Engineering Forum experiences from cooling systems for LHC
- Slides: 31
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 1
Table of Contents • CO 2 cooling and the 2 PACL method • LHCb-VELO Thermal Control System (VTCS). • Commisioning results of the VTCS. • Conclusions. 2
Why Evaporative CO 2 Cooling? The lightest way of cooling is: Evaporate at high pressure! Why? Vapor expansion is limited under high pressure d. P/P is small Volume stays low Pipe diameter stays low Mass stays low Low mass flow High latent heat Carbon Dioxide 3
Saturation curves in the PT Diagram for CO 2, C 2 F 6 & C 3 F 8 (3 used or considered refrigerants at CERN) Pressure (Bar) 75 CO 2 50 C 2 F 6 25 C 3 F 8 0 -60 -40 -20 0 20 40 Temperature (°C) 4
Property comparison Better Refrigerant “R” numbers: R 744=CO 2 R 218=C 3 F 8 R 116=C 2 F 6 Saturation Temperature (ºC ) Liquid Viscosity Saturation Temperature (ºC ) d. T/d. P (ºC/bar) Better Surface Tension (N/m) Better Liquid Viscosity (Pa*s) Better ρvapour/ ρliquid Density Ratio (ρvapour/ ρliquid) Better Latent heat of evaporation (k. J/kg) Latent Heat of Evaporation 5 Saturation Temperature (ºC )
2 evaporative cooling principles used in LHC detectors Atlas Inner Detector: Vapor compression system Liquid BP. Regulator Warm transfer Cooling plant Heater Compressor Pressure Fluid: C 3 F 8 Vapor 2 -phase Enthalpy Detector LHCb-VELO: 2 PACL pumped liquid system Fluid: CO 2 Liquid Vapor Pressure Compressor Pump Chiller Liquid circulation 2 -phase Cold transfer Enthalpy Cooling plant Detector 6
Condenser Long distance P 4 -5 6 4 2 1 Pump Heat in 5 3 evaporator Heat exchanger 2 PACL 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 (P 4 -5 = P 7) Pressure 2 -Phase Accumulator Heat out P 7 Heat in Heat out The 2 -Phase Accumulator Controlled Loop (2 PACL) P 7 Restrictor Vapor Liquid 2 3 2 -phase 4 1 6 5 7 Enthalpy
LHCb Detector Overview Goals of LHCb: Studying the decay of B-mesons to find evidence of CP-violation LHCb Cross section (Why is there more matter around than antimatter? ) Vertex Locator tron Elec Muon Proton beam Hadron 20 meter Proton beam 8
The LHCb-VELO Detector (VErtex Locator) Detectors and electronics • Temperature detectors: -7ºC • Heat generation: max 1600 W ons to ev pa VELO Thermal Control System CO 2 evaporator section an cap d r illa etu rie rn s ho se 23 el rall ra apo ati r st 9
The Velo Detector Detection Silicon Heat producing electronics Particle tracks in the VELO from an LHC injection test (22 august ’ 08) CO 2 evaporator (Stainless steel tube casted in aluminum) 10
VELO Cooling Challenges • VELO electronics must be cooled in vacuum. – Good conductive connection – Absolute leakfree • Maximum power of the electronics: 1. 6 k. W • 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 11
VTCS Evaporator liquid inlet (¼”x 0. 035”) 2 -phase outlet (⅜”x 0. 035”) Aluminium casted evaporator block details PT 100 cables vacuum feed through capillaries and return hose Inlet capillaries Finner=0. 5 mm (L~2 m) 23 parallel evaporator stations Finner=1 mm (L~1. 5 m) 12
LHCb-VTCS Overview (VELO Thermal Control System) Accessible and a friendly environment 2 CO 2 2 PACL’s: 1 for each detector half 4 m thick concrete shielding wall 2. 6 m PLC 2 R 507 A Chillers: 1 water cooled 1 air cooled Inaccessible and a hostile environment 4 m 2 Evaporators 800 Watt max per detector half 2 Concentric transfer lines 55 m VELO 13
Concentric transfer line Transfer line is a 55 m long concentric 2 -fase liquid-vapor 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 VTCS total upward column: 4 m+2. 6 m = 6. 6 m ΔT ≈ 0. 7°C → ≈ 0. 1°C/m (C 3 F 8 ≈ 2. 3°C/m) 2 -phase return line Protective cover Ø 1 4 m m Ø 16 mm Ø 6 25 mm Armaflex NH Isolation Ø 4 m m Ø 66 mm Sub-cooled liquid feed line 4 m 2. 6 m Terminals as built 14
VTCS Accumulator Control Set point Temperature Pressure Tset Temperature Cooling spiral for pressure decrease (Condensation) Accumulator properties: • • • Volume: 14. 2 liter (Loop 9 Liter) Heater capacity: 1 k. W Cooler capacity: 1 k. W System charge: 12 kg (@23. 2 liter) System design pressure: 135 bar Pset + _ ΔPfault PID + _ Evaporator Pressure Heating Cooling Paccumulator ++ Pressure drop Thermo siphon heater for pressure increase (Evaporation) 15
VTCS Schematics 2 x CO 2 2 PACL’s connected to 2 R 507 A chillers (Redundancy) Lots of sensors and valves 16
VTCS construction • CO 2 2 PACL’s – Stainless steel piping with: • (Orbital) Welding • Vacuum Brazing • Swagelok Cajon VCR fittings and line components – Lewa liquid CO 2 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 S 7 -400 series Programmable Logic Controller (PLC) 17
LHCb-VTCS Cooling Plant Freon chiller systems Accumulators Valves Pumps CO 2 2 PACL systems Condensers 18
VTCS Units Installed @ CERN Freon Unit CO 2 Unit July- August 2007 19
VTCS 2 PACL Operation From start-up to cold operation (1) + 2 2 Pump head pressure (Bar) 74 -Accumulator liquid level (vol %) 47 - Accumulator pressure (Bar) 54– Evaporator temperature (°C) 11 Pumped liquid temperature (°C) 7 Accumulator Control: 4+ = Heating - = Cooling _ -7 7 4 7 +7 2 20 1
Pressure VTCS 2 PACL Operation From start-up to cold operation (2) B C Accumulator Cooling = Pressure decrease 5 A 20 °C 2 Path of 54 D 5 1 Set-point range -20 °C 4 -40 °C Enthalpy D A B C 2 5 1 4 2 - Pump head pressure (Bar) 45 - Accumulator pressure (Bar) 54 – Evaporator temperature (°C) 11– Pumped liquid 21 temperature (°C)
March ’ 08: Commisioning of the VTCS Detector under vacuum and unpowered 22
24 June ’ 08: After a succesful commisioning of the detector at -25°C, the setpoint is increased to -5°C. Temperature (°C), Power (Watt), Level (vol %) And has been running since then smoothly! (3 sept 08) 80 Accu Heating/Cooling 60 Accu level 40 Detector half heat load (x 10) Module Heat load 20 0 -7°C Silicon temperature SP=-5°C -20 SP=-25°C -40 0 Evaporator temperature 0: 30 1: 00 Time (Hour) 1: 30 2: 00 23
VTCS performance overview for a setpoint of -5°C (Detector switched on, fully powered) Cooling block temperature = -2. 8°C CO 2 liquid temp= -42°C Evaporator liquid inlet temp = -4. 40°C 1 hour Fluctuations from the untuned chiller CO 2 liquid d. T=4. 5°C Detector offset from accu control: 0. 7°C d. P=0. 6 bar = 6. 2 m static heigth Evaporator Pressure 31. 15 bar = -4. 18°C Cooling block d. T=0. 04°C CO 2 heat transfer d. T=1. 4°C Evaporator vapor outlet temp = -4. 44°C Accumulator Pressure 30. 54 bar = -4. 90°C 24
Summary • The VTCS has successfully passed the 1 st 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) 25
What did we learn: • 2 PACL 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-footcooling 1” 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. 26
The “Cool” future • The VTCS is not yet finnished, some things have to be done: • Construction of a mini desktop 2 PACL CO 2 circulator for general purpose laboratory use. • Participation in future CO 2 cooling systems • 2 PACL upgrade: – – Implementing automatic back-up procedure. Changing the accumulator connection. Tunning the chiller. Analyse data for publication. – Atlas IBL, Goat, Next-64, RELAXed – Replace HFC chiller by CO 2 chiller • No integration of chiller and 2 PACL! – 2 PACL is much more stable (<0. 05’C) – 2 PACL has liquid overfeed and needs no boil-off heaters – CO 2 compressor needs oil as lubricant • CO 2 chiller has extended lower temperature range (CO 2 ~-50°C , HFC~40°C ) 27
Back-up Slides 28
Property Comparison (1) R 744 (CO 2) R 116 (C 2 F 6) R 218 (C 3 F 8) Source Refprop NIST R 744 (CO 2) R 218 (C 3 F 8) R 116 (C 2 F 6) Critical Point 31ºC @ 73. 8 bar 71. 9ºC @ 26. 4 bar 19. 9ºC @ 30. 5 bar Triple point -56. 6ºC -147. 7ºC -100ºC Boiling temperature @ 1 bar -78. 4ºC Sublimation ! -36. 8ºC -78. 1ºC 29
Q = 680 Watt Tube = 4 meter Example of and Atlas upgrade stave (1) 2 x 20 wafers à 17 Watt Cooling Calculations based on -35°C and 75% vapor quality at exit ΔT=-2°C 3 F 8 Pressure Drop Mass flow @ -35ºC Φ CO 2= 2. 9 g/s Φ C 3 F 8= 8. 7 g/s Φ C 2 F 6= 9. 6 g/s C 3 F 8 C 2 F 6 CO 2 1 Atlas stave : 2 meter length Generate s CO CF 2 2 =2. 7 m 6 =4. 3 mm m Temperature Drop CF 3 8 =7. 7 m m 30
D 2. 7 mm x L 25 mm = 80167 W/m 2 CO 2 Example of and Atlas upgrade stave (2) Heat exchange length 25 mm 75 mm D 4. 3 mm x L 25 mm = 50337 W/m 2 D 2. 7 mm x L 75 mm = 26722 W/m 2 C 2 F 6 C 3 F 8 D 4. 3 mm x L 75 mm = 16779 W/m 2 D 7. 7 mm x L 25 mm = 28110 W/m 2 D 7. 7 mm x L 75 mm = 9370 W/m 2 25 mm H X length C 3 F • 87. 7 Mass flux @ -35ºC Φ’ CO 2= 506 kg/m 2 s Φ’ C 3 F 8= 661 kg/m 2 s Φ’ C 2 F 6= 186 kg/m 2 s Critical Heat Flux (Bowring/Ahmad): CHF(CO 2) = 313 k. W/m 2, x=1. 1 75 mm H X length CO 2 C 2 F 6 31
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