Solubility, Miscibility, and Liquid
Viscosity of Lubricants with CO2
and Propane
Chris Seeton
Seeton C&P
University of Illinois at Urbana-Champaign
Chicago 2003 – ASHRAE Winter Meeting
Viscosity – Temperature Chart
ASTM D 341-93 (1998)
10000
0.56257
2000
1000
500
200
0.36257
100
60
Kinematic Viscosity, cSt
30
0.16257
20
10
8
-0.03743
6
5
4
3
-0.23743
2
-0.43743
1
-0.63743
2.403378
-15
-5
5
15
25
35
45
55
65
75
85
95
105
115 125
Viscosity – Temperature Chart
ASTM D 341-93 (1998)
Viscosity
Naphthene Mineral Oil
10000
0 .5
6
2
5
7
5
7
5
7
4
3
4
3
4
3
2000
1000
500
200
0 .3
6
2
100
60
30
Kinematic Viscosity, cSt
0 .1
6
2
20
10
8
-0 .0 3
7
6
5
4
3
-0 .2
3
7
0%
2
-0 .4
3
7
1
-0 .6
3
7
4
3
2
.4
0 3
3
7
8
-15
-5
5
15
25
35
45
55
65
75
85
95
105
115 125
Viscosity – Temperature Chart
ASTM D 341-93 (1998)
Viscosity and Vapor Pressure
Naphthene Mineral Oil / Propane
10000
0 .5
6
2
5
7
5
7
5
7
4
3
4
3
4
3
2000
1000
500
200
0 .3
6
2
100
60
30
Kinematic Viscosity, cSt
0 .1
6
2
20
10
8
-0 .0 3
7
6
5
4
3
-0 .2
3
7
0%
2
-0 .4
3
7
10%
20% propane
1
-0 .6
3
7
4
3
2
.4
0 3
3
7
8
-15
-5
5
15
25
35
45
55
65
75
85
95
105 115 125
Solubility
Naphthenic Mineral Oil 32 / Propane
50
30%
40
Pressure (bar)
20%
30
15% Propane
Pure
Propane
20
10%
5%
10
0
-40
-30
-20
-10
0
10
20
30
40
50
Temperature (C)
60
70
80
90 100 110 120
Viscosity – Temperature Chart
Daniel Chart
Viscosity and Vapor Pressure
Naphthene Mineral Oil / Propane
10000
0 .5
6
2
5
7
2
5
7
2
5
7
7
4
3
7
4
3
7
4
3
2000
1000
500
200
0 .3
6
10
8
-0 .0 3
3
-0 .2
3
0%
P = 15 bar
6
5
4
P = 6 bar
6
P = 5 bar
0 .1
P = 4 bar
40
20
P = 2 bar
Kinematic Viscosity, cSt
100
60
2
-0 .4
3
10%
20% propane
1
-0 .6
3
7
4
3
2
.4
0 3
3
7
8
-15
-5
5
15
25
35
45
55
65
75
85
95
105 115 125
Naphthenic Mineral Oil 32 / Propane
Daniel Chart
Viscosity and Vapor Pressure
Naphthene Mineral Oil / Propane
Assume:
Evaporator = -6°C
Suction Pressure = 4 bar
6°C Superheat
10°C Suction Line HX
20°C Rise in Compressor
10000
0 .5
6
2
5
7
2
5
7
2
5
7
2000
1000
500
200
0 .3
6
10
8
-0 .0 3
7
4
3
7
4
3
7
4
3
3
3
0%
P = 15 bar
6
5
4
-0 .2
Bearing Lubrication Temp.
30°C
P = 6 bar
6
P = 5 bar
0 .1
P = 4 bar
40
20
P = 2 bar
Kinematic Viscosity, cSt
100
60
2
-0 .4
3
10%
20% propane
1
-0 .6
3
7
4
3
2
.4
0 3
3
7
8
-15
-5
5
15
25
35
45
55
65
75
85
95
105 115 125
Pure Lubricant Viscosity
62 cSt
Mixture Viscosity
22 cSt
POE-55 / R-134a
Daniel Chart
10000
0 .6
2000
1000
500
0
100%
POE-55
P = 5 bar
10
8
6
5
4
P = 3 bar
0 .2
30
20
Kinematic Viscosity, cSt
P = 1 bar
200
100
60
P = 2 bar
0 .4
90%
80%
-0 .2
70%
3
-0 .4
2
-0 .8
-1
2
.3
Bearing Lubrication Temp.
30°C
Pure Lubricant Viscosity
85 cSt
Mixture Viscosity
48 cSt
-0 .6
1.25
Assume:
Evaporator = -6°C
Suction Pressure = 2.3 bar
6°C Superheat
10°C Suction Line HX
20°C Rise in Compressor
6
7
6
3
5
-40
-20
0
20
40
60
80
100
Viscosity Comparison
ISO 32 Lubricants with Propane
60
Viscosity (cSt)
50
40
30
20
10
0
AB
zTest
MO
POE
PAG
POE/R134a
Condition: -6°C Evaporating, 6°C Superheat,
10°C Suction Line HX, 20°C Compressor Heating
Density
Naphthenic Mineral Oil 32 / Propane
Density of Naphthene Mineral Oil / Propane
0.94
0.92
0.9
0.88
Density (g/cc)
0.86
0% Pure MO
0.84
0.82
5%
0.8
10%
0.78
15%
0.76
20%
0.74
0.72
0.7
30%Propane
0.68
-25
-15
-5
5
15
25
35
45
Temperature (C)
55
65
75
85
95
105
Density
Polyalkylene Glycol 46 / Propane
Density (g/cc)
Density of Polyalkylene Glycol / Propane
1.04
1.02
1
0.98
0.96
0.94
0.92
0.9
0.88
0.86
0.84
0.82
0.8
0.78
0.76
0.74
0.72
0.7
0.68
0.66
0.64
0% Pure PAG
5%
10%
15%
20%
30% Propane
-25
-15
-5
5
15
25
35
45
Temperature (C)
55
65
75
85
95
105
Propane Miscibility
z
z
POE, AB, and MO showed excellent solubility
with propane
PAG showed a saturated pressure close to
pure propane for 30% compositions
–
–
Could be a sign of possible immiscibility
More testing is necessary
Solubility
PAO > AB > PAG > POE
Vapor Pressure
90% by weight 220 Lubricant Concentration
60
PAO-220
Pure
CO2
50
AB-220
PAG-220
POE-220
Pressure (bar)
40
Modified Clausius-Clapeyron
30
E F
log(P ) = D + + 2
T T
20
10
0
-20
-10
0
10
20
30
40
50
Temperature (C)
60
70
80
90
100
110 120
Mixture Viscosities – 90% Lubricant
PAG > PAO > POE > AB
10000
0 .6
2000
1000
500
Pure
Lubricants
0 .4
200
100
60
0 .2
Abs olute Vis cos ity, m Pa*s ec
30
20
PA G-220
PA G
PA O
A B-220
10
8
POE
PA O-220
MO
0
AB
6
5
4
POE-220
-0 .2
3
-0 .4
2
-0 .6
-0 .8
1.25
-1
2
.4
0 3
3
7
7
9
-20
0
20
40
60
80
100
120
POE-55 / CO2
Daniel Chart
10000
0 .6
2000
1000
500
0 .4
100%
POE-55
P = 25 bar
0
-0 .2
95%
90%
P = 35 bar
10
8
6
5
4
P = 15 bar
0 .2
30
20
Kinematic Viscosity, cSt
P = 10 bar
200
100
60
3
-0 .4
Pure Lubricant Viscosity
55 cSt
Mixture Viscosity
5.5 cSt
-0 .6
-0 .8
-1
2
.3
Bearing Lubrication Temp.
40°C
85%
2
1.25
Assume:
Evaporator = 0°C
Suction Pressure = 35 bar
10°C Superheat
10°C Internal Heat Exchanger
20°C Rise in Compressor
6
7
6
3
5
-40
-20
0
20
40
60
80
100
Miscibility in CO2
3 0
2 5
P A O
2 0
Miscible
Immiscible
1 5
M
1 0
o
temperature / C
5
0
P O E
-5
-1 0
P A G
POE Miscible
-1 5
-2 0
-2 5
A B
-3 0
-3 5
-4 0
0
1 0
2 0
3 0
4 0
5 0
6 0
7 0
W t % L u b ric a n t in C O 2
8 0
9 0
1 0 0
CO2 Miscibility
z
z
Based on miscibility data design concerns
should be based on the cycle operation for the
AB, MO, PAO, and PAG lubricants
It is expected that the POE lubricant will not
experience these miscibility problems
–
HOWEVER, serious design considerations must be
weighed to account for the reduction in the mixture
viscosity
Lubricants with CO2 - Conclusions
z
POE Lubricant type showed good miscibility
–
z
PAG, PAO, MO and AB are only partially soluble in CO2
–
–
z
Transcritical AC systems Ø evaporators, receivers, Int. HX
Transcritical Heat Pump systems Ø evaporators, receivers,
compressor sump
However, the PAG type lubricant seems to give the best
lubricity for transcritical applications
–
z
Severe viscosity reduction possibly limits its use to low
temperature cascade systems
PAG maintained the highest mixture lubricity in this study
High efficiency oil separators may make MO a viable
lubricant in some cascade systems
Lubrication
Influence of CO2- Roller Bearing
Prototype AC Compressor
failed @ 10 hrs
Repeatable
POE-220
Polyol Ester 32 / Propane
Daniel Chart
Viscosity and Vapor Pressure
Polyol Ester / Propane
Assume:
Evaporator = -6°C
Suction Pressure = 4 bar
6°C Superheat
10°C Suction Line HX
20°C Rise in Compressor
10000
0 .5
6
2
5
7
5
7
5
7
2000
1000
500
200
0 .3
6
2
100
2
10
8
-0 .0 3
7
4
Bearing Lubrication Temp.
30°C
3
6
5
4
3
-0 .2
3
7
4
P = 6 bar
6
P = 4 bar
Kinematic Viscosity, cSt
0 .1
20
P = 5 bar
30
P = 2 bar
60
0%
10%
3
20% propane
2
-0 .4
3
7
1
-0 .6
3
7
4
3
4
3
2
.4
0 3
3
7
8
-15
-5
5
15
25
35
45
55
65
75
85
95
105 115 125
Pure Lubricant Viscosity
62 cSt
Mixture Viscosity
38 cSt
Polyalkylene Glycol 46 / Propane
Daniel Chart
Viscosity and Vapor Pressure
Polyalkylene Glycol / Propane
Assume:
Evaporator = -6°C
Suction Pressure = 4 bar
6°C Superheat
10°C Suction Line HX
20°C Rise in Compressor
10000
0 .5
6
2
5
7
5
7
5
7
2000
1000
500
200
0 .3
6
2
100
2
10
8
-0 .0 3
7
4
3
6
5
4
3
-0 .2
3
7
Bearing Lubrication Temp.
30°C
0%
P = 6 bar
6
P = 4 bar
Kinematic Viscosity, cSt
0 .1
20
P = 5 bar
30
P = 2 bar
60
10%
20% propane
4
3
4
3
2
-0 .4
3
7
1
-0 .6
3
7
4
3
2
.4
0 3
3
7
8
-15
-5
5
15
25
35
45
55
65
75
85
95
105 115 125
Pure Lubricant Viscosity
83 cSt
Mixture Viscosity
51 cSt
Alkylbenzene 32 / Propane
Daniel Chart
Viscosity and Vapor Pressure
Alkylbenzene / Propane
Assume:
Evaporator = -6°C
Suction Pressure = 4 bar
6°C Superheat
10°C Suction Line HX
20°C Rise in Compressor
10000
0 .5
6
2
5
7
5
7
5
7
2000
1000
500
200
0 .3
6
2
100
60
30
6
2
4
3
4
3
4
3
-0 .2
3
7
P = 6 bar
7
6
5
P = 5 bar
-0 .0 3
Bearing Lubrication Temp.
30°C
P = 4 bar
10
8
P = 2 bar
Kinematic Viscosity, cSt
0 .1
20
0%
10%
20% propane
2
-0 .4
3
7
1
-0 .6
3
7
4
3
4
3
2
.4
0 3
3
7
8
-15
-5
5
15
25
35
45
55
65
75
85
95
105 115 125
Pure Lubricant Viscosity
60 cSt
Mixture Viscosity
20 cSt