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Simulation and assessment of the leakage characteristics and suitability of Rhone-Poulenc's ‘ISCEON 69’ blends as refrigerants
Journal of
Materials Processing Technology ELSEVIER
Journal of Materials Processing Technology 55 (1995) 315-320
i
Simulation and assessment of the leakage characteristics and suitability of Rhone-Poulenc's 'ISCEON 69' blends as refrigerants D. Crombie a, M.S.J. Hashmi b' * a Thermo King Europe, Mervue, Galway, Ireland b School of Mechanical Engineering, Dublin Ci(v University, Dublin, Ireland Received 1 April 1994
Industrial summary This paper is the result of investigations into the need for an interim refrigerant to replace R502 as the standard deep-cold refrigerant for use in the demanding transport refrigeration business. The Montreal Protocol on Substances that Deplete the Ozone Layer identified HCFCs as being part of the interim solution to the phasing out of CFCs. Some designers of transport refrigeration equipment chose to move to pure R22 to meet proposed legislative constraints. This work shows that there is a better solution to deep-cold refrigeration than pure R22, one which does not render current fleets obsolete, and one which leaves the way open to chlorine-free HFC-based refrigerants as they evolve. It would clearly hasten the introduction of a HCFC blend and subsequent elimination of CFC R502 if the constituents were non-toxic and well-known chemicals: ISCEON 69L satisfies this requirement.
1. Introduction Transport refrigeration equipment encompasses mobile refrigeration units for large articulated trailers, local delivery trucks and vans, container units, and rail and bus air-conditioning. With an existing world fleet estimated at 300 000 refrigeration units currently running on R502, it was clear some years ago that an interim drop-in refrigerant, which was compatible with all of the R502-type system parameters, materials and lubricants, would be an important step on the way to chlorine-free deep-cold transport refrigeration. Since worldwide R12 annual production ran up to 450 000 t/annum, compared to R502's some tens of thousands of tonnes/annum, the chemical industry rightly concentrated its efforts on replacing R12: the result has been H F C 134a. The transport refrigeration business had been moving away from R12 anyway, in order to achieve deep-cold load temperatures (down to - 30°C), and R502 met the thermodynamic requirements of these new temperatures, when used in single-stage compression refrigeration. Since over 75% of the German trailer market in 1992, and over 90% of the French trailer market in 1992, used
* Corresponding author. 0924-0136/96/$15.00 © 1996 Elsevier Science S.A. All rights reserved SSDI 0 9 2 4 - 0 1 3 6 ( 9 5 ) 0 2 0 2 5 - H
R502 equipment, there is clearly a heavy reliance on R502 performance in the market-place. Transport refrigeration currently relies almost entirely on single-stage reciprocating piston compressors. This paper also investigates the whole fundamental question of the use of zeotropic blends as refrigerants, particularly as they affect servicability and safety, in place of the traditional pure compounds (R12, R22, R134a, for instance) or in place of the azeotropic mixtures (R500, R502, for instance). This work culminated in the acceptance by the transport refrigeration business of the world's first R502 straight substitute or drop-in replacement, Rhone Poulenc's ISCEON 69L. This is also the world's first use of a zeotropic blend refrigerant in the transport refrigeration business.
2. Interim refrigerant criteria Ideal selection criteria for an R502 replacement would include its being: 1. similar in cooling performance; 2. of comparable or lower compressor discharge temperatures; 3. compatible with R502 compressor oil; 4. comparable on compressor discharge pressures; 5. equal to or better on fuel efficiency; 6. compatible with all R502 system materials; 7. non-toxic/non-flammable; and 8. easy to handle for servicing purposes.
316
D. Crombie, M.S.J. Hashmi/Journal of Materials Processing Technology 55 (1995) 315 320
This paper covers the investigation of just two aspects investigated in the course of proving ISCEON 69L: (a) cooling performance (1, 2, 4, 5, above); and (b) blend variations due to selective leakage. Other aspects of 69L were investigated as part of a larger study.
3. Initial proposal Pearson [1] of the Star Refrigeration, Glasgow had proposed a blend of three chemicals (R22, R218 & R290) in the ratio of 85 : 9 : 6. This blend was labelled 69S (for the 6% and 9% constituents & 'S' for Star Refrigeration). R290 is better known as propane (C3Hs), whilst R218 is perfluoropropane (C3Fs), an electronics industry solvent; and R22 is the widely-used air-conditioning fluid dichlorofluoromethane (CHC1F/). Although R22 would meet the legislative Protocol on interim refrigerants, it runs too hot on compressor discharge temperature to be used on extreme pressure ratios, as occurs on deep-cold refrigeration in high ambient temperatures. The purpose of the R218 was to reduce the R22 discharge temperatures, whilst the R290 is both an excellent deep-cold refrigerant and an aid to compressor oil return. As R22 and R290 are highly soluble in AB oils, it was practical to proceed with testing 69S in a standard R502 refrigeration unit. R218 is almost totally inert (a proposed fire-extinguishing medium to replace HALONS). All trials were conducted on a 4-cylinder 30 cu.in. compressor running at 2200 RPM, via a direct-drive diesel engine of 2.2 1 displacement. The refrigeration circuit consists of an R502 expansion valve, a single evaporator coil, a single condenser coil, a heat exchanger on the evaporator liquid/suction lines, an accumulator tank and a receiver tank. Performance was measured using an isothermal calorimeter (ARI 1110) at Thermo King Galway. Initial trials showed 69S behaved in similar fashion to R502 at low to medium ambients (up to + 30°C) on load temperatures of 0°C and - 2 0 ° C , which was very encouraging. Repeating these trials for confirmation, however, produced quite different results. The discharge temperatures were higher than those for R502, and the cooling capacity was lower at 0°/30°C than for R502. Clearly, something had changed. Gas chromatograph (G.C.) analysis of the refrigerant mixture in each of the first two test units indicated different refrigerant constituent ratios. This had come about due to selective distillation of the components during gas-phase charging of the test equipment. The more encouraging results were due to the mixture being R218- enriched as a result of vapour charging. The remaining refrigerant sample was thus R218-depleted, and prone to running hot. Two conclusions could be drawn from these first brief tests: (1) mixture ratio variation could occur in 69S when traditional gas-phase charging
Table 1 69S* vs. R502 p a r a m e t e r s EAIA/CAIA
- 20"/30
TOTQ CDRT CDPI WTRT OILT
+1% +ll'C + 15 psi + 1 ~C +1 C
0°/30 ° -3% +7C + 6 psi - 2'C -3°C
- 29'/38' -15% +25C - 7 psi - 1C -3C
21/49 --4% + 12C + 5 psi - I"C -3C
was practised; and (2) Raising the R218 content whilst simultaneously reducing the R22 content had the effect of reducing the compressor discharge temperatures. Pearson proposed a second blend, of 74:20:6, and a battery of tests was begun, based on Thermo King standards. This mixture was labelled 69S*. 3.1. Refrigeration test standards
These can be summarised briefly as follows: (evaporator inlet air temp (EAIA)/condenser inlet air temperature (CAIA)): - 29°C/38°C, - 20°C/30°C, 0°C/30°C, 21°C/49°C. Along with verifying the cooling capacities under these conditions relative to R502, these tests would further examine the effects of extreme pressure ratios ( - 2 9 ° C / 3 8 ° C ) on the compressor discharge temperatures, and the effects of high gas loads on the compressor pressures (21°C/49°C). Five key parameters were measured: TOTQ cooling capacity (kW); CDRT compressor discharge temperature (°C); CDP1 compressor discharge pressure (psia)t; WTRT Engine coolant temperature (°C); and OILT Engine oil sump temperature (°C). 3.2. 69S* Results
For 69S, these five parameters, relative to R502 operation, can be summarized under the four test standards (Table 1). As the compressor discharge temperatures are all higher on 69S* than on R502, Pearson proposed a further blend of 39% R218, 55% R22 & 6% R290. This last blend was labelled 69L. 3.3. 69L Results
The 69L results, in comparison to those of R502, are summarized in Table 2. Whilst the compressor temperatures are now comparable to those of R502, the cooling capacity is greatly
1 psi
D. Crombie, M.S.J. Hashmi / Journal of Materials Processing Technology 55 (1995) 315 320
317
4.1. 69L Leakage models
Table 2 69L vs. R502 p a r a m e t e r s EAIA/CAIA TOTQ
- 20'/30 ~ + 4%
CDRT CDP1
0'C + 38
WTRT OILT
+ 1 + 3
0/30 ~
- 29°/38 °
21°/49 °
- 7%
+ 22%
- 8%
- l'C + 30
+ ll°C + 33
-4°C + 15
0 0
0 0
- 6 - 5
improved at those points where it is most needed, i.e. at low load temperatures in medium-to-high ambient temperatures.
4. Effects of leakage on non-azeotropic blends Traditional refrigerants are characterized by their nontoxicity, safety, chemical stability, and ease of handling, This last aspect is in greater part due to refrigerants having traditionally been either pure compounds, R12 (CC12F2), R22 ( C H C I F 2 ) or azeotropic mixtures (R500 = R12 + R152a, R502 = R22 + Rl15). A brief definition of an azeotrope is a mixture of two or more products, which mixture, for the present purposes, behaves as a compound. A more complete definition of an azeotrope would be that the components' ratios remain constant, whether in the gas phase or the liquid phase. Thus, R502 retains its R22 at 48.9% and Rl15 at 51.1% whether it is measured in the gas or liquid phase. This constant ratio occurs at just one temperature. In practice, this means that the refrigerant separates slightly when moving away from this one temperature. Thus in a running refrigeration system some separation occurs in either the evaporator or the condenser, or more likely both. Further, because R22 has a physically smaller molecule, it permeates seals and porous hoses more easily, resulting in some R502 equipment running on quite a different mix than that with which it started. It has been a design criterion of refrigerants that they be pure compounds, or be azeotropes. With the advent of new criteria, to accomodate scientific evidence of the link between traditional refrigerants and ozone depletion, it now seems certain that the necessary refrigerating properties will not be met by either pure compounds or by azeotropes. Not just interim replacement refrigerants, but even some longer-term chlorine-free refrigerants, will be blends which are not azeotropes. The correct nomenclature for such blends is zeotropes, but as the term nonazeotrope is most widely used in today's popular publications on the subject, the latter term will be retained for this discussion.
lsceon 69L is a blend of R22, R290, and R218. These compounds have very close boiling points (at 1000 mbar): R22 is - 40°C, R290 is - 42°C, and R218 is - 39°C. This 3°C spread of relative boiling points would lead one to expect that the mixture stays relatively intact, throughout a running system. It is clear from the kinetic gas laws that should a leak occur in a container containing only gaseous 69L, then the three components will leak in a constant ratio equal to the ratio at which they exist inside the container. Further, should a liquid leak occur in a liquid-filled container, the components' ratios will not be affected. The only time a concern may arise is should a gas leak occur in a container of both liquid and gaseous 69L. In such a case, the different boiling points of the three constituents may lead to a shift in their ratios. It was thus seen to be necessary to examine what would happen if a container of correctly blended 69L (R22 at 55%, R218 at 39%, R290 at 6%) leaked a significant proportion of its charge via a gas leak. How would the components' ratios shift, and, in the event that any percentage lost charge was replaced with correctlyblended 69L, where would the resulting blend ratios reside? Finally, from the above experiments, predict the worst-case ratios of the replenished blend would be predicted and the effect examined, if any, that this new blend would have on the performance of the refrigeration system.
4.2. Leakage test method To measure the shift in the components' ratios, a Gas Chromatograph was used equipped with a thermal conductivity detector (TCD). The column type used was a Porapak Q (packed column). The helium flow rate was 30 ml/min. The injector temp. was 150°C, and the detector temp was 200°C. The equipment was calibrated initially on known pure standards of R22, R218, and R290. A liquid sample was drawn off and analysed on the G.C. On the full container this showed a ratio of constituents of: R218(%)
R22(%)
R290(%)
38.902
56.211
5.6175
A quantity of the containers' contents (approximately 0.25-0.5 kg) was then released from the gas phase portion of the container, and the liquid was again sampled and analysed. Repeated leakage of 0.25~).5 kg as a gas reduced the charge from 100% full to almost empty in 15 steps (Table 3). The actual test results are graphed in Fig. 1.
D. Crombie, M.S.,£ Hashmi / Journal of Materials Processing Technology, 55 (1995) 315 320
318
Table 3 Blend variations due to selective leakage Charge
Step
Weight
%
R218%
R22%
R290%
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
5,2 4.95 4.65 4.2 3.7 3.2 2.7 2.2 1.7 1.2 0.95 0.7 0.45 0.2 0.05
100 95.2 89.4 80.8 71.2 61.5 51.9 42.3 32.7 23.1 18.3 13.5 8.7 3.8 1.0
38.902 39.881 36,879 36,983 38,072 37.278 35.099 31.759 30.038 28.278 24.292 21.634 17.707 12.321 4.952
56.211 56.578 58.510 58.802 59.581 59.868 62.136 65.090 68.630 70.701 73.953 76.656 81.132 86.498 97.078
5.6175 5.0889 5.3400 5.1832 4.4902 4.6380 4.4245 4.3190 3.4211 3.2723 3.1350 2.9026 2.3583 1.9345 0.0000
lo0_
40-
3550-
R22
25-
,=.,
o
20-
R218
C,
u.. 4 0 -
~15o
0
//
t
y
-.~ Test Data J
MIO. 20-
I¢Z90 O# 0
10
20
,.50
40 50 6'0 70 % OF CI-IAI~E PRESENT
do
5-
. 10
9'o
4.3. R218 Shift If a regression analysis is performed on the R218 data, the following relationship is found: for 0.01 < X < 1.00
(1)
where Y = % R218 a n d X = fraction of the original charge remaining: i.e. 1.0 = full a n d 0.0 = empty. A general replenishment equation can be developed as follows: Y = 39(1 - X) + X(7.75 In X + 39.96), Y = 39 + 0.96X + 7.75X In X
(2)
The l o c a t i o n of the m i n i m u m can be determined using the differential calculus: X --- I n - i ( _ 8.71/7.75) = 0.325 at the turning point.
30
40
5'0
8'o
' 70
8'0
' 90
' 100
% OF CHARGE PRESENT
Fig. 1. 69L leakage test, showing the shift in component ratios resulting from gas leakage out of a liquid-filled container.
Y = 7.751n X + 39.96
. .20.
Fig. 2. 69L leakage test, showing the ratio of R218.
Thus it can be said that the worst case of R218 depletion arises after replenishment occurs after a gas leak resulting in just 32.5% of the original charge remaining. By applying this value of X to Eq. (2), the worst case depletion can be calclated: Y -- 39 + 0.96(0.325) + 7.75(0.325)1n(0.325) = 36.48%
The GC test results for R218 leakage are plotted in Fig. 2. The correlating regression curve is shown also, indicating the closeness of the fit. Finally, the replenishment curve indicates the minor change that will occur whatever is the loss of R218, assuming that recharging is done with correctly-blended liquid 69L. It was felt necessary to simulate the effects on ratios of taking a worst-case depletion (i.e. R218 down to 36.48%) which is then in turn allowed to leak in the gas phase from a gas/liquid container, and be topped up in turn
D. Crombie, M.S.J. Hashmi / Journal of Materials Processing Technology 55 (1995) 315 320
319
If a replenishment curve is developed for R290, then:
Table 4 R218 variations on lopped-up blend
% R 2 9 0 = 6(1 - X) + X(3.078X + 2.606) %R218 in blend
% weight of charge remaining
36.48 37.4 34.58 34.68 35.70 34.96 32.91 29.78 26.17 26.52 22.78 20.29 16.60 11.55 4.64
= 3.078X 2 - 3.394X + 6 d(%R290)
100 95.2 89.4 80.8 71.2 61.5 51.9 42.3 32.7 23.1 18.3 13.5 8.7 3.8 1.00
dx
(4)
- 6.156X - 3.394 = 0
at the turning point. Therefore X = 0.551 and % R 2 9 0 = 5.064 at the minimum, which occurs when a unit has lost ca. 45% of its charge (Fig. 3). Applying, the repeated depletion scenario to R290, the worst-case depleted, then recharged, unit would show an R290 content of 5.064%. Thus, repeated gas-phase loss would produce R290 ratio shift as shown in Table 5. Y = 3.573X + 1,719 --- depletion curve, where X = %/100 charge remaining and Y = %290.
6.-w
from correctly blended 69L. This would allow the calculation of the c o m p o n e n t s ' ratios after two sequential worst-case depletion/top-up scenarios, again with a view to estimating the possible effects on discharge temepratures a n d / o r flammability of the resultant blend. F o r this case, the results are given in Table 4. Y = 7.458 In X + 36.74 = depletion curve, where Y = % R218 and X = % charge remaining. Therefore the replenishment equation is:
5-
,~21-
Y = 39(1 - X) + X(7.458 In X + 36.74) Y = 39 - 2.26X + 7.458X In X
I
dY - - - - 2.26 + 7.458 + 7.4581n X --- 0 dx In X -
5.198 7.458 -
I
I
i
Fig. 3. 69L leakage test, showing the ratio of R290.
0.696969.
Therefore X = 0.498 (or 49.8% charge remaining at the turning point) and Y = 35.29%, is the lowest R 2 1 8 % at this turning point. In s u m m a r y , then, it can be said that worst-case R218 depletion causes the 39% R218 content to d r o p to 36.48%, and repeated worst-case R218 depletion would cause this figure to d r o p further to 35.29%. Neither of these figures would give cause for concern with respect to raised discharge temperatures.
4.4. R290 Shift If a linear relationship is assumed between the charge and the R290 content, then: % R 2 9 0 = 3.078X + 2.606
for 0 < X < 1.0
(3)
where Y = R290%; and X = Charge (1 -- full, 0.5 = half lost, 0 = empty).
Table 5 R290 variation on topped-up blend R290%
% weight of charge remaining
5.064 4.584 4.811 4.670 4.045 4.178 3,986 &891 3,082 2,948 2.824 2.615 2.125 1,743 0
100 95.2 89.4 80.8 71.2 61.5 51.9 42.3 32.7 23.1 18.3 13.5 8.7 3.8 1
D. Crombie, M.S.J. Hashmi/Journal of Materials Processing Technology 55 (1995) 315 320
320
100-
The replenishment curve is thus: Y = 6(1 - X) + X(3.573X + 1.719) = 3.753X 2 - 4.281X + 6,
.•
-e.,-Replenish
60-
d y = 7.146X - 4.281 = 0. dx
'~
Therefore X = 0.599 (i.e. 59.9% charge remaining at the turning point). This results in Y = 4.718% R290 (propane). It can be said, therefore, that after worst-case depletion resulting in the 6 % p r o p a n e d r o p p i n g to 5.064%, a repeated worst-case depletion would bring this figure to 4.718% propane. Thus, it c a n n o t contribute to any concern a b o u t flammability.
~.r
Curve
["~ Test Doto
40
2
o
,'o
2'0 3'o 20 5'o do 7'0 8'o 9'0 ~;o %OF CH/~6E REM~JNING
Fig. 4. 69L leakage test, ratio of R22.
4.5. R22 Shift Table 6
F r o m the previous two analysis the R22 content is: Correct blend
A
B
39% + 2% 6% _+0.5% 55% (balance)
36.48% 5.064% 58.3%
35.29% 4.718% 60%
R 2 2 % = 100 - (3.078X + 2.606) - (7.751n X + 39.96) R218 R290 R22
= 100 - 3.078X - 2.606 - 7.751n X - 39.96 = 57.434 - 3.078X - 7.751n X. Finally % R 2 2 = 57.434 - 3.078X - 7.751n X for 0.01 < X < 1.00
(5)
% R 2 2 (replenishment) = 55(1 - X) + X(57.434 - 3.078X - 7.751n X) = 55 - 55X + 57.434X - 3.078X 2 - 7.75X In X = 55 + 2.434X - 3.078X 2 - 7.75X In X,
(6)
mixture p r o d u c e d high discharge temperatures under only very extreme conditions (load temp. d o w n to - 3 0 ° C ; ambient temp. 40°C). F o r the 69L blend to a p p r o a c h these ratios, over 80% of the charge would have to be lost via gas leakage. At that point, the unit would no longer cool, thus not achieving the extreme low temp of - 30°C. It is thus not possible for the 69L blend to a p p r o a c h a situation where either flammability, or high compressor discharge temperatures, are a concern.
d(R22) = 2.434 - 6.156X - 7.75 - 7.75 In X, dx d(R22) dx point,
5. Conclusions - 5.316 + 6.156X + 7.75 In X = 0 at the turning
R22 M A X = 58.3% at 62% charge loss (see Fig. 4) It follows from the previous two secondary analyses that the worst case of R22 enrichment would be 100 - (4.718 + 35.29) = 59.992%. As refrigeration units have been run with an R22 content of up to 74%, then 60% R22 is not seen as presenting any problem.
4.6. Leakage summary In summary, the changes can be listed (Table 6) that could occur after an initial worst-case depletion (column A), then a further worst-case depletion (column B). N o n e of these figures would give cause for concern, either on g r o u n d s of flammability or raised discharge temperature. An earlier p r o p o s e d blend of these chemicals, 69S*, is c o m p o s e d of 74% R22, 20% R218, and 6% R290. This
Based on these tests on I S C E O N 69L, it is feasible to run this near-azeotropic blend refrigerant, and handle it in much the same m a n n e r as R502, with the only proviso being that the charging and re-charging should always be d o n e in the liquid phase. O t h e r non-azeotropic blends would need to be assessed individually to establish how they behave in leakage tests. To, date, over 1 x 106 hours running time on 69L have been logged. The failure rates are slightly lower than those of R502. A S H R A E (American Society for Heating Refrigeration & Air conditioning Engineering) has labelled all '69' blends as R403 for the purposes of refrigeration.
References I-1] S.F. Pearson, The development of a drop-in replacement for R502 Inst. Refri9. (9 Jan. 1992),
Materials Processing Technology ELSEVIER
Journal of Materials Processing Technology 55 (1995) 315-320
i
Simulation and assessment of the leakage characteristics and suitability of Rhone-Poulenc's 'ISCEON 69' blends as refrigerants D. Crombie a, M.S.J. Hashmi b' * a Thermo King Europe, Mervue, Galway, Ireland b School of Mechanical Engineering, Dublin Ci(v University, Dublin, Ireland Received 1 April 1994
Industrial summary This paper is the result of investigations into the need for an interim refrigerant to replace R502 as the standard deep-cold refrigerant for use in the demanding transport refrigeration business. The Montreal Protocol on Substances that Deplete the Ozone Layer identified HCFCs as being part of the interim solution to the phasing out of CFCs. Some designers of transport refrigeration equipment chose to move to pure R22 to meet proposed legislative constraints. This work shows that there is a better solution to deep-cold refrigeration than pure R22, one which does not render current fleets obsolete, and one which leaves the way open to chlorine-free HFC-based refrigerants as they evolve. It would clearly hasten the introduction of a HCFC blend and subsequent elimination of CFC R502 if the constituents were non-toxic and well-known chemicals: ISCEON 69L satisfies this requirement.
1. Introduction Transport refrigeration equipment encompasses mobile refrigeration units for large articulated trailers, local delivery trucks and vans, container units, and rail and bus air-conditioning. With an existing world fleet estimated at 300 000 refrigeration units currently running on R502, it was clear some years ago that an interim drop-in refrigerant, which was compatible with all of the R502-type system parameters, materials and lubricants, would be an important step on the way to chlorine-free deep-cold transport refrigeration. Since worldwide R12 annual production ran up to 450 000 t/annum, compared to R502's some tens of thousands of tonnes/annum, the chemical industry rightly concentrated its efforts on replacing R12: the result has been H F C 134a. The transport refrigeration business had been moving away from R12 anyway, in order to achieve deep-cold load temperatures (down to - 30°C), and R502 met the thermodynamic requirements of these new temperatures, when used in single-stage compression refrigeration. Since over 75% of the German trailer market in 1992, and over 90% of the French trailer market in 1992, used
* Corresponding author. 0924-0136/96/$15.00 © 1996 Elsevier Science S.A. All rights reserved SSDI 0 9 2 4 - 0 1 3 6 ( 9 5 ) 0 2 0 2 5 - H
R502 equipment, there is clearly a heavy reliance on R502 performance in the market-place. Transport refrigeration currently relies almost entirely on single-stage reciprocating piston compressors. This paper also investigates the whole fundamental question of the use of zeotropic blends as refrigerants, particularly as they affect servicability and safety, in place of the traditional pure compounds (R12, R22, R134a, for instance) or in place of the azeotropic mixtures (R500, R502, for instance). This work culminated in the acceptance by the transport refrigeration business of the world's first R502 straight substitute or drop-in replacement, Rhone Poulenc's ISCEON 69L. This is also the world's first use of a zeotropic blend refrigerant in the transport refrigeration business.
2. Interim refrigerant criteria Ideal selection criteria for an R502 replacement would include its being: 1. similar in cooling performance; 2. of comparable or lower compressor discharge temperatures; 3. compatible with R502 compressor oil; 4. comparable on compressor discharge pressures; 5. equal to or better on fuel efficiency; 6. compatible with all R502 system materials; 7. non-toxic/non-flammable; and 8. easy to handle for servicing purposes.
316
D. Crombie, M.S.J. Hashmi/Journal of Materials Processing Technology 55 (1995) 315 320
This paper covers the investigation of just two aspects investigated in the course of proving ISCEON 69L: (a) cooling performance (1, 2, 4, 5, above); and (b) blend variations due to selective leakage. Other aspects of 69L were investigated as part of a larger study.
3. Initial proposal Pearson [1] of the Star Refrigeration, Glasgow had proposed a blend of three chemicals (R22, R218 & R290) in the ratio of 85 : 9 : 6. This blend was labelled 69S (for the 6% and 9% constituents & 'S' for Star Refrigeration). R290 is better known as propane (C3Hs), whilst R218 is perfluoropropane (C3Fs), an electronics industry solvent; and R22 is the widely-used air-conditioning fluid dichlorofluoromethane (CHC1F/). Although R22 would meet the legislative Protocol on interim refrigerants, it runs too hot on compressor discharge temperature to be used on extreme pressure ratios, as occurs on deep-cold refrigeration in high ambient temperatures. The purpose of the R218 was to reduce the R22 discharge temperatures, whilst the R290 is both an excellent deep-cold refrigerant and an aid to compressor oil return. As R22 and R290 are highly soluble in AB oils, it was practical to proceed with testing 69S in a standard R502 refrigeration unit. R218 is almost totally inert (a proposed fire-extinguishing medium to replace HALONS). All trials were conducted on a 4-cylinder 30 cu.in. compressor running at 2200 RPM, via a direct-drive diesel engine of 2.2 1 displacement. The refrigeration circuit consists of an R502 expansion valve, a single evaporator coil, a single condenser coil, a heat exchanger on the evaporator liquid/suction lines, an accumulator tank and a receiver tank. Performance was measured using an isothermal calorimeter (ARI 1110) at Thermo King Galway. Initial trials showed 69S behaved in similar fashion to R502 at low to medium ambients (up to + 30°C) on load temperatures of 0°C and - 2 0 ° C , which was very encouraging. Repeating these trials for confirmation, however, produced quite different results. The discharge temperatures were higher than those for R502, and the cooling capacity was lower at 0°/30°C than for R502. Clearly, something had changed. Gas chromatograph (G.C.) analysis of the refrigerant mixture in each of the first two test units indicated different refrigerant constituent ratios. This had come about due to selective distillation of the components during gas-phase charging of the test equipment. The more encouraging results were due to the mixture being R218- enriched as a result of vapour charging. The remaining refrigerant sample was thus R218-depleted, and prone to running hot. Two conclusions could be drawn from these first brief tests: (1) mixture ratio variation could occur in 69S when traditional gas-phase charging
Table 1 69S* vs. R502 p a r a m e t e r s EAIA/CAIA
- 20"/30
TOTQ CDRT CDPI WTRT OILT
+1% +ll'C + 15 psi + 1 ~C +1 C
0°/30 ° -3% +7C + 6 psi - 2'C -3°C
- 29'/38' -15% +25C - 7 psi - 1C -3C
21/49 --4% + 12C + 5 psi - I"C -3C
was practised; and (2) Raising the R218 content whilst simultaneously reducing the R22 content had the effect of reducing the compressor discharge temperatures. Pearson proposed a second blend, of 74:20:6, and a battery of tests was begun, based on Thermo King standards. This mixture was labelled 69S*. 3.1. Refrigeration test standards
These can be summarised briefly as follows: (evaporator inlet air temp (EAIA)/condenser inlet air temperature (CAIA)): - 29°C/38°C, - 20°C/30°C, 0°C/30°C, 21°C/49°C. Along with verifying the cooling capacities under these conditions relative to R502, these tests would further examine the effects of extreme pressure ratios ( - 2 9 ° C / 3 8 ° C ) on the compressor discharge temperatures, and the effects of high gas loads on the compressor pressures (21°C/49°C). Five key parameters were measured: TOTQ cooling capacity (kW); CDRT compressor discharge temperature (°C); CDP1 compressor discharge pressure (psia)t; WTRT Engine coolant temperature (°C); and OILT Engine oil sump temperature (°C). 3.2. 69S* Results
For 69S, these five parameters, relative to R502 operation, can be summarized under the four test standards (Table 1). As the compressor discharge temperatures are all higher on 69S* than on R502, Pearson proposed a further blend of 39% R218, 55% R22 & 6% R290. This last blend was labelled 69L. 3.3. 69L Results
The 69L results, in comparison to those of R502, are summarized in Table 2. Whilst the compressor temperatures are now comparable to those of R502, the cooling capacity is greatly
1 psi
D. Crombie, M.S.J. Hashmi / Journal of Materials Processing Technology 55 (1995) 315 320
317
4.1. 69L Leakage models
Table 2 69L vs. R502 p a r a m e t e r s EAIA/CAIA TOTQ
- 20'/30 ~ + 4%
CDRT CDP1
0'C + 38
WTRT OILT
+ 1 + 3
0/30 ~
- 29°/38 °
21°/49 °
- 7%
+ 22%
- 8%
- l'C + 30
+ ll°C + 33
-4°C + 15
0 0
0 0
- 6 - 5
improved at those points where it is most needed, i.e. at low load temperatures in medium-to-high ambient temperatures.
4. Effects of leakage on non-azeotropic blends Traditional refrigerants are characterized by their nontoxicity, safety, chemical stability, and ease of handling, This last aspect is in greater part due to refrigerants having traditionally been either pure compounds, R12 (CC12F2), R22 ( C H C I F 2 ) or azeotropic mixtures (R500 = R12 + R152a, R502 = R22 + Rl15). A brief definition of an azeotrope is a mixture of two or more products, which mixture, for the present purposes, behaves as a compound. A more complete definition of an azeotrope would be that the components' ratios remain constant, whether in the gas phase or the liquid phase. Thus, R502 retains its R22 at 48.9% and Rl15 at 51.1% whether it is measured in the gas or liquid phase. This constant ratio occurs at just one temperature. In practice, this means that the refrigerant separates slightly when moving away from this one temperature. Thus in a running refrigeration system some separation occurs in either the evaporator or the condenser, or more likely both. Further, because R22 has a physically smaller molecule, it permeates seals and porous hoses more easily, resulting in some R502 equipment running on quite a different mix than that with which it started. It has been a design criterion of refrigerants that they be pure compounds, or be azeotropes. With the advent of new criteria, to accomodate scientific evidence of the link between traditional refrigerants and ozone depletion, it now seems certain that the necessary refrigerating properties will not be met by either pure compounds or by azeotropes. Not just interim replacement refrigerants, but even some longer-term chlorine-free refrigerants, will be blends which are not azeotropes. The correct nomenclature for such blends is zeotropes, but as the term nonazeotrope is most widely used in today's popular publications on the subject, the latter term will be retained for this discussion.
lsceon 69L is a blend of R22, R290, and R218. These compounds have very close boiling points (at 1000 mbar): R22 is - 40°C, R290 is - 42°C, and R218 is - 39°C. This 3°C spread of relative boiling points would lead one to expect that the mixture stays relatively intact, throughout a running system. It is clear from the kinetic gas laws that should a leak occur in a container containing only gaseous 69L, then the three components will leak in a constant ratio equal to the ratio at which they exist inside the container. Further, should a liquid leak occur in a liquid-filled container, the components' ratios will not be affected. The only time a concern may arise is should a gas leak occur in a container of both liquid and gaseous 69L. In such a case, the different boiling points of the three constituents may lead to a shift in their ratios. It was thus seen to be necessary to examine what would happen if a container of correctly blended 69L (R22 at 55%, R218 at 39%, R290 at 6%) leaked a significant proportion of its charge via a gas leak. How would the components' ratios shift, and, in the event that any percentage lost charge was replaced with correctlyblended 69L, where would the resulting blend ratios reside? Finally, from the above experiments, predict the worst-case ratios of the replenished blend would be predicted and the effect examined, if any, that this new blend would have on the performance of the refrigeration system.
4.2. Leakage test method To measure the shift in the components' ratios, a Gas Chromatograph was used equipped with a thermal conductivity detector (TCD). The column type used was a Porapak Q (packed column). The helium flow rate was 30 ml/min. The injector temp. was 150°C, and the detector temp was 200°C. The equipment was calibrated initially on known pure standards of R22, R218, and R290. A liquid sample was drawn off and analysed on the G.C. On the full container this showed a ratio of constituents of: R218(%)
R22(%)
R290(%)
38.902
56.211
5.6175
A quantity of the containers' contents (approximately 0.25-0.5 kg) was then released from the gas phase portion of the container, and the liquid was again sampled and analysed. Repeated leakage of 0.25~).5 kg as a gas reduced the charge from 100% full to almost empty in 15 steps (Table 3). The actual test results are graphed in Fig. 1.
D. Crombie, M.S.,£ Hashmi / Journal of Materials Processing Technology, 55 (1995) 315 320
318
Table 3 Blend variations due to selective leakage Charge
Step
Weight
%
R218%
R22%
R290%
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
5,2 4.95 4.65 4.2 3.7 3.2 2.7 2.2 1.7 1.2 0.95 0.7 0.45 0.2 0.05
100 95.2 89.4 80.8 71.2 61.5 51.9 42.3 32.7 23.1 18.3 13.5 8.7 3.8 1.0
38.902 39.881 36,879 36,983 38,072 37.278 35.099 31.759 30.038 28.278 24.292 21.634 17.707 12.321 4.952
56.211 56.578 58.510 58.802 59.581 59.868 62.136 65.090 68.630 70.701 73.953 76.656 81.132 86.498 97.078
5.6175 5.0889 5.3400 5.1832 4.4902 4.6380 4.4245 4.3190 3.4211 3.2723 3.1350 2.9026 2.3583 1.9345 0.0000
lo0_
40-
3550-
R22
25-
,=.,
o
20-
R218
C,
u.. 4 0 -
~15o
0
//
t
y
-.~ Test Data J
MIO. 20-
I¢Z90 O# 0
10
20
,.50
40 50 6'0 70 % OF CI-IAI~E PRESENT
do
5-
. 10
9'o
4.3. R218 Shift If a regression analysis is performed on the R218 data, the following relationship is found: for 0.01 < X < 1.00
(1)
where Y = % R218 a n d X = fraction of the original charge remaining: i.e. 1.0 = full a n d 0.0 = empty. A general replenishment equation can be developed as follows: Y = 39(1 - X) + X(7.75 In X + 39.96), Y = 39 + 0.96X + 7.75X In X
(2)
The l o c a t i o n of the m i n i m u m can be determined using the differential calculus: X --- I n - i ( _ 8.71/7.75) = 0.325 at the turning point.
30
40
5'0
8'o
' 70
8'0
' 90
' 100
% OF CHARGE PRESENT
Fig. 1. 69L leakage test, showing the shift in component ratios resulting from gas leakage out of a liquid-filled container.
Y = 7.751n X + 39.96
. .20.
Fig. 2. 69L leakage test, showing the ratio of R218.
Thus it can be said that the worst case of R218 depletion arises after replenishment occurs after a gas leak resulting in just 32.5% of the original charge remaining. By applying this value of X to Eq. (2), the worst case depletion can be calclated: Y -- 39 + 0.96(0.325) + 7.75(0.325)1n(0.325) = 36.48%
The GC test results for R218 leakage are plotted in Fig. 2. The correlating regression curve is shown also, indicating the closeness of the fit. Finally, the replenishment curve indicates the minor change that will occur whatever is the loss of R218, assuming that recharging is done with correctly-blended liquid 69L. It was felt necessary to simulate the effects on ratios of taking a worst-case depletion (i.e. R218 down to 36.48%) which is then in turn allowed to leak in the gas phase from a gas/liquid container, and be topped up in turn
D. Crombie, M.S.J. Hashmi / Journal of Materials Processing Technology 55 (1995) 315 320
319
If a replenishment curve is developed for R290, then:
Table 4 R218 variations on lopped-up blend
% R 2 9 0 = 6(1 - X) + X(3.078X + 2.606) %R218 in blend
% weight of charge remaining
36.48 37.4 34.58 34.68 35.70 34.96 32.91 29.78 26.17 26.52 22.78 20.29 16.60 11.55 4.64
= 3.078X 2 - 3.394X + 6 d(%R290)
100 95.2 89.4 80.8 71.2 61.5 51.9 42.3 32.7 23.1 18.3 13.5 8.7 3.8 1.00
dx
(4)
- 6.156X - 3.394 = 0
at the turning point. Therefore X = 0.551 and % R 2 9 0 = 5.064 at the minimum, which occurs when a unit has lost ca. 45% of its charge (Fig. 3). Applying, the repeated depletion scenario to R290, the worst-case depleted, then recharged, unit would show an R290 content of 5.064%. Thus, repeated gas-phase loss would produce R290 ratio shift as shown in Table 5. Y = 3.573X + 1,719 --- depletion curve, where X = %/100 charge remaining and Y = %290.
6.-w
from correctly blended 69L. This would allow the calculation of the c o m p o n e n t s ' ratios after two sequential worst-case depletion/top-up scenarios, again with a view to estimating the possible effects on discharge temepratures a n d / o r flammability of the resultant blend. F o r this case, the results are given in Table 4. Y = 7.458 In X + 36.74 = depletion curve, where Y = % R218 and X = % charge remaining. Therefore the replenishment equation is:
5-
,~21-
Y = 39(1 - X) + X(7.458 In X + 36.74) Y = 39 - 2.26X + 7.458X In X
I
dY - - - - 2.26 + 7.458 + 7.4581n X --- 0 dx In X -
5.198 7.458 -
I
I
i
Fig. 3. 69L leakage test, showing the ratio of R290.
0.696969.
Therefore X = 0.498 (or 49.8% charge remaining at the turning point) and Y = 35.29%, is the lowest R 2 1 8 % at this turning point. In s u m m a r y , then, it can be said that worst-case R218 depletion causes the 39% R218 content to d r o p to 36.48%, and repeated worst-case R218 depletion would cause this figure to d r o p further to 35.29%. Neither of these figures would give cause for concern with respect to raised discharge temperatures.
4.4. R290 Shift If a linear relationship is assumed between the charge and the R290 content, then: % R 2 9 0 = 3.078X + 2.606
for 0 < X < 1.0
(3)
where Y = R290%; and X = Charge (1 -- full, 0.5 = half lost, 0 = empty).
Table 5 R290 variation on topped-up blend R290%
% weight of charge remaining
5.064 4.584 4.811 4.670 4.045 4.178 3,986 &891 3,082 2,948 2.824 2.615 2.125 1,743 0
100 95.2 89.4 80.8 71.2 61.5 51.9 42.3 32.7 23.1 18.3 13.5 8.7 3.8 1
D. Crombie, M.S.J. Hashmi/Journal of Materials Processing Technology 55 (1995) 315 320
320
100-
The replenishment curve is thus: Y = 6(1 - X) + X(3.573X + 1.719) = 3.753X 2 - 4.281X + 6,
.•
-e.,-Replenish
60-
d y = 7.146X - 4.281 = 0. dx
'~
Therefore X = 0.599 (i.e. 59.9% charge remaining at the turning point). This results in Y = 4.718% R290 (propane). It can be said, therefore, that after worst-case depletion resulting in the 6 % p r o p a n e d r o p p i n g to 5.064%, a repeated worst-case depletion would bring this figure to 4.718% propane. Thus, it c a n n o t contribute to any concern a b o u t flammability.
~.r
Curve
["~ Test Doto
40
2
o
,'o
2'0 3'o 20 5'o do 7'0 8'o 9'0 ~;o %OF CH/~6E REM~JNING
Fig. 4. 69L leakage test, ratio of R22.
4.5. R22 Shift Table 6
F r o m the previous two analysis the R22 content is: Correct blend
A
B
39% + 2% 6% _+0.5% 55% (balance)
36.48% 5.064% 58.3%
35.29% 4.718% 60%
R 2 2 % = 100 - (3.078X + 2.606) - (7.751n X + 39.96) R218 R290 R22
= 100 - 3.078X - 2.606 - 7.751n X - 39.96 = 57.434 - 3.078X - 7.751n X. Finally % R 2 2 = 57.434 - 3.078X - 7.751n X for 0.01 < X < 1.00
(5)
% R 2 2 (replenishment) = 55(1 - X) + X(57.434 - 3.078X - 7.751n X) = 55 - 55X + 57.434X - 3.078X 2 - 7.75X In X = 55 + 2.434X - 3.078X 2 - 7.75X In X,
(6)
mixture p r o d u c e d high discharge temperatures under only very extreme conditions (load temp. d o w n to - 3 0 ° C ; ambient temp. 40°C). F o r the 69L blend to a p p r o a c h these ratios, over 80% of the charge would have to be lost via gas leakage. At that point, the unit would no longer cool, thus not achieving the extreme low temp of - 30°C. It is thus not possible for the 69L blend to a p p r o a c h a situation where either flammability, or high compressor discharge temperatures, are a concern.
d(R22) = 2.434 - 6.156X - 7.75 - 7.75 In X, dx d(R22) dx point,
5. Conclusions - 5.316 + 6.156X + 7.75 In X = 0 at the turning
R22 M A X = 58.3% at 62% charge loss (see Fig. 4) It follows from the previous two secondary analyses that the worst case of R22 enrichment would be 100 - (4.718 + 35.29) = 59.992%. As refrigeration units have been run with an R22 content of up to 74%, then 60% R22 is not seen as presenting any problem.
4.6. Leakage summary In summary, the changes can be listed (Table 6) that could occur after an initial worst-case depletion (column A), then a further worst-case depletion (column B). N o n e of these figures would give cause for concern, either on g r o u n d s of flammability or raised discharge temperature. An earlier p r o p o s e d blend of these chemicals, 69S*, is c o m p o s e d of 74% R22, 20% R218, and 6% R290. This
Based on these tests on I S C E O N 69L, it is feasible to run this near-azeotropic blend refrigerant, and handle it in much the same m a n n e r as R502, with the only proviso being that the charging and re-charging should always be d o n e in the liquid phase. O t h e r non-azeotropic blends would need to be assessed individually to establish how they behave in leakage tests. To, date, over 1 x 106 hours running time on 69L have been logged. The failure rates are slightly lower than those of R502. A S H R A E (American Society for Heating Refrigeration & Air conditioning Engineering) has labelled all '69' blends as R403 for the purposes of refrigeration.
References I-1] S.F. Pearson, The development of a drop-in replacement for R502 Inst. Refri9. (9 Jan. 1992),