chapter 5 results and discussion -...

CHAPTER 5

RESULTS AND DISCUSSION

As per the procedure discussed in the previous chapter, tests

were performed with pure R134a and HC mixture

(50%R290/50%R600a). This was a baseline test and then with mixture-

1, mixture-2, mixture-3, mixture-4 and mixture-5 were kept at the

same ambient temperature of 320C in a visi cooler designed originally to

work with R134a. The original lubricating oil is not changed throughout

the experiment. The predicted system performance is compared with

the experimental values. The performance parameters such as energy

consumption of the compressor, pull down time, theoretical and actual

COP, refrigeration effect etc of the refrigerants are suitably analysed for

different calorimeter temperatures, mass and capillary lengths. The

performance of the alternative mixtures is also compared with R134a

and HC mixture.

5.1 OPTIMIZATION OF REFRIGERANT CHARGE AND CAPILLARY

LENGTH RESULTS As per the procedure discussed in the previous chapter

optimization of refrigerant charge and capillary length were carried out

for the base refrigerants and also for the selected alternative

refrigerants, the results are discussed below

5.1.1 Optimization of Refrigerant Charge and Capillary Length for

R134a

As the test rig is modified to fix the measuring instruments the

charge quantity specified by the manufacturer may not be sufficient,

there is a need for the charge optimization. Modifications made in the

test rig were minimum, it was tested with the charge of 220grams,

240grams and 260 grams of R134a and its performance at 320C

ambient temperature was studied and has been plotted in Figure 5.1.

During the study, the test rig showed better performance at the

manufacturer specified quantity of 240 grams. The power consumption

with respect to capillary length at different refrigerant charge quantity

at 320C ambient temperature is plotted in Figure 5.2. From the Figures

5.2 and 5.1 the optimum capillary length and charge were taken as

3.3m and 240 grams due to lower energy consumption. The 240 grams

charge of the R134a was taken as reference to evaluate alternative

mixture quantities.

160

165

170

175

180

220 240 260

Mass of the charge in grams

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R134a

Figure 5.1 Variation of compressor power with different charge quantity

in a visi cooler for R134a

155

165

175

185

195

205

215

1.5 2.1 2.7 3.3 3.9 4.5

Capillary length in meters

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R134a

Figure 5.2 Variation of compressor power with different capillary

lengths in a visi cooler for R134a


HC Mixture (50% R290 and 50% R600a)

After carrying out the required base line tests with R134a, the

refrigerant R134a was recovered and the system was flushed with

nitrogen gas and evacuated with the vacuum pump for 3 hours. The

system was charged with equivalent quantity of HC mixture. As mixture

is a zeotrope nature, refrigerant has to be charged in liquid form by

using an electronic weighing balance with an accuracy of ±1 gram with

a suitable charging kit. All the tests which were carried out for R134a

were also carried out for the HC mixture. To check the energy efficiency

of the equivalent charge of HC mixture, length of capillary tube and

charge optimization were studied and have been plotted on Figure 5.4

and Figure 5.3 respectively. As the HC mixture needs nearly double the

capillary length than that of the R134a. The energy consumption

184

186

188

190

192

194

196

198

94 104 114

Mass of the charge in grams

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HC mixture(50%R290,50%R600a)

Figure 5.3 Variation of compressor power with different charge quantity

in a visi cooler for HC mixture (50%R290 and 50%R600a)

180

185

190

195

200

205

210

2.7 3.6 4.5 5.4 6.3 7.2

Caillary length in meters

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HC mixture(50%R290,50%R600a)

Figure 5.4 Variation of compressor power with different capillary

lengths in a visi cooler for HC mixture (50%R290 and 50%R600a)

test was carried out at four different capillary lengths 4.5m, 5.4m, 6.3m

and 7.2m. It shows that the equivalent charge of 104 grams was the

best charge to give lower energy consumption at nearly double the

length of the capillary of 6.3m as compared to that of 3.3m for R134a.

5.1.3 Optimization of Refrigerant Charge and Capillary Length for Mixture-1(5%R134a, 95%HC mixture)

After carrying out the required base line tests with R134a and HC

mixture, the refrigerant was recovered and the system was flushed with

nitrogen gas and evacuated with the vacuum pump for 3 hours. The

system was charged with equivalent quantity of mixture-1. As the

mixture is a ternary mixture of zeotrope nature, refrigerant has to be

charged in liquid form by using an electronic weighing balance with an

accuracy of ±1 gram with a suitable charging kit. All the tests carried

out for R134a and HC mixture were also carried out for the mixture-1.

To check the energy efficiency of the equivalent charge of mixture-1

length of capillary tube and charge optimization were studied and

plotted on Figure 5.5. Mixture-1 needs more capillary length than

R134a due to lower viscosity and nearly equal or lower capillary lengths

than HC mixture. The energy consumption test is carried out at five

different capillary lengths Viz., 3.3m, 4.5m, 5.4m, 6.3m and 7.2m. It

shows that the equivalent charge of 106 grams was the best charge to

give lower energy consumption at similar capillary length of the HC

mixture of 6.3m is due to mixture contains 95% of HC mixture as

shown in Figure 5.4.


Mixture-2(15%R134a, 85%HC mixture)

After carrying out the required tests with mixture-1, the

refrigerant was recovered and the system was flushed with nitrogen gas

and evacuated with the vacuum pump for 3 hours. The system was

charged with equivalent mass of mixture-2. As the mixture is a ternary

mixture of zeotrope nature, refrigerant has to be charged in liquid form

by using an electronic weighing balance with an accuracy of ±1 gram

with a suitable charging kit. All the tests carried out for R134a and HC

mixture were also carried out for the mixture-2. To check the energy

efficiency of the equivalent charge of mixture-2 length of capillary tube

and charge optimization were studied and plotted on Figure 5.6.

Mixture-2 needs more capillary length than R134a due to lower

viscosity and lower capillary length than that of the HC mixture as the

mixture contains 15% of the R134a. The energy consumption test was

carried out at four different capillary lengths Viz., 3.3m, 4.5m, 5.4m

and 6.3m. It shows that the equivalent charge of 113 grams was the

best charge to give lower energy consumption at a capillary length of

5.4m.

170

180

190

200

210

220

2.7 3.6 4.5 5.4 6.3 7.2


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96 grams 106 grams 116 grams

Figure 5.5 Variation of compressor power with charge quantity at

different capillary lengths for mixture -1

170

180

190

200

210

220

2.7 3.6 4.5 5.4 6.3Capillary length in meters

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103grams 113 grams 123 grams

Figure 5.6 Variation of compressor power with charge quantity at different capillary lengths for mixture -2












and charge optimization were studied and have been plotted on Figure

5.7. Mixture-3 needs more capillary length than R134a due to lower

viscosity and lower capillary length than HC mixture as the mixture

contains 25% of the R134a. The energy consumption test was carried

out at four different capillary lengths Viz., 3.3m, 4.5m, 5.4m and 6.3m.

It shows that the equivalent charge of 120 grams was the best charge to

give lower energy consumption at a capillary length of 5.4m.

160

170

180

190

200

210

2.7 3.6 4.5 5.4 6.3


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Figure 5.7 Variation of compressor power with charge quantity at different capillary lengths for mixture -3












and charge optimization were studied and have been plotted on Figure

5.8. Mixture-4 needs more capillary length than R134a due to lower

viscosity and lower capillary length than HC mixture as the mixture

contains 35% of the R134a. The energy consumption test was carried

out at four different capillary lengths 3.3m, 4.5m, 5.4m and 6.3m. It

shows that the equivalent charge of 129 grams was the best charge to

give lower energy consumption at a capillary length of 5.4m.

160

170

180

190

200

2.7 3.6 4.5 5.4 6.3


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different capillary lengths for mixture -4


Mixture-5 (45%R134a, 55%HC mixture)









efficiency of the equivalent charge of mixture-5 length of the capillary

tube and charge optimization were studied and have been plotted on

Figure 5.9. Mixture-5 needs more capillary length than R134a due to

lower viscosity and lower capillary length than HC mixture as the

mixture contains 45% of the R134a. The energy consumption test was

carried out at four different capillary lengths 3.3m, 4.5m, 5.4m and

6.3m. It shows that the equivalent charge of 139 grams was the best

charge to give lower energy consumption at a capillary length of 5.4m.

160

170

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190

200

2.7 3.6 4.5 5.4 6.3


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different capillary lengths for mixture-5

The optimized length of the capillary tube and charge of the

selected alternative mixtures and base refrigerants are shown in Table

5.1.

Table 5.1 Optimization of capillary length and refrigerant charge for the

selected refrigerants

Mixture Optimum capillary length

in meters

Optimum refrigerant

charge in grams

Mixture-1 6.3 106

Mixture-2 5.4 113

Mixture-3 5.4 120

Mixture-4 5.4 129

Mixture-5 5.4 139

R134a 3.3 240

HC mixture 6.3 104

5.2 PULL DOWN TEST RESULTS

Pull-down time is the time required for changing the brine

solution (secondary refrigerant) temperature from 30OC to the desired

final temperature 2OC. This test decides the cooling rate of the system.

5.2.1 Pull Down Test for R134a and HC Mixture Refrigerants

The temperature drop of the brine solution in the refrigerated

space during pull down time is plotted in Figure 5.10. The pull down

time for HC mixture (50%R290/50%R600a) is only 37 minutes whereas

it is 56 minutes in the case of R134a.

0

5

10

15

20

25

30

35

0 10 20 30 40 50 60

Pull down time in minutes

Tem

pera

ture

of calo

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ete

r in

0C

HC R134a

Figure 5.10 Pull down test for R134a and HC mixture at 20C cut-off temperature

From the Figure 5.10, it shows that HC mixture reduces the

refrigerator cabin temperature at a faster rate as compared to R134a.

The cooling speed for HC mixture refrigerant is observed to increase by

33%. This is due to more latent heat of vaporization of the HC mixture

as that of the R134a.

5.2.2 Pull Down Test for Alternative Refrigerant Mixtures

Pull down test for alternative refrigerant mixtures of mixture-1,

mixture-2, mixture-3, mixture-4 and mixture-5 are plotted in the

following Figures 5.11 to 5.15.

0

5

10

15

20

25

30

35

0 10 20 30 40 50 60

Time in minutes

Tem

pera

ture

of calo

rim

ete

r

in

oC

R134a HC Mix-1

Figure 5.11 Pull down test for mixture-1 in comparison with R134a and

HC mixture at 20C cut-off temperature.

0

5

10

15

20

25

30

35

0 10 20 30 40 50 60

Time in minutes

Tem

pera

ture

of calo

rim

ete

r

in o

C

R134a HC Mix-2



0

5

10

15

20

25

30

35

0 10 20 30 40 50 60

Time in minutes

Tem

pera

ture

of calo

rim

ete

r

in o

C

R134a HC Mix-3



0

5

10

15

20

25

30

35

0 10 20 30 40 50 60

Time in minutes

Tem

pera

ture

of calo

rim

ete

r

in

oC

R134a HC Mix-4



0

5

10

15

20

25

30

35

0 10 20 30 40 50 60

Time in minutes

Tem

pera

ture

of calo

rim

ete

r

in o

C

R134a HC Mix-5

Figure 5.15 Pull down test for mixture-5 in comparison with R134a and HC mixture at 20C cut-off temperature.

The Figures from 5.11 to 5.15 show that the cooling speed of the

system decreases from mixture-1 to mixture-5 due to decreased HC

content of the mixtures from 95% to 55%. Pure R134a has a lower

cooling speed than that of the alternative mixtures and 100% HC

mixture has a highest cooling speed due to more latent heat of

vaporisation.The pull down time of the refrigerants are listed in the

Table 5.2.

Table 5.2 Pull down test for the selected refrigerants

Refrigerant R134a HC mix

mix-1 mix-2 mix-3 mix-4 mix-5

Pull Down time in minutes

56 37 38 40 42 44 46

5.3 Energy Consumption of the Compressor, Refrigeration Effect and Actual COP Test Results

Performance tests were carried out as per the procedure

discussed in chapter-4 at 320C ambient temperature, different

capillary lengths and different charge of the refrigerant at three

different calorimeter temperatures (20C, 50C and 80C). The results are

given in Tables 5.3 to 5.8. For the mixture-1 minimum energy

consumption is obtained at 6.3 m capillary length which is the

optimum capillary length for the HC mixture, mixture-2, mixture-3,

mixture-4 and mixture-5 minimum energy consumption is obtained at

5.4 m capillary length and the optimum capillary length for the R134a

is 3.3m. So, it is decided to conduct the performance tests of the

mixture-1 on 3.3m, 5.4m, 6.3m and 7.2m capillary lengths and

mixture-2 to mixture-5 on 3.3m, 5.4m and 6.3m capillary lengths.

Among the five alternative mixtures, mixture-1 shows higher

energy consumption and mixture-5 depicts minimum energy

consumption. The reason for decrease in energy consumption is due

to increase of R134a content in the mixture which decreases the

specific volume. Refrigeration effect is found to increase from mixture-5

to mixture-1, due to increase in percentage of HC mixture content of

the ternary mixture as the HC mixture posses more latent heat of

vaporization as compared to R134a.

Table 5.3 Experimental results of mixture-1

Refrig erant

Charge in grams

Lcap Calorimeter Tem-

perature in 0C Power in

watts Refrigeration effect in watts

COP

Mix

ture

-1

96

3.3

2 206 245 1.19

5 210 290 1.38

8 213 340 1.6

4.5

2 199 243 1.22

5 202 283 1.4

8 205 335 1.63

5.4

2 187 236 1.26

5 191 277 1.45

8 193 329 1.7

6.3

2 178 232 1.3

5 180 274 1.52

8 183 329 1.8

7.2

2 187 213 1.14

5 191 264 1.38

8 194 318 1.64

106

3.3

2 198 271 1.37

5 201 313 1.55

8 204 378 1.85

4.5

2 186 261 1.4

5 188 299 1.59

8 192 364 1.9

5.4

2 181 255 1.41

5 184 295 1.6

8 186 356 1.91

6.3

2 176 250 1.42

5 178 289 1.62

8 180 348 1.93

7.2

2 178 233 1.31

5 181 268 1.48

8 185 330 1.78

116

3.3

2 212 257 1.21

5 215 305 1.42

8 218 365 1.67

4.5

2 203 250 1.23

5 206 297 1.44

8 210 357 1.7

5.4

2 195 252 1.29

5 197 296 1.5

8 200 350 1.75

6.3

2 183 240 1.31

5 186 283 1.52

8 188 340 1.81

7.2

2 193 226 1.17

5 196 263 1.34

8 201 322 1.6


Refrig-

erant

Charge

in grams

Lcap

in meters

Calorimeter

Temperature

Power

in watts

Refrigeration

effect in watts

COP

Mix

ture

-2

103

3.3

2 199 241 1.21

5 203 282 1.39

8 206 340 1.65

5.4

2 181 230 1.27

5 184 272 1.48

8 187 326 1.74

6.3

2 188 224 1.19

5 191 262 1.37

8 195 314 1.61

113

3.3

2 192 267 1.39

5 195 304 1.56

8 199 374 1.88

5.4

2 170 247 1.45

5 172 286 1.66

8 175 343 1.96

6.3

2 179 242 1.35

5 182 277 1.52

8 185 338 1.83

123

3.3

2 202 248 1.23

5 206 293 1.42

8 210 354 1.69

5.4

2 177 239 1.35

5 180 277 1.54

8 183 331 1.81

6.3

2 191 193 1.01

5 193 264 1.37

8 197 320 1.62


Refrig -erant

Charge in

grams

Lcap in

meters

Calorimeter Temperature

in 0C

Power in

watts

Refrigeration effect in

watts

COP

Mix

ture

-3

110

3.3

2 192 234 1.22

5 196 276 1.41

8 199 336 1.69

5.4

2 170 224 1.32

5 172 263 1.53

8 175 318 1.82

6.3

2 177 214 1.21

5 180 252 1.4

8 184 306 1.66

120

3.3

2 185 263 1.42

5 187 295 1.58

8 190 361 1.9

5.4

2 163 241 1.48

5 166 279 1.68

8 168 334 1.99

6.3

2 166 229 1.38

5 170 262 1.54

8 173 321 1.86

130

3.3

2 200 250 1.25

5 203 294 1.45

8 207 353 1.71

5.4

2 173 227 1.31

5 176 269 1.53

8 179 328 1.83

6.3

2 179 222 1.24

5 182 260 1.43

8 186 313 1.68


Refrig erant

Charge in grams

Lcap in meters

Calorimeter Temperature in 0C

Power in watts

Refrigeration effect in watts

COP M

ixtu

re-4

119

3.3

2 187 224 1.2

5 189 261 1.38

8 193 318 1.65

5.4

2 165 213 1.29

5 168 252 1.5

8 171 301 1.76

6.3

2 173 206 1.19

5 176 239 1.36

8 180 292 1.62

129

3.3

2 179 247 1.38

5 181 282 1.56

8 184 343 1.86

5.4

2 160 229 1.43

5 163 267 1.64

8 165 319 1.93

6.3

2 164 223 1.36

5 167 256 1.53

8 170 312 1.84

139

3.3

2 193 234 1.21

5 196 274 1.4

8 200 330 1.65

5.4

2 168 218 1.3

5 170 258 1.52

8 174 313 1.8

6.3

2 177 212 1.2

5 181 250 1.38

8 184 299 1.63


Refrig erant

Charge in grams

Lcap in meters

Calorimeter Temperature in 0C

Power in watts

Refrigeration effect in watts

COP M

ixtu

re-5

129

3.3

2 179 213 1.19

5 182 246 1.35

8 185 303 1.64

5.4

2 163 207 1.27

5 165 241 1.46

8 168 291 1.73

6.3

2 169 198 1.17

5 172 225 1.31

8 177 283 1.6

139

3.3

2 173 236 1.36

5 175 266 1.52

8 179 326 1.82

5.4

2 158 220 1.39

5 160 253 1.59

8 163 306 1.89

6.3

2 162 214 1.32

5 164 248 1.51

8 168 303 1.8

149

3.3

2 186 223 1.2

5 189 259 1.37

8 193 315 1.63

5.4

2 165 203 1.23

5 168 227 1.35

8 171 285 1.67

6.3

2 174 197 1.13

5 177 219 1.24

8 181 272 1.5

The actual COP is calculated from the compressor power and

refrigeration effect. All the experiments were repeated and the average

of the results obtained from experiments is used for comparison. The

average of power and COP with different capillary lengths and at

different calorimeter temperatures of different mixtures have been

plotted in Figures 5.16 to 5.21.

140

160

180

200

220

2.7 3.6 4.5 5.4 6.3 7.2


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R134a HC mix Mix-1 Mix-2

Mix-3 Mix-4 Mix-5

Figure 5.16 Variation of power with the capillary lengths for the selected alternative refrigerants at 20C calorimeter temperature

140

160

180

200

220

2.7 3.6 4.5 5.4 6.3 7.2


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Mix-3 Mix-4 Mix-5

Figure 5.17 Variation of Power with the capillary lengths for the

selected alternative refrigerants at 50C calorimeter temperature

140

160

180

200

220

2.7 3.6 4.5 5.4 6.3 7.2


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Mix-3 Mix-4 Mix-5

Figure 5.18 Variation of Power with the capillary lengths for the selected alternative refrigerants at 80C calorimeter temperature

1.2

1.3

1.4

1.5

2.7 3.6 4.5 5.4 6.3 7.2


CO

P

Mix-1 Mix-2 Mix-3 Mix-4

Mix-5 R134a HC mix

Figure 5.19 Variation of COP with the capillary lengths for the selected

alternative refrigerants at 20C calorimeter temperature

1.4

1.5

1.6

1.7

2.7 3.6 4.5 5.4 6.3 7.2


CO

P


Mix-5 R134a HC mix

Figure 5.20 Variation of COP with the capillary lengths for the selected alternative refrigerants at 50C calorimeter temperature.

1.7

1.8

1.9

2

2.7 3.6 4.5 5.4 6.3 7.2


CO

P


Mix-5 R134a HC mix

Figure 5.21 Variation of COP with the capillary lengths for the selected

alternative refrigerants at 80C calorimeter temperature

From the Figures 5.16 to 5.18 it is observed that, energy

consumption of the compressor decreases from mixture-1 to mixture-5,

due to increasing of R134a quantity in the ternary mixture. Maximum

energy consumption is obtained for HC mixture due to its high specific

volume. From Tables 5.3 to 5.7 it is observed that refrigeration effect

decreases from mixture-1 to mixture-5 as latent heat of vaporization

decreases with the decreasing quantity of the HC quantity in the

ternary mixture.

R134a is having lower specific volume and latent heat of

vaporization than the HC mixture. Specific volumes and latent heat of

vaporization for the considered ternary mixtures are more than that of

R134a and less than HC mixture. From the Figures 5.19 to 5.21 it is

observed that, as the percentage of R134a increases (from mixture-1 to

mixture-5), COP starts increasing from mixture-1 to mixture-3 and

reaching maximum at mixture-3 then COP starts decreasing from

mixture-3 to mixture-5. From mixture-1 to mixture-3 decrease in

refrigeration effect is less as compared to decrease in compressor

power. Later, for mixture-4 and mixture-5 decrease in refrigeration

effect dominates the decrease in compressor power and thus COP

decreases. The specific volumes of the five alternative mixtures are

tabulated under the operating conditions of the test rig as shown in

Table 5.8

Table 5.8 Variation of specific volumes for the selected refrigerants

Refrigerant R134a Mix-1 Mix-2 Mix-3 Mix-4 Mix-5 HC mix

Specific

Volume m3/kg

0.154 0.293 0.273 0.252 0.233 0.214 0.306

5.4 COMPARISON OF EXPERIMENTAL AND THEORETICAL

RESULTS OF PERFORMANCE TESTS

At the optimum capillary settings and steady state conditions the

various parameters including the COP, energy consumption were

studied and tabulated in Table 5.9. The theoretical COP is calculated

using REFPROP 6.0 software by considering the actual working

conditions during the experimentation. The actual COP is calculated by

considering the calorimeter heater load and actual compressor power.

Experimental values of COP follow the same trend as that of the

theoretical values. The mass flow rate of the mixture-3 is decreased by

35% due its more latent heat of vaporization value and slightly less

than HC mixture due to lower pressure ratio than HC mixture and

hence more volumetric efficiency.

Table 5.9 Performance comparison of R134a, HC mixture with

mixture-3 at 320C ambient temperature in a visi cooler

S.No. Description R134a Mixture-3 HC mixture

1 Power-Theoretical 155 162 176

2 Power-Experimental 162 168 186

3 COP- Theoretical 1.89 2.11 2.04

4 COP- Experimental 1.81 1.99 1.9

5 mass flow rate(kg/sec) 0.00246 0.00161 0.00151

140

150

160

170

180

190

2 5 8

Temperature of calorimeter in OC

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R134a(T) R134a(E) Mix-3(T)

Mix-3(E) HC mix (T) HC mix (E)

Figure 5.22 Comparison of predicted and experimental values of

compressor power at different calorimeter temperatures for R134a, HC mixture and mixture-3

The compressor power obtained from theoretical calculations

and experimental data calculations for various calorimeter

temperatures at 320C ambient temperature is plotted in Figure 5.22.

For mixture-3 the theoretical values are deviating from the

experimental values by 7.6% to 8.67%, whereas it is 5.9% to 6.2% for

R134a and for HC mixture deviates 8.1% to 9.0%. This proves the

validity of the present model.

Among the five alternative refrigerant mixtures best COP

is obtained for mixture-3 (25%R134a/37.55%R600a/37.5%R290). The

performance comparison of best alternative refrigerant mixture and the

base refrigerants results are plotted from Figures 5.23 to 5.25.

From the Figure 5.24, it is observed that the compressor work of

mixture-3 is lower than that of the HC mixture due to decreased

specific volume and more than that of R134a due to higher specific

volume. Mixture-3 refrigeration effect is lower than HC mixture

(50%R290/50%R600a) as shown in Figure 5.23 which is due to

decreased latent heat of vaporization and it is superior to R134a. As

shown in Figure 5.25, for all calorimeter temperatures, mixture-3 is

having higher COP than the base refrigerants (R134a, HC mixture). For

mixture-3, when compared to decrease in refrigeration effect, decrease

in specific volume reaches a maximum value.

180

240

300

360

2 5 8

Temperature of calorimeter in 0C

Refr

igera

tion

effect

in w

att

s

R134a HC mix Mix-3

Figure 5.23 Variation of refrigeration effect at different calorimeter

temperatures

150

160

170

180

190

2 5 8


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Mix-3 R134a HC mix

Figure 5.24 Variation of compressor power at different calorimeter temperatures

1.25

1.5

1.75

2

2 5 8

Temperature of Calorimeter in 0C

CO

P

R134a HC mix Mix-3

Figure 5.25 Variation of COP at different calorimeter temperatures

Upon the successful continuous operation of the system, the

performance of mixture-3 is found to be better when compared with

either R134a or HC mixture.

At this stage optimization of parameters of the COP, power and

refrigeration effect by using Taguchi method is attempted by

considering four factors at three levels using orthogonal array L18.

5.5 TAGUCHI METHOD BASED DESIGN OF EXPERIMENTS (DOE)

It is a systematic procedure to layout the factors and levels of an

experiment in standard special partial factorial arrangements (OA) to

determine optimum design to yield an improved understanding of

process performance. It essentially uses the conventional statistical

tools and simplifies by them by identifying the set of sequence

guidelines for experiment layout and analysis of results with the least

number of experiments.

5.5.1 Factors and its Levels

Table 5.10 Factors and its levels

Factor Level 1 Level 2 Level 3

Length of Capillary(m) 3.3 5.4 6.3

Mixture Mixture-1 Mixture-3 Mixture-5

Refrigerant Charge m1 m2 m3

Temperature of

Calorimeter(0C) 2 5 8

The nomenclatures of the mixtures are as follows

Mixture-1: 5%R134a/47.5%R600a/47.5%R290

Mixture-3: 25%R134a/37.5%R600a/37.5%R290

Mixture-5: 45%R134a/27.5%R600a/27.5%R290

For each mixture the equivalent charge quantity to R134a is

calculated and tabulated in Table 5.11. The equivalent charge quantity

is assigned to a variable of m2; values of m1 and m3 were given 10g

below and above that of the mass m2.

Table 5.11 Investigated mass of the refrigerant charge for the

considered mixtures

Mixture

Mass of Refrigerant Charge in grams

m1 m2 m3

Mixture-1 96 106 116

Mixture-3 110 120 130

Mixture-5 129 139 149

Table 5.12 Experimental layout using Orthogonal Array L18

Factor A B C D

Experiment Run

Capillary Length

Mixture Charge Calorimeter Temperature

1 1 1 1 1

2 1 2 2 2

3 1 3 3 3

4 2 1 1 2

5 2 2 2 3

6 2 3 3 1

7 3 1 2 1

8 3 2 3 2

9 3 3 1 3

10 1 1 3 3

11 1 2 1 1

12 1 3 2 2

13 2 1 2 3

14 2 2 3 1

15 2 3 1 2

16 3 1 3 2

17 3 2 1 3

18 3 3 2 1

Table 5.13 Mean value and S/N ratio for COP

INPUT PARAMETERS RESPONSE

Exp.

Run

Lcap

m Mixture

Charge

grams

Temp. of

calorimet

er 0C

COP Mean

Value S/N ratio

1 3.3 mix1 m1 2 1.18 1.20 1.19 1.5109

2 3.3 mix3 m2 5 1.56 1.60 1.58 3.973

3 3.3 mix5 m3 8 1.62 1.64 1.63 4.2375

4 5.4 mix1 m1 5 1.44 1.46 1.45 3.227

5 5.4 mix3 m2 8 1.98 2.0 1.99 5.977

6 5.4 mix5 m3 2 1.21 1.25 1.23 1.798

7 6.3 mix1 m2 2 1.41 1.43 1.42 3.0456

8 6.3 mix3 m3 5 1.43 1.43 1.43 3.107

9 6.3 mix5 m1 8 1.58 1.62 1.6 4.082

10 3.3 mix1 m3 8 1.66 1.68 1.67 4.454

11 3.3 mix3 m1 2 1.20 1.24 1.22 1.727

12 3.3 mix5 m2 5 1.51 1.51 1.52 3.636

13 5.4 mix1 m2 8 1.90 1.92 1.91 5.62

14 5.4 mix3 m3 2 1.31 1.31 1.31 2.345

15 5.4 mix5 m1 5 1.45 1.47 1.46 3.287

16 6.3 mix1 m3 5 1.51 1.53 1.52 3.637

17 6.3 mix3 m1 8 1.64 1.68 1.66 4.402

18 6.3 mix5 m2 2 1.31 1.33 1.32 2.411

5.5.2 S/N Ratio Calculations for COP

Sum of the observations T = Y1 + Y2 + Y3 + Y4 + ------- +Y18 =

= 62.477 Correction factor CF = T2/n

Where n = Number of trials/experiments

= 62.4772/18

= 216.854 Total Sum of Squares = [Y1

2 + Y22 + ------- + Y18

2] –

Correction Factor

= 243.33 – 216.854

ST = 26.476

Total Sum of Squares of Factor A SSA = (A1

2/nA1) + (A22/nA2) +

(A32/nA3) + (A4

2/nA4) - CF

A1 = 1.5109 + 3.973 + 4.2375 + 4.454 + 1.727 + 3.636

= 19.5384

nA1 = 6 (Number of Trials in which factor A1 is involved)

A2 = 3.227 + 5.977 + 1.798 + 5.62 + 2.345 + 3.287

= 22.254


A3 = 3.0456 + 3.107 + 4.082 + 3.637 + 4.402 + 2.411

= 20.6846


SSA = (19.53842/6) + (22.2542/6) + (20.68462/6) – 216.854

= 217.473 – 216.854 = 0.6197

Similarly,

Total Sum of Squares of Factor B SSB = 0.47

Total Sum of Squares of Factor C SSC = 3.83

Total Sum of Squares of Factor D SSD = 21.158 Total Sum of Squares of Error E SSE = ST – [SSA + SSB + SSC

+SSD] = 26.476 – [0.6197 +

0.47 + 3.83 + 21.158]

= 0.3983 Degrees of Freedom

Total Degrees of Freedom fT = 18 – 1 = 17

Factor Degrees of Freedom for A fA = 3 – 1 = 2

Factor Degrees of Freedom for B fB = 3 – 1 = 2

Factor Degrees of Freedom for C fC = 3 – 1 = 2

Factor Degrees of Freedom for D fD = 3 – 1 = 2

Error Degrees of Freedom fE = fT – [fA + fB + fC + fD] = 17 – [2 + 2 + 2 + 2] = 9

Variance of Factor A (Va) = SA/fA = 0.02/2 = 0.309

Variance of Factor B (Vb) = SB/fB = 0.019/2 = 0.235

Variance of Factor C (Vc) = SC/fC = 0.11/2 = 0.915

Variance of Factor D (Vd) = SD/fD = 0.641/2 = 10.579

Variance of Error (Ve) = SE/fE = 0.038/9 = 0.04426

F-ratio

F-ratio for factor A (FA) = VA/Ve = 0.309/0.04426 = 6.982

Similarly

F-ratio for factor B (FB) = 5.31

F-ratio for factor C (FC) = 43.27

F-ratio for factor D (FD) = 239.04

Pure Sum of Squares

SA‘ = SA – fA x Ve = 0.531

SB‘ = SB – fB x Ve = 0.3814

SC‘ = SC – fC x Ve = 3.74

SD‘ = SD - fD x Ve = 21.06

SE‘ = 0 Percentage Contribution of Factor A = SA/ ST

= (0.6197/26.476) x 100 PA = 2.34 %

Percentage Contribution of Factor B = SB/ ST = (0.47/26.476) x 100

PB = 1.77 % Percentage Contribution of Factor C = SC/ ST

= (3.83/26.476) x 100 PC = 14.47 %

Percentage Contribution of Factor D = SD/ ST

= (21.158/26.476) x 100 PD = 79.92 %

Percentage Contribution of Error PE = 100 – [2.34 + 1.77 +

14.47 + 79.92] = 1.5 %

Table 5.14 Main effects of the process parameters for mean

Mean

Process Parameter

Level Lcap

Mixture

Charge

Temp. of calorimeter

Average value

L1 1.468 1.526 1.43 1.281

L2 1.558 1.531 1.623 1.493

L3 1.491 1.46 1.465 1.743

Main effects

L2 - L1 0.09 0.005 0.193 0.212

L3 -L2 -0.067 -0.071 -0.158 0.25

Table 5.15 Main effects of the process parameters for S/N ratio

S/N Ratio

Process Parameter

Level

Lcap

Mixture

Charge


Average

value

L1

3.2564

3.5824

3.0393

2.1395

L2

3.709

3.5885

4.1104 3.4778

L3

3.447

3.2419

3.2630 4.7954

Main effects

L2 - L1 0.4526 0.0061 1.0711 1.3383

L3 -L2 -0.262 -0.3466 -0.8474 1.3176

Table 5.16 Response table for means

Level

Lcap

Mixture

Charge

Temp. of

calorimeter

1 1.468 1.526 1.43 1.281

2 1.558 1.531 1.623 1.493

3 1.491 1.46 1.465 1.743

Delta 0.09 0.071 0.193 0.462

Rank 3 4 2 1

The optimal setting is Lcap (5.4m), mixture3, mass2,

Temperature of calorimeter (80C) based on mean

Table 5.17 Response table for signal to noise ratios

Level

Lcap

Mixture

Charge


1

3.2564

3.5824

3.0393

2.1395

2

3.709

3.5885

4.1104 3.4778

3

3.447

3.2419

3.2630 4.7954

Delta 0.4526 0.3466 1.0711 2.6559

Rank 3 4 2 1

The optimal setting is Lcap (5.4m), mixture3, mass2,

Temperature of calorimeter (80C) based on S/N ratio.

5.5.3 ANOVA ANALYSIS for COP

Analysis of Variance (ANOVA) is a statistically based decision tool

for detecting any differences in average performance of parameter

tested. This ANOVA method is based on least squares approach, (The

quantitative measure of the influence of individual factors is obtained

from ANOVA) the error variance is equal to the minimum value of the

sum of squares about some reference value divided by the degrees of

freedom for error [73, 74]. The ANOVA analysis is indicated in Table

5.17. During the analysis the property of orthogonality is undisturbed.

Table 5.18 Analysis of variance for means

Source D.O.F SS Pure SS % Contribution

Lcap

2 0.02 0.012 2.41

Mixture 2 0.019 0.011 2.29

Charge 2 0.11 0.102 13.28


2 0.641 0.633 77.4

Residual error

9 0.038 0 4.62

Total 17 0.828 0.758 100

Table 5.19 Analysis of variance for S/N ratio

Source D.O.F SS F-ratio Pure SS %

Contribution

Lcap 2 0.62 6.982 0.531 2.34

Mixture 2 0.47 5.31 0.381 1.77

Charge 2 3.83 43.27 3.74 14.47

Temp. of

calorimeter 2 21.16 239.04 21.07 79.92

Residual error

9 0.4 1 0 1.5

Total 17 26.48 295.602 25.722 100

ANOVA analysis indicated that the temperature of the calorimeter

contribute 79.92%, refrigerant charge add 14.47%, Lcap give 2.34%

and mixture has 1.77% contribution to COP as shown in Table 5.19.

The percentage contributions of each factor for means and S/N ratio

have been plotted in Figures 5.26 and 5.27 respectively. The results

show that the temperature of the calorimeter has more influence on the

output. As the calorimeter temperature varies from 80C, 50C and 20C,

temperature difference between the brine solution and the refrigerant in

the evaporator coil decreases and it influences the cooling capacity,

thus resulting in reduction in refrigeration effect. At 80C calorimeter

temperature has the highest refrigeration effect as shown in Figure

5.31. The length of the capillary tube is varied from 3.3m to 6.3m and

the minimum energy consumption is obtained at 5.4m capillary length

as shown in Figure 5.28. Mass flow rate of the refrigerant decreases

with the increase in capillary length, as the pressure drop increases

with the increase in lengths of capillary, the enthalpy difference of the

refrigerant at Pc and Pe (∆h) increases. The input power is a function of

mass flow rate of refrigerant and enthalpy difference.

Maximum COP is obtained for mixture-3 and 120 grams of

refrigerant charge which is the equivalent charge for R134a. From

mixture-1 to mixture-5 both specific volume and refrigeration effect

decreases due to increase in R134a quantity in the ternary mixture.

From the Figure 5.29 COP starts increasing from mixture-1 to mixture-

3, reaches maximum at mixture-3 and then starts decreasing from

mixture-3 to mixture-5. This is because when compared to decrease in

refrigeration effect, decrease in specific volume is more from mixture-1

to mixture-3 thus maximum COP is attained for mixture-3, later

decreasing of refrigeration effect dominates the decreasing of specific

volume which causes the lower COP for mixture-5. For overcharged

conditions, power consumption of a refrigerator increased due to rise in

refrigerant flow rate and compression ratio, or possible state of wet

compression. For undercharged conditions, refrigerating capacity is

reduced and compressor reliability may be degraded due to high

discharge temperatures. The minimum energy consumption is obtained

at optimum mass at refrigerant charge of 120grams (m2) as shown in

Figure 5.30.

Table 5.20 Optimum conditions for COP

Predicted Value of COP

Based on the experiments, the optimum level setting is

determined as shown in Table 5.20. The average values of the factors at

their levels are taken from Table 5.16 and the predicted value of the

COP is given below.

T‘ = T / 18

COP (predicted) = T‘ + (A2- T‘) + (B2-T‘) + (C2-T‘) + (D3-T‘)

= 1.5061 + (1.558-1.5061) + (1.5316-1.5016) + (1.6233-1.5016) + (1.7433-1.5061)

= 1.94 Where

A2 = average mean value of capillary length at 2 level

B2 = average mean value of mixture at 2 level

C2 = average mean value of refrigerant charge at 2 level

D3 = average mean value of calorimeter temperature at 3 level

T‘ = overall mean of COP

Factor Level Physical value

Length of Capillary m

2 5.4

Mixture 2 25%R134a/37.5%R600a/37.5%R290

Refrigerant Charge grams

2 120

Temperature of Calorimeter 0C

3 80C

Confirmation Run

The confirmation experiments were carried out by setting the

process parameters at optimum levels as shown in Table 5.20

Experimental Value of COP at optimum level setting = 1.99

Percentage Contribution of means for COP

2.29%

2.41

4.62%

13.28%

77.4%

Lcap

Mixture

Charge

Temp. of

calorimeterResidual error

Figure 5.26 Percentage contributions of means for COP

Percentage Contribution of S/N ratio for COP

2.34

14.47

79.92

1.5 1.77

Lcap

Mixture

Charge

Temp. of


Figure 5.27 Percentage Contributions of S/N ratio for COP

Main Effects Graph(data means) for Means of COP

1.46

1.48

1.5

1.52

1.54

1.56

1.58

2.7 3.6 4.5 5.4 6.3 7.2

Length of capillary in meters

Mean

s o

f m

ean

s f

or

CO

P

Figure 5.28 Variation means of means for COP at different capillary

lengths

Main Effects Graph (data means) for Means of COP

1.44

1.46

1.48

1.5

1.52

1.54

1 3 5

Mixture

Mean

s o

f m

ean

s f

or

CO

P

Figure 5.29 Variation means of means for COP at different mixtures

Main Effects Graph(data means) for Means of COP

1.44

1.48

1.52

1.56

1.6

1.64

1 2 3

Charge of the refrigerant

Mean

s o

f m

ean

s f

or

CO

P

Figure 5.30 Variation means of means for COP at different charge of

the refrigerant

Main Effects Graph (data means) for Means of COP

0

0.4

0.8

1.2

1.6

2

0 2 4 6 8 10


Mean

s o

f m

ean

s f

or

CO

P

Figure 5.31 Variation of means of means for COP at different calorimeter temperatures

Table 5.21 Mean value and S/N ratio for power


Exp.

Run

Lcap

m Mixture

Charge

grams

Temp. of

calorimet

er 0C

POWER

Mean

Value S/N ratio

1 3.3 mix1 m1 2 204 208 206 -23.138

2 3.3 mix3 m2 5 186 188 187 -22.718

3 3.3 mix5 m3 8 192 194 193 -22.856

4 5.4 mix1 m1 5 189 193 191 -22.81

5 5.4 mix3 m2 8 167 169 168 -22.25

6 5.4 mix5 m3 2 164 166 165 -22.17

7 6.3 mix1 m2 2 173 179 176 -22.45

8 6.3 mix3 m3 5 182 182 182 -22.6

9 6.3 mix5 m1 8 175 179 177 -22.48

10 3.3 mix1 m3 8 217 219 218 -23.38

11 3.3 mix3 m1 2 191 193 192 -22.83

12 3.3 mix5 m2 5 175 175 175 -22.43

13 5.4 mix1 m2 8 184 188 186 -22.69

14 5.4 mix3 m3 2 173 173 173 -22.38

15 5.4 mix5 m1 5 164 166 165 -22.174

16 6.3 mix1 m3 5 185 187 186 -22.69

17 6.3 mix3 m1 8 183 185 184 -22.648

18 6.3 mix5 m2 2 160 164 162 -22.095

Table 5.22 Main effects of the process parameters for means

Mean

Process

Parameter Level

Lcap

Mixture

Charge

Temp. of

calorimeter

Average

value

L1 195.16 193.83 185.83 179.0

L2 174.66 181.0 175.66 181

L3 177.83 172.83 186.16 187.66

Main effects

L2 - L1 -20.5 -12.83 -10.17 2.0

L3 -L2 3.17 -8.7 10.5 6.66

Table 5.23 Main effects of the process parameters for S/N ratio

S/N Ratio

Process Parameter

Level

Lcap

Mixture

Charge


Average value

L1 22.892 22.859 22.68 22.51

L2 22.412 22.571 22.438 22.57

L3 22.493 22.367 22.679 22.717

Main effects

L2 - L1 -0.48 -0.288 -0.242 0.06

L3 -L2 0.081 -0.204 0.241 0.147


The optimal setting is Lcap (5.4m), mixture3, mass2, Temperature of

calorimeter (20C) based on mean


Level

Lcap

Mixture

Charge


1 22.892 22.859 22.68 22.51

2 22.412 22.571 22.438 22.57

3 22.493 22.367 22.679 22.717

Delta 0.48 0.492 0.242 0.207

Rank 2 1 3 4


calorimeter (20C) based on S/N ratio

Level

Lcap

Mixture

Charge


1 195.16 193.83 185.83 179.0

2 174.66 181.0 175.66 181

3 177.83 172.83 186.16 187.66

Delta 20.5 21 10.5 8.66

Rank 2 1 3 4


Source D.O.F Total SS Pure SS % Contribution

Lcap

2 1461.44 1436.18 40.66

Mixture 2 1344.77 1319.51 37.41

Charge

2 427.444 402.18 11.89

Temp. of

calorimeter 2 247.11 221.85 6.87

Residual error

9 113.67 0 3.17

Total 17 3594.434 3379.72 100


Source D.O.F Total SS F-ratio Pure SS %

Contribution

Lcap

2 0.79 48.17 0.774 40.42

Mixture 2 0.736 44.87 0.72 37.66

Charge

2 0.22 13.41 0.204 11.25


2 0.135 8.23 0.119 6.9

Residual

error 9 0.073 1 0 3.77

Total 17 1.954 115.68 1.817 100

5.5.3 ANOVA Analysis for Power

ANOVA analysis indicated that the capillary length contribute

40.42%, mixture add 37.66%, refrigerant charge give 11.25% and

temperature of the calorimeter has 6.9% contribution to power as

shown in Table 5.27. The percentage contribution of each factor for

means and S/N ratio were plotted in Figures 5.32 and 5.33

respectively. The results show that the length of the capillary and

mixture has more influence on the output. Mass flow rate of the

refrigerant decreases with the increase in capillary length, as lengths of

capillary were increased pressure drop increases, the enthalpy

difference of the refrigerant at Pc and Pe (∆h) increases. From

thermodynamics, the input power is a function of mass flow rate of

refrigerant and enthalpy difference, so length of capillary is having

more influence on power as shown in Figure 5.34. Mixture-5 is showing

lower power consumption than mixture-1 and mixture-3 as shown in

Figure 5.35, specific volume of the mixture-5 is lower than the mixture-

1 and mixture-3 as shown in Table 5.8. Power consumption of the

compressor is a function of specific volume of the refrigerant. For

overcharged conditions, power consumption of the refrigerator

increased due to a rise of refrigerant flow rate and compression ratio, or

wet compression. For undercharged conditions, refrigerating capacity is

reduced and compressor reliability may be degraded due to high

discharge temperatures. The minimum energy consumption is obtained

at optimum mass at refrigerant charge (m2) as shown in Figure 5.37.

Minimum energy consumption is obtained at 20C calorimeter

temperature as shown in Figure 5.36.

Optimum Conditions Table 5.28 Optimum conditions for power

Predicted Value of Power




Power is given below

T‘ = T / 18

Power (predicted) = T‘ + (A2- T‘) + (B3-T‘) + (C2-T‘) + (D1-T‘)

= 182.55 + (174.66-182.55) + (172.8-

182.55) + (175.66-182.55) + (179-182.55)

= 154.62 Where




Length of

Capillary m 2 5.4

Mixture 3 45%R134a/27.5%R600a/27.5%R290


2 139


1 20C



T‘ = overall mean of Power

Confirmation Run

The confirmation experiments were carried out by setting the

process parameters at optimum levels as shown in Table 5.28.

Experimental Value of Power at optimum level setting = 158 W

Percentage contribution of means for power

37.41

40.66

3.176.87

11.89

Lcap

Mixture

Charge

Temp. of


Figure 5.32 Percentage contributions of means for power

Percentage contribution of S/N ratio for power

37.66

40.42

3.776.9

11.25

Lcap

Mixture

Charge

Temp. of


Figure 5.33 Percentage contributions of S/N ratio for power

Main Effects Graph (data means) for Means of Power

170

175

180

185

190

195

200

2.7 3.6 4.5 5.4 6.3 7.2


Mean

s o

f m

ean

s f

or

pow

er

Figure 5.34 Variation means of means for power at different capillary

lengths


170

175

180

185

190

195

1 3 5

Mixture

Mean

s o

f m

ean

s f

or

pow

er

Figure 5.35 Variation means of means for power at different mixtures


176

180

184

188

192

2 5 8

Temperature of Calorimeter in 0C

Mean

s o

f m

ean

s f

or

pow

er

Figure 5.36 Variation of means of means for power at different

calorimeter temperatures


172

176

180

184

188

1 2 3


Mean

s o

f m

ean

s f

or

pow

er

Figure 5.37 Variation means of means for power at different

refrigerant charge

Table 5.29 Mean value and S/N ratio for refrigeration effect


S.No. Lcap

M Mixture

Charge

grams

Temp. of calorimete

r 0C

Refrigeration

Effect

Mean

Value S/N ratio

1 3.3 mix1 m1 2 241 249 245 47.78

2 3.3 mix3 m2 5 290 300 295 49.39

3 3.3 mix5 m3 8 311 319 315 49.96

4 5.4 mix1 m1 5 272 282 277 48.84

5 5.4 mix3 m2 8 331 337 334 50.47

6 5.4 mix5 m3 2 198 207 203 46.15

7 6.3 mix1 m2 2 244 256 250 47.95

8 6.3 mix3 m3 5 260 260 260 48.3

9 6.3 mix5 m1 8 276 290 283 49.035

10 3.3 mix1 m3 8 360 370 365 51.245

11 3.3 mix3 m1 2 229 239 234 47.38

12 3.3 mix5 m2 5 264 268 266 48.49

13 5.4 mix1 m2 8 350 362 356 51.02

14 5.4 mix3 m3 2 227 227 227 47.12

15 5.4 mix5 m1 5 238 245 241 47.64

16 6.3 mix1 m3 5 279 287 283 49.03

17 6.3 mix3 m1 8 300 312 306 49.71

18 6.3 mix5 m2 2 210 218 214 46.608

Table 5.30 Main effects of the process parameters of means for refrigeration effect

Mean

Process

Parameter

Level

Lcap

Mixture

Charge

Temp. of

calorimeter

Average value

L1 286.66 296 264.33 228.83

L2 273 276 285.83 270.33

L3 266 253.66 275.5 326.5

Main effects

L2 - L1 -13.66 -20 21.5 41.5

L3 -L2 -7.0 -22.34 -10.33 56.17

Table 5.31 Main effects of the process parameters of S/N ratio for

refrigeration effect

S/N Ratio

Process Parameter

Level

Lcap

Mixture

Charge


Average value

L1 49.04 49.31 48.39 47.16

L2 48.54 48.72 48.988 48.615

L3 48.438 47.98 48.634 50.24

Main

effects

L2 - L1 -0.5 -0.59 0.598 1.455

L3 -L2 -0.102 -0.74 -0.354 1.625



calorimeter (80C) based on mean


Level Lcap Mixture

Charge


1 49.04 49.31 48.39 47.16

2 48.54 48.72 48.988 48.615

3 48.438 47.98 48.634 50.24

Delta 0.602 1.33 0.598 3.08

Rank 3 2 4 1


calorimeter (80C) based on S/N ratio

Level

Lcap

Mixture

Charge


1 286.66 296 264.33 228.83

2 273 276 285.83 270.33

3 266 253.66 275.5 326.5

Delta 20.66 42.34 21.5 97.67

Rank 4 2 3 1


Source D.O.F Total SS Pure SS % Contribution

Lcap 2 1325.78 1284.75 3.57

Mixture 2 5381.78 5340.75 14.5

Charge 2 1387.45 1346.41 3.73


2 28831.45 28790.41 77.69

Residual error

9 184.66 0 0.51

Total 17 37111.12 36762.32 100


Source D.O.F Total SS F-ratio Pure SS %

Contribution

Lcap 2 1.24 46.26 1.213 3.43

Mixture 2 5.34 199.25 5.3134 14.77

Charge 2 1.05 39.18 1.0234 2.9


2 28.4 1059.7 28.374 78.56

Residual

error 9 0.12 1 0 0.34

Total 17 36.15 1345.39 35.9238 100

5.5.4 ANOVA Analysis for Refrigeration Effect

ANOVA analysis indicated that the temperature of the calorimeter

contribute 78.56%, refrigerant charge add 2.9%, length of capillary give

3.43% and mixture has 14.77% contribution to refrigeration effect as

shown in Table 5.35. The percentage contribution of each factor for

means and S/N ratio were plotted in Figures 5.38 and 5.39

respectively. The results were plotted in Figures from 5.40 to 5.43.

Results show that the temperature of the calorimeter has more

influence on the output. As the calorimeter temperature varies from

80C to 20C temperature difference between the brine solution and the

refrigerant in the evaporator coil decreases and it influences the cooling

capacity more, results in decreased refrigeration effect as shown in

Figure 5.42. Another major influencing parameter is the refrigerant

mixtures. Compared to mixture-3 and mixture-5, mixture-1 is having

high latent heat of vaporization results in more refrigeration effect as

shown in Figure 5.41.

For overcharged conditions, the refrigeration capacity was

reduced due to a decrease of the temperature difference between the

refrigerant and the brine solution with increasing refrigerant charge.

For undercharged conditions, the capacity dropped with decreasing

refrigerant charge due to a reduction of refrigerant flow rate and

compressor efficiency resulting from an increase of suction temperature

as shown in Figure 5.43.

Optimum Conditions

Table 5.36 Optimum conditions for refrigeration effect

Predicted Value of Refrigeration Effect




refrigeration effect is given below.

T‘ = T / 18

Refrigeration Effect (predicted) = T‘ + (A1- T‘) + (B1-T‘) + (C2-T‘) + (D3-T‘)

= 275.22 + (286.66-275.22) + (296-

275.22) + (285.83-275.22) +

(326-275.22)

= 368.9

Where





T‘ = overall mean of Refrigeration effect


Length of Capillary m

1 3.3

Mixture 1 5%R134a/47.5%R600a/47.5%R290


2 106


3 80C

Confirmation Run

The confirmation experiments were carried out by setting the process

parameters at optimum levels as shown in Table 5.36

Experimental value of refrigeration effect at optimum level setting

=380W

Percentage contribution of means for refrigeration effect

77.69

3.73

14.5

0.51 3.57

Lcap

Mixture

Charge

Temp. of


Figure 5.38 Percentage contributions of means for refrigeration effect

Percentage contribution of S/N ratio for refrigeration

effect

78.56

2.9

14.77

0.34 3.43

Lcap

Mixture

Charge


Residual error

Figure 5.39 Percentage contributions of S/N ratio for refrigeration effect

Main Effects Graph (data means) for Means of

Refrigeration Effect

264

270

276

282

288

2.7 3.6 4.5 5.4 6.3 7.2


Mean

s o

f m

ean

s f

or

refr

igera

tion

eff

ect

Figure 5.40 Variation means of means for refrigeration effect at different capillary lengths



250

260

270

280

290

300

1 3 5

mixture

Mean

s o

f m

ean

s f

or

refr

igera

tion

eff

ect

Figure 5.41 Variation means of means for refrigeration effect at

different mixtures



150

200

250

300

350

2 5 8


Mean

s o

f m

ean

s f

or

refr

igera

tion

eff

ect


different calorimeter temperatures



250

260

270

280

290

1 2 3


Mean

s o

f m

ean

s for

refr

igera

tion

effect


different charge of the refrigerant

After systematic analysis by Taguchi Method for parameter

design and optimization the effect of each parameter in detail which

given in Table 5.10 to 5.36 is studied. It is revealed that the error from

the whole analysis well with in the permissible levels as shown in

Tables 5.18, 5.19, 5.26, 5.27, 5.34 and 5.35. The effect of various

parameters on output is evaluated as shown in tables 5.20, 5.28 and

5.36 for COP, power and refrigeration effect respectively.

The whole exercise helps in the importance to be given to each

parameter in the refrigeration test rig design and performance. The

optimized conditions of the Taguchi Method design of experiments were

matching with that of the full factorial design of experiments.

5.6 Cost Analysis of the Proposed Mixture-3

The cost of the proposed alternative mixture-3 is 3.43% lower

than the HC mix, which is presently used as an alternative to R134a.

The cost of the refrigerant is shown in Table 5.37.

Table 5.37 Cost comparison of the mixture-3 with the base refrigerants

Refrigerant Charge Quantity in grams Cost in Rupees

R134a 240 192

HC mix 104 233

Mixture-3 120 225

chapter 5 results and discussion -...

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