Thermoeconomic optimization for irreversible absorption refrigerators and heat pumps

Thermoeconomic optimization for irreversibleabsorption refrigerators and heat pumps

Ali Kodal a, Bahri Sahin b,*, Ismail Ekmekci c, Tamer Yilmaz b

a Department of Aeronautical Engineering, Istanbul Technical University, Maslak, 80626 Istanbul, Turkeyb Department of Naval Architecture, Yildiz Technical University, Besiktas, 80750 Istanbul, Turkeyc Department of Mechanical Engineering, Sakarya University, Esentepe, 54040 Adapazari, Turkey

Received 31 July 2001; accepted 26 December 2001

Abstract

A performance analysis using finite time thermodynamic based on a thermoeconomic objective functionhas been performed for absorption irreversible refrigerators and heat pumps. The optimal design para-meters at the maxima of the thermoeconomic objective functions for an absorption refrigerator and heatpump have been derived analytically, and the effects of the internal irreversibility, the economical parameterand the external temperatures on the global and optimal performances have been discussed.� 2002 Elsevier Science Ltd. All rights reserved.

Keywords: Absorption refrigerator; Absorption heat pump; Finite time thermodynamics; Thermoeconomic optimi-

zation

1. Introduction

Absorption refrigerators and heat pumps utilize ‘‘low-grade’’ heat energy, such as waste heat inmany industrial processes, heat engines, solar energy and geothermal energy. They have a largepotential for saving primary energy and decreasing environmental thermal pollution [1,2]. In thelast decade, many optimization and modeling studies for real absorption refrigerators and heatpumps, based on various performance criteria, have been performed by considering finite timeand finite size constraints [1–14]. In these studies, the optimal performance characteristics havebeen investigated for the coefficient of performance [1–7], cooling or heating load [1,8–10], specific

Energy Conversion and Management 44 (2003) 109–123www.elsevier.com/locate/enconman

*Corresponding author. Fax: +90-212-258-2157.

E-mail address: [email protected] (B. Sahin).

0196-8904/03/$ - see front matter � 2002 Elsevier Science Ltd. All rights reserved.

PII: S0196-8904(02)00046-8

mail to: [email protected]

cooling or heating load [11–13] and total heat transfer area objectives [14] by taking into accountabsorption refrigerators and heat pumps models operating between three or four temperaturelevels. In the above referenced works, the objective functions chosen for optimization of theabsorption refrigerators and heat pumps do not take account of the effect of economical aspects.For an economical design, more recently, Sahin and Kodal [15] have introduced a new finite timethermoeconomic performance criterion, defined as the cooling load for refrigerators and theheating load for heat pumps per unit total cost (total of investment and energy consumptioncosts). Based on this criterion, they investigated the economic design conditions of single stageand two stage vapor compression refrigerators and heat pumps [15–18]. In this paper, the finite

Nomenclature

a investment cost parameter for heat exchangersA heat transfer areab energy consumption cost parameterC costF objective functionk a/bncu national currency unit_QQ rate of heat transferS entropyT temperatureU overall heat transfer coefficiente coefficient of performance

SubscriptsA absorberC condensere energy consumptionH high temperature heat sourcehp heat pumpi investmentK heat sinkL low temperature heat sourcemax maximummscl maximum specific cooling loadref refrigeratorX working fluid in generatorY working fluid in evaporatorZ working fluid in condenser and absorber

Superscripts� optimum conditions

110 A. Kodal et al. / Energy Conversion and Management 44 (2003) 109–123

time thermoeconomic optimization technique, first introduced by Sahin and Kodal [15], has beenextended to irreversible absorption refrigerators and heat pumps.

2. The model and performance optimization for an irreversible absorption refrigerator

The main components of an absorption refrigeration system are a generator, an absorber, acondenser and an evaporator, as shown schematically in Fig. 1 [1,3,11,13]. In the model shown,_QQH is the heat input rate from the heat source at temperature TH to the generator, _QQC and _QQA are,respectively, the heat rejection rates from the condenser and the absorber to the heat sinks attemperatures TC and TA, and _QQL is the heat input rate from the cooling space at temperature TL tothe evaporator. In absorption systems, usually NH3/H2O and LiBr/H2O are used as the workingsubstances, and these substances abide by ozone depletion regulations, since they do not consist ofchlorofluorocarbons. In Fig. 1, the liquid rich solution at state 1 is pressurized to state 10 with apump. In the generator, the working fluid is concentrated to state 3 by evaporating the workingmedium by means of _QQH heat rate input. The weak solution at state 2 passes through the ex-pansion valve into the absorber with a pressure reduction (2–20). In the condenser, the workingfluid at state 3 is condensed to state 4 by removing _QQC heat rate. The condensed working fluid atstate 4 is then throttled by a valve and enters the evaporator at state 40. The liquid working fluid isevaporated due to heat transfer rate _QQL from the cooling space to the working fluid (40–5). Finally,the vaporized working fluid is absorbed by the weak solution in the absorber, and by means of _QQAheat rate release in the absorber, state 1 is reached.Absorption refrigerator systems operate between three temperature levels, if TA ¼ TC, or four

temperature levels when TA 6¼ TC. In this work, by taking TA ¼ TC, a three temperature level ir-reversible absorption model is considered. The three temperature level model is used by manyresearchers in the literature [1,2,6–10,12,14]. The considered model and its equivalent T–S dia-gram are demonstrated in Fig. 2. In this figure, _QQK is the sum of _QQA and _QQC. TX and TY are,respectively, the temperatures of the working fluid in the generator and evaporator, and it is

Fig. 1. Schematic diagram of absorption refrigeration system.

A. Kodal et al. / Energy Conversion and Management 44 (2003) 109–123 111

assumed that the working fluid in the absorber and condenser, which exchanges heat with the heatsink at the same temperature (TA ¼ TC ¼ TK) has the same temperature TZ (see [1,6,7] for a similarassumption).The heat exchanges between the working fluid and heat reservoirs obeys a linear law [3,7,9,10],

so that one has

_QQL ¼ ULALðTL � TY Þ; ð1Þ

_QQH ¼ UHAHðTH � TX Þ; ð2Þ

_QQK ¼ UKAKðTZ � TKÞ; ð3Þwhere UL, UH and UK are, respectively, the coefficients for heat transfer between the working fluidand the heat reservoirs at temperatures TL, TH and TK, and AL, AH, and AK are the correspondingheat transfer areas. The work required by the solution pump is negligible relative to the heat inputto the generator and, therefore, is often neglected in the analysis [3,11,13]. The first law ofthermodynamics requires

_QQH þ _QQL � _QQK ¼ 0: ð4ÞThe external irreversibilities arise from the temperature differences between the working fluid

and the heat sources. On the other hand, the internal irreversibilities result from friction, masstransfer and other working fluid dissipations. The total effect of the internal irreversibilities on theworking fluid can be characterized in terms of entropy production [1,2,6]. We introduce a pa-rameter

I ¼ DSZDSX þ DSY

; ð5Þ

Fig. 2. Considered irreversible absorption refrigeration model and its T–S diagram.


to characterize the internal irreversibility. On the basis of the second law of thermodynamics,DSZ > DSX þ SY for an internally irreversible cycle, so that I > 1. If the internal irreversibility canbe neglected, the cycle is endoreversible and so I ¼ 1. From the second law of thermodynamics,one has

_QQKTZ

�_QQHTX

�_QQLTY

P 0: ð6Þ

By combining Eqs. (5) and (6), we can write

_QQKTZ

� I_QQHTX

þ

_QQLTY

!¼ 0: ð7Þ

From Eqs. (1)–(7), we obtain the coefficient of performance (eref ) and the specific cooling loadof the absorption refrigerator cycle, respectively, as

eref ¼_QQL_QQH

¼ TY ðITZ � TX ÞTX ðTY � ITZÞ

: ð8Þ

_qqL ¼_QQLA

¼ 1

UHðTH � TX ÞTX ðITZ � TY ÞTY ðTX � ITZÞ

�þ 1

ULðTL � TY Þþ 1

UKðTZ � TKÞITZðTX � TY ÞTY ðTX � ITZÞ

��1; ð9Þ

where A ¼ AH þ AL þ AK.We consider optimization of the cooling load per unit total cost in order to account for both

investment and energy consumption costs. The function to be optimized is defined as [15]

Fref ¼ _QQL= Cið þ CeÞ; ð10Þ

where Ci and Ce refer to annual investment and energy consumption costs, respectively. The in-vestment cost of the absorption system is assumed to be proportional to the system size, whichmay be considered as the total heat transfer areas.

Ci ¼ aðAH þ AL þ AKÞ; ð11Þ

where the proportionality coefficient for the investment cost of the system, a, is equal to thecapital recovery factor times the investment cost per unit heat transfer area, and its dimension isncu/(year m2). The annual energy consumption cost is proportional to the heat rate input, i.e.

Ce ¼ b _QQH; ð12Þ

where the coefficient b is equal to the annual operation hours times price per unit energy, and itsdimension is ncu/(year kW). Substituting Eqs. (12) and (11) into Eq. (10), we get

Fref ¼ _QQL=baðAH þ AL þ AKÞ þ b _QQHc: ð13Þ

It should be noted that the objective function defined by Eq. (13) stands as a more general formfor some of the objective functions used in the literature [1–14]. For example, for the special caseof a ¼ 1 and b ¼ 0, the objective function becomes the specific cooling load and for a ¼ 0 andb ¼ 1, it becomes the coefficient of performance.


Using Eqs. (1)–(7) in Eq. (13), we obtain

bFref ¼1

TX ðTY�ITZ ÞTY ðITZ�TX Þ 1þ

kUHðTH�TX Þ

h iþ k

ULðTL�TY Þ þkITZ ðTY�TX Þ

UKTY ðITZ�TX ÞðTZ�TKÞ

; ð14Þ

where k ¼ a=b is the economical parameter. The objective function given in Eq. (14) can beplotted with the respect to the performance coefficient (Eq. (8)) and with respect to the specificcooling load (Eq. (9)) for various I and k values, as shown in Figs. 3–6a. As seen from the figures,there exist optimal performance coefficients and also specific cooling loads which maximize theobjective function for given I and k values. Since the eref and _qqL are functions of TX , TY and TZ , theobjective function given in Eq. (14) can be maximized with respect to TX , TY and TZ . The results are

T �X

TH¼

KRffiffiffiffiffiffiUKIUH

qþ THUK

kI þffiffiffiffiffiTHITK

q ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiK2R þ UKðTH=I�TKÞ

k

qTHUKkI þ KR

ffiffiffiffiffiTHITK


k

q ; ð15Þ

T �Y

TL¼


qþ THUK



k

qK

ffiffiffiffiffiffiUKIUH

q�

ffiffiffiffiffiffiUKIUL

q þ THUK

kI þ 1þffiffiffiffiffiffiUKIUL

q ffiffiffiffiffiTHITK


k

q ; ð16Þ

T �Z

TK¼


qþ THUK



k

qK2R þ THUK

kI

; ð17Þ

Fig. 3. Variations of the objective function for the refrigerator (a) and for the heat pump (b) with respect to the co-

efficient of performance, for various I values (TH ¼ 393 K, TL ¼ 280 K, TK ¼ 303 K for the refrigerator and TH ¼ 393 K,TL ¼ 288 K, TK ¼ 313 K for the heat pump, UK ¼ UH ¼ UL ¼ 0:5 kW/m2 K, k ¼ 0:5).


Fig. 4. Variations of the objective function for the refrigerator (a) and for the heat pump (b) with respect to the co-

efficient of performance, for various k values (TH ¼ 393 K, TL ¼ 280 K, TK ¼ 303 K for the refrigerator and TH ¼ 393K, TL ¼ 288 K, TK ¼ 313 K for the heat pump, UK ¼ UH ¼ UL ¼ 0:5 kW/m2 K, I ¼ 1).

Fig. 5. Variations of the objective function for the refrigerator with respect to the specific cooling load (a) and for the

heat pump with respect to the specific heating load (b) for various I values (TH ¼ 393 K, TL ¼ 280 K, TK ¼ 303 K for therefrigerator and TH ¼ 393 K, TL ¼ 288 K, TK ¼ 313 K for the heat pump, UK ¼ UH ¼ UL ¼ 0:5 kW/m2 K, k ¼ 0:5).


where KR ¼ 1þffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiUK=IUH

p. Substituting the optimal temperatures given in Eqs. (15)–(17) into

Eqs. (8) and (9), one can obtain the optimum performance coefficient and the specific cooling loadof the absorption refrigerator.The optimal distributions of the heat exchanger areas can also be found for a given total heat

transfer area (i.e. A ¼ AH þ AL þ AK) as,

Fig. 6. Variations of the objective function for the refrigerator with respect to the specific cooling load (a) and for the

heat pump with respect to the specific heating load (b) for various k values (TH ¼ 393 K, TL ¼ 280 K, TK ¼ 303 K forthe refrigerator and TH ¼ 393 K, TL ¼ 288 K, TK ¼ 313 K for the heat pump, UK ¼ UH ¼ UL ¼ 0:5 kW/m2 K, I ¼ 1).


AHA

� �

¼ 1

�þ

ffiffiffiffiffiffiffiUHUL

rIT �

Z � T �X

T �Y � IT �

Zþ

ffiffiffiffiffiffiffiffiIUHUK

rT �Y � T �

X

T �Y � IT �

Z

��1; ð18Þ

ALA

� �

¼ 1

�þ

ffiffiffiffiffiffiffiULUH

rT �Y � IT �

Z

IT �Z � T �

Xþ

ffiffiffiffiffiffiffiffiIULUK

rT �Y � T �

X

IT �Z � IT �

X

��1; ð19Þ

AKA

� �

¼ 1

�þ

ffiffiffiffiffiffiffiffiUKIUH

rT �Y � IT �

Z

T �Y � T �

Xþ

ffiffiffiffiffiffiffiffiUKIUL

rIT �

Z � T �X

T �Y � T �

X

��1: ð20Þ

3. Performance optimization for an irreversible absorption heat pump

The models given in Figs. 1 and 2 for an irreversible absorption refrigerator hold schematicallyfor an irreversible absorption heat pump also. However, in this case TK is the temperature of theheated space and TL is the ambient temperature. Therefore, Eqs. (1)–(7) can be used for an ir-reversible absorption heat pump. The coefficient of performance (ehp) and specific heating load( _qqK) can be written as,

ehp ¼_QQK_QQH

¼ ITZðTY � TX ÞTX ðTY � ITZÞ

: ð21Þ

_qqK ¼_QQKA

¼ 1

UHðTH � TX ÞTX ðITZ � TY ÞITZðTX � TY Þ

�þ 1

UKðTZ � TKÞþ 1

ULðTL � TY ÞTY ðITZ � TX ÞITZðTY � TX Þ

��1: ð22Þ

The objective function to be optimized for the heat pump is defined as the heating load per unittotal cost, i.e.

Fhp ¼ _QQK=baðAH þ AL þ AKÞ þ b _QQHc: ð23ÞUsing Eqs. (1)–(7) in Eq. (23), we obtain

bFhp ¼1

TX ðTY�ITZ ÞITZ ðTY�TX Þ 1þ

kUHðTH�TX Þ

h iþ kTYðITZ�TX Þ

ULITZ ðTL�TY ÞðTY�TX Þ þk

UKðTZ�TKÞ

ð24Þ

Eq. (24) can be maximized with respect to TX , TY and TZ. The results are

T �X

TH¼

�KHffiffiffiffiffiUHUL

q� TLUH

k þffiffiffiffiTLTH

q ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiK2H þ UHðTH�TLÞ

k

qK2H � TLUH

k

; ð25Þ


T �Y

TL¼


q� TLUH



k

q� TLUH

k þ KHffiffiffiffiTLTH


k

q ; ð26Þ

T �Z

TK¼


q� TLUH



k

q�KH

ffiffiffiffiffiUHUL

q�

ffiffiffiffiffiffiIUHUK

q � TLUH

k þ 1þffiffiffiffiffiffiIUHUK

q ffiffiffiffiTLTH


k

q ; ð27Þ

where KH ¼ 1�ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiUH=UL

p. Substituting the optimal temperatures given in Eqs. (25)–(27) into Eqs.

(21) and (22), one can obtain the optimum performance coefficient and the specific heating load ofthe absorption heat pump.The optimal distributions of the heat exchanger areas can also be found for a given total heat

transfer area (i.e. A ¼ AH þ AL þ AK), similar to Eqs. (23)–(25). However, in this case, the optimaltemperatures are different.

4. Discussion

The variations of the objective function for the absorption refrigerator and heat pump withrespect to the coefficient of performance for various internal irreversibility parameter values (I)and the economical parameter values (k) are shown in Figs. 3 and 4. From these figures, onecan observe the effect of the internal irreversibility and economical parameters on the generaland optimal performance. As the internal irreversibility and the economical parameters increasethe F � e characteristics and the optimal performance coefficient reduce significantly for boththe absorption refrigerator and heat pump. Eq. (8) for the absorption refrigerator and Eq. (21)for the absorption heat pump show that when there is no finite rate heat transfer irreversibility,i.e. TH ¼ TX , TL ¼ TY and TK ¼ TZ , e is equal to emax. In this case, from Eqs. (8) and (21), weobtain,

emaxð Þref ¼TLðITK � THÞTHðTL � ITKÞ

; ð28Þ

emaxð Þhp ¼ITKðTL � THÞTHðTL � ITKÞ

: ð29Þ

When e ¼ emax, the objective functions of the refrigerator and heat pump (Fref and Fhp) becomezero, as shown in Fig. 3a and b. Therefore, the upper bounds of the performance coefficientsgiven in Eqs. (28) and (29) do not have very much instructive significance for practical appli-cations. It is also seen from Fig. 3a and b that very large differences exist between the optimalperformance coefficient and the maximum performance coefficient. However, this difference re-duces with increased internal irreversibility but increases with increased economical parameter(Fig. 4a and b). The effects of I and k on the F � q characteristics of the absorption refrigerator


and heat pump are shown in Figs. 5 and 6. For the refrigerator the F � _qqL characteristic curvesare loop-shaped, passing through the origin, and differ from those of the F � _qqK of the heatpump. In Figs. 5a and 6a, the operation region described by the arc, _qq�L6 _qqL6 _qqL max, for theabsorption refrigeration system for given I and k has practical importance in terms of the plantobjective and installation location. For the economical objectives, the point (Fmax, _qq�L) and for thespecific cooling load objectives, the point (Fmscl, _qqL max) should be the design conditions (Fmscl isthe objective function at maximum specific cooling load). For mixed objectives, the designconditions would be between these two extremes. As the internal irreversibility and the eco-nomical parameter increase, the arc _qq�L6 _qqL6 _qqL max becomes narrower, and thus, _qq�L and _qqL maxget closer. In Figs. 7 and 8, the effects of internal irreversibility and economical parameter on theoptimal performances for the absorption refrigerator and heat pump (e�ref , _qq

�L;e

�hp, _qq

�K) can be seen

more clearly. By examining Fig. 7a and b, we see that the reducing effect of the internal irre-versibility on e�ref is greater in comparison to that on e�hp. It is also seen from these figures that forincreasing internal irreversibility, the optimum specific cooling load, _qq�L, decreases, while theoptimum specific heating load, _qq�K increases. From Fig. 8a and b, for the absorption refrigeratorand heat pump, we observe that the optimal performance coefficients decrease and the optimalcooling and heating loads increase as the economical parameter increases, and the curves are innear parabolic forms. It should be noted that k emphasizes the relative investment cost withrespect to the energy consumption cost. The increase in k means the relative increase in theinvestment cost, and this causes reduced heat exchanger areas due to economical reasons and,thus, for given cooling or heating load ( _QQL, _QQK), leads to increases in the specific loads ( _qq�L, _qq

�K).

Fig. 7. Effects of the internal irreversibility on the optimal coefficient of performance and specific cooling load for

absorption refrigerator (a) and on the optimal coefficient of performance and specific heating load for absorption heat

pump (TH ¼ 393 K, TL ¼ 280 K, TK ¼ 303 K for the refrigerator and TH ¼ 393 K, TL ¼ 288 K, TK ¼ 313 K for the heatpump, UK ¼ UH ¼ UL ¼ 0:5 kW/m2 K, k ¼ 0:5).


The reason for the decrease in the optimal performance coefficients for increased k is the in-creased finite temperature difference heat transfer irreversibilities at the heat exchangers due tothe reduced heat transfer areas. The variations of the optimal performance coefficient andspecific cooling load with respect to the cooling space temperature for the absorption refrigeratorand the variations of the optimal performance coefficient and the specific heating load withrespect to the heated space temperature are shown in Fig. 9a and b, respectively. As shown inFig. 9a, as the cooled space temperature increases, the performance coefficient and the specificcooling load of the absorption refrigerator increase monotonically. As the heated space tem-perature increase, the optimum performance coefficient of the absorption heat pump mono-tonically decreases, however the optimum specific heating load increases linearly (Fig. 9b). Thevariations of the optimal distributions of the heat exchanger areas for the absorption refrigeratorand heat pump with respect to the internal irreversibility parameter, the economical parameterand the cooling or heating space temperature are given in Figs. 10–12, respectively. From thesefigures, we see that the optimum distribution of the heat exchanger areas for the total of theabsorber and condensersides, AK=Að Þ�, is independent of k and TL or TK, and it stays constant at0.5 (i.e., A�

K ¼ A�H þ A�

L). However, it deviates from 0.5 very slightly with the internal irrevers-ibility. On the other hand, the optimal distributions of the heat exchanger areas for the generatorside ðAH=AÞ� and the evaporator side ðAL=AÞ� are strongly dependent on I, k and TL or TK. Thearea ratio ðAH=AÞ� increases and ðAL=AÞ� decreases for increasing I, k and TK (Figs. 10, 11 and12b). However, ðAH=AÞ� decreases and ðAL=AÞ� increases for increasing TL, the cooled spacetemperature for the absorption refrigeration case (Fig. 12a).

Fig. 8. Effects of the economical parameter, k, on the optimal coefficient of performance and specific cooling load for

absorption refrigerator (a) and on the optimal coefficient of performance and specific heating load for absorption heat

pump (TH ¼ 393 K, TL ¼ 280 K, TK ¼ 303 K for the refrigerator and TH ¼ 393 K, TL ¼ 288 K, TK ¼ 313 K for the heatpump, UK ¼ UH ¼ UL ¼ 0:5 kW/m2 K, I ¼ 1).


Fig. 10. Variations of the optimal heat transfer area distributions with respect to the internal irreversibility parameter

for the absorption refrigerator (a) and for the absorption heat pump (b) (TH ¼ 393 K, TL ¼ 280 K, TK ¼ 303 K for therefrigerator and TH ¼ 393 K, TL ¼ 288 K, TK ¼ 313 K for the heat pump, UK ¼ UH ¼ UL ¼ 0:5 kW/m2 K, k ¼ 0:5).

Fig. 9. Effects of the cooled space temperature on the optimal coefficient of performance and specific cooling load for

absorption refrigerator (a) and the effects of the heated space temperature on the optimal coefficient of performance and

specific heating load for absorption heat pump (TH ¼ 393 K, TK ¼ 303 K for the refrigerator and TH ¼ 393 K, TL ¼ 288K for the heat pump, UK ¼ UH ¼ UL ¼ 0:5 kW/m2 K, k ¼ 0:5).


Fig. 11. Variations of the optimal heat transfer area distributions with respect to the economical parameter for the

absorption refrigerator (a) and for the absorption heat pump (b) (TH ¼ 393 K, TL ¼ 280 K, TK ¼ 303 K for the re-

frigerator and TH ¼ 393 K, TL ¼ 288 K, TK ¼ 313 K for the heat pump, UK ¼ UH ¼ UL ¼ 0:5 kW/m2 K, I ¼ 1).

Fig. 12. Variations of the optimal heat transfer area distributions with respect to the cooled space temperature for the

absorption refrigerator (a) and with respect to the heated space temperature for the absorption heat pump (b) (TH ¼ 393K, TK ¼ 303 K for the refrigerator and TH ¼ 393 K, TL ¼ 288 K for the heat pump, UK ¼ UH ¼ UL ¼ 0:5 kW/m2 K,

k ¼ 0:5, I ¼ 1).


5. Conclusion

A thermoeconomic optimization study is performed to determine the optimal operation anddesign parameters for irreversible absorption refrigerator and heat pump systems. By maximizingthe defined thermoeconomic objective function for the irreversible absorption refrigerator andheat pump, we have obtained analytical relations for optimal working and design conditions, suchas the working fluid temperatures and the heat transfer area distributions. The primary perfor-mances, such as performance coefficients, heat exchanger area distributions and specific cooling orheating loads at maximum objective function conditions are investigated. The effects of the in-ternal irreversibility, the economical parameter and the external temperatures on the global andoptimal performances were demonstrated with plots and discussed. The optimal design para-meters can be easily obtained by the given analytical method for varying technical and economicalconditions. The performed study may constitute a basis for the design of real absorption refrig-erator and heat pump systems.

References

[1] Chen J, Schouten JA. Energ Convers Manage 1998;39:999–1007.

[2] Lin G, Yan Z. J Phys D 1999;32:94–8.

[3] Chen J, Andresen B. Heat Recov Syst CHP 1995;15:723–31.

[4] Goktun S, Ozkaynak S. Energy 1997;22:481–5.

[5] Goktun S, Yavuz H. J Phys D 1997;30:3317–21.

[6] Chen J. J Phys D 1997;30:582–7.

[7] Chen J. Energ Convers Manage 1994;35:1009–14.

[8] Yan Z, Chen J. J Appl Phys 1989;65:1–4.

[9] Bejan A, Vargas JVC, Sokolov M. Int J Heat Mass Transfer 1995;38:2997–3004.

[10] Wijeysundera NE. Energy 1995;20:123–30.

[11] Chen J. Energy 1995;20:995–1003.

[12] Chen J. J Phys D 1997;30:2953–7.

[13] Chen J. J Phys D 1999:3085–91.

[14] Chen J. Energy 1994;19:1031–6.

[15] Sahin B, Kodal A. Energ Convers Manage 1999;40:951–60.

[16] Kodal A, Sahin B, Yilmaz T. Energ Convers Manage 2000;41:607–19.

[17] Kodal A, Sahin B, Oktem AS. Energ Convers Manage 2000;41:1989–98.

[18] Sahin B, Kodal A, Koyun A. Energ Convers Manage 2001;42:451–65.


Thermoeconomic optimization for irreversible absorption refrigerators and heat pumps

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