1. Wim de Boer, Univ. Karlsruhe 1Jan.2009 Design considerations for a CMS CO2 cooling system CMS specials: 50 kW cooling system at -40 0 C (see below) Difficulties: membrane pumps to -25 0 C, condensors at low pressure No high pressure allowed (max. 70 bar, preferred <35 bar) Difficulties: have to separate room temperature storage cylinders (70 bar) from operating system (extra pump or cooled storage cylinders)

2. Wim de Boer, Univ. Karlsruhe 2Jan.2009 25 W/10x10 cm sensor at -25 0 C, factor 1.5 reduction/5 0 C Hybrids for strixel design of 2.2 cm: 2 W Want to reduce by factor 8: from -25 to -40 0 C -> x3.4 Additionally: reduce V by factor 1.5-> factor 2.3 in power=VxI Why -40 0 C?

3. Wim de Boer, Univ. Karlsruhe 3Jan.2009 Temperature profile for 25W in 10x10 Si sensor Cooling: 240 K at edge-> 40 K increase towards middle for 25 W (Si = SEMI-conductor!) High risk of thermal run away for such high gradients ! Have to run at lower voltage or still lower temperature.

4. Wim de Boer, Univ. Karlsruhe 4Jan.2009

5. Wim de Boer, Univ. Karlsruhe 5Jan.2009

6. Wim de Boer, Univ. Karlsruhe 6Jan.2009 Choices for evaporative cooling systems Compressor (gas) Condensor Evaporator Pressure regulator Condensor at high pressure, Do not need external chiller. Have to avoid that liquid enters compressor, so need heaters in case heat load drops or TEV (Thermal expansion valve) which regulates flow. Condensor at low pressure, Need external chiller Have to avoid evaporation in or before pump, so need subcooled liquid, which need to be heated before evaporator to have well defined temp. Liquid pump Evaporator Condensor Pressure regulator Chiller

7. Need pressure reduction between condensor and evaporator 3 methods: a) capillary b) expansion valve c) pressure reducer a) Capillary pressure drop flow dependent, so need additional pressure control (accumulator in LHC-b) b) Expansion valve usual method in commercial cooling systems, but different for different fluids. Not available for CO2 (as far as we know) c) Simple pressure reducer used on bottles work excellent (but not used as such, as far as we know)

8. Pressure reduction by temperature controlled expansion valve

9. Wim de Boer, Univ. Karlsruhe 9Jan.2009 Pressure reduction by pressure sensitive valve (used on bottles) Tested to work very well for controlling temperature of CO2 two phase mixture. Can avoid complicated accumulator used in LHC-b

10. Wim de Boer, Univ. Karlsruhe 10Jan.2009 Choices from ATLAS and LHCb From B. Verlaat, NIKHEF Liquid Vapor 2-phase Pressure Enthalpy Liquid Vapor 2-phase Pressure Enthalpy Vapor compression system Always vapor needed Dummy heat load when switched off Oil free compressor, hard to find Pumped liquid system Liquid overflow, no vapor needed No actuators in detector Oil free pump, easy to find Standard commercial chiller Detector Cooling plant Warm transfer over distance Detector Cooling plant ChillerLiquid circulation Cold transfer over distance  Direct expansion into detector with C 3 F 8 compressor  Warm transfer lines  Boil-off heater and in detector  Temperature control by back-pressure regulator  CO 2 liquid pumping  Cold concentric transfer line  No components in detector  Temperature control by 2-phase accumulator LHCb method: Atlas method: Heater Compressor Pump Compressor BP. Regulator

11. LHCb-VTCS Overview (B. Verlaat) A 2-Phase Accumulator Controlled Loop Evaporator : VTCS temperature ≈ -25ºC Evaporator load ≈ 0-1600 Watt Complete passive Cooling plant: Sub cooled liquid CO 2 pumping CO 2 condensing to a R507a chiller CO 2 loop pressure control using a 2-phase accumulator Accessible and a friendly environment Inaccessible and a hostile environment R507a Chiller

12. LHCb-VTCS Overview (B. Verlaat) A 2-Phase Accumulator Controlled Loop Evaporator : VTCS temperature ≈ -25ºC Evaporator load ≈ 0-1600 Watt Complete passive Cooling plant: Sub cooled liquid CO 2 pumping CO 2 condensing to a R507a chiller CO 2 loop pressure control using a 2-phase accumulator Accessible and a friendly environment Inaccessible and a hostile environment R507a Chiller

13. Wim de Boer, Univ. Karlsruhe 13Jan.2009 CO2 bottle in household freezer Advantage: Initial pressure reduced by cooling of CO2 to 12 bar (instead of 70 bar at room temp) No heat exchanger needed Whole system <500 Euro Standard Swagelock connectors Fast cooldown since liquid has already detector temperature The simplest CO2 cooling system you can image AND IT WORKS! Detectors Flowmeter regulates flow, i.e. cooling power Pressure reducer regulates temperature long nylon tube to air nylon tube to see boiling of CO2 Relief valve

14. Wim de Boer, Univ. Karlsruhe 14Jan.2009 Flow meters hybrid with heater and T-sensor Some pictures Cold liquid sent through ladder. Blue temperature curve shows position of liquid. Isolation box

15. Wim de Boer, Univ. Karlsruhe 15Jan.2009 Regulating temperature with pressure 11,5bar 8bar 6,5 5,5  very easy to set and hold temperature: just keep pressure constant CO2 pressure in [bar]

16. Wim de Boer, Univ. Karlsruhe 16Jan.2009 Test results easy to cool large powers with little flow of CO2, flow was tested up to 3,7 kg/hour (max. of flowmeters) with negligible pressure drop Even much bigger flow seems possible with tolerable pressure drop

17. Why CMS cannot use any of these systems CMS cannot use high pressure CO2 closed system, since 1 mm Cu cooling pipes should have max. 70 bar. CMS has large varying heat loads (detectors cannot be switched on during cooldown) and 50 kW heaters are a nightmare in cooling circuit Possible solution: try liquid pump down to -40C and design low pressure CO2 system. For sLHC we would like to cool down to -40C to avoid risk of thermal run away.

18. Wim de Boer, Univ. Karlsruhe 18Jan.2009 scale A recirculating CO2 system Commercial condensor Pressure reducer regulates temperature to 10 bar=-40C  Detector=evaporator 9 bar <25 bar fill line Vacuum pump for leaktests  Chiller -50 C Pump for subcooled CO2 Transferline 60m as concentric heat exchanger to heat up subcooled liquid and reduce pressure in outlet 70 bar shut down line with high pressure pump 10 bar 25 bar 

19. Wim de Boer, Univ. Karlsruhe 19Jan.2009 Heat exchangers: www.geawtt.comHeat exchangers: www.geawtt.com. Double Wall For extra protection against leakage a special double wall system is developed. This system consists of two stainless steel plates instead of one. In case of internal damage, due to strong pressure variations for example, the chance of fluid contamination is prevented

20. Wim de Boer, Univ. Karlsruhe 20Jan.2009 GEAWTT Condensors

21. Wim de Boer, Univ. Karlsruhe 21Jan.2009 Safety Chamber™ The patented Safety Chamber™, the Non-Plus-Ultra for big brazed heat exchangers is the industrial standard for GEA WTT heat exchanger types 7, 8, 9 and 10. The contact points (brazing points), which are responsible to take off the stress in the port area, are separated. Overloading of these contact points and cracking of the material do not lead to a mix with the other side - a maximum of safety for the user The Full-Flow-System™ special developed for GEA WTT nickel brazed heat exchangers. To avoid freezing problems in the port area when using nickel brazed heat exchangers as an evaporator GEA WTT has developed the Full-Flow- System™. Continuous flow without stagnation around the port avoids "Port Freezing". XCR the plates consist of high grade corrosion resistant stainless steel, named SMO 254. XCR series has been developed for special applications, such as pool heating, ground water heat pumps, etc. Depend on the particular application we offer XCR models either copper brazed or nickel brazed Delta-Injektion™...Distribution System The Delta-Injektion™ distribution system on Advanced Evaporator AE models is made from AISI 316L stainless steel and provides precise allocation of refrigerant to the channels Double Wall For extra protection against leakage a special double wall system is developed. This system consists of two stainless steel plates instead of one. In case of internal damage, due to strong pressure variations for example, the chance of fluid contamination is prevented.

22. Wim de Boer, Univ. Karlsruhe 22Jan.2009 Choice of liquid pump Pressure firm pump characteristic 22 flowrate pressure membrane displacement pumps rotary positive displacement pumps centrifugal pumps

23. Wim de Boer, Univ. Karlsruhe 23Jan.2009 LEWA diaphragm pumps (ECOFLOW)

24. Wim de Boer, Univ. Karlsruhe 24Jan.2009 Diaphragm exchange simple

25. Wim de Boer, Univ. Karlsruhe 25Jan.2009 Output pressure limited

26. Wim de Boer, Univ. Karlsruhe 26Jan.2009 Flow adjustment

27. Wim de Boer, Univ. Karlsruhe 27Jan.2009 CMS: Control and Monitoring System

28. Wim de Boer, Univ. Karlsruhe 28Jan.2009 28 frequency n fowrate Q Q = k 1 *n stroke length h flowrate Q Q = k 2 *(h- h 0 ) h0h0 limiting stroke length h 0 Adjusting the flowrate

29. Wim de Boer, Univ. Karlsruhe 29Jan.2009 Vh time t Flowrate Q Pulsating flowrate Need either: a) 3 phase-shifted pump heads b) pulsation damper c) maybe pressure reducer does the job to prevent temperature variations

30. Wim de Boer, Univ. Karlsruhe 30Jan.2009 1mm diameter, 0.5 mm thick pmax 550 bar 2mm diameter, 0.5 mm thick pmax 367 bar Flow regimes in small tubes 0.0002 kg/s=66W rhoflowvelocitydiameterviscositySurface tensionReynoldSuratman REG/RE L kg/m3kg/sm/smmPas=cPN/m(x10^6) 11380,00020,220,0010,150,0121697,700,61CO2 liq -44 220,000211,580,0010,0110,01223150,49CO2 gas -4413,64 11380,00020,060,0020,150,012848,851,21CO2 liq -44 220,00022,890,0020,0110,01211575,25CO2 gas -4413,64 11380,00020,220,0010,150,0121697,700,61CO2 liq -44 220,000021,160,0010,0110,0122315,05CO2 gas -441,36 11380,00020,060,0020,150,012848,851,21CO2 liq -44 220,000020,290,0020,0110,0121157,52CO2 gas -441,36 Pressure drop in 1 mm tube still small enough, especially with heat exchange between in- and output by the electrical connections pads, so almost no T-gradient on ladder To be verified for CO2 at low temp. annular bubble slug

31. Wim de Boer, Univ. Karlsruhe 31Jan.2009 Questions to be resolved Diaphragm pump to be tested at -40 0 C Started collaboration with LEWA. They will give us a pump and we will test different diaphragms Heat exchanger at low temperature and low pressure: Started collaboration with GEA. Their design program says it is possible for high flow of primary liquid Accumulator: Can one use large volume of return tubes as accumulator? (It would act as pulsation damper! No need for triple, phase shifted pumps, one pump with CMS control preferred? Price tag: 20 kEuro/pump, 20 kEuro/CMS) Do we need accumulator above tracker to guarantee always liquid in upper part of tracker?

32. Wim de Boer, Univ. Karlsruhe 32Jan.2009 Summary low pressure CO2 system with STANDARD commercial pumps, heat exchangers and pressure reducers seems feasible. Require cooling of sensors below -40 0 C to get leakage current noise down and limit risk of thermal runaway# (main difficulty: find membrane material for low temp.) Strixels of 2.2 cm could then yield S/N similar as for LHC (signal down by ¼, so capacitance down by ¼) All connections outside volume possible by CO2 cooling, which allows 6m long cooling pipes Reduction of material budget possible by powering via cooling pipes, since pure Al cold pipes have VERY low resistivity. No need for DC/DC converters inside tracker

33. Wim de Boer, Univ. Karlsruhe 33Jan.2009 Backup slides

34. Wim de Boer, Univ. Karlsruhe 34Jan.2009 Summary of cooling liquids at LHC Notes:  Single phase cooling simplest, but large pumps needed  Two-phase evaporation in principle much better, because heat of evaporation much larger than specific heat, but any pressure changes means a temperature change, so be careful about tube bending, tube sizes etc.  CO2 has largest heat of evaporation, is non-toxic, non-flammable, industrial standard, liquid at room temperature, but high pressure (73 bar at 31 0 C) 300

35. Wim de Boer, Univ. Karlsruhe 35Jan.2009 Supermarkets start to use CO2

36. Wim de Boer, Univ. Karlsruhe 36Jan.2009 CO2 phase diagram