chapter 5 results and discussion -...
TRANSCRIPT
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
Com
pre
ssor
pow
er
in w
att
s
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
Com
pre
ssor
pow
er
in w
att
s
R134a
Figure 5.2 Variation of compressor power with different capillary
lengths in a visi cooler for R134a
5.1.2 Optimization of Refrigerant Charge and Capillary Length for
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
Com
pre
ssor
pow
er
in w
att
s
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
Com
pre
ssor
pow
er
in w
att
s
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.
5.1.4 Optimization of Refrigerant Charge and Capillary Length for
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
Capillary length in meters
Com
pre
ssor
pow
er
in w
att
s
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
Com
pre
ssor
pow
er
in w
att
s
103grams 113 grams 123 grams
Figure 5.6 Variation of compressor power with charge quantity at different capillary lengths for mixture -2
5.1.5 Optimization of Refrigerant Charge and Capillary Length for
Mixture-3(25%R134a, 75%HC mixture)
After carrying out the required tests with mixture-2, 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-3. 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-3. To check the energy
efficiency of the equivalent charge of mixture-3 length of capillary tube
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
Capillary length in meters
Com
pre
ssor
pow
er
in w
att
s
110 grams 120 grams 130 grams
Figure 5.7 Variation of compressor power with charge quantity at different capillary lengths for mixture -3
5.1.6 Optimization of Refrigerant Charge and Capillary Length for
Mixture-4(35%R134a, 65%HC mixture)
After carrying out the required tests with mixture-3, 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-4. 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-4. To check the energy
efficiency of the equivalent charge of mixture-4 length of capillary tube
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
Capillary length in meters
Com
pre
ssor
pow
er
in w
att
s
119 grams 129 grams 139 grams
Figure 5.8 Variation of compressor power with charge quantity at
different capillary lengths for mixture -4
5.1.7 Optimization of Refrigerant Charge and Capillary Length for
Mixture-5 (45%R134a, 55%HC mixture)
After carrying out the required tests with mixture-4, 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-5. 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-5. To check the energy
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
180
190
200
2.7 3.6 4.5 5.4 6.3
Capillary length in meters
Com
pre
ssor
pow
er
in w
att
s
129 grams 139 grams 149 grams
Figure 5.9 Variation of compressor power with charge quantity at
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
rim
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
Figure 5.12 Pull down test for mixture-2 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-3
Figure 5.13 Pull down test for mixture-3 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
oC
R134a HC Mix-4
Figure 5.14 Pull down test for mixture-4 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-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
Table 5.4 Experimental results of mixture-2
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
Table 5.5 Experimental results of mixture-3
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
Table 5.6 Experimental results of mixture-4
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
Table 5.7 Experimental results of mixture-5
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
Capillary length in meters
Com
pre
ssor
pow
er
in w
att
s
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
Capillary length in meters
Com
pre
ssor
pow
er
in w
att
s
R134a HC mix Mix-1 Mix-2
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
Capillary length in meters
Com
pre
ssor
pow
er
in w
att
s
R134a HC mix Mix-1 Mix-2
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
Capillary length in meters
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
Capillary length in meters
CO
P
Mix-1 Mix-2 Mix-3 Mix-4
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
Capillary length in meters
CO
P
Mix-1 Mix-2 Mix-3 Mix-4
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
Com
pre
ssor
pow
er
in
watt
s
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
Temperature of calorimeter in 0C
Com
pre
ssor
pow
er
in w
att
s
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
nA2 = 6 (Number of Trials in which factor A2 is involved)
A3 = 3.0456 + 3.107 + 4.082 + 3.637 + 4.402 + 2.411
= 20.6846
nA3 = 6 (Number of Trials in which factor A3 is involved)
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
Temp. of calorimeter
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
Temp. of calorimeter
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
Temp. of calorimeter
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
calorimeterResidual error
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
Temperature of calorimeter in 0C
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
INPUT PARAMETERS RESPONSE
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
Temp. of calorimeter
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
Table 5.24 Response table for means
The optimal setting is Lcap (5.4m), mixture3, mass2, Temperature of
calorimeter (20C) based on mean
Table 5.25 Response table for signal to noise ratios
Level
Lcap
Mixture
Charge
Temp. of calorimeter
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
The optimal setting is Lcap (5.4m), mixture5, mass2, Temperature of
calorimeter (20C) based on S/N ratio
Level
Lcap
Mixture
Charge
Temp. of calorimeter
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
Table 5.26 Analysis of variance for means
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
Table 5.27 Analysis of variance for S/N ratio
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
Temp. of calorimeter
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
Based on the experiments, the optimum level setting is
determined as shown in Table 5.28. The average values of the factors at
their levels are taken from Table 5.24 and the predicted value of the
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
A2 = average mean value of capillary length at 2 level
B3 = average mean value of mixture at 3 level
Factor Level Physical value
Length of
Capillary m 2 5.4
Mixture 3 45%R134a/27.5%R600a/27.5%R290
Refrigerant Charge grams
2 139
Temperature of Calorimeter 0C
1 20C
C2 = average mean value of refrigerant charge at 2 level
D1 = average mean value of calorimeter temperature at 1 level
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
calorimeterResidual error
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
calorimeterResidual error
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
Capillary length in meters
Mean
s o
f m
ean
s f
or
pow
er
Figure 5.34 Variation means of means for power at different capillary
lengths
Main Effects Graph (data means) for Means of Power
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
Main Effects Graph (data means) for Means of Power
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
Main Effects Graph (data means) for Means of Power
172
176
180
184
188
1 2 3
Charge of the refrigerant
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
INPUT PARAMETERS RESPONSE
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
Temp. of calorimeter
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
Table 5.32 Response table for means
The optimal setting is Lcap (3.3m), mixture1, mass2, Temperature of
calorimeter (80C) based on mean
Table 5.33 Response table for signal to noise ratios
Level Lcap Mixture
Charge
Temp. of calorimeter
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
The optimal setting is Lcap (3.3m), mixture1, mass2, Temperature of
calorimeter (80C) based on S/N ratio
Level
Lcap
Mixture
Charge
Temp. of calorimeter
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
Table 5.34 Analysis of variance for means
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
Temp. of calorimeter
2 28831.45 28790.41 77.69
Residual error
9 184.66 0 0.51
Total 17 37111.12 36762.32 100
Table 5.35 Analysis of variance for S/N ratio
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
Temp. of calorimeter
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
Based on the experiments, the optimum level setting is
determined as shown in Table 5.36. The average values of the factors at
their levels are taken from Table 5.32 and the predicted value of the
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
A2 = average mean value of capillary length at 2 level
B3 = average mean value of mixture at 3 level
C2 = average mean value of refrigerant charge at 2 level
D1 = average mean value of calorimeter temperature at 1 level
T‘ = overall mean of Refrigeration effect
Factor Level Physical value
Length of Capillary m
1 3.3
Mixture 1 5%R134a/47.5%R600a/47.5%R290
Refrigerant Charge grams
2 106
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 5.36
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
calorimeterResidual error
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
Temp. of calorimeter
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
Capillary length in meters
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
Main Effects Graph (data means) for Means of
Refrigeration Effect
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
Main Effects Graph (data means) for Means of
Refrigeration Effect
150
200
250
300
350
2 5 8
Temperature of calorimeter in 0C
Mean
s o
f m
ean
s f
or
refr
igera
tion
eff
ect
Figure 5.42 Variation means of means for refrigeration effect at
different calorimeter temperatures
Main Effects Graph (data means) for Means of
Refrigeration Effect
250
260
270
280
290
1 2 3
Charge of the refrigerant
Mean
s o
f m
ean
s for
refr
igera
tion
effect
Figure 5.43 Variation means of means for refrigeration effect at
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