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Ann Van Lysebetten

CO 2 cooling experience in the LHCb Vertex Locator. Ann Van Lysebetten. Vertex 2007 Lake Placid 24/09/2007. Outline. VeLo Introduction VELO CO 2 Cooling system Evaporator Lab performance Cooling plant operation Major challenges

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Ann Van Lysebetten

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  1. CO2 cooling experience in the LHCb Vertex Locator Ann Van Lysebetten Vertex 2007 Lake Placid 24/09/2007

  2. Outline • VeLo Introduction • VELO CO2 Cooling system • Evaporator Lab performance • Cooling plant operation • Major challenges • Final Cooling plant performance • Module Thermal performance • Conclusions Vertex2007, Lake Placid

  3. VErtex LOcator rectangular bellows Vacuum vessel rf-box Silicon sensors exit window kaptons wake field suppressor Vertex2007, Lake Placid

  4. VELO detector half manifold kaptons 21 + 2 silicon sensors Beam(7mm) cooling pipes + cookies Vertex2007, Lake Placid

  5. VELO cooling requirements • Harsh non-uniform radiation environment • avoid thermal runaway in silicon • hold reverse annealing • radiation hard refrigerant • Vacuum • Direct contact between cooling and module • No connections but failsafe orbital welds • In LHCb acceptance  low mass system • No mechanical stress on the module • Cooling capacity up to 800W/half Temperature silicon sensors ~-5ºC at all times  cooling temperature of -25ºC VELO Thermal Control System based on CO2 Evaporator Vertex2007, Lake Placid

  6. No local evaporator control, evaporator is passive in detector Detector waste heat 2-Phase Accumulator prim. System H2O 10C Sec. System (freon) Flooded evaporator Tert. System (CO2) Heat out Condenser Heat out Heat in Heat in Heat exchanger Restriction Pump The CO2 cooling principle Tertiary System: two-phase accumulator controlled system Vertex2007, Lake Placid

  7. The CO2 cooling cycle 2-Phase Accumulator Flooded evaporator Heat out Heat out Condenser Heat in Heat in Heat exchanger Restriction Pump 6 7 Transfer tube heat exchange brings evaporator pre expansion per definition right above saturation 5 4 3 2 1 Saturation line Accumulator pressure = detector temperature Detector load Capillary expansion brings evaporator blocks in saturation Vertex2007, Lake Placid

  8. The implementation Accessible and a friendly environment Inaccessible and a hostile environment 6 Evaporator 2-phase R507a Chiller 5 4 • Cooling plant: • Sub cooled liquid CO2 pumping • 12.5 kg CO2per half • CO2 condensing to a R507a chiller • CO2 loop pressure control using a 2-phase accumulator • Redundancy with spare pump and backup chiller • Control of the system by Siemens PLC • Evaporator : • VTCS temperature ≈ -25ºC • Total Evaporator load • ≈ 0-1600 Watt • Completely passive Vertex2007, Lake Placid

  9. The cooling plant Accumulators Heat exchanger 3 CO2 pumps 2 Compressors (Air and water chiller) freon chiller CO2unit Vertex2007, Lake Placid 9 9 Ann Van Lysebetten

  10. CO Freon 2 valves Accumulator Compressors CO2 pumps Vertex2007, Lake Placid

  11. Installation at CERN Controls PLC Freon Unit CO2 Unit July- August 2007 Vertex2007, Lake Placid

  12. The Evaporator 23 parallel evaporator stations + Al cast cooling blocks vacuum feed through capillaries and return hose PT100 cables capillaries Finner=0.5mm vapor outlet liquid inlet Vertex2007, Lake Placid

  13. The Evaporator vacuum feed through capillaries and return hose 23 parallel evaporator stations + Al cast cooling blocks liquid inlet vapor outlet capillaries Finner=0.5mm PT100 cables Vertex2007, Lake Placid

  14. Evaporator Lab Performance Mass flow Mod25 Mod16 evaporator nominal flow = 12 g/s dry out temperature [oC] total mass flow [g/s] annular gas+liquid flow heat load 1.4x nominal Vertex2007, Lake Placid

  15. Operation: start-up From room temperature to set-point of-25 ºC Pump pressure (Bar) Accumulator pressure (Bar) Accu level (%) Temp (C), Pressure (bar), Level (%) Accu heating/cooling (W) time Evaporator (ºC) Transfer return (ºC) Pumped liquid (ºC) A C B D Ann Van Lysebetten Start-up in ~2 hours

  16. Major Challenges • Hardware concerns • Pumps • problems for cold start-up  sphere valve secured by a spring • pump-membrane failure as result of vacuuming  pump filling now done by flushing. • pump discharge burst discs replaced by spring relieves • Heat exchanger • from food industry (no mixing between coolants) + reinforced to withstand 200bar • Safety Procedures • Accu working pressure 130bar, V =14l  European directive for high pressure vessels  CE certification • PLC control loops • Accu control see next slides Vertex2007, Lake Placid 16 Ann Van Lysebetten

  17. VTCS Accumulator Control 2PACL Start-up Cooling spiral for pressure decrease (Condensation) Pump head (Bar) Accumulator Pressure (Bar) Heater temp. (ºC) Accu Level (%) Decrease heater power near critical point to prevent dry-out Liquid temp. (ºC) Heater power (%) Pump inlet (ºC) • Accumulator Properties: • Volume 14.2 liter (Loop 9 Liter) • Heater capacity 1kW • Cooling capacity 1 kW Thermal Resistance (mK/W) Thermo siphon heater for pressure increase (Evaporation) Accumulator pressure (bar) Vertex2007, Lake Placid

  18. VTCS Accumulator Control Accu PID control loop not adequate  temperature oscillations of a few degrees Needed tuning of PID control loop to solve problem Evaporator liquid in (ºC) Evaporator pressure (Bar) Evaporative temp. (ºC) Condenser Inlet (ºC) Pump inlet (ºC) Vertex2007, Lake Placid 18 Ann Van Lysebetten

  19. VTCS Evaporator performanceStability and response to heat-load changes @Setpoint =-25ºC: Accumulator temp: -24.8ºC Evaporator temp(No Load): -23.4ºC Evaporator temp(600 W Load):-23.0ºC Stabilization time from 0 to 600 Watt: ca. 7min Temperature stability: <0.25ºC Evaporator Temp (ºC) Accu Temp ≈ Set-point (ºC) Accu level (‰) Temperature (C) 600 Watt Detector Power (Watt) Power (Watt) Accu Cooling Power (Watt) Temperatures stable without pressure change Pumped Liquid Temp (ºC) Vertex2007, Lake Placid

  20. Module Cooling Module Powered Module Unpowered Cooling system at -25 oC Total Chip Power : ~19W NTC1 NTC0 2 NTCs to monitor temperature on hybrid Vertex2007, Lake Placid

  21. Module Cooling & Performance Right/C half Left/A half DT(Setpoint – NTC1) Cooling system to silicon DT(Cool. Cookie-NTC0) Transfer cool-module DT(NTC0-NTC1) Module performance DT(setpoint-cool. Cookie) <T silicon> with setpoint of -25C: <T silicon> with setpoint of -25C: (-4.2±1.4 ) C (-5.2±1.5) C Min. -7.2 C Max. -1.0 C Min. -8.4 C Max. -2.1 C Measurement conditions not exactly as! final system (vacuum, not all modules cooled simultaneously, …) Small variations in power consumption, modules assembly, evaporator stations  variations in T Vertex2007, Lake Placid

  22. Conclusions • All stringent requirements met • Setpoint temperatures go down to ~ -35C • System proves stable operation: • without loads/with loads up to 800W • Module thermal performance + CO2 cooling at -25 C •  All modules at all times below 0C • Low mass system without mechanical stress on module • Redundancy built in • VELO CO2 cooling system is installed and commissioned • PLC control successful • all routines implemented • 1 button start/stop for main system Looking forward to enter the final commissioning phase with the VELO installed! Vertex2007, Lake Placid

  23. Back Up Slides Vertex2007, Lake Placid

  24. The cooling plant: CO2 unit Accumulator CO2-part Heat exchanger 3 CO2 pumps Vertex2007, Lake Placid 24

  25. The cooling plant: Freonunit 2 Compressors (Air and water chiller) Vertex2007, Lake Placid

  26. VELO detector half manifold kaptons 23 + 2 silicon sensors Beam (7mm) cooling pipes + cookies Vertex2007, Lake Placid

  27. Stand-alone test results of the VTCS cooling plant(No external evaporator, cooling over by-pass) Main chiller performance • Dynamic range of main chiller works properly. • Full operational range (0 to 1800 Watt) possible in evaporator range (-25ºC to -30ºC) • Isolation needs improvement around injection valves • CO2 condensers/ Freon evaporator works beyond expectation (Hardly no dT between Freon and CO2 ) Back-up chiller performance • Able to maintain an un-powered CO2 evaporator at -10ºC

  28. Transfer line Operation(Internal heat exchanger) A C A B Accumulator set-point B [5] Evaporator liquid in (ºC) [10] Evaporator pressure (Bar) C [14] Accumulator pressure (Bar) Cooling plant side Evaporator side [10] Evaporative temp. (ºC) [13] Condenser Inlet (ºC) Transfer line temperature profile [1] Pump inlet (ºC) A: Condenser and evaporator single phase B: Evaporator 2-phase, condenser single phase C: Both evaporator and Condenser 2- phase Vertex2007, Lake Placid

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