Wim de Boer, Univ. Karlsruhe 1Jan.2009 Design considerations for a CMS CO2 cooling system CMS specials: 50 kW cooling system at -40 0 C (see below) Difficulties:

Wim de Boer, Univ. Karlsruhe 1Jan.2009

Design considerations for a CMS CO2 cooling system

CMS specials:

50 kW cooling system at -40 0C (see below) Difficulties: membrane pumps to -250C, condensors at low pressure

No high pressure allowed (max. 70 bar, preferred <35 bar)

Difficulties: have to separate room temperature storage cylinders (70 bar) from operating system (extra pump or cooled storage cylinders)


25 W/10x10 cm sensor at -25 0C, factor 1.5 reduction/5 0CHybrids for strixel design of 2.2 cm: 2 WWant to reduce by factor 8: from -25 to -40 0C -> x3.4Additionally: reduce V by factor 1.5-> factor 2.3 in power=VxI

Why -40 0C?


Temperature profile for 25W in 10x10 Si sensor

Cooling: 240 K at edge-> 40 K increase towards middle for 25 W (Si = SEMI-conductor!)

High risk of thermal run away for such high gradients !Have to run at lower voltage or still lower temperature.




Choices for evaporative cooling systems

Compressor (gas)Condensor

Evaporator

Pressureregulator

Condensor at high pressure,Do not need external chiller.

Have to avoid that liquidenters compressor, so needheaters in case heat load dropsor TEV (Thermal expansion valve)which regulates flow.

Condensor at low pressure,Need external chiller

Have to avoid evaporation inor before pump, so need subcooledliquid, which need to be heated beforeevaporator to have well defined temp.

Liquid pump

Evaporator

Condensor

Pressureregulator

Chiller

Need pressure reductionbetween condensor and evaporator

3 methods: a) capillary b) expansion valve c) pressure reducer

a) Capillary pressure drop flow dependent, so needadditional pressure control (accumulator in LHC-b)

b) Expansion valve usual method in commercial cooling systems, but different for different fluids.Not available for CO2 (as far as we know)

c) Simple pressure reducer used on bottles work excellent(but not used as such, as far as we know)

Pressure reduction by temperaturecontrolled expansion valve


Pressure reduction by pressure sensitive valve (used on bottles)

Tested to work very well for controlling temperature of CO2 two phase mixture.Can avoid complicated accumulator used in LHC-b


Choices from ATLAS and LHCbFrom B. Verlaat, NIKHEF

Liquid Vapor

2-phase

Pre

ssu

re

Enthalpy

Liquid Vapor

2-phase

Pre

ssu

re

Enthalpy

Vapor compression system•Always vapor needed•Dummy heat load when switched off•Oil free compressor, hard to find

Pumped liquid system•Liquid overflow, no vapor needed•No actuators in detector•Oil free pump, easy to find•Standard commercial chiller

Detector

Cooling plant

Warm transfer over distance

Detector

Cooling plant

Chiller Liquid circulation

Cold transfer over distance

Direct expansion into detector with C3F8 compressorWarm transfer linesBoil-off heater and in detectorTemperature control by back-pressure regulator

CO2 liquid pumpingCold concentric transfer lineNo components in detectorTemperature control by 2-phase accumulator

LHCb method:

Atlas method:

Hea

ter

Compressor

Pump

Compressor

BP. Regulator

LHCb-VTCS Overview (B. Verlaat) A 2-Phase Accumulator Controlled Loop

2-phase

gas

R404a chiller

22

33

6677

11

88

44

2-phase2-phase

liquid liquid liquid

2-phase

Con

den

ser Evaporators

Concentric tubePump

Rest

rict

ion

AccumulatorCooling plant area

Transfer lines(~50m) VELO area

55

liquid

Evaporator :• VTCS temperature ≈ -25ºC• Evaporator load ≈ 0-1600 Watt• Complete passive

Cooling plant:• Sub cooled liquid CO2 pumping• CO2 condensing to a R507a

chiller• CO2 loop pressure control using

a 2-phase accumulator

Accessible and a friendly environment

Inaccessible and a hostile environment

R507aChiller

LHCb-VTCS Overview (B. Verlaat) A 2-Phase Accumulator Controlled Loop

2-phase

gas

R404a chiller

22

33

6677

11

88

44

2-phase2-phase

liquid liquid liquid

2-phase

Con

den

ser Evaporators

Concentric tubePump

Rest

rict

ion

AccumulatorCooling plant area

Transfer lines(~50m) VELO area

55

liquid

Evaporator :• VTCS temperature ≈ -25ºC• Evaporator load ≈ 0-1600 Watt• Complete passive

Cooling plant:• Sub cooled liquid CO2 pumping• CO2 condensing to a R507a

chiller• CO2 loop pressure control using

a 2-phase accumulator

Accessible and a friendly environment

Inaccessible and a hostile environment

R507aChiller


CO2 bottle in household freezer

Advantage:Initial pressure reduced by cooling of CO2 to 12 bar(instead of 70 bar at room temp)

No heat exchanger needed

Whole system <500 EuroStandard Swagelock connectorsFast cooldown since liquidhas already detector temperature

The simplest CO2 cooling system you can imageAND IT WORKS!

Det

ecto

rs

Flowmeterregulates flow, i.e.cooling power

Pressure reducerregulates temperature long nylon

tube to air

nylon tube to see boilingof CO2

Relief valve


Flowmeters

hybrid withheater andT-sensor

Some pictures

Cold liquid sent through ladder. Blue temperature curve shows position of liquid.

Isolation box


-70

-60

-50

-40

-30

-20

-10

0

10

20

30

0 10 20 30 40 50 60

time [min]

tem

pera

ture

[°C

]

sensor1

sensor2

sensor4

Regulating temperature with pressure

11,5bar 8bar 6,5 5,5

very easy to set and hold temperature: just keep pressure constant

CO2 pressurein [bar]


beginning dry-out

0

50

100

150

200

250

300

0 0,5 1 1,5 2 2,5 3

flow in kg/hour (both tubes)

tota

l hea

tin

g p

ow

er [

W]

Test results

easy to cool large powers with little flow of CO2,

flow was tested up to 3,7 kg/hour (max. of flowmeters) with negligible pressure drop

Even much bigger flow seems possible with tolerable pressure drop

Why CMS cannot use any of these systems

CMS cannot use high pressure CO2 closed system, since 1 mm Cu coolingpipes should have max. 70 bar.

CMS has large varying heat loads (detectors cannot be switched onduring cooldown) and 50 kW heaters are a nightmare in cooling circuit

Possible solution: try liquid pump down to -40Cand design low pressure CO2 system.

For sLHC we would like to cool down to -40C to avoid risk of thermalrun away.


scale

A recirculating CO2 system

Com

mer

cial

con

den

sor

Pressure reducer

regulates temperature

to 10 bar=-40C

Detector=

evaporator

9 bar

<25 bar fill line

Vacuumpump for leaktests

Chiller -50 C

Pump for subcooledCO2

Transferline 60m asconcentric heat exchangerto heat up subcooled liquid

and reduce pressure in outlet

70 bar shut down line withhigh pressurepump

10 bar

25 bar


Heat exchangers: www.geawtt.com.

Double WallFor extra protection against leakage a special double wall system is developed. This system consists of two stainless steel plates instead of one. In case of internal damage, due to strong pressure variations for example, the chance of fluid contamination is prevented


GEAWTT Condensors


Safety Chamber™The patented Safety Chamber™, the Non-Plus-Ultra for big brazed heat exchangers is the industrial standard for GEA WTT heat exchanger types 7, 8, 9 and 10. The contact points (brazing points), which are responsible to take off the stress in the port area, are separated. Overloading of these contact points and cracking of the material do not lead to a mix with the other side - a maximum of safety for the userThe Full-Flow-System™special developed for GEA WTT nickel brazed heat exchangers. To avoid freezing problems in the port area when using nickel brazed heat exchangers as an evaporator GEA WTT has developed the Full-Flow-System™. Continuous flow without stagnation around the port avoids "Port Freezing".XCRthe plates consist of high grade corrosion resistant stainless steel, named SMO 254. XCR series has been developed for special applications, such as pool heating, ground water heat pumps, etc. Depend on the particular application we offer XCR models either copper brazed or nickel brazedDelta-Injektion™...Distribution SystemThe Delta-Injektion™ distribution system on Advanced Evaporator AE models is made from AISI 316L stainless steel and provides precise allocation of refrigerant to the channelsDouble WallFor extra protection against leakage a special double wall system is developed. This system consists of two stainless steel plates instead of one. In case of internal damage, due to strong pressure variations for example, the chance of fluid contamination is prevented.


Choice of liquid pump

Pressure firm pump characteristic

22

flow

rate

pressure

membrane displacement pumps

rotary positive displacement pumps

centrifugal pumps


LEWA diaphragm pumps (ECOFLOW)


Diaphragm exchange simple


Output pressure limited


Flow adjustment


CMS: Control and Monitoring System


frequency n

fow

rate

Q

Q = k1*n

stroke length h

flow

rate

Q

Q = k2*(h-h0)

h

0

limiting stroke length h0

Adjusting the flowrate


Vh Vh Vh

time t

Flo

wra

te Q

Pulsating flowrate

Need either: a) 3 phase-shifted pump heads b) pulsation damper c) maybe pressure reducer does the job to prevent temperature variations


1mm diameter, 0.5 mm thick pmax 550 bar

2mm diameter, 0.5 mm thick pmax 367 bar

Flow regimes in small tubes

0.0002 kg/s=66W

rho flow velocity diameter viscosity Surface tension Reynold SuratmanREG/REL

kg/m3 kg/s m/s m mPas=cP N/m (x10^6)

1138 0,0002 0,22 0,001 0,15 0,012 1697,70 0,61 CO2 liq -44

22 0,0002 11,58 0,001 0,011 0,012 23150,49 CO2 gas -44 13,64

1138 0,0002 0,06 0,002 0,15 0,012 848,85 1,21 CO2 liq -44

22 0,0002 2,89 0,002 0,011 0,012 11575,25 CO2 gas -44 13,64

1138 0,0002 0,22 0,001 0,15 0,012 1697,70 0,61 CO2 liq -44

22 0,00002 1,16 0,001 0,011 0,012 2315,05 CO2 gas -44 1,36

1138 0,0002 0,06 0,002 0,15 0,012 848,85 1,21 CO2 liq -44

22 0,00002 0,29 0,002 0,011 0,012 1157,52 CO2 gas -44 1,36

Pressure drop in 1 mm tube still small enough, especially with heat exchange betweenin- and output by the electrical connections pads, so almost no T-gradient on ladder

To be verifiedfor CO2 atlow temp.

annular

bubble

slug


Questions to be resolved

Diaphragm pump to be tested at -400C Started collaboration with LEWA. They will give us a pump and we will test different diaphragms

Heat exchanger at low temperature and low pressure: Started collaboration with GEA. Their design program says it is possible for high flow of primary liquid

Accumulator: Can one use large volume of return tubes as accumulator? (It would act as pulsation damper! No need for triple, phase shifted pumps, one pump with CMS control preferred? Price tag: 20 kEuro/pump, 20 kEuro/CMS) Do we need accumulator above tracker to guarantee always liquid in upper part of tracker?


Summary

• low pressure CO2 system with STANDARD commercial pumps, heat exchangers and pressure reducers seems feasible.

• Require cooling of sensors below -40 0C to get leakage current noise down and limit risk of thermal runaway# (main difficulty: find membrane material for low temp.)

• Strixels of 2.2 cm could then yield S/N similar as for LHC (signal down by ¼, so capacitance down by ¼)

• All connections outside volume possible by CO2 cooling, which allows 6m long cooling pipes

• Reduction of material budget possible by powering via cooling pipes, since pure Al cold pipes have VERY low resistivity. No need for DC/DC converters inside tracker


Backup slides


Summary of cooling liquids at LHC

Notes: Single phase cooling simplest, but large pumps needed Two-phase evaporation in principle much better, becauseheat of evaporation much larger than specific heat, butany pressure changes means a temperature change, so be careful about tube bending, tube sizes etc. CO2 has largest heat of evaporation, is non-toxic, non-flammable, industrial standard, liquid at room temperature, but high pressure (73 bar at 31 0C)

300


Supermarkets start to use CO2


CO2 phase diagram

Documents

Wim de Boer, Univ. Karlsruhe 1Jan.2009 Design considerations for a CMS CO2 cooling system CMS specials: 50 kW cooling system at -40 0 C (see below) Difficulties: