NA62 CO 2 Cooling - Microchannels Analysis-

João Noite PH-CMX-DS

NA62 CO2 Cooling- Microchannels Analysis-

João Noite PH-CMX-DS 2

Boundary Conditions

• 2-Phase correlation is valid for heat fluxes within the range of 1.8 to

46kW/m2 and tube diameters of 0.6 to 10mm

• Sensor heat flux = 4W/cm2 = 40kW/m2

• Sensor dimensions = 6 x 60mm

• Maximum channel height = 250μm

• Evaporator thickness = 380μm

• Calculated square channel sizes: 250, 200, 150 and 100μm

• Equivalent diameter sizes: 0.28, 0.22, 0.17 and 0.11mm

• Channel length = 40mm (to save space for manifold).


250 μm Channel

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-20

-18

-16

-14

-12

Length [m]

Tem

pera

ture

[°C

]

NA62 GigaTracker | m = 0.01g/s | Qtotal = 1.42W | dP = 15.01Bar | dT = -5.22°C

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.0418

23.5

29

34.5

40

Pre

ssur

e [B

ar]

Theory Wall TemperatureTheory CO2 Temperature

Theory CO2 Pressure

100 150 200 250 300 350

10

20

30

40

50

60

70

80

-40°C -30°C -20°C -10°C 0°C 10°C 20°C 30°C

Enthalpy [kJ/kg]

Pre

ssur

e [B

ar]

m = 0.01g/s | Qtotal = 1.42W | Pin = 34.70Bar | Tin = -20.00°C | dP = 15.01Bar | xout = 0.49

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

100

200

300

400

500

600

Vapor Quality

Mas

s V

eloc

ity [k

g/m

2 .s]

G = 160kg/m2.s | q = 40.00kW/m2 | Psat = 19.69Bar | xout = 0.50 | xdryout = 0.80

Observations:

• Stratified wavy flow regime has low HTC.

• Low HTC increases the temperature gradually along channel length.

• ΔT is more than 5°C due to low HTC.

• Mass flow of 0.008g/s has to be increased to be able to reach annular flow.


250 μm Channel

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-21

-19

-17

-15

-13

Length [m]

Tem

pera

ture

[°C

]

NA62 GigaTracker | m = 0.02g/s | Qtotal = 1.42W | dP = 55.06Bar | dT = 3.19°C

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.0419

34

49

64

79

Pre

ssur

e [B

ar]


Theory CO2 Pressure

100 150 200 250 300 350

10

20

30

40

50

60

70

80

-40°C -30°C -20°C -10°C 0°C 10°C 20°C 30°C

Enthalpy [kJ/kg]

Pre

ssur

e [B

ar]


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

100

200

300

400

500

600

700

800

Vapor Quality

Mas

s V

eloc

ity [k

g/m

2 .s]


Observations:

• Flow increased to 0.016g/s.

• Although the Annular flow regime is now present, it’s very close to Stratified-Wavy flow.

• Maximum ΔT across the channel is 3.21°C due to HTC.


200 μm Channel

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-21

-19

-17

-15

-13

Length [m]

Tem

pera

ture

[°C

]


0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.0419

34

49

64

79

Pre

ssur

e [B

ar]


Theory CO2 Pressure

100 150 200 250 300 350

10

20

30

40

50

60

70

80

-40°C -30°C -20°C -10°C 0°C 10°C 20°C 30°C

Enthalpy [kJ/kg]

Pre

ssur

e [B

ar]


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

100

200

300

400

500

600

700

800

900

1000

Vapor Quality

Mas

s V

eloc

ity [k

g/m

2 .s]


Observations:

• Decreasing the size of the channel from 250 to 200μm doesn’t seem to affect the ΔP.

• The flow regime is now clearly Annular.

• Maximum ΔT across the channel is 3.21°C due to CO2 HTC.

• ΔT along the length of the channel is negligible, due to very low ΔP.

• This is a good example for the channel size.


150 μm Channel

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-20

-19

-18

-17

-16

-15

-14

Length [m]

Tem

pera

ture

[°C

]


0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.0415

20

25

30

35

40

45

Pre

ssur

e [B

ar]


Theory CO2 Pressure

100 150 200 250 300 350

10

20

30

40

50

60

70

80

-40°C -30°C -20°C -10°C 0°C 10°C 20°C 30°C

Enthalpy [kJ/kg]

Pre

ssur

e [B

ar]


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

100

200

300

400

500

600

700

800

900

1000

Vapor Quality

Mas

s V

eloc

ity [k

g/m

2 .s]


Observations:

• Decreasing the size of the channel from 200 to 150μm shows a ΔT along the length of about 1°C due to increased ΔP.

• The flow regime is still clearly Annular.

• Maximum ΔT across the channel is slightly increased to 3.27°C due to CO2 HTC.


100 μm Channel

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04-20

-18

-16

-14

Length [m]

Tem

pera

ture

[°C

]


0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.0410

20

30

40

Pre

ssur

e [B

ar]


Theory CO2 Pressure

100 150 200 250 300 350

10

20

30

40

50

60

70

80

-40°C -30°C -20°C -10°C 0°C 10°C 20°C 30°C

Enthalpy [kJ/kg]

Pre

ssur

e [B

ar]


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

200

400

600

800

1000

1200

Vapor Quality

Mas

s V

eloc

ity [k

g/m

2 .s]


Observations:

• As said, decreasing the size of the channel increases ΔP.

• When ΔP increases the evaporator temperature gradient increases and it can also can be flooded with sub cooled liquid.

• The presence of liquid will increase the temperature in the first section of the channel until it starts boiling.


Conclusions

• This is a preliminary study.

• Inlet restriction for flow balance has not been done. Inlet ΔP should not be considered in

this exercise.

• Annular flow regime has optimum HTC.

• Required mass flow should be enough for the presence of this regime.

• Increasing mass flow to assure the presence of this regime will reduce vapor quality and in

some cases increase ΔP. This has to be carefully tuned to avoid the presence of sub-cooled

liquid in the evaporator. Sub-cooled liquid has a low HTC when compared with 2-phase.

• Increasing ΔP will therefore increase ΔT.

• Depending on the size, the heat flow on each channel will be between 0.56 and 1.41W.

• Channel size of 200x200μm shows good performance.

• 200x200μm channel results in 14 parallel channels per evaporator.

NA62 CO 2 Cooling - Microchannels Analysis-

Documents

Transcript of NA62 CO 2 Cooling - Microchannels Analysis-