Limits of CO 2 Cooling A clear explanation that an yone can understand (the goal )

Hans Postema & Joao Noite PH-CMX-DS 1

Limits of CO2 CoolingA clear explanation that anyone can understand (the goal)


Introduction

• The Production Readiness Review for the CO2 cooling for the Pixel Phase 1 upgrade is foreseen for the 9th of May.

• This presentation is aimed at the referees who do not necessarily have extensive experience in 2-phase cooling.

• Please let me know if you see anything in this presentation that could be explained clearer or simpler.

3

Limits of CO2 Cooling• Evaporative CO2 cooling is complex.

• Tube is fixed as 1.4mm ID due to space limitation inside the detector.

• Dry-out phenomena limits the maximum power that can successfully be extracted.

• Dry-out can lead to high temperatures at the detector.

Hans Postema & Joao Noite PH-CMX-DS

4

Limits of CO2 Cooling


BUBBLY

INTERMITTENT

ANNULAR

DRYOUT

MIST

• Cooling capacity disappears before all the liquid is evaporated.

• Mist flow: the wall is dry, mist around the center of tube

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

500

1000

1500

2000

2500

Vapor Quality

Mass V

elo

city [

kg/m

2 .s]

G = 1948kg/m2.s | q = 23.94kW/m2 | Psat = 23.25Bar | xout = 0.33 | xdryout = 0.38

B

I

A

M

1.7g/s

3.0g/s

D

BUBBLY

INTERMITTENT

ANNULAR

DRYOUT

MIST

Dryout line

The dryout line represents the points of maximum heat transfer coefficient.

6



•At -20°C the heat transfer

coefficient decreases

extremely rapidly at powers

above the dryout line.

• At 15°C dryout starts at a

much lower power but the

heat transfer coefficient

decreases more gradually

above the dryout line.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

5

10

15

20

25

30

35

Vapor Quality

HT

C [

kW/m

2 .K]

-Z Layer #1 m=2.6g/s

-20°C Old Max Power

15°C Old Standby


0 2 4 6 8 10 12-20

-18

-16

-14

-12

-10

-8

Length [m]

Tem

pera

ture

[°C

]

L2D2PN & L2D1PF OHL | m = 1.98g/s | Qtotal

= 262.35W | dP = 7.17Bar | dT = 8.51°C

0 2 4 6 8 10 1218

20

22

24

26

28

30

Pre

ssur

e [B

ar]

Theory Wall TemperatureTheory CO

2 Temperature

Theory CO2 Pressure

BPix Critical Layers @ -20°C Max Power “Old”

Safety margin OKQexit = 46%

Qdryout = 55%

0 1 2 3 4 5 6 7 8 9 10-20

-18

-16

-14

-12

-10

Length [m]

Tem

pera

ture

[°C

]

L1D2MN & L1D1MF OHL | m = 2.60g/s | Qtotal

= 289.12W | dP = 8.64Bar | dT = 7.51°C

0 1 2 3 4 5 6 7 8 9 1018

20

22

24

26

28

Pre

ssur

e [B

ar]


2 Temperature

Theory CO2 Pressure

Very low safety marginQexit = 38%

Qdryout = 41%

+Z Layer #2 -Z Layer #1


0 1 2 3 4 5 6 7 8 9 1014

16

18

20

22

24

Length [m]

Tem

pera

ture

[°C

]

L1D2MN & L1D1MF OHL | m = 2.60g/s | Qtotal

= 289.12W | dP = 9.39Bar | dT = 6.50°C

0 1 2 3 4 5 6 7 8 9 1050

52

54

56

58

60

Pre

ssur

e [B

ar]


2 Temperature

Theory CO2 Pressure

0 2 4 6 8 10 1214

16

18

20

22

24

Length [m]

Tem

pera

ture

[°C

]

L2D2PN & L2D1PF OHL | m = 1.98g/s | Qtotal

= 262.35W | dP = 7.22Bar | dT = 4.54°C

0 2 4 6 8 10 1250

52

54

56

58

60

Pre

ssur

e [B

ar]


2 Temperature

Theory CO2 Pressure

BPix Critical Layers @ 15°C Max Power “Old”(for comparison, not part of the requirements)

NO safety marginQexit = 75%

Qdryout = 40%Deep inside dry-out region



Qdryout = 26%Deep inside dry-out region


0 1 2 3 4 5 6 7 8 9 1015

16

17

18

19

20

Length [m]

Tem

pera

ture

[°C

]

L1D2MN & L1D1MF OSB | m = 2.60g/s | Qtotal

= 175.15W | dP = 8.05Bar | dT = 2.63°C

0 1 2 3 4 5 6 7 8 9 1050

52

54

56

58

60

Pre

ssur

e [B

ar]


2 Temperature

Theory CO2 Pressure

0 2 4 6 8 10 1215

16

17

18

19

20

Length [m]

Tem

pera

ture

[°C

]

L2D2PN & L2D1PF OSB | m = 1.98g/s | Qtotal

= 194.68W | dP = 6.10Bar | dT = 3.49°C

0 2 4 6 8 10 1250

52

54

56

58

60

Pre

ssur

e [B

ar]


2 Temperature

Theory CO2 Pressure

BPix Critical Layers @ 15°C Standby “Old”


Qdryout = 44%11% inside dry-out region



Qdryout = 33%4% inside dry-out region


BPix Critical Layers @ 15°C Standby “Old”

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

500

1000

1500

2000

2500

Vapor Quality

Mass V

elo

city [

kg/m

2 .s]

-Z Layer #1 OSB | Tset

= 15°C | q = 13.67 kW/m2

B

I

A

D M

1.6g/s

1.8g/s

2g/s

2.2g/s

2.4g/s

2.6g/s

2.8g/s

3g/s

3.2g/s

3.4g/s

3.6g/s

Counter intuitive: More flow does not always solve the problem.


BPix Numbers


Conclusions

• Assumption:– Values for power include sufficient safety margin, a

safety margin in the cooling system is therefore not needed

• At -20°C, max power operation is close to the dry-out line, is this safe enough?

• At +15°C, standby power operation is deep inside the dry-out region, is this safe enough?

• Increasing the flow might not provide a solution


Afterword

• Building the lightest pixel detector in the history of high energy physics is an admirable quest that I am happy to participate in.

• Extreme performance is generally achieved using the absolute minimum safety factors.

• Extremely low safety factors can only be used safely when experience is at a high level and unforeseen issues are unlikely to occur.

• In how far does the above apply to our project?

Limits of CO 2 Cooling A clear explanation that an yone can understand (the goal )

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