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Performance characteristics of the water-lithium bromide-zinc chloride-calcium bromide absorption refrigerating machine, absorption heat pump and absorption heat transformer
Performance characteristics of the water-lithium bromidc zinc chloridc calcium bromide absorption refrigerating machine, absorption heat pump and absorption heat transformer S. lyoki and T. U e m u r a Faculty of Engineering, Kansai University, 3-3-35 Yamate-cho, Suita, Osaka 564, Japan Received 1 December 1988; revised 25 July 1989
A theoretical analysis of the coefficient of performance was undertaken to examine the performance characteristics of the water-lithium bromide-zinc chloride--calcium bromide system (1.0:1.0:0.13 by mass, respectively). The coefficient of performance for absorption refrigerating machines, absorption heat pumps and absorption heat transformers was calculated using the enthalpies at various temperatures, pressures and absorbent concentrations. The performance characteristics of this system were compared with that of the water-lithium bromide system and that of the other systems using water, methanol and ammonia as working media. This system was found to be suitable for an air-cooled single-stage absorption refrigerating machine, a single-stage, high temperature double-effect absorption heat pump and a two-stage absorption heat transformer. (Keywords: working medium; coefficient of performance; absorption refrigerating machine; absorption heat pump; absorption heat transformer)
Caract6ristiques de la performance d'un r6frig6rateur, d'une pompe ~t chaleur et d'un transformateur de chaleur ~t absorption utilisant un syst6me eau-bromure de lithium--chlorure de zinc-bromure de calcium On a entrepris une analyse thkorique du COP afin d'examiner les caractkristiques de performance d'un systbme eau-bromure de lithium-chlorure de zinc-bromure de calcium (1.0.'1.0:0.13 par masse, respectivement). On a calculb le COP pour des rbfrig~rateurs ~ absorption, des pompes h chaleur ?tabsorption et des transformateurs de chaleur h absorption en utilisant les enthalpies h diffbrentes tempbratures, pressions et concentrations de solvant. On a comparb les caract~ristiques de performance de ce systbme avec celles du systbme eau-bromure de lithium et celles d'autres systbmes utilisant l'eau, le mbthanol et l'ammoniac comme fluides actifs. On a constatb que ce systbme convenait le mieux pour un rbfrigbrateur h absorption monobtagb refroidi h l'air, pour une pompe chaleur h absorption h double effet et haute tempkrature et pour un transformateur de chaleur h absorption bibtagb.
(Mots cl6s: milieu actif; COP; r6frig~rateur~. absorption; pompe ~.chaleur fi absorption; transformateurde chaleur absorption)
The water-lithium bromide-zinc chloride-calcium bromide system has been proposed as an improvement on the performance characteristics of the water-lithium bromide system. In a previous paper 1, the properties of lithium bromide-zinc chloride-calcium bromide aqueous solutions, i.e. density, viscosity, solubility, vapour pressure, heat capacity and heat of mixing were measured in order to evaluate the performance characteristics of this system. The optimum mixing ratio of lithium bromide, zinc chloride and calcium bromide was determined by measuring the crystallization temperature of sample solutions. The optimum mixing ratio of lithium bromide, zinc chloride and calcium bromide was found to be 1.0:1.0:0.13 by mass 1'2. The enthalpies of this system at various temperatures, pressures and absorbent concentrations were calculated from physical (solubility and vapour pressure) and thermal properties (heat capacity 0140-7007/90/030191-06 © 1990 Butterworth & Co (Publishers) Ltd and IIR
and heat of mixing). The performance characteristics for absorption refrigerating machines, absorption heat pumps and absorption heat transformers have been studied by many workers z-19. The theoretical coefficient of performance (COP) was calculated by using the enthalpies at various temperatures, pressures and absorbent concentrations for the following systems: single-stage, two-stage and double-effect refrigerating machines; single-stage, double-effect and high temperature double-effect heat pumps; and single-stage and two-stage heat transformers. The performance characteristics of this four-component refrigeration, heat pump and heat transformer system were compared with those of the water-lithium bromide system and those of the other working mediumabsorbent systems using water, methanol and ammonia as working media.
Rev. Int. Froid 1990 Vol 13 Mai
191
Performance characteristics of various working media: S. lyoki and T. Uemura
Theoretical analysis For the absorption refrigerating machines, absorption heat pumps and absorption heat transformers, the following conditions were assumed for the theoretical calculations of the COP. The pressure in the generator and condenser is the vapour pressure of the working medium at condenser temperature t c. The pressure in the evaporator and absorber is the vapour pressure of the working medium at evaporator temperature t E. The work required to pump the strong solution and liquid working medium to the high pressure side of the cycle is negligible. Heat losses to the surroundings as well as pressure drops due to friction, etc. were assumed to be negligible. The effectiveness of the intermediate heat exchanger was assumed to be 1.0. A theoretical analysis was carried out to examine the effect on the performance characteristics of absorption refrigerating machines, absorption heat pumps and absorption heat transformers when their operating conditions were changed.
energy is supplied to generator (I) to liberate the working medium which flows to the condenser through generator (II). The heat (q~) supplied at generator (II) is used as the latent heat of th~ working medium vapour generated at generator (I). The working medium vapour from generator (II) is condensed in the condenser and expanded in the evaporator. The vapour is absorbed by the weak solution in the absorber. The strong solution produced in the absorber is pumped through heat exchangers (I) and (II) to generator (I). The COP of the double-effect absorption refrigerating machine is given by: COP = qE/qG,
(3)
where qE is the heat removed at the evaporator and qc, is the heat supplied at generator (I).
Absorption heat pumps Absorption refrigerating machines The single-stage absorption refrigerating machine consists primarily of a generator, an absorber, a condenser, an evaporator and a heat exchanger. Energy is supplied to the generator as heat to drive out the working medium. In the generator, the working fluid is concentrated in the absorbent by evaporating the working medium. The weak solution passes through the heat exchanger into the absorber. The working medium is then condensed in the condenser. The liquid working medium is evaporated due to the additional heat load in the evaporator. The vaporized working medium is then transferred to the absorber where it is absorbed by the weak solution. The strong solution produced in the absorber is pumped through the heat exchanger to the generator. The COP of the single-stage absorption refrigerating machine is defined as follows: COP = qE/q6
(1)
where qE is the heat removed at the evaporator and qG is the heat supplied at the generator. The two-stage absorption refrigerating machine consists primarily of two generators, two absorbers, a condenser, an evaporator and two heat exchangers. Heat energy is supplied to the high pressure generator and the low pressure generator to drive out the working medium. The working medium vapour liberated in the high pressure generator is condensed into a liquid and evaporated due to the additional heat load in the evaporator. The vapour is absorbed by the weak solution in the low pressure absorber. On the other hand, the working medium generated in the low pressure generator is absorbed by the weak solution in the high pressure absorber. The COP of the two-stage absorption refrigerating machine is given by: COP = qE/(qGrt+ qGU)
(2)
where qE is heat removed at the evaporator, q~n is heat supplied at the high pressure generator and q~L is heat supplied at the low pressure generator. The double-effect absorption refrigerating machine consists primarily of two generators, an absorber, a condenser, an evaporator and two heat exchangers. Heat
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Int. J. Refrig. 1990 Vol 13 May
The single-stage absorption heat pump consists primarily of a generator, an absorber, a condenser, an evaporator and a heat exchanger. Energy is supplied as heat to the generator at a high temperature and to the evaporator at a low temperature. Heat is released in the absorber and condenser. The COP of the single-stage absorption heat pump is given by: COP = (qA + qc)/qG
(4)
where qA is the heat released at the absorber, qc is the heat released at the condenser and qG is the heat supplied at the generator. The double-effect absorption heat pump consists primarily of two generators, an absorber, a condenser, an evaporator and two heat exchangers. Energy is supplied to generator (I) as heat at a high temperature and to the evaporator at a low temperature. Heat is released in the absorber and condenser. The COP of the double-effect absorption heat pump is given by: COP = (qa + qc)/qG,
(5)
where qA is the heat released at the absorber, qc is the heat released at the condenser and qG, is the heat supplied at generator (I). The high temperature double-effect absorption heat pump 9 consists primarily of two generators, two absorbers, a condenser, two evaporators and two heat exchangers. Heat energy is supplied to generator (I) at a high temperature, whereas heat at a low temperature is supplied to evaporators (I) and (II). The working medium generated in generator (I) flows to evaporator (I) through generator (II). The liquid working medium is evaporated due to the additional heat load in evaporator (I) at low temperature. The vapour is absorbed by the weak solution in absorber (I). The strong solution is pumped through heat exchanger (I) to generator (I). Then the vapourized working medium in generator (II) is condensed in the condenser. The liquid working medium is evaporated due to the additional heat load in evaporator (II) at low temperature. The vapour is absorbed by a weak solution in absorber (II). The strong solution is pumped through heat exchanger (II) to generator (II). Heat is released in absorber (I), absorber
Performance characteristics of various working media: S. lyoki and T. Uemura I
I
I
(8)
COP = qAn/(q6 + qEL)
where qAH is heat released at the high pressure absorber, qG is the heat supplied at the generator and qEL is the heat supplied at the low pressure evaporator. vI
=29 .1 K Results and discussion
0,6
b. =.~2?R.1R K~~ ~ C=3
n O
TM
~ .
tc 303.15K tc=313,15K
tc:333.!5 K
0.7
-
_
tc=343.15 K 0.6"
I 323.15
tc =353.15 K
373.15
I 423.15
473.15
Generator temperature t G ( K ) Figure 1 RelationshipbetweenCOP and generatortemperature tGfor single-stage absorption refrigeratingmachine Figure 1 Relation entre le C O P et la tempdrature du gkn&ateur t o pour un rrfrigbrateur h absorption monoktag6
(II) and the condenser. The COP of the high temperature double-effect absorption heat pump is given by: C O P = (qA, + qA2 +
qc)/qG,
(6)
w h e r e qA, is the heat released at absorber (I), qA2 is the heat
released at absorber (II), qc is the heat released at the condenser and qG, is the heat supplied at generator (I).
Absorption heat transformers The single-stage absorption heat transformer consists primarily of a generator, an absorber, a condenser, an evaporator and a heat exchanger. Waste heat energy is supplied to the generator and the evaporator. In the generator, the working fluid is concentrated in the absorbent by evaporating the working medium. The weak solution is pumped through the heat exchanger to the absorber. The working medium generated in the generator is then condensed in the condenser. The liquid working medium is pumped to the evaporator, and is evaporated due to the additional waste heat load in the evaporator. The vapour is absorbed by the weak solution in the absorber. The strong solution passes through the heat exchanger into the generator. Heat is released in the absorber. The COP of the single-stage absorption heat transformer is given by:
COP=qA/(qG+qE)
(7)
where qA is the heat released at the absorber, qc is the heat supplied at the generator and qE is the heat supplied at the evaporator. The two-stage absorption heat transformer consists primarily of a generator, two absorbers, a condenser, two evaporators and two heat exchangers. The two-stage absorption heat transformer can attain a higher temperature than the single-stage absorption heat transformer. Waste heat energy is supplied to the generator and the low pressure evaporator. Heat is released in the high pressure absorber. The COP of the two-stage absorption heat transformer is given by:
Figure I shows the results of the theoretical calculations for the single-stage absorption refrigerating machine with this system. The parameter t c is the condenser temperature. The evaporator temperature t E was fixed at 281.15 K. The COP of this system decreases from 0.91 to 0.62 as t c increases from 293.15 to 353.15 K. Increasing the generator temperature t G tends to decrease the COP at constant condenser temperature t c. The most important characteristic of this system is that it can theoretically operate at a condenser temperature greater than 313.15 K. The results of the calculations for the single-stage absorption refrigerating machine are shown in Figure 2. The evaporator temperature t e and condenser temperature t c were fixed at 281.15 and 303.15 K, respectively. The results of this system were compared with those for the following working medium-absorbent systems: water-lithium bromide1 o; water-calcium chloride-lithium chloride-zinc chloride 1~; water-lithium bromide-zinc chlorideZ; water-lithium bromide-lithium thiocyanate~ z; water-lithium bromide-lithium chloride a3; and waterlithium bromide-ethylene glycol (C2H602) t4. Under these conditions, the COP of this system is better than that of the water-lithium bromide system, but is not superior to that of the water-lithium bromidelithium chloride system and that of the water-lithium bromide-ethylene glycol system. However, this system has a wide generator and condenser temperature range, compared with those of the three-component system. The results of the calculations for the two-stage absorption refrigerating machine are shown in Fioure 3. The evaporator temperature t E and condenser temperature t c were fixed at 281.15 and 303.15 K, respectively. 0.9
I
I
'~. x.~"x':.x., 2.. .... "X...'x.~'~ 3
T
tE=281.15 K tc=303.15 K 7
a_ 0.8 o t.)
--..<.. 05
I 323.15
I 373.15
Generator temperature
I 423.15 tG
(E)
Figure 2 Comparison of H20-LiBr-ZnCl2~aBr 2 system and the other systems for single-stage absorption refrigerating machine.
(1) H20-LiBr-ZnClz-CaBr2; (2) H20--LiBr; (3) H20-CaC12-LiC1ZnCI 2; (4) H20-LiBr-ZnCI 2; (5) H20--LiBr-LiSCN; (6) H20-LiBr-LiC1; and (7) H20-LiBr-C2HrO 2 Figure 2 Comparaison entre le systbme H20-LiBr-ZnC12-CaBr 2 et les autres systbmes pour une machine frigorifique & absorption monobtagbe
Rev. Int, Froid 1990 Vol 13 Mai
193
Performance characteristics of various working media. S. lyoki and T. Uemura 0.50
I
I
I
I
tE=281.15 K
f
tc=303.15 K 0.45 o
0.4 0 -
~~4
i
0.35 ..... 303.15
I
I
343.15 Generator
383.15
temperature
to
(K)
Figure 3 Comparison of H20-LiBr-ZnC12-CaBr2 system and the other systems for two-stage absorption refrigerating machine. (1) H20 LiBr-ZnCI2-CaBr2; (2) H20-LiBr; (3) H20-CaCI2-LiCIZnCI2; (4) H20-LiBr-ZnCI2; (5) H20-LiBr-LiSCN; (6) HzO-LiBr LiCI_ZnC12Js; and (7) H20-LiBr-C2H602 Figure 3 Comparaison entre le systbme H20 LiBr-ZnCl 2 CaBr 2 et les autres systbmes pour une machine .frigortfique 27 absorption bibtagke
"1
1.6
I
_
I
I
tc=303.i 5 .
-
tG2 =353.15 K
I v
O-1. 2 O (.D
",
0.8 i
~ I
393.15
I
403.15
-
I
413.15
wide generator (I) temperature range, compared with that of the water-lithium bromide system. Figure 5 shows the C O P for the single-stage, double-effect and high temperature double-effect absorption heat pump using this system. The evaporator temperature t E and generator (II) temperature tG2 were fixed at 283.15 and 358.15 K, respectively. The variation in the COP for the single-stage absorption heat pump is very small compared with the double-effect absorption heat pump. The single-stage absorption heat pump has a C O P between 1.73 and 1.90. The double-effect absorption heat pump has a C O P between 1.80 and 2.68. The high temperature double-effect absorption heat pump has a C O P between 2.31 and 2.49. The results of the calculations for the single-stage absorption heat pump are shown in Figure 6. The evaporator temperature t E and generator temperature t o were fixed at 283.15 and 373.15K, respectively. The results of this system were compared with that for the following working medium-absorbent systems: waterlithium bromidel°; water-lithium bromide-zinc bromide-lithium chloride16; water-lithium bromide-zinc chloride2; water-lithium bromide-zinc bromide 1T; and methanol-lithium bromide-zinc bromide 18. Under these conditions, the C O P of this system is better than that of the other systems. This system has a wide attainable temperature range, compared with that of the water-lithium bromide system. The results of the calculations for the high temperature double-effect absorption heat pump are shown in Figure 7. The evaporator temperature tE, generator (I) temperature to, and generator (II) temperature tG2 were fixed at 283.15, 423.15 and 368.15K, respectively. The results of this system were compared with that of the water-lithium bromide system 1° and that of the water-lithium bromide-zinc bromide-lithium chloride system 16. Under these conditions, the C O P of this system is better than that of the other systems. This system has a wide attainable temperature range.
I
423.15 2.8
Generator(I)
temperature
b
tG1 ( K )
Figure 4 Comparison of H20-LiBr-ZnCl2~aBr 2 system and the other systems for double-effect absorption refrigerating machine. (1) H20-LiBr-ZnC124SaBr2; (2) H20-LiBr; (3) H20-LiBr-ZnC12; (4) H20-LiBr-LiCI ZnCl215; (5) H20-LiBr-ZnBr2-LiCI; and (6) H20-CaCI2-LiC1 ZnC12 Figure 4 Comparaison entre le systbme H20-13Br-ZnCI2-CaBr 2 et les autres syst~mes pour un r~friy&ateur h absorption h double effet
194
Int. J. Refrig. 1 9 9 0 Vol 13 M a y
I tE=283.15 K
/ /
I
tG2=358.15 K
/ 2.4 --
-- ~ ' - ~ / . . . ~ _ _
~tGI=423.15 K ~
t'~ tG1=403.15K
O U
2.0-
The results of this system were compared with those of the other systems using water as the working medium. The advantage of this system is that it has a wide generator temperature range, compared with the other systems. The results of the calculations for the double-effect absorption refrigerating machine are shown in Figure 4. The evaporator temperature, condenser temperature and generator (II) temperature to, were fixed at 283.15, 303.15 and 353.15 K, respectively. The results obtained with this system were compared with those of the other systems using water as the working medium. Under these conditions, the C O P of this system is better than that of the water-lithium bromide system ~°. This system has a
I
tG1=393.15 K
•
1.61
~ ~ ~
tG1=433.15 K "~tGi=443.15 K
tG1 =413.15 K t~1=423.15K~
~ ~
~
tG=353.15K
I
I
293.15
303.15
Attainable
temperature
I t6=t'13.15 K 313.15
323J5
tc (K)
Figure 5 Coefficientof performancefor single-stage,double-effectand high temperature double-effectabsorption heat pump. ( ) Singlestage; (- - -) double-effect;and (-- ---) high temperaturedouble-effect
Figure 5 COP d'une pompe it chaleur mono~tagbe, d'une pompe 27 chaleur h double effet et d'une pompe it chaleur it absorption it double effet et haute tempbrature. (--) Monobtagbe; ( - - - ) double effet; et ( - - - ) double effet et haute temperature
Performance characteristics of various working media." S. lyoki and T. Uemura
2.0
The results of the calculations for the two-stage absorption heat transformer are shown in Figure 9. The condenser temperatures were fixed at 283.15 and 303.15 K. The generator temperatures t C were fixed at
I tE=283.15 K
l
4 %
v
1.9
tG=373"15K
0.53
I
I
I
tc =283.15K
-
tG;323"15K
t ~ -- ~ ~ 2
Q.
0.51
0 (J
•
/ / /
]
1.8-
/ ~ -
5"--
/
/,/
. /
-6
0.49 13.. O U 0.47 -
1.;-
I 293.5
273.15
,
I 313.15
333.15
f100~ 0.45 -
Attainable t e m p e r a t u r e t c ( K ) Figure 6 Comparison of H20-LiBr-ZnC12-CaBr2 system and the other systems for single-stage absorption heat pump. (1) HEO-LiBrZnC12--CaBr2; (2) H20-LiBr; (3) H20-LiBr-ZnBr2-LiCI; (4) H20LiBr-ZnC12; (5) H20-LiBr-ZnBr2; and (6) CHaOH-LiBr-ZnBr 2 Figure 6 Comparaison entre le systbme H 2 0 - L i B r - Z n C I 2 - C a B r 2 et les
t
0.43 I 313.15
autres systbmes pour une pompe ~ chaleur it absorption rnonobtagbe
2.5
I
I
I
I
I v
I
i
353.15 Attainable
393.15
temperature
tA ( K )
Figure 8 Comparison of H20-LiBr-ZnCI2-CaBr2 system and the
other systems for single-stage absorption heat transformer. (1) H20LiBr-ZnC12-CaBr2; (2) H20-LiBr; (3) H20-LiBr-ZnBr2; (4) H20LiBr-ZnBr2-LiC1; (5) H20-CaCI2-LiCI-ZnC12; (6) CHaOH-LiBrZnBr2; and (7) NHa-H20 (tG=322.15 K) Figure 8 Comparaison entre le systkme H 20-LiBr-ZnCI2-CaBr 2 et les autres systbmes pour un transformateur de chaleur it absorption rnonobtagb
13. 2.3 O u --
0.34 tE= 283.15 K
-4.3
tG1=423.15 K
/
/
X
/
"4",.
tG2=368.15 K
2.1 I 293.15
I
/
I
I
I
303.15
313.15
323.15
Attainable temperature t C (K) Figure 7 Comparison of H20-LiBr-ZnCI2-CaBr2 system and the other systems for high temperature double-effect absorption heat pump. (1) H20-LiBr-ZnCI2-CaBr2; (2) I-[20-LiBr; and (3) H20-LiBrZnBr2-LiC1 Figure 7 Comparaison entre le systbme H 20-LiBr-ZnCI2-CaBr 2 et les
--
I
\
tc=283.15 K \ \ . tG=333.15K \
/
/
I
/
\
/
/
tc =303.15K t~=333.15K
/--'/'---/
0.32
t
)/ ~ ~ t G = 3 4 3 . 1 5
\ \
tc =303.15 K K
x\ \, \
_
autres systbmes pour une pompe it chaleur it absorption it double effet et it haute temprrature
The results of the calculations for the single-stage absorption heat transformer are shown in Figure 8. The condenser temperature tc and generator temperature to were fixed at 283.15 and 323.15K (except for the ammonia-water system), respectively. The generator temperature of the ammonia-water system was fixed at 322.15 K. The results of this system were compared with those of the other systems using water, methanol and ammonia as working media. Under these conditions, the C O P of this system is not superior to that of the other systems except for the water-calcium chloride-lithium chloride-zinc chloride system 11 and the ammonia-water system 19.
0.3C 333.1E
I 373.15 Attainable
I 413.15 temperature
I 453.15 tAH
(K)
Figure 9 Comparison of H20-LiBr-ZnCl2~aBr 2 system and H20-LiBr system for two-stage absorption heat transformer. ( ) H20-LiBr-ZnCI2-CaBr2; ( - - - ) H20-LiBr Figure 9 Comparaison entre le syst~me H 2 0 - L i B r - Z n C I 2 - C a B r 2 et le systkme H 2 0 - L i B r pour un transformateur de chaleur it absorption bidtag~
Rev. Int. Froid 1990 Vol 13 Mai 195
Performance characteristics of various working media: S. lyoki and 1". Uemura 333.15 a n d 343.15K. The results of this system were c o m p a r e d with those of the w a t e r - l i t h i u m b r o m i d e system 1o. The C O P of this system is not superior to that of the w a t e r - l i t h i u m b r o m i d e system at a c o n d e n s e r t e m p e r a t u r e of 283.15 K and a g e n e r a t o r t e m p e r a t u r e of 333.15 K. H o w e v e r , the w a t e r - l i t h i u m b r o m i d e system c a n n o t o p e r a t e at a c o n d e n s e r t e m p e r a t u r e of 303.15 K. O n the other h a n d , this system has a wide condenser and g e n e r a t o r t e m p e r a t u r e range.
5 6 7
8 9
Conclusions
The theoretical C O P values of the w a t e r - l i t h i u m b r o m i d e - z i n c c h l o r i d e - c a l c i u m b r o m i d e system were calculated for the single-stage, two-stage a n d d o u b l e effect a b s o r p t i o n refrigerating machines, single-stage, double-effect and high t e m p e r a t u r e double-effect a b s o r p tion heat p u m p s , and single-stage a n d two-stage a b s o r p t i o n heat transformers at various o p e r a t i n g conditions. In a d d i t i o n , the C O P of this system was c o m p a r e d with that of the other systems using water, m e t h a n o l a n d a m m o n i a as w o r k i n g media. This system can o p e r a t e as an a i r - c o o l e d single-stage a b s o r p t i o n refrigerating m a c h i n e a n d m a y be a d o p t e d in c o m m e r c i a l designs. This system was found to be suitable for a single-stage a b s o r p t i o n refrigerating machine, a singlestage, high t e m p e r a t u r e double-effect a b s o r p t i o n heat p u m p and a two-stage a b s o r p t i o n heat transformer.
10 II
12 13
14 15
performance analysis of absorption heat pumps for waste heat utilization Int J Refri9 (1982) 5 361 Perez-Blaneo, H. Absorption heat pump performance for different types of solutions lnt J Refrig (1984) 7 115 Bokelmann, H. and Steimle, F. Development of advanced heat transformers utilizing new working fluids Int J Refri9 (1986) 9 51 Vliet, G. C., Lawson, M. B. and Lithgow, R. A. Water-lithium bromide double-effect absorption cooling cycle analysis ASHRAE Trans (1982) 88 Part I 811 Tyagi, K. P. and Rag, K. S. Choice of absorbent-refrigerant mixtures Int J Eng Res (1984) 8 361 Takada, S. Kyushureitoki Japanese Association of Refrigeration, Tokyo, Japan (1982) Uemura, T. and Hasaba, S. Studies on the lithium bromide-water absorption refrigerating machine Technol Rep Kansai Univ (1964) No. 6 31 Uemura, T. and Iyoki, S. Physical, thermodynamic properties and performance characteristics of absorption heat pump using water as working medium Reports on Research and Survey of Heat Pump Technology Japanese Association of Refrigeration, Tokyo, Japan (1987) 267 lyoki, S., Hanafusa, Y., Koshiyama, H. and Uemura, T, Studies on the water-lithium bromide-lithium thiocyanate absorption refrigerating machine Reito (Japan) (1981) 56 661 Hasaba, S. and Uemura, T. Studies on the water-lithium bromide-lithium chloride absorption refrigerating machine Proceedings of the 4th Air Conditioning and Refrigeration Conference Tokyo, Japan (1970) 39 Iyoki, S. and Uemura, T. Studies on the water-lithium bromide-ethylene glycol absorption refrigerating machine Reito (Japan) (1981) 56 279
Takigawa, T., Nakanishi, M., lyoki, S. and Uemura, T. Studies on the water-lithium bromide-lithium chloride-zinc chloride absorption refrigerating machine and absorption heat pump Proceedings of the 1986 Japanese Association of Refrigeration Annual Conference Japanese Association of Refrigeration,
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Iyoki, S. and Uemura, T. Physical and thermal properties of the watei--lithium bromide-zinc chloride-calcium bromide system Int J Refrig (1989) 12 272 Uemura, T, and lyoki, S. Studies on the water lithium bromide zinc chloride absorption refrigerating machine Proceedings of 1982 Japanese Association of Refrigeration Annual Conference Japanese Association of Refrigeration, Tokyo, Japan
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(1982) 17 Iedema, P. D. Mixtures for the absorption heat pump lnt d Refri9 (1982) 5 262 Grossman, G. and Perez-Blaneo, H. Conceptual design and
Int. J. Refrig. 1990 Vol 13 May
16 17
18 19
Tokyo, Japan (1986) 17 Takigawa, T. Master's Thesis Kansai University, Japan (1988) Nakanishi, M., Iyoki, S. and Uemura, T. Studies on the water-lithium bromide-zinc bromide absorption refrigerating machine Proceedings of the 1983 Japanese Association of Refrigeration Annual Conference Japanese Association of Refrigeration, Tokyo, Japan (1983) 21 Hasaba, S. and Uemura, T. Studies on the methanol-lithium bromide-zinc bromide absorption refrigerating machine Reito (Japan) (1969) 44 720-730 Uemura, T., Higuchi, Y., Seki, A. and Hasaba, S. The effects of working conditions on the characteristics of the ammonia-water absorption air conditioner Kogaku to Gijutsu (1964) 2 49
A theoretical analysis of the coefficient of performance was undertaken to examine the performance characteristics of the water-lithium bromide-zinc chloride--calcium bromide system (1.0:1.0:0.13 by mass, respectively). The coefficient of performance for absorption refrigerating machines, absorption heat pumps and absorption heat transformers was calculated using the enthalpies at various temperatures, pressures and absorbent concentrations. The performance characteristics of this system were compared with that of the water-lithium bromide system and that of the other systems using water, methanol and ammonia as working media. This system was found to be suitable for an air-cooled single-stage absorption refrigerating machine, a single-stage, high temperature double-effect absorption heat pump and a two-stage absorption heat transformer. (Keywords: working medium; coefficient of performance; absorption refrigerating machine; absorption heat pump; absorption heat transformer)
Caract6ristiques de la performance d'un r6frig6rateur, d'une pompe ~t chaleur et d'un transformateur de chaleur ~t absorption utilisant un syst6me eau-bromure de lithium--chlorure de zinc-bromure de calcium On a entrepris une analyse thkorique du COP afin d'examiner les caractkristiques de performance d'un systbme eau-bromure de lithium-chlorure de zinc-bromure de calcium (1.0.'1.0:0.13 par masse, respectivement). On a calculb le COP pour des rbfrig~rateurs ~ absorption, des pompes h chaleur ?tabsorption et des transformateurs de chaleur h absorption en utilisant les enthalpies h diffbrentes tempbratures, pressions et concentrations de solvant. On a comparb les caract~ristiques de performance de ce systbme avec celles du systbme eau-bromure de lithium et celles d'autres systbmes utilisant l'eau, le mbthanol et l'ammoniac comme fluides actifs. On a constatb que ce systbme convenait le mieux pour un rbfrigbrateur h absorption monobtagb refroidi h l'air, pour une pompe chaleur h absorption h double effet et haute tempkrature et pour un transformateur de chaleur h absorption bibtagb.
(Mots cl6s: milieu actif; COP; r6frig~rateur~. absorption; pompe ~.chaleur fi absorption; transformateurde chaleur absorption)
The water-lithium bromide-zinc chloride-calcium bromide system has been proposed as an improvement on the performance characteristics of the water-lithium bromide system. In a previous paper 1, the properties of lithium bromide-zinc chloride-calcium bromide aqueous solutions, i.e. density, viscosity, solubility, vapour pressure, heat capacity and heat of mixing were measured in order to evaluate the performance characteristics of this system. The optimum mixing ratio of lithium bromide, zinc chloride and calcium bromide was determined by measuring the crystallization temperature of sample solutions. The optimum mixing ratio of lithium bromide, zinc chloride and calcium bromide was found to be 1.0:1.0:0.13 by mass 1'2. The enthalpies of this system at various temperatures, pressures and absorbent concentrations were calculated from physical (solubility and vapour pressure) and thermal properties (heat capacity 0140-7007/90/030191-06 © 1990 Butterworth & Co (Publishers) Ltd and IIR
and heat of mixing). The performance characteristics for absorption refrigerating machines, absorption heat pumps and absorption heat transformers have been studied by many workers z-19. The theoretical coefficient of performance (COP) was calculated by using the enthalpies at various temperatures, pressures and absorbent concentrations for the following systems: single-stage, two-stage and double-effect refrigerating machines; single-stage, double-effect and high temperature double-effect heat pumps; and single-stage and two-stage heat transformers. The performance characteristics of this four-component refrigeration, heat pump and heat transformer system were compared with those of the water-lithium bromide system and those of the other working mediumabsorbent systems using water, methanol and ammonia as working media.
Rev. Int. Froid 1990 Vol 13 Mai
191
Performance characteristics of various working media: S. lyoki and T. Uemura
Theoretical analysis For the absorption refrigerating machines, absorption heat pumps and absorption heat transformers, the following conditions were assumed for the theoretical calculations of the COP. The pressure in the generator and condenser is the vapour pressure of the working medium at condenser temperature t c. The pressure in the evaporator and absorber is the vapour pressure of the working medium at evaporator temperature t E. The work required to pump the strong solution and liquid working medium to the high pressure side of the cycle is negligible. Heat losses to the surroundings as well as pressure drops due to friction, etc. were assumed to be negligible. The effectiveness of the intermediate heat exchanger was assumed to be 1.0. A theoretical analysis was carried out to examine the effect on the performance characteristics of absorption refrigerating machines, absorption heat pumps and absorption heat transformers when their operating conditions were changed.
energy is supplied to generator (I) to liberate the working medium which flows to the condenser through generator (II). The heat (q~) supplied at generator (II) is used as the latent heat of th~ working medium vapour generated at generator (I). The working medium vapour from generator (II) is condensed in the condenser and expanded in the evaporator. The vapour is absorbed by the weak solution in the absorber. The strong solution produced in the absorber is pumped through heat exchangers (I) and (II) to generator (I). The COP of the double-effect absorption refrigerating machine is given by: COP = qE/qG,
(3)
where qE is the heat removed at the evaporator and qc, is the heat supplied at generator (I).
Absorption heat pumps Absorption refrigerating machines The single-stage absorption refrigerating machine consists primarily of a generator, an absorber, a condenser, an evaporator and a heat exchanger. Energy is supplied to the generator as heat to drive out the working medium. In the generator, the working fluid is concentrated in the absorbent by evaporating the working medium. The weak solution passes through the heat exchanger into the absorber. The working medium is then condensed in the condenser. The liquid working medium is evaporated due to the additional heat load in the evaporator. The vaporized working medium is then transferred to the absorber where it is absorbed by the weak solution. The strong solution produced in the absorber is pumped through the heat exchanger to the generator. The COP of the single-stage absorption refrigerating machine is defined as follows: COP = qE/q6
(1)
where qE is the heat removed at the evaporator and qG is the heat supplied at the generator. The two-stage absorption refrigerating machine consists primarily of two generators, two absorbers, a condenser, an evaporator and two heat exchangers. Heat energy is supplied to the high pressure generator and the low pressure generator to drive out the working medium. The working medium vapour liberated in the high pressure generator is condensed into a liquid and evaporated due to the additional heat load in the evaporator. The vapour is absorbed by the weak solution in the low pressure absorber. On the other hand, the working medium generated in the low pressure generator is absorbed by the weak solution in the high pressure absorber. The COP of the two-stage absorption refrigerating machine is given by: COP = qE/(qGrt+ qGU)
(2)
where qE is heat removed at the evaporator, q~n is heat supplied at the high pressure generator and q~L is heat supplied at the low pressure generator. The double-effect absorption refrigerating machine consists primarily of two generators, an absorber, a condenser, an evaporator and two heat exchangers. Heat
192
Int. J. Refrig. 1990 Vol 13 May
The single-stage absorption heat pump consists primarily of a generator, an absorber, a condenser, an evaporator and a heat exchanger. Energy is supplied as heat to the generator at a high temperature and to the evaporator at a low temperature. Heat is released in the absorber and condenser. The COP of the single-stage absorption heat pump is given by: COP = (qA + qc)/qG
(4)
where qA is the heat released at the absorber, qc is the heat released at the condenser and qG is the heat supplied at the generator. The double-effect absorption heat pump consists primarily of two generators, an absorber, a condenser, an evaporator and two heat exchangers. Energy is supplied to generator (I) as heat at a high temperature and to the evaporator at a low temperature. Heat is released in the absorber and condenser. The COP of the double-effect absorption heat pump is given by: COP = (qa + qc)/qG,
(5)
where qA is the heat released at the absorber, qc is the heat released at the condenser and qG, is the heat supplied at generator (I). The high temperature double-effect absorption heat pump 9 consists primarily of two generators, two absorbers, a condenser, two evaporators and two heat exchangers. Heat energy is supplied to generator (I) at a high temperature, whereas heat at a low temperature is supplied to evaporators (I) and (II). The working medium generated in generator (I) flows to evaporator (I) through generator (II). The liquid working medium is evaporated due to the additional heat load in evaporator (I) at low temperature. The vapour is absorbed by the weak solution in absorber (I). The strong solution is pumped through heat exchanger (I) to generator (I). Then the vapourized working medium in generator (II) is condensed in the condenser. The liquid working medium is evaporated due to the additional heat load in evaporator (II) at low temperature. The vapour is absorbed by a weak solution in absorber (II). The strong solution is pumped through heat exchanger (II) to generator (II). Heat is released in absorber (I), absorber
Performance characteristics of various working media: S. lyoki and T. Uemura I
I
I
(8)
COP = qAn/(q6 + qEL)
where qAH is heat released at the high pressure absorber, qG is the heat supplied at the generator and qEL is the heat supplied at the low pressure evaporator. vI
=29 .1 K Results and discussion
0,6
b. =.~2?R.1R K~~ ~ C=3
n O
TM
~ .
tc 303.15K tc=313,15K
tc:333.!5 K
0.7
-
_
tc=343.15 K 0.6"
I 323.15
tc =353.15 K
373.15
I 423.15
473.15
Generator temperature t G ( K ) Figure 1 RelationshipbetweenCOP and generatortemperature tGfor single-stage absorption refrigeratingmachine Figure 1 Relation entre le C O P et la tempdrature du gkn&ateur t o pour un rrfrigbrateur h absorption monoktag6
(II) and the condenser. The COP of the high temperature double-effect absorption heat pump is given by: C O P = (qA, + qA2 +
qc)/qG,
(6)
w h e r e qA, is the heat released at absorber (I), qA2 is the heat
released at absorber (II), qc is the heat released at the condenser and qG, is the heat supplied at generator (I).
Absorption heat transformers The single-stage absorption heat transformer consists primarily of a generator, an absorber, a condenser, an evaporator and a heat exchanger. Waste heat energy is supplied to the generator and the evaporator. In the generator, the working fluid is concentrated in the absorbent by evaporating the working medium. The weak solution is pumped through the heat exchanger to the absorber. The working medium generated in the generator is then condensed in the condenser. The liquid working medium is pumped to the evaporator, and is evaporated due to the additional waste heat load in the evaporator. The vapour is absorbed by the weak solution in the absorber. The strong solution passes through the heat exchanger into the generator. Heat is released in the absorber. The COP of the single-stage absorption heat transformer is given by:
COP=qA/(qG+qE)
(7)
where qA is the heat released at the absorber, qc is the heat supplied at the generator and qE is the heat supplied at the evaporator. The two-stage absorption heat transformer consists primarily of a generator, two absorbers, a condenser, two evaporators and two heat exchangers. The two-stage absorption heat transformer can attain a higher temperature than the single-stage absorption heat transformer. Waste heat energy is supplied to the generator and the low pressure evaporator. Heat is released in the high pressure absorber. The COP of the two-stage absorption heat transformer is given by:
Figure I shows the results of the theoretical calculations for the single-stage absorption refrigerating machine with this system. The parameter t c is the condenser temperature. The evaporator temperature t E was fixed at 281.15 K. The COP of this system decreases from 0.91 to 0.62 as t c increases from 293.15 to 353.15 K. Increasing the generator temperature t G tends to decrease the COP at constant condenser temperature t c. The most important characteristic of this system is that it can theoretically operate at a condenser temperature greater than 313.15 K. The results of the calculations for the single-stage absorption refrigerating machine are shown in Figure 2. The evaporator temperature t e and condenser temperature t c were fixed at 281.15 and 303.15 K, respectively. The results of this system were compared with those for the following working medium-absorbent systems: water-lithium bromide1 o; water-calcium chloride-lithium chloride-zinc chloride 1~; water-lithium bromide-zinc chlorideZ; water-lithium bromide-lithium thiocyanate~ z; water-lithium bromide-lithium chloride a3; and waterlithium bromide-ethylene glycol (C2H602) t4. Under these conditions, the COP of this system is better than that of the water-lithium bromide system, but is not superior to that of the water-lithium bromidelithium chloride system and that of the water-lithium bromide-ethylene glycol system. However, this system has a wide generator and condenser temperature range, compared with those of the three-component system. The results of the calculations for the two-stage absorption refrigerating machine are shown in Fioure 3. The evaporator temperature t E and condenser temperature t c were fixed at 281.15 and 303.15 K, respectively. 0.9
I
I
'~. x.~"x':.x., 2.. .... "X...'x.~'~ 3
T
tE=281.15 K tc=303.15 K 7
a_ 0.8 o t.)
--..<.. 05
I 323.15
I 373.15
Generator temperature
I 423.15 tG
(E)
Figure 2 Comparison of H20-LiBr-ZnCl2~aBr 2 system and the other systems for single-stage absorption refrigerating machine.
(1) H20-LiBr-ZnClz-CaBr2; (2) H20--LiBr; (3) H20-CaC12-LiC1ZnCI 2; (4) H20-LiBr-ZnCI 2; (5) H20--LiBr-LiSCN; (6) H20-LiBr-LiC1; and (7) H20-LiBr-C2HrO 2 Figure 2 Comparaison entre le systbme H20-LiBr-ZnC12-CaBr 2 et les autres systbmes pour une machine frigorifique & absorption monobtagbe
Rev. Int, Froid 1990 Vol 13 Mai
193
Performance characteristics of various working media. S. lyoki and T. Uemura 0.50
I
I
I
I
tE=281.15 K
f
tc=303.15 K 0.45 o
0.4 0 -
~~4
i
0.35 ..... 303.15
I
I
343.15 Generator
383.15
temperature
to
(K)
Figure 3 Comparison of H20-LiBr-ZnC12-CaBr2 system and the other systems for two-stage absorption refrigerating machine. (1) H20 LiBr-ZnCI2-CaBr2; (2) H20-LiBr; (3) H20-CaCI2-LiCIZnCI2; (4) H20-LiBr-ZnCI2; (5) H20-LiBr-LiSCN; (6) HzO-LiBr LiCI_ZnC12Js; and (7) H20-LiBr-C2H602 Figure 3 Comparaison entre le systbme H20 LiBr-ZnCl 2 CaBr 2 et les autres systbmes pour une machine .frigortfique 27 absorption bibtagke
"1
1.6
I
_
I
I
tc=303.i 5 .
-
tG2 =353.15 K
I v
O-1. 2 O (.D
",
0.8 i
~ I
393.15
I
403.15
-
I
413.15
wide generator (I) temperature range, compared with that of the water-lithium bromide system. Figure 5 shows the C O P for the single-stage, double-effect and high temperature double-effect absorption heat pump using this system. The evaporator temperature t E and generator (II) temperature tG2 were fixed at 283.15 and 358.15 K, respectively. The variation in the COP for the single-stage absorption heat pump is very small compared with the double-effect absorption heat pump. The single-stage absorption heat pump has a C O P between 1.73 and 1.90. The double-effect absorption heat pump has a C O P between 1.80 and 2.68. The high temperature double-effect absorption heat pump has a C O P between 2.31 and 2.49. The results of the calculations for the single-stage absorption heat pump are shown in Figure 6. The evaporator temperature t E and generator temperature t o were fixed at 283.15 and 373.15K, respectively. The results of this system were compared with that for the following working medium-absorbent systems: waterlithium bromidel°; water-lithium bromide-zinc bromide-lithium chloride16; water-lithium bromide-zinc chloride2; water-lithium bromide-zinc bromide 1T; and methanol-lithium bromide-zinc bromide 18. Under these conditions, the C O P of this system is better than that of the other systems. This system has a wide attainable temperature range, compared with that of the water-lithium bromide system. The results of the calculations for the high temperature double-effect absorption heat pump are shown in Figure 7. The evaporator temperature tE, generator (I) temperature to, and generator (II) temperature tG2 were fixed at 283.15, 423.15 and 368.15K, respectively. The results of this system were compared with that of the water-lithium bromide system 1° and that of the water-lithium bromide-zinc bromide-lithium chloride system 16. Under these conditions, the C O P of this system is better than that of the other systems. This system has a wide attainable temperature range.
I
423.15 2.8
Generator(I)
temperature
b
tG1 ( K )
Figure 4 Comparison of H20-LiBr-ZnCl2~aBr 2 system and the other systems for double-effect absorption refrigerating machine. (1) H20-LiBr-ZnC124SaBr2; (2) H20-LiBr; (3) H20-LiBr-ZnC12; (4) H20-LiBr-LiCI ZnCl215; (5) H20-LiBr-ZnBr2-LiCI; and (6) H20-CaCI2-LiC1 ZnC12 Figure 4 Comparaison entre le systbme H20-13Br-ZnCI2-CaBr 2 et les autres syst~mes pour un r~friy&ateur h absorption h double effet
194
Int. J. Refrig. 1 9 9 0 Vol 13 M a y
I tE=283.15 K
/ /
I
tG2=358.15 K
/ 2.4 --
-- ~ ' - ~ / . . . ~ _ _
~tGI=423.15 K ~
t'~ tG1=403.15K
O U
2.0-
The results of this system were compared with those of the other systems using water as the working medium. The advantage of this system is that it has a wide generator temperature range, compared with the other systems. The results of the calculations for the double-effect absorption refrigerating machine are shown in Figure 4. The evaporator temperature, condenser temperature and generator (II) temperature to, were fixed at 283.15, 303.15 and 353.15 K, respectively. The results obtained with this system were compared with those of the other systems using water as the working medium. Under these conditions, the C O P of this system is better than that of the water-lithium bromide system ~°. This system has a
I
tG1=393.15 K
•
1.61
~ ~ ~
tG1=433.15 K "~tGi=443.15 K
tG1 =413.15 K t~1=423.15K~
~ ~
~
tG=353.15K
I
I
293.15
303.15
Attainable
temperature
I t6=t'13.15 K 313.15
323J5
tc (K)
Figure 5 Coefficientof performancefor single-stage,double-effectand high temperature double-effectabsorption heat pump. ( ) Singlestage; (- - -) double-effect;and (-- ---) high temperaturedouble-effect
Figure 5 COP d'une pompe it chaleur mono~tagbe, d'une pompe 27 chaleur h double effet et d'une pompe it chaleur it absorption it double effet et haute tempbrature. (--) Monobtagbe; ( - - - ) double effet; et ( - - - ) double effet et haute temperature
Performance characteristics of various working media." S. lyoki and T. Uemura
2.0
The results of the calculations for the two-stage absorption heat transformer are shown in Figure 9. The condenser temperatures were fixed at 283.15 and 303.15 K. The generator temperatures t C were fixed at
I tE=283.15 K
l
4 %
v
1.9
tG=373"15K
0.53
I
I
I
tc =283.15K
-
tG;323"15K
t ~ -- ~ ~ 2
Q.
0.51
0 (J
•
/ / /
]
1.8-
/ ~ -
5"--
/
/,/
. /
-6
0.49 13.. O U 0.47 -
1.;-
I 293.5
273.15
,
I 313.15
333.15
f100~ 0.45 -
Attainable t e m p e r a t u r e t c ( K ) Figure 6 Comparison of H20-LiBr-ZnC12-CaBr2 system and the other systems for single-stage absorption heat pump. (1) HEO-LiBrZnC12--CaBr2; (2) H20-LiBr; (3) H20-LiBr-ZnBr2-LiCI; (4) H20LiBr-ZnC12; (5) H20-LiBr-ZnBr2; and (6) CHaOH-LiBr-ZnBr 2 Figure 6 Comparaison entre le systbme H 2 0 - L i B r - Z n C I 2 - C a B r 2 et les
t
0.43 I 313.15
autres systbmes pour une pompe ~ chaleur it absorption rnonobtagbe
2.5
I
I
I
I
I v
I
i
353.15 Attainable
393.15
temperature
tA ( K )
Figure 8 Comparison of H20-LiBr-ZnCI2-CaBr2 system and the
other systems for single-stage absorption heat transformer. (1) H20LiBr-ZnC12-CaBr2; (2) H20-LiBr; (3) H20-LiBr-ZnBr2; (4) H20LiBr-ZnBr2-LiC1; (5) H20-CaCI2-LiCI-ZnC12; (6) CHaOH-LiBrZnBr2; and (7) NHa-H20 (tG=322.15 K) Figure 8 Comparaison entre le systkme H 20-LiBr-ZnCI2-CaBr 2 et les autres systbmes pour un transformateur de chaleur it absorption rnonobtagb
13. 2.3 O u --
0.34 tE= 283.15 K
-4.3
tG1=423.15 K
/
/
X
/
"4",.
tG2=368.15 K
2.1 I 293.15
I
/
I
I
I
303.15
313.15
323.15
Attainable temperature t C (K) Figure 7 Comparison of H20-LiBr-ZnCI2-CaBr2 system and the other systems for high temperature double-effect absorption heat pump. (1) H20-LiBr-ZnCI2-CaBr2; (2) I-[20-LiBr; and (3) H20-LiBrZnBr2-LiC1 Figure 7 Comparaison entre le systbme H 20-LiBr-ZnCI2-CaBr 2 et les
--
I
\
tc=283.15 K \ \ . tG=333.15K \
/
/
I
/
\
/
/
tc =303.15K t~=333.15K
/--'/'---/
0.32
t
)/ ~ ~ t G = 3 4 3 . 1 5
\ \
tc =303.15 K K
x\ \, \
_
autres systbmes pour une pompe it chaleur it absorption it double effet et it haute temprrature
The results of the calculations for the single-stage absorption heat transformer are shown in Figure 8. The condenser temperature tc and generator temperature to were fixed at 283.15 and 323.15K (except for the ammonia-water system), respectively. The generator temperature of the ammonia-water system was fixed at 322.15 K. The results of this system were compared with those of the other systems using water, methanol and ammonia as working media. Under these conditions, the C O P of this system is not superior to that of the other systems except for the water-calcium chloride-lithium chloride-zinc chloride system 11 and the ammonia-water system 19.
0.3C 333.1E
I 373.15 Attainable
I 413.15 temperature
I 453.15 tAH
(K)
Figure 9 Comparison of H20-LiBr-ZnCl2~aBr 2 system and H20-LiBr system for two-stage absorption heat transformer. ( ) H20-LiBr-ZnCI2-CaBr2; ( - - - ) H20-LiBr Figure 9 Comparaison entre le syst~me H 2 0 - L i B r - Z n C I 2 - C a B r 2 et le systkme H 2 0 - L i B r pour un transformateur de chaleur it absorption bidtag~
Rev. Int. Froid 1990 Vol 13 Mai 195
Performance characteristics of various working media: S. lyoki and 1". Uemura 333.15 a n d 343.15K. The results of this system were c o m p a r e d with those of the w a t e r - l i t h i u m b r o m i d e system 1o. The C O P of this system is not superior to that of the w a t e r - l i t h i u m b r o m i d e system at a c o n d e n s e r t e m p e r a t u r e of 283.15 K and a g e n e r a t o r t e m p e r a t u r e of 333.15 K. H o w e v e r , the w a t e r - l i t h i u m b r o m i d e system c a n n o t o p e r a t e at a c o n d e n s e r t e m p e r a t u r e of 303.15 K. O n the other h a n d , this system has a wide condenser and g e n e r a t o r t e m p e r a t u r e range.
5 6 7
8 9
Conclusions
The theoretical C O P values of the w a t e r - l i t h i u m b r o m i d e - z i n c c h l o r i d e - c a l c i u m b r o m i d e system were calculated for the single-stage, two-stage a n d d o u b l e effect a b s o r p t i o n refrigerating machines, single-stage, double-effect and high t e m p e r a t u r e double-effect a b s o r p tion heat p u m p s , and single-stage a n d two-stage a b s o r p t i o n heat transformers at various o p e r a t i n g conditions. In a d d i t i o n , the C O P of this system was c o m p a r e d with that of the other systems using water, m e t h a n o l a n d a m m o n i a as w o r k i n g media. This system can o p e r a t e as an a i r - c o o l e d single-stage a b s o r p t i o n refrigerating m a c h i n e a n d m a y be a d o p t e d in c o m m e r c i a l designs. This system was found to be suitable for a single-stage a b s o r p t i o n refrigerating machine, a singlestage, high t e m p e r a t u r e double-effect a b s o r p t i o n heat p u m p and a two-stage a b s o r p t i o n heat transformer.
10 II
12 13
14 15
performance analysis of absorption heat pumps for waste heat utilization Int J Refri9 (1982) 5 361 Perez-Blaneo, H. Absorption heat pump performance for different types of solutions lnt J Refrig (1984) 7 115 Bokelmann, H. and Steimle, F. Development of advanced heat transformers utilizing new working fluids Int J Refri9 (1986) 9 51 Vliet, G. C., Lawson, M. B. and Lithgow, R. A. Water-lithium bromide double-effect absorption cooling cycle analysis ASHRAE Trans (1982) 88 Part I 811 Tyagi, K. P. and Rag, K. S. Choice of absorbent-refrigerant mixtures Int J Eng Res (1984) 8 361 Takada, S. Kyushureitoki Japanese Association of Refrigeration, Tokyo, Japan (1982) Uemura, T. and Hasaba, S. Studies on the lithium bromide-water absorption refrigerating machine Technol Rep Kansai Univ (1964) No. 6 31 Uemura, T. and Iyoki, S. Physical, thermodynamic properties and performance characteristics of absorption heat pump using water as working medium Reports on Research and Survey of Heat Pump Technology Japanese Association of Refrigeration, Tokyo, Japan (1987) 267 lyoki, S., Hanafusa, Y., Koshiyama, H. and Uemura, T, Studies on the water-lithium bromide-lithium thiocyanate absorption refrigerating machine Reito (Japan) (1981) 56 661 Hasaba, S. and Uemura, T. Studies on the water-lithium bromide-lithium chloride absorption refrigerating machine Proceedings of the 4th Air Conditioning and Refrigeration Conference Tokyo, Japan (1970) 39 Iyoki, S. and Uemura, T. Studies on the water-lithium bromide-ethylene glycol absorption refrigerating machine Reito (Japan) (1981) 56 279
Takigawa, T., Nakanishi, M., lyoki, S. and Uemura, T. Studies on the water-lithium bromide-lithium chloride-zinc chloride absorption refrigerating machine and absorption heat pump Proceedings of the 1986 Japanese Association of Refrigeration Annual Conference Japanese Association of Refrigeration,
References
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Iyoki, S. and Uemura, T. Physical and thermal properties of the watei--lithium bromide-zinc chloride-calcium bromide system Int J Refrig (1989) 12 272 Uemura, T, and lyoki, S. Studies on the water lithium bromide zinc chloride absorption refrigerating machine Proceedings of 1982 Japanese Association of Refrigeration Annual Conference Japanese Association of Refrigeration, Tokyo, Japan
3 4
196
(1982) 17 Iedema, P. D. Mixtures for the absorption heat pump lnt d Refri9 (1982) 5 262 Grossman, G. and Perez-Blaneo, H. Conceptual design and
Int. J. Refrig. 1990 Vol 13 May
16 17
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