CO2 Cooling:

Overview over

CMS activities

Jennifer Merz

RWTH Aachen University, 1. Physikalisches Institut B

May 18 2011 CEC General Meeting, Karlsruhe

Outline

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Overview CO2 Cooling

Overview over CMS activities• CERN• Lyon• Aachen

Cooling Organization within CMS

Plans/Needs for the Future

Conclusions

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Effective cooling: high heat load can be cooled with little flow

Evaporating more effective than heating up a liquid

Low viscosity at low temperatures

Lower temperatures are possible

Benefit for silicon sensors

Reduction of material budget:

- Low CO2 density

- Little flow

- Thin pipes, CO2 under high pressure

High heat transfer coefficient

Evaporative CO2 cooling system: dissipate power by evaporating liquid CO2

Idea inspired by LHCb cooling for VELO

Why CO2 ?

Liquid CO2 @ -20°C:

Heating up to -19°C: 2 J/g

Evaporate: 282 J/g

x100

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CO2 Cooling – Some Facts

SolidLiquid

Vapour

Temperature-Pressure-Diagram- lowest possible temperature: ~40°C

- in two-phase flow:

pressure drop temperature drop

- cooling systems have to cope with

high pressures (~100bar)

- 1-2bar pressure drop on cooling

lines uncritical

- vapour quality x (fraction of vapour)

important parameter for measurements

- dryout has to be avoided: liquid not in touch with wall pipes

efficient cooling not guaranteed

liquid vapourx=0 x=1

x: vapour quality

55

Expansion Vessel:Saturated mixture of CO2 liquid and vapour

pre

ssu

re, b

ar

Enthalpy, kJ/kg

Heat Exchanger:- Subcooling of incoming CO2

(only liquid in pump)- Dissipation of detector heat load

Heat Exchanger:- Warm incoming CO2 to nominal

temperature (given by chiller 1)- Partial condensation of returning CO2

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Chiller 1: Chiller temp. vapour pressure system temp.

Schematic View of CO2 System

Liquid

Liquid + Gas

Example: Aachen Setup

CERN - Cryolab

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Large Scale System Small Scale System

-27°C – +25°C -40°C – 0°C

1 – 15 g/s 0.45 – 0.95 g/s

5.5 m tube 300mm, heated: 150 mm

- Systems can vary vapour quality of incoming CO2

- Vacuum boxes for insulation

- Measurements have been performed to investigate differences in both systems

- Last months: improvements of large scale system

- Large scale system can be used by different groups to test their cooling configuration,

e.g. recently Belle-II collaboration tested thermal structure for pixel detector

- Precision measurements performed with small scale system

CERN

Large Scale System

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Location in 158:

- Commissioning of the system at 25°C,

- Possible mass flow rate 1...15 g/s,

- Run only at ambient temperature at the moment,

- Next step => accumulator to vary Tsat.

Joao Noite, Lukasz Zwalinski, Torsten Koettig

CO2 pumpCO2 bottle

heat exchanger

CERN

Small Scale System – Exp. Results (I)

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Results from paper:Investigation of heat transfer and pressure drop of CO2 two-phase flow in a horizontal channel, International Journal of Heat and Mass Transfer

- Measurement of heat transfer coefficient for different conditions

- HTC dependent on saturation temperature and heat flux

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CERN

Small Scale System – Exp. Results (II)

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Results from paper:Investigation of heat transfer and pressure drop of CO2 two-phase flow in a horizontal channel, International Journal of Heat and Mass Transfer

- Measurement of pressure drop for different conditions

- Pressure drop dependent on saturation temperature and mass flux

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CERN

CERN - DT

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- Talk by Jerome Daguin (CERN DT)

- R & D Pixel upgrade: can existing copper pipes for C6F14 be reused for CO2 cooling

- Issues to adress: pipes and joint pressure resistance

geometrical arrangement of existing

pipes

- want to build small scale mock-up for tests at different pressures

- want to build large scale mock-up for tests of geometrical arrangement tensile tests

pressuretests

CERN

CERN - DT

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- Development of two cooling systems:

one small and portable (100W), one bigger “not-so-portable” (1kW)

- Studies to scale up existing methods for future (bigger) experiments

- Investigations to find suitable accumulator (expansion vessel)

- Standard concept requires: 2m3, 100 bar, certified for -30°C or larger number of

accumulators with same total volume

very expensive and complex object(s)

CERN

IPN Lyon

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- Recirculating system built

- works down to -15°C

- further improvements needed to go further down in temperature

• Silicon area: 60 x 18 mm• Heating foils exactly cover this area• Heat input to capillary @ max. power = 25 W/m

from Feb 2010:

Pixel test structure tested with blow system

Information by Nick Lumb

Lyon

CO2-FlascheCO2-Bottle

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HeatExchanger

ExpansionVessel

Detector CO2 Bottle

Aachen: CO2 Test System (I)

19cm

7.6cm

16cm

42cm

Aachen

CO2 Test System (II)

Alu-Box Vakuum zur Isolierung

Bedien-fläche

14

Aluminium Box Vacuum

for Insulation

Panel

- 4 x 6m stainless-steel pipes, 1.6mm inner diameter

- Thermistors along pipes: measurement of temperature distribution

- Simulation of uniform heat load, current through pipes ( Ohmic losses)Cooling Pipes

Position on Pipe

Det

ecto

r Te

mp

erat

ur,

°C

CO2 @ -20 g/minHeat Load: 60W

No VacuumVacuum

ΔT~1K

Restriction Valves

Aachen

Parallel Cooling Pipes (I)

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Parallel Cooling Pipes:

- Needed because of space constraints

- Dedicated measurements have to be done: high heat load low mass flow

- Restrictions necessary in each branch

80W100W120W

4 parallel branchesL = 5,5mdi = 1,5mmϕ = 3 g/s

same heat load on all pipes

Aachen

uniform temperature distribution with applied heat load

Parallel Cooling Pipes (II)

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4 parallel branchesL = 5,5mdi = 1,5mmϕ = 3 g/s

3 pipes: 100W1 pipes: 100-130W

Heat Load on Pipe 2:100W120W130W

Aachen

uniform temperature distribution even if one pipe sees higher heat load

- Measurements needed on what happens if one branch sees significantly higher heat load

- Effect can be reduced by restrictions- Measurements so far with open restrictions

Organization

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- Convener: Hans Postema and Antti Onnela, both CERN

- Recent decision: focus on phase-I activities (Pixel upgrade), “observe” these

developments for phase-II

- meetings during Tracker Week, last: October 2010

- meetings attended also by non-CMS people: ATLAS and LHCb, knowledge is very

much shared between collaborations, Hans called it “open source style”

Implications for module design when implementing CO2 cooling:

- Small pipe diameters: mechanical support has to be guaranteed

- Low temperatures: large temperature gradient between room and operating

temperature: module parts have to stand thermal stress

thermal measurements on mechanical structures need to be done

- Heat transfer coefficient of CO2 dependent on many parameters: cooling contacts

between pipes and heat dissipating devices has to be adapted

different sizes, shapes and materials should be investigated

- Optimal pipe routing needs to be found

Module Design

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future contribution from Aachen

System Aspects

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Implications for system design when implementing CO2 cooling:

- Operation of parallel cooling branches under different conditions

- Measurements with non-uniform heat load, simulating modules with different power

consumption

- Devices for flow and temperature/pressure control might be needed on/near module

Conclusions

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- CO2 is promising coolant for the CMS tracker upgrade

- Participating groups: CERN, Lyon and Aachen

- So far good progress on “basic” (and important) measurements (heat transfer

coefficient, pressure drop)

- Measurement of thermal contacts, pipe routings need to start soon

- Further investigation and measurements on parallel piping