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Aachen Status Report: CO 2 Cooling for the CMS Tracker

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 2010 MEC 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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  1. 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 2010 MEC Upgrade Meeting

  2. Jennifer Merz Outline • Test System in Aachen • Goals and specifications • Schematic design • Set-up • Performance • Results • Dryout • Pressure and temperature drop • Summary and Outlook

  3. 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

  4. 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)

  5. 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

  6. Jennifer Merz CO2 Test System (I) CO2-Bottle CO2-Flasche Expansion Vessel 16cm CO2 Bottle Detector 42cm 7.6cm Heat Exchanger 19cm

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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

  20. Jennifer Merz Back-Up...

  21. Jennifer Merz Temperature-Pressure-Diagram

  22. 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

  23. 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

  24. 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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