominent feature for this refrigerant: Chemical reaction kept for a long time; COP larger than 30 because of no compressor, evaporator and condenser for cooling system; no environmental
problem, all of them make it potential and promising.
ACKNOWLEDGEMENT The authors gratefully acknowledge the national foundation committee of natural science for Grant No. 59376294 which supported the research work for desiccant cooling system. REFERENCES Charoensupaya,
D. and W. M. Worek (1988).. Parametric study of an open-cycle adiabatic, solid, deaic-
cant cooling system. -Energy, 13(19), 739-747. Collier, R. K. , B. M. Cohen and R. B. So&erg (1992). Desiccant properties and their effects on the performance of desiccant cooling systems, In : Desiccant Cooling and Dehumidification (L. Harriman, Ed. ), ASHRAE, Inc. , 75-81. Feng, Q. , J. D. Yu and H. E. Zhang (1994). Simularity analysis and computation of a rotary solid de iccant dehumidifier. Acta Energiae Solaris Sinica (China), 15(2), 113-124. Feng, Q. , J. D. Yu and H. F. Zhang (1994). The mathematical model of a rotary solid desiccant dehumidifier and the code RDEH. Acta Energiae Solaris Sinica (China), 15(3), 209-217. Worek, W. M. and Z. Lavan (1982). Solar Energy Eng. , -104, 187-196.
Performance of a cross-cooled desiccant dehumidifier prototype.
THE RESEARCH AND DEVELOPMENT OF THE KEY COMPONENTS FOR DESICCANT COOLING SYSTEM HE-FE1 ZHANG and JIN-DI W Institute of Air-Conditioning
and Solar Energy,
Northwestern Polytechnical University,
Xi’an, 710072, P. R. China zu-SHE Aeronautic
Industry
Civilian
LIU
Products Company,
Xi’an,
7 10075,
P. R. China
ABSTRACI An air conditioning option, that is, desiccant cooling system (DCS) in which alternative energy source, such as solar energy,
nature gas and rejected heat, can play their part for the benefit of environment and
saving energy is constructed by regenerative (recuperator)
dehumidification
component combined with heat exchanger
and evaporative cooler.
The mathematical model of an rotary desiccant wheel that can be used to calculate the performance of stationary or rotary bed and transient or steady state operation is founded by considering many terms. A computer program for this new model has been compiled and some results of computer simulation compared with experimental value, they are good in agreement. The performance of evaporator is estimated by computer. We developed some kinds of evaporator of which the COP is about lo-15
to decrease the room temperature and clean the air in drier climates. Using a new
kind of chemical refrigerant invented by Zu-She Liu , the air conditioner will be simple in construction and very efficient (COP>30).
KEY WORDS Desiccant cooling system; rotary desiccant wheel ; evaporator ; chemical refrigerant.
PERFORMANCE OF DESICCANT WHEEL Mathematical
Model of a Rotary Solid Desiccant Dehumidifier
The key component of a desiccant cooling system is the dehumidifier which is slowly rotated through the 653
WREX 1996 process air and regeneration air streams. The following set of governing equations are derived by considering the transient air humidity,
temperature and circumfurencial
convection terms, heat diffusion and mass
diffusion in solid desiccant. The air moisture balance equation
(1) The air enthalpy balance equation
(2) The desiccant moisture balance equation
gY+ =$$(Y
0 g
-
D,,(l
- f.)
21n(kg aw + e
azz 1
[ rlZj7 -
(3)
Y,).
Y)
The desiccant enthalpy balance equation
(4)
= CM,(C,u+
Ati)+m&l
[a.f.(t - L) + K,f,.(Y - Y&?l.
In addition to the governing equations the following boundary conditions are required, (Zn-@,&@
for regeneration air
Y Ill=Yr and Il,l=fZ.
For Prowss air (O<@
Y I&=Y, and ~l,=t,.
Cyclical B. C. are
Y(O,Z,z)= Y(Z?z,Z,T)
KO,Z,T)
W(O,Z,z)
L(O,Z,r)
= WV(Zn,Z,z)
= t(zn,Z,z) = t,(2n,z,z).
(5)
(I) =t,,. If flow is steady, the ini_ tial conditions of Y and t equal their inlet conditions. For regeneration air Y (0, Z , 0) =Y2 and t(@,Z, 0) = h. For process air Y(O,Z,O)=YI and t(@,Z,O)=t,. For transient problem initial conditions are W(O,Z,
0) =W,, and t,(@,Z,
Results of Simulation A computer program according to this new model- RDCS has been compiled.
The differential
equations
can be solved by relaxation and iteration method ; for space difference two kinds of schemes, one order up 654
WREC 1996 wind differencing
for convection and central differencing for diffusion,
are adapted; for time difference
many schemes can be choosed, that is ,fully implicit or semi-implicit and explicit schemes. The results of computer simulation from RDCS have been compared with theoretical and experimental values given by references. Both of them are good in agreement indicated in Fig. 1 and Fig. 2.
0.012
.
0.012
s 0.01 5 g 0.008 E 0.006 5: 3 0.004 X 0.002
REGEN
TEMP 95-c
REGEN
TFMP
95%
01
0
2
4 8
8 10 12 14 16 18 20
0 2
??Experimental
value, -Predicted
RH= l.235W+267.99Wz-3170. RH=O. Fig. 1.
??Experimental
value
Relative humidity expression :
+10087.16W’
RD, GEL
value ,-Predicted
value
Relative humidity expression :
RH=O. 0078-O.
7Ws
05759W+24.1655w2
- 124. 478W3+204.
W
3316+3.18W
10 12 14 16 18 ;O
TIME(MIN)
TIME(MN
ID, GEL.
8
4 6
226W’
W>O. 07 Fig. 2.
DAMIN Gel (Dynamic character)
SEIBU
GIKEN
Gel
(Dynamic Character)
EVAPORATIVE COOLER The primary component of a desiccant cooling system is the dehumidifier,
but without evaporative cooler
the system cannot be consisted. Although not directly solar, evaporative cooling for comfort control is extensively used in drier climates. We studied two kinds of evaporator made by ceramic and compound honeycomb which should have superior character such as the high absorptivity of water, ratio of surface area and wet intension.
In general,
the COP which is a measure of the energy required to meet the cooling load is
very high for evaporative cooler (between 10-15). sumed),
the COP will be infinity theoretically.
If it is natural evaporation (no mechanical work con-
Using the first law of thermodynamics for adiabatic evap
ration process, The energy balance eqation is 4 (h, - h,) = C,(T, - 2’1) + a&.
(6)
The inlet and outlet parameters of airflow can be obtained by solving equation (6) combined with continuous equation.
A program has been complied. From this code some typical results are given in Fig. 3 and
Fig. 4, one for small mass flow rate of air (0. 2M3/s>, another for 10000M3/h.
655
tWTtEC 1996 hzR RATE OF now
0.2(M1/S)
AIR RATE OF FLOW 1000O(Ms/H)
0 10 20 30 40 50 60 70 80 901;; 35- . I 9 . .-- , ' w * \ \ ; '\ b '\ 34 ;p.5 \ \ \ '\ \ \ ,34 , 5 11 \ 1, 33 : '$ & '1, '\ '\ ' ' 1 33 32: ;“' ' 'i '\ ' ' \ 32
\l. 5;
28 27 26 25
,
‘\
\
‘\ ‘\
I \ \ x-31 ',2.d[K6'&0/"3 '\ '\ 30 x \ :\ '',2* ;,, Y, '\ '\ ' 29
31:
p 130 c= 29
,
:,
', ' '\ '\ '\ 28 ; $3.o‘, s t '. 27 \ \ \ -z '\ '. '\ '\3.5', '\ '\ 26 1' '-.'*!*.1 0 10 20 30 40 50 60 70 80 9010i5
Relative humidity (RI&/%)
350 10 2030 4050 60.70 80 gOIO,o, 34 151 \ \ \ \ \ \ \34 3 \ \lO, \ \ \ \ 1 \ I33 3 \ \15\ \ \ \ \ \ \'32 32 \ \iO\ 1 \ \ \ 1 _31 31 \ \25\ \ \ \ \ \ 30 e30 I .a ' 30[KgH,O/h] \ ' 2g +29 28
\ \
' 35\
'
'
'
',28
'40' ' ' ' \.27 27 \ , 45' ' ' 26 ' ',50', '. '. 26 25- * ). . s . . . . 0 10 2030 4050 60 70 80 9010i5
ReIative humidity (RI&/%)
Fig. 3.
Fig. 4.
NEW CHEMICAL REFRIGERANT A new chemical refrigerant, chemical reaction,
which consists of thirty-six chemicals through many steps, for example, heat
composition,
combination,
decomposition and distillation etc. crossw&e to form cold
source, can be used to all kind of refrigeratory apparatus such as air conditioner, refrigerator and storage. There are some prominent feature for this refrigerant: Chemical reaction kept for a long time; COP larger than 30 because of no compressor, evaporator and condenser for cooling system; no environmental
problem, all of them make it potential and promising.
ACKNOWLEDGEMENT The authors gratefully acknowledge the national foundation committee of natural science for Grant No. 59376294 which supported the research work for desiccant cooling system. REFERENCES Charoensupaya,
D. and W. M. Worek (1988).. Parametric study of an open-cycle adiabatic, solid, deaic-
cant cooling system. -Energy, 13(19), 739-747. Collier, R. K. , B. M. Cohen and R. B. So&erg (1992). Desiccant properties and their effects on the performance of desiccant cooling systems, In : Desiccant Cooling and Dehumidification (L. Harriman, Ed. ), ASHRAE, Inc. , 75-81. Feng, Q. , J. D. Yu and H. E. Zhang (1994). Simularity analysis and computation of a rotary solid de iccant dehumidifier. Acta Energiae Solaris Sinica (China), 15(2), 113-124. Feng, Q. , J. D. Yu and H. F. Zhang (1994). The mathematical model of a rotary solid desiccant dehumidifier and the code RDEH. Acta Energiae Solaris Sinica (China), 15(3), 209-217. Worek, W. M. and Z. Lavan (1982). Solar Energy Eng. , -104, 187-196.
Performance of a cross-cooled desiccant dehumidifier prototype.