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Aachen Status Report: CO 2 Cooling for the CMS Tracker . Lutz Feld, Waclaw Karpinski, Jennifer Merz , Michael Wlochal. RWTH Aachen University, 1. Physikalisches Institut B. 21 July 2010MEC Upgrade Meeting. Outline. Test System in Aachen Goals and specifications Schematic design

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Aachen Status Report: CO 2 Cooling for the CMS Tracker

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Aachen status report co 2 cooling for the cms tracker

Aachen Status Report:

CO2 Cooling

for the CMS Tracker

Lutz Feld, Waclaw Karpinski, Jennifer Merz, Michael Wlochal

RWTH Aachen University, 1. Physikalisches Institut B

21 July 2010MEC Upgrade Meeting


Aachen status report co 2 cooling for the cms tracker

Jennifer Merz

Outline

  • Test System in Aachen

    • Goals and specifications

    • Schematic design

    • Set-up

    • Performance

  • Results

    • Dryout

    • Pressure and temperature drop

  • Summary and Outlook


Aachen status report co 2 cooling for the cms tracker

Jennifer Merz

R & D in Aachen

  • Ongoing:

    • Gain experience with a closed recirculating CO2 system

    • Determine lowest operating temperature

    • Find out ideal operating conditions ( stable system), depending on heat load and CO2 temperature

  • Midterm plans:

    • Measurements on pipe routing inside the tracker (number of bendings, bending radius, inner diameter, ...)

    • Determine optimal cooling contact between cooling system and heat dissipating devices (different materials, different types of thermal connections, ...)

    • Contribute to final module design for tracker at SLHC


Aachen status report co 2 cooling for the cms tracker

Jennifer Merz

System Specifications

  • Maximum cooling power: 500W

  • CO2 temperature in detector: -45°C to +20°C

  • Precise flow and temperature control

  • Continuous operation

  • Safe operation (maximum pressure:100bar)


Aachen status report co 2 cooling for the cms tracker

Schematic View of the CO2 System

Chiller 1: Chiller temperature vapour pressure  system temperature

Expansion Vessel:

Saturated mixture of CO2 liquid and vapour

ΔQ

pressure, bar

ΔQ

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

Up to 500 W

heat load

5


Aachen status report co 2 cooling for the cms tracker

Jennifer Merz

CO2 Test System (I)

CO2-Bottle

CO2-Flasche

Expansion Vessel

16cm

CO2

Bottle

Detector

42cm

7.6cm

Heat Exchanger

19cm


Aachen status report co 2 cooling for the cms tracker

Jennifer Merz

CO2 Test System (II)

Thermistors

CO2-Bottle

CO2-Flasche

Users

panel

Electrical connections

  • 6m stainless steel pipe, 1.7mm inner diameter

  • 14 Thermistors along the pipe: Measurement of temperature distribution

  • Simulation of uniform heat load, by current through pipe ( ohmic losses)

Box for insulation


Aachen status report co 2 cooling for the cms tracker

Jennifer Merz

Influence of Chiller 2

  • Chiller 2 should only subcool CO2 to ensure liquid in the pump

  • Keep chiller 1 temperature (= detector temperature) constant

  • Vary chiller 2 temperature and observe detector temperature

  • For chiller 2 temperatures from +15 to -5°C: detector temperature at +20°C

  • For lower chiller 2 temperatures: the detector temperature drops drastically

Chiller 1 @ +20°C

Average detector temp., °C

  • In the following: ΔT = 10K between chillers  detector temperature determined by chiller 1

  • More investigation at different temperatures needed

Temp. of chiller 2, °C


Aachen status report co 2 cooling for the cms tracker

Jennifer Merz

Heat Load at -45°C

14

12

10

8

6

4

2

14 thermistors along pipe

13

11

9

7

5

3

1

-45°C CO2 temperature

Detector temperature, °C

Additional heat input from environment influences measurements, especially at low temperatures

6m long pipe

1.7mm inner diameter

~ 50 g/min flow

Increase heat load by 140W

Heat Load

  • Low temperatures can be reached

  • No significant change in detector temperature with applied heat load


Aachen status report co 2 cooling for the cms tracker

Jennifer Merz

Dryout Measurement

  • Dryout: pipe walls not in touch with liquid anymore

  •  No heat dissipation by evaporating CO2

  • Rise in detector temperature

x: vapour quality

x=1

x=0

liquid

gas

Temperature distribution over detector

14

12

10

8

6

4

2

14 thermistors along pipe

Detector temperature, °C

CO2 temperature: +20°C

13

11

9

7

5

3

1

  • Keep heat load constant

  • Decrease flow step by step

  • Determine where detector temperature rises over nominal value

Time, s

Decrease flow


Aachen status report co 2 cooling for the cms tracker

Jennifer Merz

Measurement of Dryout @ +20°C

30 W

40 W

50 W

60 W

70 W

80 W

90 W

100 W

CO2-Temperature: +20°C

  • The higher the heat load, the larger the flow at which dryout is observed


Aachen status report co 2 cooling for the cms tracker

Jennifer Merz

Measurement of Dryout @ 0°C

60 W

80 W

100 W

CO2-Temperature: 0°C

  • At a lower operating temperature: smaller slope, dryout is observed at smaller flows


Aachen status report co 2 cooling for the cms tracker

Jennifer Merz

Comparison Flow vs. Heat Load

  • Determine flow for which just no dryout is observed (from plots on previous slides)

  • For future detector layout safety factor will be applied to avoid dryout by all means inside detector volume

CO2 @ +20°C

CO2 @ 0°C

Flow, g/min

Heat Load, W

  • The higher the heat load, the more flow is needed to dissipate the power

  • At a lower operating temperature less flow is needed to dissipate certain heat load


Aachen status report co 2 cooling for the cms tracker

Jennifer Merz

Pressure Drop along Detector Pipe

Temperature distribution over detector pipe

14

12

10

8

6

4

2

14 thermistors along pipe

13

11

9

7

5

3

1

Detector temperature, °C

Determine pressure drop from temperature distribution over detector pipe

No heat load

-20°C CO2 temperature

No heat load

-20°C CO2 temperature

Δp, bar

Decrease flow

Time, s

  • In a 2-phase system: pressure drop = temperature drop

  • Measurement of pressure gradient important to precisely control detector temperature

  • Determine Δp between in- and outlet

Flow, g/min


Aachen status report co 2 cooling for the cms tracker

Jennifer Merz

Pressure Drop with Heat Load

-20°C CO2 temperature

100 W

50 W

20 W

0 W

  • Heat input from environment visible for small flows

  • Heat load affects pressure drop

  • The higher the heat load, the higher the pressure drop


Aachen status report co 2 cooling for the cms tracker

Jennifer Merz

Pressure Drop: Comparison with Theory

Theory curves:

Thome model

x=0.15

x=0.10

x=0.09

x=0.05

-30°C

-20°C

-10°C

0°C

  • Measurement agrees with theory for high flows

  • Measured Δp higher for small flows

  • Discrepancy can be explained by creation of vapour due to heat input from environment  higher flow resistance


Aachen status report co 2 cooling for the cms tracker

Jennifer Merz

Summary of Results

Results for: L=5.5m, di = 1.7mm, Φ = 50g/min

*With a safety factor of 2, corresponding to a maximum vapour quality of 0.5 inside detector volume


Aachen status report co 2 cooling for the cms tracker

Jennifer Merz

Summary

  • CO2 test system fully commissioned and operational

  • First measurements to low temperatures show:reasonable cooling power at -45°C

  • Pressure drop measurements:at higher temperatures (0°C, -10°C): good agreement, small heat input from environmentat lower temperatures (-20°C, -30°C): worse agreement, significant heat input

  • Dryout Measurements: important to determine point of dryout for a given pipe layout, more measurements will be done and compared with theory

  • For the given layout (L=5.5m, di = 1.7mm, Φ = 50g/min) at least 70W (incl. safety factor) can be dissipated at -45°C with a pressure drop of 1.3bar


Aachen status report co 2 cooling for the cms tracker

Jennifer Merz

Outlook

  • Improvements of test system ongoing:- Vacuum box for detector pipe: minimize heat input from environment- New heat exchanger: less massive, should allow faster measurements- Install dedicated pressure drop sensor: improve accuracy of measurement

  • Perform more measurements on pressure and temperature drop along different pipes:- Vary inner diameter and form/bending - Investigate influence of parallel piping on performance

  • Determine optimal cooling contact between heat dissipating devices and cooling system


Aachen status report co 2 cooling for the cms tracker

Jennifer Merz

Back-Up...


Aachen status report co 2 cooling for the cms tracker

Jennifer Merz

Temperature-Pressure-Diagram


Aachen status report co 2 cooling for the cms tracker

Jennifer Merz

Dryout – Comparison with Theory

  • Want to compare results to so-called Flow Pattern Maps

  • Different flow regimes can be identified

50 g/min

60 g/min

70 g/min

80 g/min

90 g/min

100 g/min

CO2-Temperatur: +20°C

Mass Velocity kg/(m2s)

Vapour Quality


Aachen status report co 2 cooling for the cms tracker

Jennifer Merz

Dryout – Comparison with Theory

60 g/min

80 g/min

100 g/min

CO2-Temperatur: 0°C

Mass Velocity kg/(m2s)

Vapour Quality


Aachen status report co 2 cooling for the cms tracker

Jennifer Merz

Heat Load at -45°C

14

12

10

8

6

4

2

14 thermistors along pipe

13

11

9

7

5

3

1

-45°C CO2 temperature

Detector temperature, °C

Zusätzlicher wärmeeintrag, insbes. Bei tiefen temperaturen

6m long pipe

1.7mm inner diameter

~ 50 g/min flow

Increase heat load by 140W

  • Remark: Enormous temperature differences between pipe and room temperature (here 60K!!) lead to heat input from environment despite insulation

  • Detector pipe will be placed into vacuum box soon

  • Further: heat load means power that was applied from power supply (heat input from environment not taken into account so far)

Heat Load

  • Low temperatures can be reached

  • Constant (?) detector temperature with applied heat load


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