Performance evaluation of single effect Li/Br-H2O vapour absorption refrigeration system with three cascaded vapour compression refrigeration systems using HFO refrigerants for ultra-low temperature applications

1.          Introduction

For reducing global warming and ozone depletion and maximizing the use of natural and renewable energy resources with minimal environmental impacts is key building of an energy efficient sustainable system. Although completely sustainable energy efficient system would require a fully reversible process, exploits the second law of thermodynamics which proves is not possible, which indicating that all real processes are irreversible and impact on the environment. Approaching sustainability can yield greater benefits both the current and future environment. The utilization of natural and renewable resources in a responsible fashion and by using efficient methods is important aspect when developing new technologies and analyzing current refrigeration and air conditioning systems. The conventional vapour compression refrigeration systems and vapour absorption systems utilize different working fluids. Many of the vapour compression systems use the ozone depleting chloro-fluoro-carbon refrigerants (CFCs), Hydro-chloro-fluoro-carbon refrigerants (HCFCs), Hydro-fluoro-carbon refrigerants (CFCs), because of the thermo-physical properties obtainable by them. Many industrial processes frequently produce a significant amount of thermal energy; regularly by burning fossil fuels for heat or steam. The opportunities to convert wastes or excess heat into useful cooling can be done by integration of absorption refrigeration systems into these systems. Szargut et al [1]. suggested that exergy methods should be considered to better realize increased efficiencies and environmental impacts because exergy is normally considered to be the measure of work potential (i.e. maximum work) that can be obtained from a system with respect to its environment. The exergy, is a non-conserved quantity, and exergy balances account for inputs, losses and wastes of a process. the exergy input and destruction rates provide an accounting of the utilized efficiency of resources used. Rosen and Dincer [2] have given links between energy, exergy and sustainable development, which shows that exergy may allow for measuring impacts on the environment

Gebreslassie et al [3] had evaluated exergy in Lithium bromide (Li/Br) absorption systems by using structural method to obtain a simplified equation to estimate the optimum heat exchanger area for absorption cooling system and assessed the relationship between heat exchange area and exergy. Also concluded that in the optimum case, the maximum exergy destruction was in the solution heat exchanger and the condenser while in all other components, the destruction rates decreasing as increased heat exchange area and presented at detailed analysis of exergy for half to triple effect absorption chillers. Bereche et al [4] analyzed single and double-effect LiBr systems using a thermo-economic analysis and exergy and concluded that the single-effect absorption refrigeration systems are suitable utilizing waste heat or operating in cogeneration systems because of their operation at lower temperatures compared to double-effect chillers, Morosuk and Tsatsaron [5] is presented an exergy analysis of the internal components of absorption refrigeration machines. And concluded that the absorber and generator destroyed about 40% of their exergy and are main (primary) candidates for improvement. Kilic and Kaynakli [6] carried out a second law(exergy) thermodynamic analysis of water and lithium bromide absorption refrigeration and found the evaporator is a major component for the exergy loss rates and concluded that the generator, absorber and evaporator were the largest sources of exergy destruction. Garimella et al [7] proposed absorption/vapour compression cascade refrigeration system driven by waste heat used in naval ship and concluded that electricity consumption is reduced by 31% than that of conventional vapour compression refrigeration system.

The large number of research studies on cascade refrigeration systems have been done. These research studies provide valuable insights about energy and exergy analysis of VCR, VAR cycles in the single, double and triple stage and compression-absorption in the form of cascade cycles. Most of the research studies considered till date emphasize on VCR and VAR cycles (single and double effect, triple and half effect in Li/Br-H2O and NH3H2O). Mishra [8] carried out exergy- energy analysis of compression-absorption (combined) or cascade cycles. Though, exhaustive research has been carried out on cascade cycles, but very less consideration has been given to explore the thermodynamic performance using HFO refrigerants in the range from -30oC to -150oC and none of the research work is available on performance analysis of compression-absorption cascade refrigeration system using HFO refrigerants. Radhey Shyam Mishra [9-10] carried out thermodynamic performance of the HFO refrigerants in the medium temperature compression stage between 5oC to -50oC and NH3H2O, Li/Br-H2O refrigerants in the absorption stage and its overall effect on the cascade system. The effect of these HFO refrigerants on the intermediate temperature in the range of (-50oC to 95oC) using R245fa of medium temperature cycle cascade system using R32 refrigerant/ hydrocarbons in ultra-low evaporator temperature first and second law performances using the pair of NH3–H2O in the high temperature absorption stage and HFO refrigerants at the evaporator temperature of 223K (-50oC) and R245fa in the medium temperature compression cycle for evaporator temperature of -95oC evaluated the effect of various performance parameters of multi cascade refrigeration system in which a compression system at the low temperature stage using R32 in low temperature cycle at evaporator temperature of -130oC . It is found that R1233zd (E), R1225ye(Z) and HFO-1336mzz(z) gives better thermodynamic performances than using R1243yf. The studies carried out so far on the double and triple effect cycles in the use of HFO refrigerants up to evaporator temperature of -50oC in cascaded vapour compression refrigeration systems. to some extent, the effect of HFO refrigerants in the intermediate temperature cycle at -75oC and -95oC is missing. Also the effect of HFO –refrigerants in ultra-low temperature cycle of compression –absorption refrigeration systems have not been investigated so far. The present study has therefore been carried out the effect of HFO refrigerants in intermediate temperature cycle(ITC) up to -95oC and LTC evaporator of -135oC and -150oC.

 

2.       Results and Discussion

 

System-1

 Li/Br-H2O single effect vapour absorption refrigeration system at 10oC of evaporator temperature cascaded with three stages vapour compression refrigeration system using R1233zd(E) in medium temperature cycle at evaporator temperature =-50oC, R-1225ye(Z) in intermediate temperature cycle at evaporator temperature = -95oC and using HFO-1336mzz(Z) in lower temperature cycle at evaporator temperature = -150oC.

 

System-2

Li/Br-H2O single effect vapour absorption refrigeration system at 10oC of evaporator temperature cascaded with three stages vapour compression refrigeration system using R1233zd(E) in medium temperature cycle at evaporator temperature =-50oC, HFO-1336mzz(Z) in intermediate temperature cycle at evaporator temperature = -95oC and using R-1225ye(Z) in lower temperature cycle at evaporator temperature = -150oC.

 

System-3

Li/Br-H2O single effect vapour absorption refrigeration system at 10oC of evaporator temperature cascaded with three stages vapour compression refrigeration system using R1234yf in medium temperature cycle at evaporator temperature =-50oC, R-1225ye(Z) in intermediate temperature cycle at evaporator temperature = -95oC and using HFO-1336mzz(Z) in lower temperature cycle at evaporator temperature = -150oC.

 System-4

 Li/Br-H2O single effect vapour absorption refrigeration system at 10oC of evaporator temperature cascaded with three stages vapour compression refrigeration system using R1234yf) in medium temperature cycle at evaporator temperature =-50oC, HFO-1336mzz(Z) in intermediate temperature cycle at evaporator temperature = -95oC and using R-1225ye(Z) in lower temperature cycle at evaporator temperature = -150oC.

Following numerical values have been used for validation of code developed for Integrated single effect Li/Br-H2O VARS using eco-friendly refrigerants.

 ·         Generator temperature= 110oC

·         Absorber temperature=35oC

·         Condenser temperature =35oC

·         VARS evaporator temperature=10oC

·         load on VARS Evaporator= 175 kW

·         Ambient (dead state) temperature=25oC

·         Temperature overlapping in MTC = 10oC

·         VCR evaporator temperature of MTC=-50oC

·         VCR evaporator temperature of ITC=-95oC

·         VCR evaporator temperature of LTC=-150oC

·         VCR compressor efficiency of MTC= 80%

·         VCR compressor efficiency of ITC= 80%

·         VCR compressor efficiency of MTC= 80%

·         Ambient (dead state) temperature=25oC

 

Thermodynamic first law energy performances of integrated single effect Li/Br-H2O VARS system cascaded with three stages vapour compression cascaded systems shown in table 2(a) respectively. It was observed that system-6 has lowest thermodynamic performances than system-5, however first law thermodynamic performance improvement is less. Similarly, Thermodynamic second law exergy performances of cascaded single effect Li/Br-H2O VARS system cascaded with three stages vapour compression cascaded systems shown in table-2(b) respectively. It was observed that system-6 has higher thermodynamic exergetic performances than system-5.


Table-1(a) Thermodynamic first law (energetic) Performances of Integrated single effect Li/Br-H2O VARS using ecofriendly refrigerants at evaporator temperature=-150oC

Integrate system

COP_VARS

COP _MTC

COP _ITC

COP _

L TC

% Improvement in COP _MTC

% Improvement in COP _ITC

% Improvement in COP _ LTC

System-1

0.7560

0.8759

0.9847

0.9236

15.86

30.65

22.17

System-2

0.7560

0.8759

0.9847

0.9282

15.86

30.26

22.79

System-3

0.7560

0.8102

0.9120

0.8634

7.168

20.64

14.22

System-4

0.7560

0.8102

0.9120

0.8674

7.168

20.31

14.74

 

Table-1(b) Thermodynamic second law (exergetic) Performances of Integrated single effect Li/Br-H2O VARS using ecofriendly refrigerants at evaporator temperature=-150oC

Integrate system

ETA_VARS

ETA_MTC

ETA_ITC

ETA_

L TC

% Improvement in ETA_MTC

% Improvement in ETA_ITC

% Improvement in ETA_ LTC

System-1

0.1564

0.321

0.5331

0.5539

77.98

195.3

206.8

System-2

0.1564

0.321

0.5293

0.5639

77.98

193.1

212.3

System-3

0.1564

0.2680

0.4561

0.4890

48.94

152.6

170.9

System-4

0.1564

0.2689

0.4530

0.4974

48.94

150.9

175..5

 

Table-1(c) Thermodynamic exergy destruction ratio of Integrated single effect Li/Br-H2O VARS using ecofriendly refrigerants at evaporator temperature= -150oC

Integrate system

EDR_VARS

EDR_MTC

EDR_ITC

ED R_

L TC

% Improvement in EDR_MTC

% Improvement in EDR_ITC

% Improvement in EDR_ LTC

System-1

4.539

2.112

0.8754

0.8053

-53.47

-80.7

-82.26

System-2

4.539

2.112

0.8894

0.7735

-53.47

-80.4

-82.96

System-3

4.539

2.719

0.8754

0.8053

-40.10

-73.72

-76.98

System-4

4.539

2.719

0.8754

0.8053

40.10

-73.40

-77.74


However, second law thermodynamic exergetic performance improvement for -150oC evaporator temperature is less. It means by putting HFO-1336mzz(Z) in lower temperature cycle in system-5 gives lower first and second law thermodynamic performances than using R-1225ye(Z) in low temperature cycle. However, first law(energy) and second law exegetic performances of double stage cascaded integrated system-5 is higher than double stage cascaded integrated system-6 at evaporator temperature of -95oC.It means by putting HFO-1336mzz(Z) in intermediate temperature cycle gives lower first and second law thermodynamic performances than using R-1225ye(Z). The exergy destruction ratio of whole cascaded system is shown in Table-2(c) respectively.

 System-5

 Li/Br-H2O single effect vapour absorption refrigeration system at 10oC of evaporator temperature cascaded with three stages vapour compression refrigeration system using R1234ze(Z) in medium temperature cycle at evaporator temperature =-30oC, R1225ye(Z) in intermediate temperature cycle at evaporator temperature = -75oC and using HFO-1336mzz(Z) in lower temperature cycle at evaporator temperature = -135oC.

 System-6

 Li/Br-H2O single effect vapour absorption refrigeration system at 10oC of evaporator temperature cascaded with three stages vapour compression refrigeration system using R1234ze(Z) in medium temperature cycle at evaporator temperature =-30oC, HFO-1336mzz(Z) in intermediate temperature cycle at evaporator temperature = -75oC and using R1225ye(Z) in lower temperature cycle at evaporator temperature = -135oC.

 System-7

 Li/Br-H2O single effect vapour absorption refrigeration system at 10oC of evaporator temperature cascaded with three stages vapour compression refrigeration system using R1234ze(E) in medium temperature cycle at evaporator temperature =-30oC, R1225ye(Z) in intermediate temperature cycle at evaporator temperature = -75oC and using HFO-1336mzz(Z) in lower temperature cycle at evaporator temperature = -135oC.

 System-8

 Li/Br-H2O single effect vapour absorption refrigeration system at 10oC of evaporator temperature cascaded with three stages vapour compression refrigeration system using R1234ze(E) in medium temperature cycle at evaporator temperature =-30oC, HFO-1336mzz(Z) in intermediate temperature cycle at evaporator temperature = -75oC and using R1225ye(Z) in lower temperature cycle at evaporator temperature = -135oC.

 System-9

 Li/Br-H2O single effect vapour absorption refrigeration system at 10oC of evaporator temperature cascaded with three stages vapour compression refrigeration system using R1243zf in medium temperature cycle at evaporator temperature =-50oC, R-1225ye(Z) in intermediate temperature cycle at evaporator temperature = -95oC and using HFO-1336mzz(Z) in lower temperature cycle at evaporator temperature = -135oC.

 System-10

 Li/Br-H2O single effect vapour absorption refrigeration system at 10oC of evaporator temperature cascaded with three stages vapour compression refrigeration system using R1243zf in medium temperature cycle at evaporator temperature =-30oC, HFO-1336mzz(Z)in intermediate temperature cycle at evaporator temperature = -75oC and using R-1225ye(Z) in lower temperature cycle at evaporator temperature = -135oC.

 System-11

 Li/Br-H2O single effect vapour absorption refrigeration system at 10oC of evaporator temperature cascaded with three stages vapour compression refrigeration system using R1233zd(E) in medium temperature cycle at evaporator temperature =-50oC, R-1225ye(Z) in intermediate temperature cycle at evaporator temperature = -95oC and using HFO-1336mzz(Z) in lower temperature cycle at evaporator temperature = -135oC.

 System-12

 Li/Br-H2O single effect vapour absorption refrigeration system at 10oC of evaporator temperature cascaded with three stages vapour compression refrigeration system using R1233zd(E) in medium temperature cycle at evaporator temperature =-50oC, HFO-1336mzz(Z) in intermediate temperature cycle at evaporator temperature = -95oC and using R-1225ye(Z) in lower temperature cycle at evaporator temperature = -150oC.

 System-13

 Li/Br-H2O single effect vapour absorption refrigeration system at 10oC of evaporator temperature cascaded with three stages vapour compression refrigeration system using R1234yf in medium temperature cycle at evaporator temperature =-50oC, R-1225ye(Z) in intermediate temperature cycle at evaporator temperature = -95oC and using HFO-1336mzz(Z) in lower temperature cycle at evaporator temperature = -135oC.

 System14

 Li/Br-H2O single effect vapour absorption refrigeration system at 10oC of evaporator temperature cascaded with three stages vapour compression refrigeration system using R1234yf in medium temperature cycle at evaporator temperature =-50oC, HFO-1336mzz(Z) in intermediate temperature cycle at evaporator temperature = -95oC and using R-1225ye(Z) in lower temperature cycle at evaporator temperature = -135oC.

 System-15

 Li/Br-H2O single effect vapour absorption refrigeration system at 10oC of evaporator temperature cascaded with three stages vapour compression refrigeration system using R-1225ye(Z) in medium temperature cycle at evaporator temperature =-50oC, R1233zd(E) in intermediate temperature cycle at evaporator temperature = -95oC and using HFO-1336mzz(Z) in lower temperature cycle at evaporator temperature = -135oC.

 System-16

 Li/Br-H2O single effect vapour absorption refrigeration system at 10oC of evaporator temperature cascaded with three stages vapour compression refrigeration system using R1234yf in medium temperature cycle at evaporator temperature =-50oC, R1233zd(E) in intermediate temperature cycle at evaporator temperature = -95oC and using R-1225ye(Z) in lower temperature cycle at evaporator temperature = -135oC.

Following numerical values have been used for validation of code developed for Integrated single effect Li/Br-H2O VARS using ecofriendly refrigerants

·         Generator temperature= 110oC

·         Absorber temperature=35oC

·         Condenser temperature =35oC

·         VARS evaporator temperature=10oC

·         load on VARS Evaporator= 175 kW

·         Ambient (dead state) temperature=25oC

·         Temperature overlapping in MTC = 10oC

·         VCR evaporator temperature of MTC=-30oC

·         VCR evaporator temperature of ITC=-75oC

·         VCR evaporator temperature of LTC=-135oC

·      VCR compressor efficiency of MTC= 80%

·      VCR compressor efficiency of ITC= 80%

·      VCR compressor efficiency of MTC= 80%

·      Ambient (dead state) temperature=25oC

 Thermodynamic first law energy performances of integrated single effect Li/Br-H2O VARS system cascaded with three stages vapour compression cascaded systems shown in table 2(a) respectively. It was observed that system-2 has lowest thermodynamic performances than system-1, however first law thermodynamic performance improvement is less

Table-2(a) Thermodynamic first law (energetic) Performances of Integrated single effect Li/Br-H2O VARS using ecofriendly refrigerants at evaporator temperature=-135oC

Integrate system

COP_VARS

COP _MTC

COP _ITC

COP _

L TC

%Improvement in COP _MTC

%Improvement in COP _ITC

% Improvement in COP _ LTC

System-5

0.7560

1.002

1.145

1.05

32.56

51.44

38.96

System-6

0.7560

1.002

1.143

1.057

32.58

51.15

39.82

System-7

0.7560

0.9662

1.104

1.020

27.81

46.032

34.92

System-8

0.7560

0.9662

1.102

1.057

27.81

45.82

35.75

System-9

0.7560

0.9698

1.108

1.057

28.29

46.62

35.35

System-10

0.7560

0.9698

1.106

1.057

28.29

46.36

36.16

System-11

0.7560

0.9961

1.138

1.057

31.76

50.53

38.28

System-12

0.7560

0.9961

1.138

1.045

31.76

50.53

38.28

System-13

0.7560

0.9431

1.078

1.0

24.76

42.62

32.31

System-14

0.7560

0.9431

1.076

1.006

24.76

42.37

32.08

System-15

0.7560

0.9634

1.102

1.018

2744

45.74

34.68

System-16

0.7560

0.9794

1.120

1.039

29.56

48.13

37.5

 

Table-2(b) Thermodynamic second law (exergetic) Performances of Integrated single effect Li/Br-H2O VARS using ecofriendly refrigerants at evaporator temperature=-135oC

Integrate system

ETA_VARS

ETA_MTC

ETA_ITC

ETA_

L TC

%Improvement in ETA_MTC

% Improvement in ETA_ITC

%Improvement in ETA_ LTC

System-5

0.1560

0.322

0.5278

0.5383

78.49

192.3

198.1

System-6

0.1560

0.3223

0.5255

0.5491

78.49

191.0

204.1

System-7

0.1560

0.2970

0.4936

0.5126

64.50

173.5

183.5

System-8

0.1560

0.2970

0.4917

0.5227

64.5

172.3

189.5

System-9

0.1560

0.2992

0.4972

0.5152

65.86

175.4

185.3

System-10

0.1560

0.2995

0.4951

0.5253

65.86

174.5

191.0

System-11

0.1560

0.3170

0.5219

0.5339

76.04

189.1

195.7

System-12

0.1560

0.3170

0.5219

0.5339

76.04

189.1

195.7

System-13

0.1560

0.2817

0.4723

0.4958

55.96

161.6

174.6

System-14

0.1560

0.2816

0.4704

0.5054

55.96

160.5

179.9

System-15

0.1560

0.2950

0.4918

0.5110

55.96

172.4

183.0

System-16

0.1560

0.3061

0.5068

0.5347

69.54

180.7

196.1


Table-2(c) Thermodynamic exergy destruction ratio of Integrated single effect Li/Br-H2O VARS at evaporator temperature=-135oC

Integrate system

EDR_VARS

EDR_MTC

EDR_ITC

ED R_

L TC

% Improve in EDR_MTC

%Improvement in EDR_ITC

%Improvement in EDR_ LTC

System-5

4.539

2.103

0.9031

0.8212

-53.66

-80.10

-81.91

System-6

4.539

2.103

0.8947

0.8577

-53.66

-80.29

-81.1

System-7

4.539

2.367

1.025

0.9529

-47.85

-77.41

-79.05

System-8

4.539

2.367

1.034

0.9133

-47.82

-77.23

-79.88

System-9

4.539

2.339

1.011

0.9410

-48.46

-77.72

-79.23

System-10

4.539

2.339

1.02

0.9036

-48.46

-77.53

-80.09

System-11

4.539

2.146

0.916

0.8729

-52.71

-79.82

-80.77

System-12

4.539

2.146

0.916

0.8729

-52.71

-79.82

-80.77

System-13

4.539

2.551

1.117

1.017

-43.79

-75.39

-77.6

System-14

4.539

2.551

1.126

0.9785

-47.37

-77.23

-78.92

System-15

4.389

2.551

1.033

0.9569

-43.79

-75.19

-78.44

System-16

4.539

2.267

0.9730

0.8703

-50.06

-78.56

-80.83

Similarly, Thermodynamic second tlaw exergy performances of cascaded single effect Li/Br-H2O VARS system cascaded with three stages vapour compression cascaded systems shown in table-2(b) respectively. It was observed that system-2 has higher thermodynamic exergetic performances than system-1. However, second law thermodynamic exergetic performance improvement for -150oC evaporator temperature is less. It means by putting HFO-1336mzz(Z) in lower temperature cycle in system-1 gives lower first and second law thermodynamic performances than using R-1225ye(Z) in low temperature cycle. However, first law(energy) and second law exegetic performances of double stage cascaded integrated system-1 is higher than double stage cascaded integrated system-2 at evaporator temperature of -95oC.It means by putting HFO-1336mzz(Z) in intermediate temperature cycle gives lower first and second law thermodynamic performances than using R-1225ye(Z). The exergy destruction ratio of whole cascaded system is shown in Table-2(c) respectively.

Thermodynamic first law energy performances of integrated single effect Li/Br-H2O VARS system cascaded with three stages vapour compression cascaded systems with varying evaporator temperature is shown in table -3 respectively. It was observed that by increasing VAR evaporator temperature, the thermodynamic first law (energy) performance is increases while second law (exergy)efficiency is decreases and exergy destruction ratio is increases. Similarly, Thermodynamic second law exergy performances of cascaded single effect Li/Br-H2O VARS system cascaded with three stages vapour compression cascaded systems with variation of absorber temperature is shown in table-4 respectively. It was observed thermodynamic performances

is decreases, by increasing absorber temperature.

 Table-3 Thermodynamic (exergy) performances of Integrated single effect Li/Br-H2O VARS using R1233zd(E) ecofriendly refrigerants at MTC evaporator temperature=-65oC, T_Eva_VARS= 5oC, Approach=, 5oC

Evaporator temperature of VARS (oC)

COP_VARS

EDR

Exergetic Efficiency

COP_ cascade

EDR_ cascade

Exergetic Efficiency_ cascade

% Improvement in COP _ cascade

% Decrement in EDR _ cascade

%Improv-ment in Exergetic Efficiency _ cascade

3

0.7360

2.783

0.2643

0.7789

1.933

0.3410

5.03

-30.56

29.0

4

0.7410

2.964

0.2523

0.7808

1.970

0.3367

5.03

-33.55

33.48

5

0.7560

3.163

0.2402

0.7827

2.008

0.3325

5.03

-36.52

38.41

6

0.7438

3.382

0.2282

0.7848

2.046

0.3283

5.03

-39.49

43.84

7

0.7466

3.624

0.2163

0.7869

2.085

0.3241

5.03

-42.46

49.87

8

0.7496

3.894

0.2043

0.7892

2.125

0.320

5.03

-45.42

56.60

9

0.7525

4.197

0.1924

0.7916

2.166

0.3159

5.16

-48.40

64.16

10

0.7560

4.539

0.1805

0.7940

2.207

0.3119

5.03

-51.38

72.73


Table-4 Effect of Absorber temperature on thermodynamic performances of Integrated single effect Li/Br-H2O VARS using R1233zd(E) ecofriendly refrigerants at MTC evaporator temperature=-65oC, T_Eva_VARS= 5oC, Approach=, 5oC

Absorber temperature of VARS (oC)

COP_VARS

EDR

Exergetic Efficiency

COP _ cascade

EDR_ cascade

Exergetic Efficiency_ cascade

% Improvement in COP _ cascade

% Decrement in EDR _ cascade

% Improvement in Exergetic Efficiency _ cascade

30

0.7486

3.121

0.2427

0.7885

1.997

0.3337

5.323

-36.02

37.51

35

0.7410

3.163

0.2402

0.7827

2.008

0.3325

5.627

-36.52

38.41

40

0.7353

3.195

0.2384

0.7784

2.016

0.3315

5.856

-36.90

39.09

45

0.7312

3.219

0.2370

0.7752

2.022

0.3309

6.023

-37.17

39.59

Thermodynamic first law energy performances of integrated single effect Li/Br-H2O VARS system cascaded with three stages vapour compression cascaded systems with varying Condenser temperature is shown in table -5 respectively. It was observed that by increasing VARS Condenser temperature, the thermodynamic first law (energy) performance is decreases while second law (exergy)efficiency is decreased and exergy destruction ratio is increases. Similarly, Thermodynamic performances of cascaded single effect Li/Br-H2O VARS system cascaded with three stages vapour compression cascaded systems with variation of generator temperature is shown in table-6 respectively. It was observed thermodynamic performances is decreases, by increasing generator temperature.

Table-5 Effect of condenser temperature on thermodynamic performances of Integrated single effect Li/Br-H2O VARS using R1233zd(E) ecofriendly refrigerants at MTC evaporator temperature=-65oC, T_Eva_VARS= 5oC, Approach=, 5oC

Condenser temperature of VARS (oC)

COP_VARS

EDR

Exergetic Efficiency

COP _ cascade

EDR_ cascade

Exergetic Efficiency_ cascade

% Improvement in

COP _ cascade

% Decrement in EDR _ cascade

%Improv-ment in Exergetic Efficiency _ cascade

30

0.7472

3.129

0.2422

0.7874

2.003

0.3330

5.38

-36.11

37.61

32

0.7449

3.141

0.2415

0.7857

2.004

0.3328

5.470

-36.26

37.94

34

0.7423

3.156

0.2406

0.7837

2.006

0.3327

5.574

-36.44

38.25

35

0.7410

3.163

0.2402

0.7827

2.008

0.3325

5.627

-36.52

38.41

36

0.7398

3.170

0.2398

0.7818

2.070

0.3323

5.678

-36.61

38.56

38

0.7374

3.183

0.2390

0.780

2.013

0.3319

5.773

-36.76

38.84

40

0.7353

3.195

0.2384

0.7784

2.016

0.3315

5.856

-36.90

39.09

42

0.7336

3.205

0.2378

0.7771

2.019

0.3313

5.925

-37.01

39.30

44

0.7322

3.213

0.2373

0.7760

2.021

0.3310

5.983

-37.11

39.47

45

0.7315

3.217

0.2371

0.7755

2.022

0.3309

6.009

-37.15

39.55

Table-6 Effect of generator temperature on thermodynamic performances of Integrated single effect Li/Br-H2O VARS using R1233zd(E) ecofriendly refrigerants at MTC evaporator temperature=-65oC, T_Eva_VARS= 5oC, Approach=, 5oC

Generator temperature of VARS (oC)

COP_VARS

EDR_VARS

Exergetic Efficiency_VARS

COP _MTC

EDR _MTC

Exergetic Efficiency _ M TC

%Improve-ment in COP _MTC

%Improve-ment in COP _ITC

%Improv-ment in COP _ LTC

90

0.7596

2.277

0.3052

0.8194

1.599

0.3849

7.881

-29.79

26.10

95

0.7532

2.510

0.2849

0.8145

1.657

0.3761

8.132

-33.98

32.10

100

0.7478

2.737

0.2676

0.8103

1.715

0.3684

8.346

-37.37

37.67

105

0.7437

2.955

0.2528

0.8070

1.770

0.3611

8.509

-40.13

42.82

110

0.7410

3.163

0.2402

0.8049

1.822

0.3544

8.618

-42.40

47.53

115

0.7388

3.364

0.2291

0.8031

1.873

0.3481

8.709

-44.34

51.93

120

0.7399

3.541

0.2202

0.8040

1.917

0.3428

8.665

-45.87

55.68


Thermodynamic first law energy performances of integrated single effect Li/Br-H2O VARS system cascaded with three stages vapour compression cascaded systems with varying generator temperature for constant evaporator temperature of -75oC in lower vapour compression cycle is shown in tables -7 for R1233zd(E), R1225ye(Z) and HFO-1336mzz(Z) respectively. It was observed that by increasing VARS Condenser temperature, the thermodynamic first law (energy) performance is decreases while second law (exergy)efficiency is decreases and exergy destruction ratio is increases. Similarly, Thermodynamic performances of cascaded single effect Li/Br-H2O VARS system cascaded with three stages vapour compression cascaded systems with variation of generator temperature is shown in table-6 respectively. It was observed thermodynamic performances

 Table-7(a) Effect of generator temperature on thermodynamic performances of Integrated single effect Li/Br-H2O VARS using R1233zd(E) ecofriendly refrigerants at MTC evaporator temperature=-75oC, T_Eva_VARS= 5oC, Approach=, 5oC

Generator temperature of VARS (oC)

COP_Cascade

EDR_ Cascade

Exergetic

Efficiency_ Cascade

90

0.8194

1.599

0.3849

95

0.8145

1.657

0.3761

100

0.8103

1.715

0.3684

105

0.8070

1.770

0.3611

110

0.8049

1.822

0.3544

115

0.8031

1.873

0.3481

120

0.8040

1.917

0.3428

Table-7(b) Effect of generator temperature on improvement in thermodynamic performances of Integrated single effect Li/Br-H2O VARS using R1233zd(E) ecofriendly refrigerants at MTC evaporator temperature=-75oC, T_Eva_VARS= 5oC, Approach=, 5oC

Generator temperature of VARS (oC)

% improvement in COP_ Cascade

% decre-ment in EDR_ Cascade

% improvement in Exergetic

Eff_ Cascade

90

7.881

-29.79

26.10

95

8.132

-33.98

32.10

100

8.346

-37.36

37.67

105

8.509

-40.13

42.82

110

8.618

-42.40

47.53

115

8.709

-44.34

51.93

120

8.665

-45.87

55.68

 able-7(c) Effect of generator temperature on thermodynamic performances of Integrated single effect Li/Br-H2O VARS using HFO1336mzz(Z) ecofriendly refrigerants at MTC evaporator temperature=-75oC, T_Eva_VARS= 5oC, Approach=, 5oC

Generator temperature of VARS (oC)

COP_ cascade

EDR_ cascade

Exergetic

Efficiency_ cascade

90

0.7950

1.790

0.3594

95

0.7902

1.852

0.3507

100

0.7478

1.911

0.3435

105

0.7437

1.968

0.3369

110

0.7410

2.022

0.3309

115

0.7388

2.075

0.3252

120

0.7399

2.122

0.3204

 able-7(d) Effect of generator temperature on percentage improvement in thermodynamic performances of Integrated single effect Li/Br-H2O VARS using HFO1336mzz(Z) ecofriendly refrigerants at MTC evaporator temperature=-65oC, T_Eva_VARS= 5oC, Approach=, 5oC

Generator temperature of VARS (oC)

% improvement in COP_cascade

% decrement in EDR_ cascade

% improvement in Exergetic

Efficiency_ cascade

90

4.662

-21.36

17.43

95

4.914

-26.26

23.10

100

5.129

-30.18

28.38

105

5.293

-33.41

33.26

110

5.402

-36.06

37.73

115

5.493

-38.32

41.92

120

5.449

-40.09

45.49

 able-7(e) Effect of generator temperature on thermodynamic performances of Integrated single effect Li/Br-H2O VARS using R1225ye(Z) ecofriendly refrigerants at MTC evaporator temperature=-65oC, T_Eva_VARS= 5oC, Approach=, 5oC

Generator temperature of VARS (oC)

COP_ cascade

EDR_ cascade

Exergetic

Efficiency_ cascade

90

0.7851

1.874

0.3479

95

0.7532

1.936

0.3406

100

0.7478

1.997

0.3337

105

0.7437

2.055

0.3274

110

0.7410

2.11

0.3216

115

0.7388

2.163

0.3161

120

0.7399

2.211

0.3115

 able-7(f) Effect of generator temperature on percentage improvement thermodynamic performances of Integrated single effect Li/Br-H2O VARS using R1225ye(Z) ecofriendly refrigerants at MTC evaporator temperature=-75oC, T_Eva_VARS= 5oC, Approach=, 5oC

Generator temperature of VARS (oC)

% improve-ment in COP_ cascade

% decre-ment in EDR_ cascade

% improvement in Exergetic

Efficiency_ cascade

90

3.359

-17.69

17.43

95

3.612

-22.87

23.10

100

3.827

-27.06

28.38

105

3.991

-30.48

33.26

110

4.10

-33.29

37.73

115

4.192

-35.70

41.92

120

4.148

-37.58

45.49

 3.       Conclusions

 

Following conclusions were drawn from present investigations

 ·         By reducing the exergy destruction rate by using HFO refrigerants therefore, sustainability improved.

·         The best thermodynamic performances were observed by using R1234ze(Z) and R1233zd(E), HFO-1336mzz(Z), and R1225ye(Z) and R1234ze(E) and R1243zf performance

·          The lowest thermodynamic performances were fund by using R1234yf in cascaded system in lower circuit up to a VCR evaporator temperature

·         In single cascading with VARS, at low temperature applications up to -30oC evaporator temperature, HFO ecofriendly refrigerants (R-1234ze(Z), R-1234ze(E), R1233zd(E), R-1243zf, R1225ye(Z), HFO-1336mzz(Z) and R1234yf will be certainly useful for replacing HFC, HCFC and CFC refrigerants, while R1224yd(Z) will be suitable for -10oC above evaporator temperature for replacing R134a.

·         In single cascading with VARS, at low temperature applications up to -50oC evaporator temperature, HFO ecofriendly refrigerants (R1225ye(Z), R1233zd(E), HFO-1336mzz(Z) and R1234yf will be certainly useful for replacing HFC, HCFC and CFC refrigerants.

·         In the double cascading with VARS, at low temperature applications up to -75oC evaporator temperature, HFO ecofriendly refrigerants (R1225ye(Z), R1233zd(E), HFO-1336mzz(Z) will be certainly useful for replacing HFC, HCFC and CFC refrigerants and can be better than replacing R134a

·         In the triple cascading with VARS, at ultra-low temperature applications up to -150oC evaporator temperature, HFO ecofriendly refrigerants (R1225ye(Z), HFO-1336mzz(Z) will be certainly useful for replacingR32, and, HCFC and CFC refrigerants.

 

References

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[8]      Radhey Shyam Mishra, (2019), Thermal performance of cascaded vapour compression absorption systems, International Journal of Research in Engineering and Innovation, 3 (1), 61-67.

[9]      Radhey Shyam Mishra, (2019), Performance evaluation of half effect Li/Br-H2O vapour absorption systems using multi cascading of vapour compression cycles for ultra-low temperature applications International Journal of Research in Engineering and Innovation, 3 (1), 509-526.

[10]   Radhey Shyam Mishra, (2020), Single and multiple cascading of VCRS in NH3H2O vapour absorption refrigeration systems for improving thermodynamic (energy-exergy) performances using five ecofriendly new HFOs and other low GWP refrigerants for replacing R134a, International Journal of Research in Engineering and Innovation, 4 (2), 96-104.


 

 




 

 

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