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Engineering Forum: experiences from cooling systems for LHC detectors

CO. 2. Engineering Forum: experiences from cooling systems for LHC detectors. CO 2 cooling experiences in the LHCb Velo Thermal Control System. Bart Verlaat National Institute for Subatomic Physics (NIKHEF) Amsterdam, The Netherlands. CERN, 30 October 2008. Table of Contents.

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Engineering Forum: experiences from cooling systems for LHC detectors

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  1. CO 2 Engineering Forum: experiences from cooling systems for LHC detectors CO2 cooling experiences in the LHCb Velo Thermal Control System Bart Verlaat National Institute for Subatomic Physics (NIKHEF) Amsterdam, The Netherlands CERN, 30 October 2008

  2. Table of Contents • CO2 cooling and the 2PACL method • LHCb-VELO Thermal Control System (VTCS). • Commisioning results of the VTCS. • Conclusions.

  3. Why Evaporative CO2 Cooling? The lightest way of cooling is: Evaporate at high pressure! Why? Vapor expansion is limited under high pressure Volume stays low dP/P is small Low mass flow Pipe diameter stays low High latent heat Carbon Dioxide Mass stays low

  4. Saturation curves in the PT Diagram for CO2, C2F6 & C3F8 (3 used or considered refrigerants at CERN) 75 CO2 50 C2F6 Pressure (Bar) 25 C3F8 0 40 -40 20 -20 0 -60 Temperature (°C)

  5. Density Ratio (ρvapour/ ρliquid) Better Liquid Viscosity ρvapour/ ρliquid Better Liquid Viscosity (Pa*s) Latent Heat of Evaporation Saturation Temperature (ºC ) Surface Tension Saturation Temperature (ºC ) Latent heat of evaporation (kJ/kg) Better dT/dP Better Surface Tension (N/m) Better dT/dP (ºC/bar) Saturation Temperature (ºC ) Saturation Temperature (ºC ) Saturation Temperature (ºC ) Property comparison Refrigerant “R” numbers: R744=CO2 R218=C3F8 R116=C2F6

  6. 2 evaporative cooling principles used in LHC detectors Atlas Inner Detector: Vapor compression system Fluid: C3F8 Liquid Vapor Compressor Heater Pressure Warm transfer BP. Regulator 2-phase Enthalpy Cooling plant Detector LHCb-VELO: 2PACL pumped liquid system Fluid: CO2 Liquid Vapor Compressor Pump Pressure Chiller Liquid circulation 2-phase Cold transfer Enthalpy Cooling plant Detector

  7. 2PACL principle ideal for detector cooling: Liquid overflow => no mass flow control Low vapor quality => good heat transfer No local evaporator control, evaporator is passive in detector Very stable evaporator temperature control at a distance (P4-5 = P7) The 2-Phase Accumulator Controlled Loop (2PACL) Long distance P4-5 P7 5 Heat out Heat out Condenser 6 Heat in 4 Heat in 2 3 evaporator Heat exchanger 1 2-Phase Accumulator Restrictor Pump Vapor Liquid Pressure 2 3 2-phase 4 P7 5 1 6 Enthalpy

  8. Electron Proton beam Proton beam Hadron LHCb Detector Overview Goals of LHCb: Studying the decay of B-mesons to find evidence of CP-violation (Why is there more matter around than antimatter?) LHCb Cross section Vertex Locator Muon 20 meter

  9. The LHCb-VELO Detector (VErtex Locator) Detectors and electronics • Temperature detectors: -7ºC • Heat generation: max 1600 W 23 parallel evaporator stations capillaries and return hose VELO Thermal Control System CO2 evaporator section

  10. The Velo Detector Heat producing electronics Detection Silicon Particle tracks in the VELO from an LHC injection test (22 august ’08) CO2 evaporator (Stainless steel tube casted in aluminum)

  11. VELO Cooling Challenges • VELO electronics must be cooled in vacuum. • Good conductive connection • Absolute leakfree • Maximum power of the electronics: 1.6 kW • Silicon sensors must stay below -7°C at all times (on or off). • Adjustable temperature for commisioning. • -5°C to -30°C in vacuum (Nominal -25°C) • +10°C to-10°C under Neon vented condition • Maintenance free in (inaccessable) detector area

  12. VTCS Evaporator vacuum feed through capillaries and return hose liquid inlet (¼”x0.035”) 2-phase outlet (⅜”x0.035”) Inlet capillaries Finner=0.5mm (L~2m) Aluminium casted evaporator block details PT100 cables 23 parallel evaporator stations Finner=1mm (L~1.5m)

  13. LHCb-VTCS Overview(VELO Thermal Control System) Accessible and a friendly environment Inaccessible and a hostile environment 2.6 m PLC 4 m 4m thick concrete shielding wall 2 Evaporators 800 Watt max per detector half 2 CO2 2PACL’s: 1 for each detector half 2 R507A Chillers: 1 water cooled 1 air cooled 2 Concentric transfer lines 55 m VELO

  14. Ø4mm Ø6mm Concentric transfer line Transfer line is a 55m long concentric 2-fase liquid-vapor line 2-phase return line Functions: • Transferring liquid to evaporators • Regulate liquid temperature • Pick up environmental heat in return line for unloaded evaporator cooling • Provide low-pressure drop return flow for distant evaporator pressure control Protective cover 25mm Armaflex NH Isolation Ø14mm Ø16mm Ø66mm VTCS total upward column: 4m+2.6m = 6.6m ΔT ≈ 0.7°C → ≈ 0.1°C/m (C3F8≈ 2.3°C/m) Sub-cooled liquid feed line 4m 2.6m Terminals as built

  15. + Heating Cooling _ VTCS Accumulator Control Set point Temperature Cooling spiral for pressure decrease (Condensation) Tset Accumulator properties: • Volume: 14.2 liter (Loop 9 Liter) • Heater capacity: 1 kW • Cooler capacity: 1 kW • System charge: 12 kg (@23.2 liter) • System design pressure: 135 bar Pressure Temperature Pset Evaporator Pressure PID ΔPfault + _ + + Thermo siphon heater for pressure increase (Evaporation) Pressure drop Paccumulator

  16. VTCS Schematics2x CO2 2PACL’s connected to 2 R507A chillers (Redundancy) Lots of sensors and valves

  17. VTCS construction • CO2 2PACL’s • Stainless steel piping with: • (Orbital) Welding • Vacuum Brazing • Swagelok Cajon VCR fittings and line components • Lewa liquid CO2 pump (100 bar) • In house designed accumulator (130 bar) • Reinforced SWEP condenser (130 bar) • Now commercial available at SWEP. • 55 meter concentric transfer line • Aluminium casted cooling blocks • Test pressure 170 bar • Chillers designed in house with standard commercial chiller components. • Copper piping with hard solder joints • Danfoss line components • Bitzer compressors • SWEP heat exchangers • Siemens S7-400 series Programmable Logic Controller (PLC)

  18. CO 2 LHCb-VTCS Cooling Plant Freon chiller systems Accumulators Valves Pumps Condensers CO2 2PACL systems

  19. CO 2 VTCS Units Installed @ CERN Freon Unit CO2 Unit July- August 2007

  20. CO 2 VTCS 2PACL Operation From start-up to cold operation (1) + 2 Pump head pressure (Bar) 2 4-Accumulator liquid level (vol %) 7 4 - Accumulator pressure (Bar) 7 5 – Evaporator temperature (°C) 4 1 Pumped liquid temperature (°C) 1 4- Accumulator Control: + = Heating - = Cooling 7 _ 7 -7 4 7 +7 2 1 time A C B D 20 Start-up in ~2 hours

  21. CO 2 VTCS 2PACL Operation From start-up to cold operation (2) Pressure B C Accumulator Cooling = Pressure decrease 5 20 °C A 0 °C 2 Path of 5 Set-point range 4 D -20 °C 5 1 4 -40 °C Enthalpy D 2 - Pump head pressure (Bar) 2 B A C 2 4 - Accumulator pressure (Bar) 5 5 5 – Evaporator temperature (°C) 4 4 1 1 – Pumped liquid temperature (°C) 1 time A C B D 21 Start-up in ~2 hours

  22. March ’08: Commisioning of the VTCSDetector under vacuum and unpowered

  23. 24 June ’08: After a succesful commisioning of the detector at -25°C, the setpoint is increased to -5°C.And has been running since then smoothly! (3 sept 08) 80 Accu Heating/Cooling 60 Accu level 40 Detector half heat load (x10) Module Heat load 20 Temperature (°C), Power (Watt), Level (vol %) 0 Silicon temperature -7°C SP=-5°C -20 Evaporator temperature SP=-25°C -40 1:30 0 1:00 2:00 0:30 Time (Hour)

  24. VTCS performance overview for a setpoint of -5°C (Detector switched on, fully powered) CO2 heat transfer dT=1.4°C Evaporator Pressure 31.15 bar = -4.18°C Cooling block dT=0.04°C Cooling block temperature = -2.8°C 1 hour CO2 liquid temp= -42°C dP=0.6 bar = 6.2 m static heigth Fluctuations from the untuned chiller Detector offset from accu control: 0.7°C CO2 liquid dT=4.5°C Evaporator liquid inlet temp = -4.40°C Evaporator vapor outlet temp = -4.44°C Accumulator Pressure 30.54 bar = -4.90°C

  25. Summary • The VTCS has successfully passed the 1st commissioning phase and was ready to be used in the experiment in July 2008 • Operational temperature range is between -5°C and -30°C set point for the water cooled chiller • It has run for 3½months continuously with only minor problems • It behaves very stable with the chiller still to be tuned (evaporator stability less than 0.05°C) • The silicon temperature is below the required -7°C @ -25°C set point temperature. (This is consistent with the prediction)

  26. What did we learn: • 2PACL dynamics work better with the accumulator connection at inlet of condenser (instead of outlet as it is now) • No saturated liquid feed from accu to pump. • Free pre-cooling at cold start-up due to thermal capacity of condensers. • Concentric transfer tube heat exchanger works beyond expectations as the so-called “Duck-foot-cooling1” pinciple is boosting the operational temperature range. • The current system is not always initiating boiling at higher operational temperatures (>-10°C), resulting in temporary reduced heat-exchange. 1 The way a duck can have cold feet without loosing body heat, by exchanging heat between the in- and outlet bloodstream.

  27. The “Cool” future • The VTCS is not yet finnished, some things have to be done: • Implementing automatic back-up procedure. • Changing the accumulator connection. • Tunning the chiller. • Analyse data for publication. • Construction of a mini desktop 2PACL CO2 circulator for general purpose laboratory use. • Participation in future CO2 cooling systems • Atlas IBL, Goat, Next-64, RELAXed • 2PACL upgrade: • Replace HFC chiller by CO2 chiller • No integration of chiller and 2PACL! • 2PACL is much more stable (<0.05’C) • 2PACL has liquid overfeed and needs no boil-off heaters • CO2 compressor needs oil as lubricant • CO2 chiller has extended lower temperature range (CO2 ~-50°C , HFC~-40°C )

  28. Back-up Slides

  29. Property Comparison (1) R744 (CO2) R218 (C3F8) R116 (C2F6)

  30. Q = 680 Watt Tube = 4 meter Example of and Atlas upgrade stave (1) 2x 20 wafers à 17 Watt Cooling Calculations based on -35°C and 75% vapor quality at exit 1 Atlas stave : 2 meter length CO2 CO2 ΔT=-2°C C2F6 C3F8 C2F6 C3F8 Pressure Drop Generates Temperature Drop Mass flow @ -35ºC Φ CO2= 2.9 g/s Φ C3F8= 8.7 g/s Φ C2F6= 9.6 g/s CO2=2.7mm C2F6=4.3mm C3F8=7.7mm

  31. Heat exchange length 25mm 75mm Example of and Atlas upgrade stave (2) D2.7mm x L25mm = 80167 W/m2 CO2 D4.3mm x L25mm = 50337 W/m2 D2.7mm x L75mm = 26722 W/m2 C2F6 D4.3mm x L75mm = 16779 W/m2 D7.7mm x L25mm = 28110 W/m2 D7.7mm x L75mm = 9370 W/m2 C3F8 25mm HX length C3F8 • 7.7 75mm HX length Mass flux @ -35ºC Φ’ CO2= 506 kg/m2s Φ’ C3F8= 661 kg/m2s Φ’ C2F6= 186 kg/m2s CO2 C2F6 Critical Heat Flux (Bowring/Ahmad): CHF(CO2) = 313 kW/m2, x=1.1

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