Cold Operation of a Recirculating CO 2 System at Aachen

Cold Operation of aRecirculating CO2 System

at Aachen

Lutz Feld, Waclaw Karpinski, Jennifer Merz, Michael Wlochal

RWTH Aachen University, 1. Physikalisches Institut B

10.02.2010 CMS Upgrade Cooling and Mechanics Meeting

Outline

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Description of CO2 test system in Aachen

Specifications of new chiller

Dryout measurements at room temperature

First measurement at low temperature

Conclusion and outlook

CO2 Test System Aachen - Specs

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Goals:

- Gain experience with a recirculating (closed) CO2 cooling system

- Find the lowest possible operating temperature

- Determine ideal operating conditions ( stable operation)

depending on heat load and coolant temperature

Specifications:

Maximum heat load: 500W

Coolant temperature at detector: -45°C - +20°C

Precise temperature control and flow measurement

Continous operation

Safe operation (maximum pressure 100bar)

Schematic of Test System

4

Expansion Vessel: Filled with saturated mixture of CO2-liquid and -vapour

CO2 Pump

Flow Meter

Vacuum Pump

CO2 Bottle

Chiller 2: Heat removal

Heat Exchanger 2

Heat Exchanger 1

Detector:500 W heat load

Heat Exchanger 2:- Removes heat from the system- Cools incoming CO2 down to about

-50°C

4

6

3

1

4

5

2

-45°C

-50°C

Heat Exchanger 1:- Heats liquid CO2 to appropriate

temperature- Partial condensation of returning CO2

1 4

ΔQ

ΔQ

56

32

Chiller 1: Chiller temperature vapour pressure system temperature

Burst Disk

Burst Disk

Burst Disk

CO2-FlascheCO2-Bottle

Vacuum-Pump

CO2 Cooling Test System

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Heat Exchanger 1

Expansion Vessel

Detector

CO2 Bottle

CO2-Flasche

Vacuum-Pump

Cooling of Expansion Vessel

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Copper piping replaced by copper shell

Improvement of thermal contact

Reduction of flow resistance

CO2-FlascheCO2-Bottle

Vacuum-Pump

CO2 Cooling Test System

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- 6m long stainless steel pipe with 1.5mm

outer diameter, in insulated box

- 14 thermistors to measure temperature

distribution over pipe

- Electrical connections to simulate heat load

CO2-FlascheCO2-Bottle

Chillers: unistat 815

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- Originally ordered chiller had to be replaced; cooling power was not sufficient

- New chiller was damaged during transport

- “Old” chiller had to be repaired by company

- Chillers now achieve required low temperatures

Delay in commissioning,

system is fully operational since

end of January

Chiller specifications: (both chillers identical)

unistat 815

- Company: Peter Huber Kältemaschinenbau,

Offenburg, Germany

- Temperature range: -85°C to 250°C

- Cooling power: 1.5kW @ -20°C1.4kW @

-40°C1.2kW @

-60°C- Pump: max. 40 l/min, max. 0.9bar

Heat load: 70W - Vary revolutions per minute of CO2 pump

variation of CO2 flow- Keep heat load constant- Determine when temperature rises over

certain level

Dryout Measurement at Room Temp.

9

Dryout: Pipe walls not in touch with liquid anymore no power dissipation by evaporating CO2

temperature rises

Liquid Gas

Heat load: 70W

2468101214

1357 91113

Vacuum-Pump

Dryout Measurement at Room Temp.

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30W40W50W60W70W

The lower the flow, the earlier a rise

in temperature is observed The higher the heat load,

the more flow is needed

Vacuum-Pump

First Measurement at Low Temperature

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- Expansion vessel at -27°C- Chiller 2 at -44°C

No stable operation Fast variations in CO2 flow Beginning of dryout visible System behaviour not yet

understood

Operation at low temperatures possible (down to -45°C) if bypass is open; nearly no flow through detector pipe

Chillers work fine (see also next slide) Flow resistance too high? More investigation and measurements needed

Vacuum-Pump

Chiller Performance

Both chillers show excellent performanceLow temperatures Stable operation

Nominal Temp.Internal Temp.Temp. at Exp. Vessel

Nominal Temp.Internal Temp.

Chiller 1

Chiller 2

Conclusions and Outlook

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- CO2 test system in Aachen is finally fully operational

- First measurements show that system works in principal

- New chillers manage to reach low temperatures

- No stable operation at low temperatures possible yet

Investigate how to bring low temperature to detector

Install filter to avoid water and other disturbing particles in system

Determine pressure drop and temperature distribution for different

pipe routings and diameter

Back Up....

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CO2 Enthalpy-Pressure Diagram

15Enthalpy, kJ/kg

Pre

ssu

re,

bar

liquid

gas

liquid + gas

Design of cooling plant in p-H-digramEnthalpy:H = U + pV “internal energy + expansion work”ΔH is exchanged heat at constant pressure

CO2 Enthalpy-Pressure Diagram

16Enthalpy, kJ/kg

Pre

ssu

re,

bar

liquid

gas

liquid + gas

Design of cooling plant in p-H-digramEnthalpy:H = U + pV “internal energy + expansion work”ΔH is exchanged heat at constant pressure

Re-Circulating System(closed system)

41 6 5

32

ΔQ

ΔQ

Detector load (4-5)

CO2 Cooling System

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Power consumption with DC-DC converters: 84W per petal- Including 18.8W power loss of converters, due to converter efficiency of 80%- One aluminium cooling block per converter implemented to dissipate converter

power loss

CO2 : low density small contribution to material budget Operation at high pressures small pipe diameter Low temperatures (-45°C) good for sensor performance

Current tracker (C6F14) vs. tracker with DC-DC converters cooled with CO2

TEC Cooling

TEC Total Material Budget

Current tracker with C6F14

Layout with DC-DC converters with CO2

A total reduction of 14.3% seems possible with CO2 cooling and DC-DC conversion.

-38.5% -14.3%

Advantages: