Estimation of Refrigerant-Oil Mixture
Viscosities for Alternative Refrigerants
Using Solubility Data
Chris Seeton
Seeton C&P
University of Illinois at Urbana-Champaign
Air Conditioning and Refrigeration Center
seeton@uiuc.edu
Chicago 2006 – ASHRAE Winter Meeting
Why Estimate/Measure Mixture Viscosity?
z
Refrigerant drastically cuts the lubricant viscosity
–
Primarily: Compressor Lubrication
–
Secondary:
z
z
–
Lubricating auxiliary valves and seals
Sealing microscopic leaks
Heat Exchanger / Piping Design Considerations
z
Heat transfer enhancement or fouling
–
z
Increased Pressure drop
–
z
Heat Exchanger length - Nu ~ f(Pr, Re,…)
G
⎛ VD ⎞
Re = ⎜
⎟
ν
⎝
⎠
Heat Exchanger circuiting or tube sizing - ΔP ~ f(Re,…)
Oil Management
–
Retention, “Hold-up” & Oil Return
Chicago 2006 – ASHRAE Winter Meeting
Viscosity – Temperature Chart
10000
5000
3000
2000
Viscosity (cSt)
1000
700
500
400
300
200
100
80
60
50
40
30
20
10
9
8
7
6
5
4
3
2
-20
-10
0
10
20
30
40
50
60
70
80
90
100
110
120
Temperature (°C)
ASTM Standard D341-93 (1998)
Chicago 2006 – ASHRAE Winter Meeting
Historical Lubricant Blending
500
400
300
200
Viscosity (cSt)
100
90
80
70
60
50
40
30
ISO 120
74% by Volume
20
10
9
8
7
26%
6
5
Mix
4
3
130
120
110
100
90
80
70
60
50
40
30
20
10
0
Problem: Find ISO 32 Blend
ISO 22
Temperature (ºC)
Chicago 2006 – ASHRAE Winter Meeting
ASTM Chart – Application to Refrigerants
3
2
1
0.9
0.8
0.7
0.6
0.5
Viscosity (cSt)
0.4
0.3
0.28
0.26
0.24
0.22
0.2
0.18
0.16
0.14
R410A
R123
Propane
CO2
R134a
0.12
130
120
110
100
90
80
70
60
50
40
30
20
10
0
-10
-20
-30
-40
-50
-60
ASTM Standard D 341-93 (ν ≥ 0.21);
Manning equation (ν < 0.21)
Temperature (ºC)
Chicago 2006 – ASHRAE Winter Meeting
2006 Refrigeration Handbook, Chapter 7
z
Relationship between temperature and
kinematic viscosity (ASTM D341)
(
)
Log10 Log10 (ν + 0.7 + f ASTM (ν ) ) = A − B * Log10 (T )
f ASTM (ν ) = C − D + E − F + G − H
z
C = exp ( −1.14883 − 2.65868ν )
;
D = exp ( −0.00381308 − 12.5645ν )
E = exp ( 5.46491 − 37.6289ν )
;
F = exp (13.0458 − 74.6851ν )
G = exp ( 37.4619 − 192.643ν )
; H = exp ( 80.4945 − 400.468ν )
Undefined below 0.21 cSt!
Chicago 2006 – ASHRAE Winter Meeting
Criteria for a new Viscosity-Temperature Chart
It is desired to construct a generalized chart that is
able to:
–
–
–
–
–
Cover entire temperature range (cryogenic to high
temperatures)
Cover entire viscosity range (~0.04 cSt to glass transition)
Linearize fluids that do not exhibit excessive molecular
coiling, molecular bonding, or wax precipitation
Maintain the existing ASTM format for lubricants for
viscosities greater than 2 cSt.
Provide blending of lubricant and refrigerant mixtures
Chicago 2006 – ASHRAE Winter Meeting
New Scaling Rule
(
)
Log e Log e (ν + 0.7 + fCS (ν ) ) = A − B * Log e (T )
fCS (ν ) = e−ν K 0 (ν +ψ )
z
Scaling the LHS to approach -infinity as ν → 0
ψ = 1.244 067
(
)
Log e Log e (ν + 0.7 + e −ν K 0 (ν + 1.244067 ) ) = A − B * Log e (T )
y = mx + b
Chicago 2006 – ASHRAE Winter Meeting
New Viscosity Chart
3
2
Viscosity (cSt)
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.28
0.26
0.24
0.22
0.2
0.18
0.16
0.14
0.12
Propane
0.1
0.08
0.06
R134a
R410A
CO2
0.04
130
120
110
100
90
80
70
60
50
40
30
20
10
0
-10
-20
-30
-40
-50
-60
Temperature (ºC)
201
Chicago 2006 – ASHRAE Winter Meeting
ASTM Blending Rule
z
Volume based blending rule
(
)
Log10 Log10 (ν mix + 0.7 + f ASTM (ν mix ) ) = ∑ Vi * ( Ai − Bi * Log10 (T ) )
Voli
Vi =
Voltotal
Voltotal = ∑ Voli
ymix = ∑ Vi * ( Ai − Bi * Log10 (T ) )
For lubricants only, accuracy is generally better than ±15%
Chicago 2006 – ASHRAE Winter Meeting
Estimation depends on prior knowledge
z
Assume density of fluids and their mixture are equal
Volume fraction = Mass Fraction
Vi = wi
ymix = ∑ wi * ( Ai − Bi * Log e (T ) )
For refrigerant/lubricant mixtures, accuracy is generally
better than ±20%
Chicago 2006 – ASHRAE Winter Meeting
Estimation depends on prior knowledge
z
Recognize that the density of individual fluids are
different, but they mix ideally
ρ mix (T )
Voli
Vi =
= wi
Voltotal
ρi (T )
ymix
⎛
wi ⎞
ρ mix (T ) = ⎜⎜ ∑
⎟⎟
⎝ ρi (T ) ⎠
−1
ρ mix (T )
= ∑ wi
* ( Ai − Bi * Log e (T ) )
ρi ( T )
i
For refrigerant/lubricant mixtures, accuracy is generally
better than ±15%
Chicago 2006 – ASHRAE Winter Meeting
Estimation depends on prior knowledge
z
If measured data is available…
ymix
⎛⎛
⎞
⎞
ρ mix (T )
* ( Ai − Bi * Log e (T ) ) ⎟
= ∑ ⎜ ⎜1 + ∑ ϕij wi w j ⎟ * wi
⎜
⎟
ρi (T )
i ⎝⎝
j
⎠
⎠
ϕij = ϕ ji
;
ϕii = ϕ jj = 0
ϕij = f (T , w )
Accuracy is greatly enhanced ~ ±2%
Chicago 2006 – ASHRAE Winter Meeting
Viscosity Prediction – POE + R134a
1000
400
200
100
50
30
20
10
7
5
4
3
POE 32
5% g/g
10% g/g
2
Viscosity (cSt)
20% g/g
1
0.9
0.8
0.7
0.6
0.5
30% g/g
50% g/g
0.4
0.3
0.26
0.22
0.2
0.18
0.16
0.14
0.12
0.1
70% g/g
90% g/g
0.08
R134a
0.06
100
90
80
70
60
50
40
30
20
10
0
-10
-20
Temperature (ºC)
201
Chicago 2006 – ASHRAE Winter Meeting
Basic Solubility Measurement
201
Chicago 2006 – ASHRAE Winter Meeting
Results of Solubility Measurements
Pure R134a
40
70%
50%
35
30%
Pressure (bar)
30
25
20% R134a
20
15
10%
10
5% R134a
5
0
-40
-30
-20
-10
0
10
20
30
40
Temperature (C)
50
60
70
80
90 100 110 120
Chicago 2006 – ASHRAE Winter Meeting
Results of Solubility Measurements
Pure R134a 70% 50%
15
Pressure = 3 bar
20% R134a
30%
10%
Pressure (bar)
10
5% R134a
5
0
-20
-10
0
10
20
30
40
50
60
Temperature (C)
70
80
90
100
110 120
Conc.
% R134a
Temp.
°C
5%
60
10%
32
20%
15
30%
10
50%
5
70%
2.5
90%
1.3
100%
0.67
Chicago 2006 – ASHRAE Winter Meeting
Constant Pressure Curves
1000
400
200
100
50
30
20
10
7
5
4
3
POE 32
5% g/g
10% g/g
2
Viscosity (cSt)
20% g/g
1
0.9
0.8
0.7
0.6
0.5
30% g/g
50% g/g
0.4
0.3
0.26
0.22
0.2
0.18
0.16
0.14
0.12
0.1
70% g/g
90% g/g
0.08
R134a
0.06
100
90
80
70
60
50
40
30
20
10
0
-10
-20
201
Temperature (ºC)
Chicago 2006 – ASHRAE Winter Meeting
Daniel Chart – POE32 / R-134a
1000
400
200
100
50
30
20
10
7
5
4
3
POE 32
5% g/g
10% g/g
2
1
0.9
0.8
0.7
0.6
0.5
0.4
30% g/g
50% g/g
P=12 bar
P=6 bar
P=4 bar
70% g/g
P=3 bar
0.3
0.26
0.22
0.2
0.18
0.16
0.14
0.12
0.1
0.08
P=2 bar
Viscosity (cSt)
20% g/g
0.06
90% g/g
R134a
100
90
80
70
60
50
40
30
20
10
0
-10
-20
201
Temperature (ºC)
Chicago 2006 – ASHRAE Winter Meeting
Real Motivation - CO2
Estimated viscosity does not represent experimental measurements!
PAG 46
5% g/g
2
10% g/g
1
0.9
0.8
0.7
0.6
0.5
20% g/g
0.3
0.26
0.22
0.2
0.18
0.16
0.14
0.12
0.1
0.08
30% g/g
P=120 bar
P=50 bar
0.4
P=35 bar
P=25 bar
Viscosity (cSt)
1000
400
200
100
50
30
20
10
7
5
4
3
50% g/g
70% g/g
90% g/g
CO2
0.06
100
90
80
70
60
50
40
30
20
10
0
-10
-20
Temperature (ºC)
Chicago 2006 – ASHRAE Winter Meeting
Conclusions
z
z
z
Refrigerant – lubricant mixture viscosities
can be estimated
HFCs and hydrocarbons behave well on the
proposed chart
CO2 does not mix ideally.
–
–
A new mixing rule is under development.
Experimental data is required!
z
Pressures must be over 35 bar (500 psia) to capture
“in operation” conditions for air conditioning
Chicago 2006 – ASHRAE Winter Meeting