1 Engineering Forum: experiences from cooling systems for LHC detectors Bart Verlaat National...

1

Engineering Forum: experiences from cooling systems for LHC detectors

Bart VerlaatNational Institute for Subatomic Physics

(NIKHEF)Amsterdam, The Netherlands

CO2 cooling experiences in the LHCb Velo Thermal Control System

CERN, 30 October 2008

2

Table of Contents

• CO2 cooling and the 2PACL method

• LHCb-VELO Thermal Control System (VTCS).

• Commisioning results of the VTCS.

• Conclusions.

[email protected]@NIKHEF.NL

3

Why Evaporative CO2 Cooling?The lightest way of cooling is:

Evaporate at high pressure!

Why?Vapor expansion is limited under high pressure

Volume stays low

Pipe diameter stays low

Carbon Dioxide

High latent heat

Low mass flow


Mass stays low

dP/P is small

4

75

50

25

00 20 40-20-40-60

Temperature (°C)

Pre

ssu

re (

Ba

r)

Saturation curves in the PT Diagram for CO2, C2F6 & C3F8

(3 used or considered refrigerants at CERN)

CO2

C2F6

C3F8


5

Property comparison

Refrigerant “R” numbers:R744=CO2

R218=C3F8

R116=C2F6

-40 -30 -20 -10 0 10 200

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

DratioR744

DratioR218

DratioR116

Density Ratio (ρvapour/ ρliquid)

Saturation Temperature (ºC )

ρva

po

ur/

ρliq

uid

Be

tte

r

-40 -30 -20 -10 0 10 200

0.002

0.004

0.006

0.008

0.01

0.012

0.014

SurfTR744

SurfTR218

SurfTR116

Surface Tension


Sur

face

Ten

sion

(N

/m)

Be

tte

r

-40 -30 -20 -10 0 10 200.5

1

1.5

2

2.5

3

3.5

4

4.5

5x 10

-4

DVliqR744

DVliqR218

DVliqR116

Liquid Viscosity


Liqu

id V

isco

sity

(P

a*s)

Be

tte

r

-40 -30 -20 -10 0 10 200

50

100

150

200

250

300

350

dHR744

dHR218

dHR116

Latent Heat of Evaporation


Late

nt h

eat

of e

vapo

ratio

n (k

J/kg

)

Be

tte

r

-40 -30 -20 -10 0 10 200

5

10

15

20

25

dT/dP


dT/d

P (

ºC/b

ar) Be

tte

r

6

2 evaporative cooling principles used in LHC detectors

DetectorCooling plant

Warm transfer

Chiller Liquid circulationCold transfer

LHCb-VELO:

Atlas Inner Detector: Vapor compression systemFluid: C3F8

2PACL pumped liquid systemFluid: CO2

Hea

terCompressor

Pump

Compressor

BP. Regulator

Liquid Vapor

2-phase

Pre

ssur

e

Enthalpy

Liquid Vapor

2-phase

Pre

ssu

reEnthalpy

DetectorCooling plant


7

The 2-Phase Accumulator Controlled Loop (2PACL)

2PACL principle ideal for detector cooling:

- Liquid overflow => no mass flow control

- Low vapor quality => good heat transfer

- No local evaporator control, evaporator is passive in detector

- Very stable evaporator temperature control at a distance (P4-5 = P7)

Con

dens

er

PumpHeat exchanger

evaporatorRestrictor2-Phase

Accumulator

Hea

t in

Hea

t in

Hea

t out

Hea

t out

1

2 34

5

6

Liquid Vapor

2-phase

Enthalpy

Pre

ssu

re1

2 3

45

6P7

P7P4-5


Long distance

8

Electron

HadronProton beam

Proton beam

LHCb Detector Overview

Muon

LHCb Cross sectionGoals of LHCb:Studying the decay of B-mesons to find evidence of CP-violation(Why is there more matter around than antimatter?)

20 meter

Vertex Locator


9VELO Thermal Control System CO2 evaporator section

Detectors and electronics

23 parallel evaporator stations

capi

llarie

s

and

retu

rn h

ose

•Temperature detectors: -7ºC •Heat generation: max 1600 W

The LHCb-VELO Detector (VErtex Locator)


10

Particle tracks in the VELO from an LHC injection test (22 august ’08)

The Velo Detector

Heat producing electronics

CO2 evaporator(Stainless steel tube casted in aluminum)

Detection Silicon


11

VELO Cooling Challenges

• VELO electronics must be cooled in vacuum.– Good conductive connection– Absolute leakfree

• Maximum power of the electronics: 1.6 kW

• Silicon sensors must stay below -7°C at all times (on or off).

• Adjustable temperature for commisioning.– -5°C to -30°C in vacuum (Nominal -25°C)– +10°C to-10°C under Neon vented condition

• Maintenance free in (inaccessable) detector area


12

VTCS Evaporator

23 parallel evaporator stationsinner=1mm (L~1.5m)

Inlet capillariesinner=0.5mm (L~2m)

Aluminium casted evaporator block details

vacuum feed through

capillariesand return

hoseliquid inlet (¼”x0.035”)

2-phase outlet (⅜”x0.035”)

PT100 cables

13

4 m

2.6

m

2 R507A Chillers:1 water cooled1 air cooled

2 CO2 2PACL’s:1 for each detector half

55 m

Accessible and a friendly environment

Inaccessible and a hostile environment

2 Evaporators 800 Watt max per detector half

VELO

LHCb-VTCS Overview(VELO Thermal Control System)


PLC

2 Concentric transfer lines

4m th

ick

conc

rete

shi

eldi

ng w

all

14

Concentric transfer line

Ø4mm

Ø6mmØ14mm

Ø16mm

Ø66mm

Sub-cooled liquid feed line

2-phase return line

25mm Armaflex NH Isolation

Protective cover

Transfer line is a 55m long concentric 2-fase liquid-vapor line

Functions:•Transferring liquid to evaporators•Regulate liquid temperature•Pick up environmental heat in return line for unloaded evaporator cooling

•Provide low-pressure drop return flow for distant evaporator pressure control

Terminals as built

VTCS total upward column: 4m+2.6m = 6.6mΔT ≈ 0.7°C → ≈ 0.1°C/m (C3F8 ≈ 2.3°C/m)

2.6m

4m

15

VTCS Accumulator Control

Thermo siphon heater for pressure increase(Evaporation)

Cooling spiral for pressure decrease(Condensation)

Accumulator properties:• Volume: 14.2 liter (Loop 9 Liter)• Heater capacity: 1 kW• Cooler capacity: 1 kW• System charge: 12 kg (@23.2 liter)• System design pressure: 135 bar


++

+_+

_

Heating

Cooling

Set point Temperature

Temperature

Pre

ssur

e

Evaporator Pressure

Pressure drop

PIDPset

Tset

Paccumulator

ΔPfault

16

VTCS Schematics2x CO2 2PACL’s connected to 2 R507A chillers

(Redundancy)

Lots of sensors and valves

TR_AC101

TR_PM101

Tertiary VTCS Right Detector (TR)

TR_PT101TR_PT104

TR_PT102

TR_VL101

TR_VL103

TR_VL104 TLR_VL105

TR_VL106

TR_VL107

TR_VL108

TR_VL109

TR_VL110

TR_VL111

TR_VL113

TR_LT101

TR_BD103

SA_HX105 / TR_HX101 SB_HX105 /

TR_HX102

SA_HX108 / TR_HX103

TL_HT103

TR_HT104

SB_HX108 / TR_HX104

TR_HT101

TR_VL102

TR_PT103TR_HT102

TR_BD101

TR_BD102

TR_BD104

TR_BD106

TR_BD107

TLR_VL101

TLR_PM101

TLR_VL107

TLR_VL109

TLR_VL110

TLR_VL111

Liquid to concentric tube

Vapor mixture from concentric tube



TL_AC101

TL_PM101

Tertiary VTCS Left Detector (TL)

TL_PT101TL_PT104

TL_PT102

TL_VL101

TL_VL103

TL_VL104TL_VL105

TL_VL106

TL_VL107

TL_VL108

TL_VL109

TL_VL110

TL_VL111

TL_VL113

TL_LT101

TL_BD103

SA_HX103 / TL_HX101

SB_HX103 / TL_HX102

SA_HX107 / TL_HX103

TL_HT103

TL_HT104

SB_HX107 / TL_HX104

TL_HT101

TL_VL115

TL_VL102

TL_PT103TL_HT102

TL_BD101

TL_BD102

TL_BD104

TL_BD106

TL_BD107

TLR_PT103

TLR_HT102

(101)

(103) (104)

(106)

(105)

(112)

(115)

(116)

(117)

(118)

(121)

(123)

(122) (114)

(113)

(120)

(107)

(102) (119)

(110)

(108)

(109)

(101)

(103) (104)

(106)(105)

(111)

(112)

(115)

(116)

(117) (118)

(121)

(123)

(122)(114)

(113)

(120)

(107)

(110)

(108)

(109)

(124) (124)

(112)

(115)

(122)

(114)

(113)

TL_VL112 TR_VL112

TL_HT105

(125)

TR_HT105(125)

TR_FL101

TL_FL102 TR_FL102

TL_FL101

TR_HX105

(102) (119)

Tambient

TL_VL114

TLR_VL115

TR_VL115

TR_VL114

TLR_VL114

TL_S.01

S.02

S.04

S.05

S.03

S.15

S.16

S.17

S.19

S.18.01

S.18.02

S.09.29

S.20

S.21

S.22

S.23

TLR_S.20

TLR_S.01

TR_S.01

S.02

S.05

S.04

S.03

S.23

S.15

S.16

S.17

S.18.01 S.18.02

S.19

S.22

S.20

S.21

S.12.29S.09.29

S.12.29

TR_AC101

TR_PM101

Tertiary VTCS Right Detector (TR)

TR_PT101TR_PT104

TR_PT102

TR_VL101

TR_VL103

TR_VL104 TLR_VL105

TR_VL106

TR_VL107

TR_VL108

TR_VL109

TR_VL110

TR_VL111

TR_VL113

TR_LT101

TR_BD103

SA_HX105 / TR_HX101 SB_HX105 /

TR_HX102

SA_HX108 / TR_HX103

TL_HT103

TR_HT104

SB_HX108 / TR_HX104

TR_HT101

TR_VL102

TR_PT103TR_HT102

TR_BD101

TR_BD102

TR_BD104

TR_BD106

TR_BD107

TLR_VL101

TLR_PM101

TLR_VL107

TLR_VL109

TLR_VL110

TLR_VL111





TL_AC101

TL_PM101

Tertiary VTCS Left Detector (TL)

TL_PT101TL_PT104

TL_PT102

TL_VL101

TL_VL103

TL_VL104TL_VL105

TL_VL106

TL_VL107

TL_VL108

TL_VL109

TL_VL110

TL_VL111

TL_VL113

TL_LT101

TL_BD103

SA_HX103 / TL_HX101

SB_HX103 / TL_HX102

SA_HX107 / TL_HX103

TL_HT103

TL_HT104

SB_HX107 / TL_HX104

TL_HT101

TL_VL115

TL_VL102

TL_PT103TL_HT102

TL_BD101

TL_BD102

TL_BD104

TL_BD106

TL_BD107

TLR_PT103

TLR_HT102

(101)

(103) (104)

(106)

(105)

(112)

(115)

(116)

(117)

(118)

(121)

(123)

(122) (114)

(113)

(120)

(107)

(102) (119)

(110)

(108)

(109)

(101)

(103) (104)

(106)(105)

(111)

(112)

(115)

(116)

(117) (118)

(121)

(123)

(122)(114)

(113)

(120)

(107)

(110)

(108)

(109)

(124) (124)

(112)

(115)

(122)

(114)

(113)

TL_VL112 TR_VL112

TL_HT105

(125)

TR_HT105(125)

TR_FL101

TL_FL102 TR_FL102

TL_FL101

TR_HX105

(102) (119)

Tambient

TL_VL114

TLR_VL115

TR_VL115

TR_VL114

TLR_VL114

TL_S.01

S.02

S.04

S.05

S.03

S.15

S.16

S.17

S.19

S.18.01

S.18.02

S.09.29

S.20

S.21

S.22

S.23

TLR_S.20

TLR_S.01

TR_S.01

S.02

S.05

S.04

S.03

S.23

S.15

S.16

S.17

S.18.01 S.18.02

S.19

S.22

S.20

S.21

S.12.29S.09.29

S.12.29


17

VTCS construction• CO2 2PACL’s

– Stainless steel piping with:• (Orbital) Welding• Vacuum Brazing • Swagelok Cajon VCR fittings and line components

– Lewa liquid CO2 pump (100 bar)– In house designed accumulator (130 bar)– Reinforced SWEP condenser (130 bar)

• Now commercial available at SWEP.– 55 meter concentric transfer line– Aluminium casted cooling blocks– Test pressure 170 bar

• Chillers designed in house with standard commercial chiller components.– Copper piping with hard solder joints – Danfoss line components– Bitzer compressors– SWEP heat exchangers

• Siemens S7-400 series Programmable Logic Controller (PLC)


18

LHCb-VTCS Cooling Plant

Pumps

Accumulators

Valves


CondensersCO2 2PACL systems

Freon chiller systems

19

VTCS Units Installed @ CERN

July- August 2007

CO2 Unit

Freon Unit

20

13 13.5 14 14.5 15 15.5

-100

-75

-50

-25

0

25

50

75

Clock time (hour)

Tem

pera

ture

(°C

) P

ress

ure

(B

ar)

Leve

l (%

)C

oolin

g/H

eatin

g P

ow

er (%

kW)

VTCS 2PACL Operation From start-up to cold operation (1)

2 Pump head pressure (Bar)

4 - Accumulator pressure (Bar)

1 Pumped liquid temperature (°C)

5 – Evaporator temperature (°C)

4-Accumulator liquid level (vol %)

4- Accumulator Control: + = Heating - = Cooling _

+

4

1

2

7

7

7

7

1

2

7

4

+7

-7


21

AccumulatorCooling

= Pressure decrease

13 13.5 14 14.5 15 15.5-50

-25

0

25

50

75

Clock time (hour)

Tem

pera

ture

(°C

)

Pre

ssure

(B

ar)

VTCS 2PACL Operation From start-up to cold operation (2)

AB

C

D2 - Pump head pressure (Bar)

4 - Accumulator pressure (Bar)

1 – Pumped liquid temperature (°C)

5 – Evaporator temperature (°C)

50 100 150 200 250 300 350 4005x100

101

102

2x102

h [kJ/kg]

P [bar]

-40°C

-20°C

0°C

20°C

40°C

0.2 0.4 0.6 0.8

VTCS start-up and operating cycles

1

3,5

810,13

1

3 5

8

9,10,13

1

35

8

9,10131

3 5

8

9 10 13

CB

D E

A

50 100 150 200 250 300 350 4005x100

101

102

2x102

h [kJ/kg]

P [bar]

-40°C

-20°C

0°C

20°C

40°C

0.2 0.4 0.6 0.8

VTCS start-up and operating cycles

1

3,5

810,13

1

3 5

8

9,10,13

1

35

8

9,10131

3 5

8

9 10 13

CB

D E

A

20 °C

0 °C

-20 °C

-40 °C

1

2

4

A

BC

D Path of 54

41

2

5

2

5

4

1

5

5

Enthalpy

Pre

ssu

re

Set-point range


22

March ’08: Commisioning of the VTCSDetector under vacuum and

unpowered

10 15 20 25 30 35 40 45 50 55 60 65 70-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

30

Time from 29 March clock time (Hours)

Mea

sure

d Te

mpe

ratu

re (º

C)

C-Side CO2 Cooling System Performance During Detector Vacuum Tests(29 march 08 - 31 March 08)

Accumultor saturation temperature (TRPT102tsat) = SetpointTR Evaporator Temperature (TRTT048pvss)

Condenser Inlet (TRTT101pvss)

Condenser Out- / Pump Inlet Temperature (TRTT112pvss)

Pump Outlet Temperature (TRTT120pvss)

C-Side RF-Foil temperature (TRTT043pvss)C-Side Module Base Temperature (TRTT038pvss)

Sp=-10ºC

Sp=-20ºC

Sp=-30ºC

Sp=0ºC

Sp=-25ºC

Sp=-30ºC

Sp=0ºC

2 Days + 6 hours cooling under vacuum at several set point temperatures

Start-up

10 15 20 25 30 35 40 45 50 55 60 65 70-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

30


Mea

sure

d Te

mpe

ratu

re (º

C)


Accumultor saturation temperature (TRPT102tsat) = SetpointTR Evaporator Temperature (TRTT048pvss)




C-Side RF-Foil temperature (TRTT043pvss)C-Side Module Base Temperature (TRTT038pvss)

Sp=-10ºC

Sp=-20ºC

Sp=-30ºC

Sp=0ºC

Sp=-25ºC

Sp=-30ºC

Sp=0ºC


Start-up

Sp=-10ºC

Sp=-20ºC

Sp=-30ºC

Sp=0ºC

Sp=-25ºC

Sp=-30ºC

Sp=0ºC


Start-up

10 15 20 25 30 35 40 45 50 55 60 65 70-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

30


Measure

d Temp

erature

(ºC)


Accumultor saturation temperature (TRPT102tsat) = Setpoint

TR Evaporator Temperature (TRTT048pvss)




C-Side RF-Foil temperature (TRTT043pvss)

C-Side Module Base Temperature (TRTT038pvss)

Sp=-10ºC

Sp=-20ºC

Sp=-30ºC

Sp=0ºC

Sp=-25ºC

Sp=-30ºC

Sp=0ºC


Start-up

10 15 20 25 30 35 40 45 50 55 60 65 70-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

30


Measure

d Temp

erature

(ºC)









Sp=-10ºC

Sp=-20ºC

Sp=-30ºC

Sp=0ºC

Sp=-25ºC

Sp=-30ºC

Sp=0ºC


Start-up

Sp=-10ºC

Sp=-20ºC

Sp=-30ºC

Sp=0ºC

Sp=-25ºC

Sp=-30ºC

Sp=0ºC


Start-up Condenser outlet / Pump sub cooling Pump outlet RF-foil

10 15 20 25 30 35 40 45 50 55 60 65 70-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

30


Measure

d Temp

erature

(ºC)









Sp=-10ºC

Sp=-20ºC

Sp=-30ºC

Sp=0ºC

Sp=-25ºC

Sp=-30ºC

Sp=0ºC


Start-up

10 15 20 25 30 35 40 45 50 55 60 65 70-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

30


Measure

d Temp

erature

(ºC)









Sp=-10ºC

Sp=-20ºC

Sp=-30ºC

Sp=0ºC

Sp=-25ºC

Sp=-30ºC

Sp=0ºC


Start-up

Sp=-10ºC

Sp=-20ºC

Sp=-30ºC

Sp=0ºC

Sp=-25ºC

Sp=-30ºC

Sp=0ºC


Start-up Accumulator saturation (Set-point) Evaporator temperature Condenser inlet


2316.5 17 17.5 18 18.5

-40

-20

0

20

40

60

80

Clock time (Hour)

Tem

pera

ture

('C)

, Liq

uid

leve

l (vo

l %),

Powe

r (%

kW o

r Wat

t)

Total C detector load (% kW)Evaporator Temperature ('C)Accumulator Liquid Level (vol %)Acumulator heating/cooling (% kW)Module VL11-C power (Watt)Module VL11-C cookie temperature ('C)Module VL11-C NTC00 temperature ('C)Module VL11-C NTC01 temperature ('C)

SP=-25°C

SP=-5°C

(3 sept 08)


Accu level

Module Heat load

Silicon temperature

Evaporator temperature

Accu Heating/Cooling

24 June ’08: After a succesful commisioning of the detector at -25°C, the setpoint is increased to -5°C.

And has been running since then smoothly!

80

60

40

20

0

-20

-400 0:30 1:00 1:30 2:00

Time (Hour)Te

mp

era

ture

(°C

), P

ower

(W

att)

, Le

vel (

vol %

)

Detector half heat load (x10)

-7°C

24

CO

2 li

quid

dT=

4.5

°CC

oolin

g bl

ock

dT=

0.0

4°C

1 hour

Evaporator Pressure 31.15 bar = -4.18°C

Cooling block temperature = -2.8°C

CO2 liquid temp= -42°C

Evaporator liquid inlet temp = -4.40°C

Evaporator vapor outlet temp = -4.44°C

Accumulator Pressure 30.54 bar = -4.90°C

Det

ect

or o

ffse

t fr

om a

ccu

cont

rol:

0.7

°CCO2 heat transfer dT=1.4°C

VTCS performance overview for a setpoint of -5°C (Detector switched on, fully powered)[email protected]@NIKHEF.NL

dP=

0.6

bar

= 6

.2 m

sta

tic h

eigt

h

Fluctuations from the untuned chiller

25

Summary

• The VTCS has successfully passed the 1st commissioning phase and was ready to be used in the experiment in July 2008

• Operational temperature range is between -5°C and -30°C set point for the water cooled chiller

• It has run for 3½months continuously with only minor problems

• It behaves very stable with the chiller still to be tuned (evaporator stability less than 0.05°C)

• The silicon temperature is below the required -7°C @ -25°C set point temperature. (This is consistent with the prediction)


26

What did we learn:

• 2PACL dynamics work better with the accumulator connection at inlet of condenser (instead of outlet as it is now)– No saturated liquid feed from accu to pump.– Free pre-cooling at cold start-up due to thermal

capacity of condensers.

• Concentric transfer tube heat exchanger works beyond expectations as the so-called “Duck-foot-cooling1” pinciple is boosting the operational temperature range.

• The current system is not always initiating boiling at higher operational temperatures (>-10°C), resulting in temporary reduced heat-exchange.

1 The way a duck can have cold feet without loosing body heat, by exchanging heat between the in- and outlet bloodstream.

27

The “Cool” future

• The VTCS is not yet finnished, some things have to be done:– Implementing automatic back-up procedure.– Changing the accumulator connection.– Tunning the chiller.– Analyse data for publication.

• Construction of a mini desktop 2PACL CO2 circulator for general purpose laboratory use.

• Participation in future CO2 cooling systems – Atlas IBL, Goat, Next-64, RELAXed

• 2PACL upgrade:– Replace HFC chiller by CO2 chiller

• No integration of chiller and 2PACL!– 2PACL is much more stable (<0.05’C)– 2PACL has liquid overfeed and needs no boil-off heaters– CO2 compressor needs oil as lubricant

• CO2 chiller has extended lower temperature range (CO2 ~-50°C , HFC~-40°C )

28

Back-up Slides

29

Property Comparison (1)R744 (CO2)

R116 (C2F6)

R218 (C3F8)

Source Refprop NIST

R744 (CO2)

R218 (C3F8)

R116 (C2F6)

Critical Point

31ºC @ 73.8 bar

71.9ºC @26.4 bar

19.9ºC @30.5 bar

Triple point -56.6ºC -147.7ºC -100ºC

Boiling temperature @ 1 bar

-78.4ºC Subli-mation !

-36.8ºC -78.1ºC

30

2 3 4 5 6 7 8 9 10-5

-4.5

-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

Hydraulic Diameter (mm)

Pres

sure

Dro

p (b

ar)

2 3 4 5 6 7 8 9 10-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

0


Tem

pera

ture

Dro

p (º

C)

CO2 =2.7mm

2 3 4 5 6 7 8 9 10-5

-4.5

-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0


Pres

sure

Dro

p (b

ar)

C2 F

6 =4.3mm

C3 F

8 =7.7mm

ΔT=-2°C

2x 20 wafers à 17 Watt

1 Atlas stave : 2 meter length

Cooling

Q = 680 WattTube = 4 meter

Example of and Atlas upgrade stave (1)

CO 2

C 3F 8

C2F 6

CO 2

C 3F 8

C2F 6

Calculations based on -35°C and 75% vapor quality at exit

Mass flow @ -35ºC Φ CO2= 2.9 g/s

Φ C3F8= 8.7 g/s

Φ C2F6= 9.6 g/s

Pressure Drop

Temperature Drop

Generates

31

•7.7

0 0.5 1 1.5 2 2.5 3 3.5 40

5000

10000

15000

Tube Length (m)

Hea

t Tra

nsfe

r C

oeffic

ient

(W

/m2K

)

0 0.5 1 1.5 2 2.5 3 3.5 4-36

-34

-32

-30

-28

-26

-24

-22

Tube length (m)

Tem

pera

ture

(°C

)

CO2

C3F8

C2F6

D2.7mm x L25mm = 80167 W/m2

D2.7mm x L75mm = 26722 W/m2

D4.3mm x L25mm = 50337 W/m2

D4.3mm x L75mm = 16779 W/m2

D7.7mm x L25mm = 28110 W/m2

D7.7mm x L75mm = 9370 W/m2

CO2

C3F8

C2F6

25mm HX length

75mm HX length

Example of and Atlas upgrade stave (2)

Mass flux @ -35ºC Φ’ CO2= 506 kg/m2s

Φ’ C3F8= 661 kg/m2s

Φ’ C2F6= 186 kg/m2s

Critical Heat Flux (Bowring/Ahmad): CHF(CO2) = 313 kW/m2, x=1.1

25mm

75mm

Heat exchange length

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