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Applied Thermal Engineering 40 (2012) 311e317

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Applied Thermal Engineering

journal homepage: www.elsevier .com/locate/apthermeng

Analysis of compressioneabsorption cascade refrigeration cycles

Canan Cimsit a, Ilhan Tekin Ozturk b,*

a Program of Mechanical Engineering, Graduate School of Natural and Applied Sciences, Kocaeli University, Umuttepe Yerleskesi, 41040 Kocaeli, TurkeybDepartment of Mechanical Engineering, Faculty of Engineering, Kocaeli University, Umuttepe Yerleskesi, 41040 Kocaeli, Turkey

a r t i c l e i n f o

Article history:Received 24 March 2011Accepted 16 February 2012Available online 24 February 2012

Keywords:RefrigerationAbsorption CascadeCoefficient of performance

* Corresponding author. Tel.: þ90 262 3033032; faE-mail address: ilhan@kocaeli.edu.tr (I.T. Ozturk).

1359-4311/$ e see front matter � 2012 Elsevier Ltd.doi:10.1016/j.applthermaleng.2012.02.035

a b s t r a c t

In this study, LiBreH2O pair was used for the first time for absorption section of compressioneabsorptioncascade refrigeration cycles. These cycles were analyzed theoretically and compared with using differentrefrigerants in the compression and absorption sections. While LiBreH2O and NH3eH2O are used as fluidpair in cascade absorption section, R134a, R-410A and NH3 fluids were used in the vapour compressionsection of cascade cycle. It was presented that electrical energy consumption in the cascade refrigerationcycle is 48e51% lower than classical vapour compression refrigeration cycles that use R134a, R-410A andNH3 as working fluids under the same operating conditions, that are an evaporator temperature of 263 Kand a condenser temperature of 313 K. Separately the results show that by using LiBreH2O pair forabsorption section the thermal energy consumption of cascade refrigeration cycle could be reduced by35% and also general coefficient of performance (COPcyclegen) could be improved by 33% compared to theNH3eH2O pair.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Theuseof compressioneabsorption refrigeration cycles provideselectrical energy saving compared to vapour compression cycles.The structure of the system is more complex but they use theadvantages of both the absorption and vapour compression refrig-eration cycles. These systems provide the usage of electricity andheat energy together at the same time for refrigeration. Further-more, non-conventional sources of energy such as solar, geothermal,and waste heat could be supplied as heat energy for these cycles.

There are a lot of studies on the compressioneabsorptionrefrigeration cycles in the literature. When considering thesestudies they could be categorized as two groups and called ascombined and cascade refrigeration cycles. In the combined cycleboth of absorption and vapour compression sections have the samecompression rate and this rate is equal the total compression rate ofthe combined cycle. But in the cascade cycle that vapourcompression and absorption cycle are connected in serial form.

Kairouani et al. [1] studied the performance of compressioneabsorption refrigeration (cascade) cycles and NH3eH2O fluid pairwas used at the absorption section of the refrigeration cycle andthree different working fluids (R717, R22, R134a) were used at thevapour compression section. Kairouani et al. concluded that thecoefficient of performance of the cycle is 37e54% higher than the

x: þ90 262 3033033.

All rights reserved.

vapour compression cycle using R717, R22 and R134a refrigerantsfor the same operating conditions.

A comparison has been done between classic vapour compres-sion system using ammonia and the compressioneabsorption(combined) refrigeration system using NH3eNaSCN at the sameoperating conditions according to economy and performance [2]. Itwas found that the capital and running costs of the compressors inthe NH3 þ NaSCN were highly reduced as compared to the cycleusing only pure ammonia.

Thermodynamic analysis was made of the compressioneabsorption (combined) refrigeration cycle by using fluid pair asR22 and DMETEG (Dimethyl Ether of Tetraethylene Glycol) forsimultaneous heating and cooling application for the milk pro-cessing [3]. It was found that the compressioneabsorption systemyielded much better overall performance especially when thetemperature lifts are high as compared to the a single stage vapourcompression system.

Ahlby et al. [4] performed a comparison study between thevapour compression cycle and the compressioneabsorption(combined) refrigeration cycle by using absorption section withNH3eH2O fluid pair and the vapour compression systems usingR12. Ahlby et al. concluded that the coefficient of performance forthe former always results in a higher coefficient and the capacity ofthe NH3eH2O system is also considerably higher.

Ayala et al. [5] found that the vapour compressioneabsorption(combined) refrigeration cycle using NH3eNaSCN fluid pair hasgreater performance than the vapour compression or absorption

C. Cimsit, I.T. Ozturk / Applied Thermal Engineering 40 (2012) 311e317312

refrigeration cycle. Separately also compressioneabsorption(combined) refrigeration cycle has been studied; the main param-eters of the cycle have been investigated and compared with thecompression cycle by Hulten et al. [6].

Herold et al. [7] studied the analysis of hybridcompressioneabsorption cycle using LiBreH2O as the workingfluid. In this analysis steam compressor was used for improvingperformance of absorption cycle and all of the cycle used water(steam) as refrigerant. Due to high cost and low isentropic effi-ciency of the steam compressor this cycle analysis resulted in pooreconomics.

The literature review shows that there is no usage of LiBreH2Oin absorption section of compressioneabsorption cascade refrig-eration cycle. The present study addresses this point. The analysisof the cycles will be done using LiBreH2O and NH3eH2O pairs inthe absorption section, and R134a, R-410A and NH3 in the vapourcompression section of the compressioneabsorption cascaderefrigeration cycle. So, totally six cascade cycles will be analyzedand compared. The cycle analysis will be done according to theperformance of the cascade cycle for different evaporator temper-atures of the vapour compression section, different temperaturedifferences at the cascade heat exchanger, and different generator,condenser and absorption temperatures.

Fig. 1. Schematic view of the single effect compressioneabsorption cascade refriger-ation cycle.

2. The analysis of the cycles

The theoretical analyses of total six cycles were done using thesame methodology. In this section to show how the analysis isdone, a sample of single effect compressioneabsorption cascaderefrigeration cycle is presented in Fig. 1. LiBreH2O was used in theabsorption section and R-134awas used in the vapour compressionsection of this sample cycle. In this cycle, the weak solution of LiBris drawn from the heat exchanger by a pump. The high pressurecool mixture enters the generator, where the heat is added to drivethe water from the solution. The strong solution of LiBr leaves thegenerator, its pressure is reduced to absorption pressure by a solu-tion expansion valve (sev), and then it enters the absorber. Toincrease the temperature of stream (6) and decrease the temper-ature of the stream (9), a counter flow heat exchanger is locatedbetween strong and weak solutions. The refrigerant (water) iscondensed in the condenser 2, leaves it as a saturated liquid; then itpasses through the refrigerant expansion valve (rev-1). Afterwards,the refrigerant passes through the evaporator 2, where it evapo-rates by absorbing the heat released by the condenser 1 of thevapour compression cycle. This cold vapour then enters theabsorber, where it mixes with a hot solution, and it is absorbed. Inthe vapour compression section, the fluid is compressed to a highpressure in the compressor, and then enters the condenser 1. Then,the condensed refrigerant passes through the refrigerant expansionvalve (rev-2), and enters the evaporator 1.

2.1. The thermodynamic analysis of the cycle

The thermodynamic analysis of the cycles was performed usingthe following assumptions:

1. The system is in steady state.2. Ammonia and water lithium bromide and water solutions in

the generator and the absorber are assumed to be in equilib-rium at their respective temperatures and pressures.

3. Refrigerants (water and ammonia) at condenser and evapo-rator are in saturated states.

4. Strong solution and weak solution of refrigerant leavingabsorber and generator are saturated.

5. To avoid crystallization of the LiBreH2O solution, the temper-ature of the solution entering the throttling valve should be atleast 7e8 �C above crystallization temperature.

6. All the pressure losses in the system (heat exchangers and thepipelines) are neglected (At the absorption system the workexpended by the circulation pump has been neglected).

7. At the entry of the compressor, the vapour is saturated.

The calculation of the thermal capacities can be done by writingthe mass and energy balance of each component in the cycle as thefollowing equations.

For absorption section of cascade cycle:Condenser 2

_m11 ¼ _m12 (1)

_Qcon2 ¼ _m11$ðh11 � h12Þ (2)

Absorber

_m5 ¼ _m10 þ _m14 (3)

_Qabs ¼ _m10$h10 þ _m14$h14 � _m5$h5 (4)

C. Cimsit, I.T. Ozturk / Applied Thermal Engineering 40 (2012) 311e317 313

Generator

_m1 ¼ _m11 þ _m8 (5)

_Qgen ¼ _m11$h11 þ _m8$h8 � _m7$h7 (6)

Evaporator 2

_m13 ¼ _m14 (7)

_Qevap2 ¼ _m13$ðh14 � h13Þ (8)

Circulation ratio

f ¼ _m8_m11

¼ X7

X8 � X7(9)

For vapour compression section of cascade cycle:CompressorObviously there are two main ways of minimizing the

compressor work. First of all the compression process must be asmuch as close to isentropic process and another way is to use intercooling between stages of compression. Well-designed compres-sors isentropic efficiency is between 0.75 and 0.85. For cascadecycle vapour compression section the reciprocating type and onestage compressor is used and the isentropic and electrical efficiency(including mechanic and electric motor efficiencies) of thecompressor are taken as his ¼ 0.80 and he ¼ 0.90, respectively.Compressor exit enthalpy and power are decided using isentropicand electrical efficiencies by following equations.

_m1 ¼ _m2 (10)

h2 ¼ h2s þh2s � h1

his(11)

_Wcomp ¼ _m1$ðh2 � h1Þ=he (12)

Condenser 1

_m2 ¼ _m3 (13)

_Qcon1 ¼ _m3$ðh2 � h3Þ (14)

Evaporator 1

_m1 ¼ _m4 (15)

_Qevap1 ¼ _m1$ðh1 � h4Þ (16)

The coefficients of the performance for the vapour compressionsection of the cascade refrigeration cycle is calculated as

COPvapor�comp ¼ _Qevap1=_Wcomp (17)

Table 1Temperature, pressure, enthalpy, concentration and mass flow rate data for the compres

State T (K) P (kPa) h (kJkg�1) X (%LiBr) _ms (kgs�1) (LiBreH2O

1 263 200.52 392.750 e e

2 298 537.06 417.719 e e

3 291 537.06 224.590 e e

4 263 200.52 224.590 e e

5 313 1.23 93.702 55 e

6 313 7.38 93.702 55 e

7 337 7.38 143.575 55 e

8 363 7.38 220.781 62 0.19179 333 7.38 164.559 62 0.191710 333 1.23 164.559 62 0.191711 363 7.38 2670 e e

12 313 7.38 167.50 e e

13 283 1.23 167.50 e e

14 283 1.23 2518.9 e e

The coefficient of the performance for the absorption section ofthe cascade refrigeration cycle is calculated as

COPabs ¼ _Qevap2=_Qgen (18)

The coefficient of performance for the entire cascade cycle isdefined as

COPcyclegen ¼ _Qevap1=�_Qgen þ _Wcomp

�(19)

Calculation of the solution enthalpies can be found in moredetail in the Appendix A.

2.2. The base case compressioneabsorption cascade refrigerationcycle

In this section, using LiBreH2O in the absorption section andusing R-134a in the vapour compression section of thecompressioneabsorption cascade refrigeration cycle has beentheoretically analyzed to make effective cooling at lower tempera-tures, and a sample application has been done. The cooling load ofthe system has been assumed as 50 kW for base case. In all analysistheeffectivenessof the solutionheatexchangerhasbeenassumedasε¼0.60. The thermodynamicproperties at thedifferent points of thecompressioneabsorption cascade refrigeration cycle (referring toFig. 1) has been calculated and given in Table 1 for T1 ¼ 263 K and atT12 ¼ 313 K evaporator and condenser temperatures, respectively.

The LiBreH2O and NH3eH2O are used in the absorption sectionand R-134a, R-410A and NH3 are used in the vapour compressionsection of the cascade cycles (six cascade cycles), and the classicvapour compression refrigeration cycles that are running with R-134a, R-410A and NH3 refrigerants have been analyzed under thesame operating conditions (T1 ¼ 263 K, T12 ¼ 313 K, cooling load50 kW as base case). Then a comparison has been done over thesecycles and the thermal capacity and performance of the cycles andcomponents have been shown in Table 2.

3. Results and discussion

The analysis has been done of the compressioneabsorptioncascade refrigeration cycle for different evaporator temperaturesof the vapour compression section, different temperature differ-ences at the cascade heat exchanger, and different generator,condenser and absorption temperatures. The performance of thecascade cycles are discussed as follows.

3.1. The analysis for different evaporator temperatures

The analysis of the compressioneabsorption cascade refrigera-tion system has been done theoretically for different evaporator

sioneabsorption cascade refrigeration cycle of Fig. 1.

) _mw (kgs�1) (LiBreH2O) _mref (kgs�1) (H2O) _mref (kgs

�1) (R-134a)

e e 0.2973e e 0.2973e e 0.2973e e 0.29730.2161 e e

0.2161 e e

0.2161 e e

e e e

e e e

e e e

e 0.0244 e

e 0.0244 e

e 0.0244 e

e 0.0244 e

Table 2Thermal capacity and performance of the system component of compressioneabsorption cascade refrigeration cycles and classical vapour compression refrigeration cycles forbase case.

Compressioneabsorption (cascade) refrigeration systems Classical vapourcompression refrigerationsystems

LiBreH2O R-134a LiBreH2O NH3 LiBreH2O R-410A NH3eH2O R-134a NH3eH2O NH3 NH3eH2O R-410A R-134a NH3 R-410A

Qgen (kW) 76.45 76.45 76.76 117.86 117.64 118.52 e e e

Qevap2 (kW) 57.41 57.30 57.72 57.41 57.30 57.72 e e e

Qabs (kW) 72.76 72.76 73.06 109.24 109.03 109.85 e e e

Qcon2 (kW) 61.06 61.06 61.31 66 65.87 66.37 e e e

Wcomp (kW) 8.25 8.08 8.58 8.25 8.08 8.58 17.24 15.73 18.23Qevap1 (kW) 50 50 50 50 50 50 50 50 50Qcon1 (kW) 57.41 57.30 57.72 57.41 57.30 57.72 65.52 64.16 66.41COPabs 0.750 0.750 0.750 0.487 0.487 0.487 e e e

COPvapourecomp 6.061 6.188 5.827 6.061 6.188 5.827 2.90 3.18 2.74COPcyclegen 0.590 0.592 0.586 0.396 0.398 0.393 e e e

C. Cimsit, I.T. Ozturk / Applied Thermal Engineering 40 (2012) 311e317314

temperatures (T1) with the following assumptions: T12 ¼ 313 K,ε ¼ 0.6, T14 ¼ 283 K, Tgen ¼ 363 K, T3 ¼ 291 K and cooling load asbase case. The results are summarized in Figs. 2 and 3.

As seen from Fig. 2, when the evaporator temperatures (T1)decrease, the coefficients of performance of the vapour compres-sion section of cascade cycle (COPvapourecomp) reduces by a consid-erable amount. NH3 which is one of the three refrigerants used hasa better performance.

As seen from Fig. 3, when the evaporator temperature increasesthe heat supplied to the generator of the cascade cycle is reduced.The refrigerant type which is used in the vapour compressionsection has no effect on this drop. Also it is seen that whenLiBreH2O pair is used in the absorption section, less heat energy isneeded for the generator than NH3eH2O pairs, and this situation iskept for all the evaporator temperatures.

3.2. The analysis for different temperature differences of thecascade heat exchanger

Again the same operating conditions are used, i.e. T1 ¼ 263 K,T12 ¼ 313 K and cooling load Qevap ¼ 50 kW. The temperaturedifferences (DT) of the cascade heat exchanger is taken as

256 258 260 262 264 266 268 270 272 2744

5

6

7

8

9

10

11

T1 (K)

CO

P vapo

ur-c

omp

NH3

R-134a R-410A

Fig. 2. Variation of the coefficient of performance (COPvapourecomp) with T1 tempera-ture for the vapour compression section of the cascade cycle.

temperature differences between condenser temperature of thevapour compression section of cascade cycle, that is fixed as at(T3 ¼ 293 K), and the evaporator temperature of the absorptionrefrigeration section of cascade cycle, that is taken as T14 ¼ 278,280.5, 283, 285.5 and 288 K. The results of the analysis aredescribed as following.

As seen from Fig. 4, when DT (T3 � T14) increases, the energywhichmust be given to the generator is increased. It is seen that therefrigerant type used in the vapour compression cycle has negli-gible effect, but the fluid type used at the absorption section has aneffect on the heat needed in the generator. Also using LiBreH2Ofluid pair in the absorption section of the cascade cycle alwaysneeds considerably less generator heat than using NH3eH2O withthis temperature differences level.

In the case of using LiBreH2O fluid pair instead of NH3eH2Ofluid pair in the compressioneabsorption cascade cycle, thetemperature difference at the cascade heat exchanger for DT ¼ 5 K(for LiBreH2O/R134a Qgen ¼ 72.86 kW; for NH3eH2O/R134aQgen ¼ 100.5 kW) 27% and for DT ¼ 15 K (for LiBreH2O/R134aQgen ¼ 84.73 kW; for NH3eH2O/R134a Qgen ¼ 156.15 kW) 46% lessheat supplied to the generator (Fig. 4).

In the case of using LiBreH2O/R134a pair in the absorptionsection of the cascade cycle, when the temperature difference at thecascade heat exchangerDT¼ (T3� T14) is varied from5K to15K. The

256 258 260 262 264 266 268 270 272 27470

80

90

100

110

120

T1 (K)

NH3/H2O-R410A NH3/H2O-R-134a NH3/H2O-NH3

LiBr/H2O-R410A LiBr/H2O-R-134a LiBr/H2O-NH3

Qge

n(kW

)

Fig. 3. Qgen(kW) versus T1 temperature.

4 6 8 10 12 14 1660

70

80

90

100

110

120

130

140

150

160

170 NH3/H2O-R410A NH3/H2O-R134a NH3/H2O-NH3

LiBr/H20-R410A LiBr/H2O-R134a LiBr/H2O-NH3

Qge

n(kW

)

T (K)

Fig. 4. Qgen (kW) versus DT temperature differences.

300 305 310 315 320 32560

70

80

90

100

110

120

130

140

150

160

170

180

NH3/H2O LiBr/H2O

T12

(K)

Qge

n(kW

)

Fig. 6. Qgen (kW) versus T12 temperature.

C. Cimsit, I.T. Ozturk / Applied Thermal Engineering 40 (2012) 311e317 315

heat supplied to the generator increases by approximately 14% andat the same conditions in case of using NH3eH2O/R134a pair in theabsorption section this increase is 36%, as shown in Fig. 4.

As seen from Fig. 5, when DT (T3 � T14) temperature differenceincreases, the general coefficient of performance for thecompressioneabsorption cascade cycle (COPcyclegen) reduces. Thisreduction becomes more evident when NH3eH2O pair is used inthe absorption section.

3.3. The analysis for different condenser temperatures

The analysis of the absorption section of the compressioneabsorption cascade cycle refrigeration system has been donetheoretically for different condenser temperatures (T12). At thisanalysis, operating conditions are assumed as T1 ¼ 263 K, ε ¼ 0.6,T14 ¼ 283 K, Tgen ¼ 263 K, T3 ¼ 291 K and the cooling load (Qevap) is50 kW.

When the condenser temperature increases in the cascade cycle,the heat energy supplied to the generator increases (Fig. 6). When

4 6 8 10 12 14 16

0,30

0,35

0,40

0,45

0,50

0,55

0,60

LiBr/H20-NH3

LiBr/H20-R134a LiBr/H20-R410A NH3 /H2O-NH3 NH3/H2O-R134a NH3/H2O-R410A

T (K)

CO

P cycl

egen

Fig. 5. COPcyclegen versus DT temperature differences.

ammoniaewater is used as fluid pair, energy given to the generatoris higher than LiBreH2O fluid pair. So, coefficient of performance ofthe cascade cycle reduces.

As seen from Fig. 7, when the condenser temperature increases,the coefficient of performance for the absorption section of cascadecycle (COPabs) and the coefficient of performance for the entirecascade cycle (COPcyclegen) reduce as expected. The effect of fluidtypes in the absorption section is consistently in favour of LiBreH2Ofluid pair. As the condenser temperatures exceed 318 K, theperformances reduces faster for all the cascade cycles. In thesample work, at the condenser temperature of 310 K and whenusing LiBreH2O fluid pair, the general coefficient of performance ofthe cascade cycle is approximately 33% more than the NH3eH2Ofluid pair in absorption section of the cascade cycle.

3.4. The analysis for different generator temperatures

The theoretical analysis of the system has been done when thetemperature of the generator in the absorption section of thecompressioneabsorption (cascade) refrigeration system has different

300 305 310 315 320 3250,25

0,30

0,35

0,40

0,45

0,50

0,55

0,60

0,65

0,70

0,75

0,80

NH3/H

2O-COP

cyclegen

NH3/H

2O-COP

abs

LiBr/H2O-COP

cyclegen

LiBr/H2O-COP

abs

T12

(K)

CO

P

Fig. 7. COP versus T12 temperature.

355 360 365 370 375 38060

70

80

90

100

110

120 NH3/H2O LiBr/H20

Generator Temperature (K)

Qge

n(kW

)

Fig. 8. Qgen(kW) versus generator temperature.

C. Cimsit, I.T. Ozturk / Applied Thermal Engineering 40 (2012) 311e317316

values. Again the same operating conditions are assumed as atT1 ¼ 263 K, T12 ¼ 313 K, T14 ¼ 283 K, T3 ¼ 291 K and the cooling load50 kW.

In Fig. 8, when using the NH3eH2O and LiBreH2O pairs inabsorption section of cascade cycle with the varying temperature ofgenerator, the variations in the generator capacity are shown.According to this figure, when the generator temperature increases,the thermal capacity needed for the generator reduces and lowervalues are obtained for using LiBreH2O pair in absorption section.

As seen in Fig. 9, when the generator temperature of the cycleincreases, the coefficients of performance of the absorption sectionCOPabs and cascade cycle COPcyclegen increase, too. It is seen thatusing LiBreH2O in the absorption section has high COP values thanNH3eH2O. This tendency continues with increasing generatortemperatures. As a result when using LiBreH2O fluid pair instead ofNH3eH2O fluid pair in the absorption section of the cascade cycle,34% and 30% higher coefficients of performance of cascade cycle(COPcyclegen) can be obtained at generator temperature of 358 K and378 K, respectively.

355 360 365 370 375 3800,35

0,40

0,45

0,50

0,55

0,60

0,65

0,70

0,75

Generator Temperature (K)

NH3/H

2O-COP

cyclegen.

NH3

/H2

O-COPabs

LiBr/H2O-COP

cyclegen.

LiBr/H2O-COP

abs.

CO

P

Fig. 9. COP versus generator temperature.

4. Conclusions

The thermodynamic analysis of the compressioneabsorptioncascade refrigeration cycles was done. It is seen that using theabsorption and vapour compression cascade refrigeration cycle havethe advantage that cooling can be done by using less electric energyconsumption than classical vapour compression cycle for lowtemperature cooling applications. When the compressioneabsorption cascade refrigeration cycles and the classic vapourcompression refrigeration cycles are compared for sample applica-tion at the same conditions for the same cooling capacity, dependingon absorption fluid pairs such as LiBreH2O and NH3eH2O, 48e51%less electric energy is consumed in the cascade systems, but heat issupplied to the cascade cycle at 363 K generator temperature from76.45 kW to 117.86 kW, respectively.

The LiBreH2O fluid pair was used for the first time in the absorp-tion section of the cascade cycles and compared with NH3eH2O pair.Using LiBreH2O fluid pair in the absorption section of the cascadecycle, the highest coefficient of performance could be obtained as0.592 and the coefficients of performance is 33% better than usingNH3eH2O fluid pair for same application. The thermal energyconsumptionwas reduced considerably by using LiBreH2O fluid pairinsteadofNH3eH2Ofluidpair for cascade absorption section. Also, forthe case of using NH3eH2O fluid pair and considering the energyrequirement of the water rectifier added to cycle after the generator,the advantageous of the LiBreH2O fluid pair increases more.

The coefficient of performance of the cascade cycle usingLiBreH2O and NH3eH2O fluid pairs in absorption section increasesby increasing the generator and evaporator temperatures, but itreduces by increasing the condenser temperatures.

Cascade cycles that use LiBreH2O fluid pair in absorptionsection could yield the highest coefficient of performancecomparatively with the NH3eH2O fluid pair for all cases. With thistype of cascade cycle it is possible to operate refrigeration systemsby consuming less electrical energy and less heat energy from lowgrade heat sources such as solar and geothermal energy.

Appendix A. Thermodynamic properties

For LiBreH2O solution

The relation among temperature, concentration and enthalpy oflithium bromideewater mixture is as follows [8]:

h ¼ 2:326hAþ Bð1:8T � 459:67Þ þ Cð1:8T � 459:67Þ2

ið289:15 � T � 439:15 KÞð40 � X � 70 %Þ

(A1)

where:

A ¼ �1015:07þ 79:5387X � 2:358016X2 þ 0:03031583X3

�0:0001400261X4

B ¼ 4:68108� 0:3037766X þ 0:00844845X2

�0:0001047721X3 þ 0:000000480097X4

C ¼ �0:0049107þ 0:000383184X � 0:00001078963X2

�0:00000013152X3 � 0:0000000005897X4

For NH3eH2O solution

The relation among temperature, concentration and enthalpy ofammoniaewater mixture is as follows, with coefficients given inTable A1 [9]:

C. Cimsit, I.T. Ozturk / Applied Thermal Engineering 40 (2012) 311e317 317

h�T ;X

�¼ 100

X16ai

�ðT � 273:16Þ � 1�mi

Xni (A2)

i¼1

273:16

where X is the ammonia mole fraction and is given as follows:

X ¼ 18:015X18:015X þ 17:03ð1� XÞ (A3)

Table A1Coefficients of equation (A2).

i mi ni ai i mi ni ai

1 0 1 �7.61080 9 2 1 2.841792 0 4 25.6905 10 3 3 7.416093 0 8 �247.092 11 5 3 891.8444 0 9 325.952 12 5 4 �1613.095 0 12 �158.854 13 5 5 622.1066 0 14 61.9084 14 6 2 �207.5887 1 0 11.4314 15 6 4 �6.873938 1 1 1.18157 16 8 0 �3.50716

References

[1] L. Kairouani, E. Nehdi, Cooling performance and energy saving of com-pressioneabsorption refrigeration system assisted by geothermal energy,Applied Thermal Engineering 26 (2006) 288e294.

[2] S. Tarique, M.A. Siddiqui, Performance and economic study of the combinedabsorption/compression heat pump, Energy Conversion Management 40 (1999)575e591.

[3] P.K. Satapathy, M.R. Gopal, R.C. Arora, Studies on compressioneabsorption heatpump for simultaneous cooling and heating, International Journal of EnergyResearch 28 (2004) 567e580.

[4] L. Ahlby, D. Hodgett, T. Berntsson, Optimization study of the com-pressioneabsorption cycle, International Journal of Refrigeration 14 (1991)16e23.

[5] R. Ayala, C.L. Heard, F. Holland, Ammonia/lithium nitrate absorption/compres-sion refrigeration cycle. Part I, Applied Thermal Engineering 3 (1997) 223e233.

[6] M. Hulten, T. Berntsson, The compression/absorption cycle e influence of somemajor parameters on COP and a comparison with the compression cycle,International Journal of Energy Research 22 (1999) 91e106.

[7] K.E. Herold, L.A. Howe, R. Radermacher, Analysis of a hybrid compression eabsorption cycle using lithium bromide and water as the working fluid, Inter-national Journal of Refrigeration 14 (1991) 264e272.

[8] Y. Kaita, Thermodynamic properties of lithium bromideewater solutions athigh temperatures, International Journal of Refrigeration 24 (2001) 374e390.

[9] D.W. Sun, Comparison of the performance of NH3eH2O, NH3eLiNO3 and absorp-tion refrigeration systems, Energy Conversion Management 5/6 (1997) 357e368.

Nomenclature

X: concentrationε: effectiveness of the solution heat exchangerf: circulation ratioh: enthalpy (kJ kg�1)_m: mass flow rate (kg s�1)P: pressure (kPa)_Q: heat flow rate (kW)T: temperature (K)_W: work flow rate or power of compressor (kW)COP: coefficient of performance

Subscriptss: isentropic for enthalpy and strong for solutionw: weakref: refrigerantcomp: compressorgen: generatorcon: condenserevap: evaporatorabs: absorber, absorption systemcyclegen: cycle generalvapour comp: vapour compression