Transient separation of refrigerant from oil/refrigerant ...Internat ionalCo nference onCom presors andRefrig eration, 2017 Refrigeration cycle and refrigeration oil oRequired properties

Shizuoka University

Transient separation of refrigerant from oil/refrigerant mixture

7/21/2017

Mitsuhiro Fukuta

Shizuoka University

[email protected]

The 8th International Conference onCompressors and Refrigeration, 2017

福田　充宏

Shizuoka University

The 8th International Conference on Compressors

and Refrigeration, 2017

Contentso Introductionn Research activities in my laboratory

oHow complicated the oil related matters are.

oTransient dissolution and separation of refrigerant from oil/refrigerant mixturen Separation of CO2 from PAG

oSummary

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Shizuoka, Japan

To access Shizuoka University 1.5~2 hours from Tokyo or Osaka by Shinkansen (bullet train)

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Campus LocationMt. Fuji

World Heritage(2013～)

pOptical device Hamamatsu photonics

pMotor cycle Suzuki, Yamaha, Honda

pMusic instrument Yamaha, Kawai, Roland

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Major Products of Shizuoka Prefecture

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Refrigeration industry in Shizuoka

Hitachi Johnson controlsShimizu works

Mitsubishi Electric Shizuoka works

Toshiba CarrierFuji works

Toshiba CarrierKakegawa R&D center

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Research activities in our laboratory

oCompressor and expanderoRefrigeration systemoFunctional fluid

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Research activities in our Lab.o Compressor and expandern Operating characteristics, High

performance, High reliabilityo Refrigeration systemn Instrumentation techniquesn Clarifying flow phenomenao Two-phase flow, Foam, Oil droplet…

n Properties of oil/refrigerant mixturen Nano-oil

o Functional fluidn Drag reductionn Measurement of physical propertiesn Enhancement of heat transfer

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Research activities

Expansion device

Evaporator

Condenser

Compressor

Use of natural refrigerant

Internal flow

Lubrication

Performance simulation

Leakage

Dynamics

Refrigerant concentration in oil

Oil separationOCR measurement

Power recovery

Flow analysis

Cycle configuration Control

Oil return

Quality measurement

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Refrigeration cycle and Refrigeration oil

How complicated the oil related matters are.

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Refrigeration cycle and refrigeration oil

oRoles of refrigeration oiln Lubricationn Seal of compression chambern Coolingn Cleaning

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Refrigeration cycle and refrigeration oiloRequired propertiesn Lubricity（appropriate viscosity, strong

oil film）

n Stability（against heat, acid, and moisture）

n Fluidity (low freezing point)n Material compatibilityn Miscibility with refrigerant 　←　Oil return, Lubricationn Electric insulation (hermetic compressor)

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Refrigerant/Oil mixture

o Good solubility of oil with refrigerant

Influence on operating characteristics of compressors and cyclesn Viscosity of oiln Foaming phenomenon in compressor shelln Oil return to compressorn Amount of refrigerant circulating in cyclen Heat transfer and pressure drop in heat

exchangers

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Influence of refrigeration oilSuction oil ratio Internal

circulationOil supply

Seal Cooling

Oil amount

Lubrication

Solubility

Viscosity Out gassing

Separation

Pressure lossLeakage

to suction

Leakage to compression

chamber

Over compression

Suction superheat

Temperature in cylinder

Pressure in cylinder

Cylinder temperature

Influence on cycle

Volumetric efficiency

Discharge temperature

Total efficiency

Frictional lossWear Noise

Foaming

Radiation

Parts behavior

Indicated efficiency

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Properties of refrigerant/oil mixture

oRefractive indexoDielectric constantoAcoustic velocityoDensityoSurface tension

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Properties of oil/refrigerant mixture

0 0.5 11.1

1.2

1.3

1.4

1.5

Refrigerant volume fraction

Ref

ract

ive

inde

x

R410A/PVE

30 ℃40 ℃50 ℃

Temperature

Immiscible region at 50℃

Refractive index Dielectric constant

Surface tension

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Transient separation of CO2 from PAG

oMeasurements of concentration and viscosity of CO2/PAG mixture

oSeparation characteristicsn Depressurization in pressure vesseln Depressurization through valve

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Experimental setup for concentration and viscosity measurement

18/38

Refrigerant : CO2Refrigeration oil : PAG

Procedure1. Evacuation after charging oil2. Refrigerant charge with

stirring3. Set to given pressure and

temperature

Thermo- couple

Sight glassStop valve

Regulation valve Pressure gauge

ViscometerRefractive Index sensor

Sampling port

4. Measurement of pressure, temperature, refractive index, viscosity

5. Sampling

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　)1()1( cnnn or

0 20 40 60 80 1000

0.04

0.08

0.12

0.16

0.2

c va

lue

Temperature [℃]

n : Refractive index of mixturenr: Refractive index of refrigerant no: Refractive index of oil

c : Coefficient β: Weight fraction of refrigerant

20 40 60 80 1001

1.1

1.2

1.3

1.4

1.5

Ref

ract

ive

Inde

x[−]

Temperature [℃]

PAG

CO2

Extrapolation

Concentration measurement based on refractive index

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　)1()1( cnnn or Deviation from sampling value

Approx. 0.5%

10 20 30 401.36

1.38

1.40

1.42

Ref

ract

ive

inde

x [−

]

Concentration[％]

1.4420℃

40℃60℃

80℃

100℃

SamplingCalculation

Refrigerant concentration can be obtained from refractive index and temperature from 20 ℃ to 100℃.

Correlation curve

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)15.273log(7.01000loglog TBA

μ : Viscosity [mPa･s]ρ : Density [kg/m3]T : Temperature [℃]A,B : Coefficients

Relative error:　　　　　　　 approx. 10 ％

0 0.1 0.2 0.3 0.4100

101

102

Concentration[−]

Vis

cosi

ty[m

Pa・

s]

40℃60℃

80℃

100℃

SamplingCorrelating equationFrom R.I.

Correlation of viscosity

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Separation characteristics

oDepressurization in pressure vessel

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Experimental setup for depressurization in vessel

23/38

Refrigerant : CO2Refrigeration oil : PAG

Procedure1. Evacuation after charging oil2. Refrigerant charge with

stirring3. Set to given pressure and

temperature

Thermo- couple

Sight glassStop valve

Regulation valve Pressure gauge

ViscometerRefractive Index sensor

Sampling port

4. Open the stop valve to reduce pressure in the vessel

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Mixture under depressurization

16 sec

0 sec

6 sec

1 sec

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Pressure and temperature change

0 100 200 3000

2

4

6

8

10

12

68

72

76

80

84

88

Time [s]

Pres

sure

[MPa

]

Tem

pera

ture

[℃]

Pressure

Temperature

Valve open

Valve close

Pressure : 10.2 MPa 4.0 MPaInitial temp.: 78 °C Duration: 14.6 s

Solubility is obtained from pressure and temperature

0 0.1 0.2 0.30

5

10

Pres

sure

[MPa

]

Concentration[−]

100℃

20℃

40℃

60℃80℃

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Solubility and concentration

0 100 200 3000

4

8

12

16

20

24

Time [s]

Con

cent

ratio

n [％

]

Solubility

Concentration

Valve open

Valve close

The concentration has larger value than the solubility

The mixture becomes super-saturated condition.

Maximum : 7.8%After 100 seconds : 2.2%

Super-saturation degree

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Viscosity change

0 100 200 3000

4

8

12

16

20

24

Time [s]

Vis

cosi

ty [m

Pa・

s]

Measurement

Saturated condition

Valve close

Valve open

Viscosity is lower than that under the saturation condition

Maximum : 10.0 mPa･sAfter 100 seconds　　

: 2.2 mPa･s

Viscosity difference

The mixture is under the super-saturated condition

Viscosity under the saturation condition is calculated from temperature and the solubility

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Influence of initial temperature

Pressure 10 MPa 4 MPa, 　Duration 15 s

60 70 80 90 1000

4

8

12

16

20

Supe

r sat

urat

ion

degr

ee [ ％

]V

isco

sity

diff

eren

ce [m

Pa・

s]

Initial temperature [℃]

Super saturation degreeViscosity difference

n The super-saturation degree is about 6%.

n The viscosity difference decreases with the initial temperature.

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Influence of press. reduction timePressure 10 MPa 4 MPa, 　Initial temp. 80°C

0 50 100 150 2000

4

8

12

16

20

Supe

r sat

urat

ion

degr

ee [ ％

]V

isco

sity

diff

eren

ce [m

Pa・

s]

Depressurization time [s]


Steep pressure reduction

The super-saturation degree and the viscosity difference become large.

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Influence of mechanical stimulationPressure 10 MPa 4 MPa, 　Initial temp. 100℃Duration 30s

0 200 400 600 8000

4

8

12

16

20

Supe

r sat

urat

ion

degr

ee [ ％

]V

isco

sity

def

fere

nce

[mPa

・s]

Rotational speed [rpm]

Super saturation degreeViscosity difference Increase of rotational speed of

the stirrer

The super-saturation degree and the viscosity difference become small.

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Condition after 100 sec.

The super-saturation condition continues relatively long time after the pressure reduction

60 70 80 90 1000

4

8

12

16

20

Supe

r sat

urat

ion

degr

ee [ ％

]V

isco

sity

diff

eren

ce [m

Pa・

s]

Initial temperature [℃]

Super saturation degreeViscosity differenceMax After 100s At 100 seconds after the

pressure reduction

n The super-saturation degree : 2%

n The viscosity deference : 2 mPa·s

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Separation characteristics

oDepressurization through valve

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Experimental setup for depressurization through valve

Concentration Viscosity

Refractive index

<R.I.-Temperature>　 <Temp.－Concentration>

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Flow after passing valve

Flow pattern with separation

Channel with sensors

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Comparison between two ways of depressurization

Under vigorously-stirred condition

separation is promoted.

Super-saturation degree 0.98%

Viscosity difference 2.28mPa･s

Pressure vesselThrough valve

0 50 100 150 2000

4

8

12

16

20

Supe

r sat

urat

ion

degr

ee [ ％

]V

isco

sity

diff

eren

ce [m

Pa・

s]

Depressurization time [s]


Depressurization through valve

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Ongoing project

oTransient dissolution of refrigerant into oil during compressionn Pressure increase by compression

Refrigerant dissolves? Compression is too fast to dissolve? Influence of oil film thickness?

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Conclusionso Transient change of the concentration can

be measured by the refractive index.o The separation of refrigerant from PAG/CO2

mixture by the depressurization is accompanied by super-saturated condition. It causes viscosity reduction.

o In the case of depressurization through valve, the super-saturation degree and the viscosity reduction have smaller value as compared with those by the depressurization in the vessel.

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Summaryo The existence of oil makes phenomena in the

compressor complicated, and influences the performance and reliability of the compressor and heat exchangers.

o It is important to understand characteristics of the refrigerant/oil mixture for better understandings of the refrigeration cycle and consequently for the improvement of the system.

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Documents

Transient separation of refrigerant from oil/refrigerant ...Internat ionalCo nference onCom presors andRefrig eration, 2017 Refrigeration cycle and refrigeration oil oRequired properties