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 needed at -40 c C, condensors at low pressure No high pressure allowed (max. 70 bar, preferred <45 bar?) (use pressure reducer on storage cylinders or store CO2 at 10 0 C(=45 bar)

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 reduce V by factor 1.5-> factor 2.3 in power=VxI Why -40 0 C?

3. Wim de Boer, Univ. Karlsruhe 3Jan.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

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

5. 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) But simple method to assure every parallel pipe gets liquid b) Expansion valve is 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 works excellent (but needs check of distribution in many parallel channels)

6. Wim de Boer, Univ. Karlsruhe 6Jan.2009 Pressure reduction Pressure reducer tested to work very well for controlling temperature of CO2 two phase mixture. Possible solution: pressure reducing valve combined with capillary “washer” Advantage: pressure reducer on each layer allows to regulate flow on each layer independently and capillary washer would ensure equal distribution between ladders. Washer can be different for different layers (with different power, like trigger layer, stereo layer)

7. Service connections in CMS tracker

8. Wim de Boer, Univ. Karlsruhe 8Jan.2009 CMS tracker services

9. Wim de Boer, Univ. Karlsruhe 9Jan.2009 Long ladder with Interconnect Board at end 100 mm Interconnect board for 2 ladders (200 mm) Analog signals, clock, HV on Al kapton or micro twisted pair cables FADC, DOH HV+LV+Temp CO2 Optical fiber ribbons CO2 in CO2 out

10. Wim de Boer, Univ. Karlsruhe 10Jan.2009 machineable ceramic Macor Copper/Ni Connector can slide into slit on flangeor ICB CO2 feed line Al union nut 3 mm OD Al cooling pipe with Al flange Washer Washer with capillary hole Nut Connection between feed line and ladder thermal expansion Macor: 9×10 -6 m/(m·K). Al: 23x10 -6 m/(m·K).

11. Wim de Boer, Univ. Karlsruhe 11Jan.2009 scale “low” pressure” CO2 system Commercial condensor Pressure reducer (outside CMS)+ capillary in detector regulates temperature to 10 bar=-40C  Detector=evaporator 9 bar <45 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 45 bar shut down to 10 0 C storage cylinder 10 bar 45 bar

12. Wim de Boer, Univ. Karlsruhe 12Jan.2009 2.3bar/ 0 C 0.3bar/ 0 C CO2 PT-diagram

13. 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

14. Wim de Boer, Univ. Karlsruhe 14Jan.2009 Instrumented evaporator Isolation box hybrid with heater and T-sensor Evaporator Temp.

15. Wim de Boer, Univ. Karlsruhe 15Jan.2009 Instrumented evaporator

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 (  1g/s) (max. of flowmeters) with negligible pressure drop Even much bigger flow seems possible with tolerable pressure drop

17. Wim de Boer, Univ. Karlsruhe 17Jan.2009 Choice of liquid pump pump characteristics 17 flowrate pressure membrane displacement pumps rotary positive displacement pumps centrifugal pumps

18. Wim de Boer, Univ. Karlsruhe 18Jan.2009 LEWA diaphragm pumps (ECOFLOW)

19. Wim de Boer, Univ. Karlsruhe 19Jan.2009 Output pressure limited

20. Wim de Boer, Univ. Karlsruhe 20Jan.2009 CMS: Control and Monitoring System

21. Available at CERN: Karlsruhe chiller Chiller (R404) Heatexchanger liquid pump C6F14 -20 0 C 3 kW at 33 l/min -20°C ---> power 6,1 KW > -30°C ---> power 3,9 KW > -35°C ---> power 3,1 KW

22. Wim de Boer, Univ. Karlsruhe 22Jan.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

23. Accumulator Purpose: allow for expansion of liquid during heating Can also be used to control pressure (=temperature) of detector LHCb solution: Special CO2 cylinder with temperature control by heater and heat exchanger to chiller Possible with standard equipment????? E.g.use standard CO2 cylinders upside down in 2 or more fridges in parallel? (large heat capacity!) (if one fridge fails, close bottle and other fridges should have enough capacity for one fridge failing). Fridges on upper balcony would guarantee liquid in detector, if liquid in accumulator.

24. Wim de Boer, Univ. Karlsruhe 24Jan.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 All service connections outside tracking volume possible by CO2 cooling, which allows 6m long cooling pipes Additional reduction of material budget possible by powering via cooling pipes, since pure Al cold pipes have VERY low resistivity.

25. Wim de Boer, Univ. Karlsruhe 25Jan.2009 Backup slides

26. Wim de Boer, Univ. Karlsruhe 26Jan.2009 26 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 Can adjust frequency (electrically) and stroke (mechanically) of LEWA pump

27. Wim de Boer, Univ. Karlsruhe 27Jan.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

28. Wim de Boer, Univ. Karlsruhe 28Jan.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

29. Wim de Boer, Univ. Karlsruhe 29Jan.2009 Supermarkets start to use CO2

30. Wim de Boer, Univ. Karlsruhe 30Jan.2009 CO2 phase diagram

31. Wim de Boer, Univ. Karlsruhe 31Jan.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. GEA heat exchangers

32. Wim de Boer, Univ. Karlsruhe 32Jan.2009 Diaphragm exchange simple

33. Wim de Boer, Univ. Karlsruhe 33Jan.2009 Flow adjustment

34. Wim de Boer, Univ. Karlsruhe 34Jan.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 For 50 W cooling circuit (=strixels): 1 mm seems preferred For 300 W/ cooling circuit (=pixels): 2 mm seems preferred To be verified for CO2 at low temp. annular bubble slug

35. Wim de Boer, Univ. Karlsruhe 35Jan.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. Or have thermal bridge glued to Si (bad for material budget) Note: very difficult to cool bumpbonded pixel detectors. Better strixel with hybrids thermally isolated.