1. CO 2 Cooling: Overview over CMS activities Jennifer Merz RWTH Aachen University, 1. Physikalisches Institut B May 18 2011 CEC General Meeting, Karlsruhe

2. Outline 2Jennifer Merz  Overview CO 2 Cooling  Overview over CMS activities CERN Lyon Aachen  Cooling Organization within CMS  Plans/Needs for the Future  Conclusions

3. 3Jennifer Merz Effective cooling: high heat load can be cooled with little flow  Evaporating more effective than heating up a liquid Low viscosity at low temperatures Lower temperatures are possible  Benefit for silicon sensors Reduction of material budget: - Low CO 2 density - Little flow - Thin pipes, CO 2 under high pressure High heat transfer coefficient Evaporative CO 2 cooling system: dissipate power by evaporating liquid CO 2 Idea inspired by LHCb cooling for VELO Why CO 2 ? Liquid CO 2 @ -20°C:  Heating up to -19°C: 2 J/g  Evaporate: 282 J/g x100

4. 4Jennifer Merz CO 2 Cooling – Some Facts Solid Liquid Vapour Temperature-Pressure-Diagram -lowest possible temperature: ~40°C -in two-phase flow: pressure drop  temperature drop -cooling systems have to cope with high pressures (~100bar) -1-2bar pressure drop on cooling lines uncritical -vapour quality x (fraction of vapour) important parameter for measurements -dryout has to be avoided: liquid not in touch with wall pipes  efficient cooling not guaranteed liquidvapour x=0 x=1 x: vapour quality

5. 55 Expansion Vessel: Saturated mixture of CO 2 liquid and vapour pressure, bar Enthalpy, kJ/kg Heat Exchanger:  Subcooling of incoming CO 2 (only liquid in pump)  Dissipation of detector heat load Heat Exchanger:  Warm incoming CO 2 to nominal temperature (given by chiller 1)  Partial condensation of returning CO 2 Jennifer Merz Chiller 1: Chiller temp.  vapour pressure  system temp. Schematic View of CO 2 System Liquid Liquid + Gas Example: Aachen Setup

6. CERN - Cryolab 6Jennifer Merz Large Scale SystemSmall Scale System -27°C – +25°C-40°C – 0°C 1 – 15 g/s0.45 – 0.95 g/s 5.5 m tube300mm, heated: 150 mm -Systems can vary vapour quality of incoming CO 2 -Vacuum boxes for insulation -Measurements have been performed to investigate differences in both systems -Last months: improvements of large scale system -Large scale system can be used by different groups to test their cooling configuration, e.g. recently Belle-II collaboration tested thermal structure for pixel detector -Precision measurements performed with small scale system CERN

7. Large Scale System 7Jennifer Merz Location in 158: - Commissioning of the system at 25°C, - Possible mass flow rate 1...15 g/s, - Run only at ambient temperature at the moment, - Next step => accumulator to vary T sat. Joao Noite, Lukasz Zwalinski, Torsten Koettig CO 2 pump CO 2 bottle heat exchanger CERN

8. Small Scale System – Exp. Results (I) 8 Results from paper: Investigation of heat transfer and pressure drop of CO 2 two-phase flow in a horizontal channel, International Journal of Heat and Mass Transfer -Measurement of heat transfer coefficient for different conditions -HTC dependent on saturation temperature and heat flux 8Jennifer Merz CERN

9. Small Scale System – Exp. Results (II) 9 Results from paper: Investigation of heat transfer and pressure drop of CO 2 two-phase flow in a horizontal channel, International Journal of Heat and Mass Transfer -Measurement of pressure drop for different conditions -Pressure drop dependent on saturation temperature and mass flux Jennifer Merz CERN

10. CERN - DT 10Jennifer Merz -Talk by Jerome Daguin (CERN DT) -R & D Pixel upgrade: can existing copper pipes for C 6 F 14 be reused for CO 2 cooling -Issues to adress: pipes and joint pressure resistance geometrical arrangement of existing pipes -want to build small scale mock-up for tests at different pressures -want to build large scale mock-up for tests of geometrical arrangement tensile tests pressure tests CERN

11. CERN - DT 11Jennifer Merz -Development of two cooling systems: one small and portable (100W), one bigger “not-so-portable” (1kW) -Studies to scale up existing methods for future (bigger) experiments -Investigations to find suitable accumulator (expansion vessel) -Standard concept requires: 2m 3, 100 bar, certified for -30°C or larger number of accumulators with same total volume  very expensive and complex object(s) CERN

12. IPN Lyon 12Jennifer Merz -Recirculating system built -works down to -15°C -further improvements needed to go further down in temperature Silicon area: 60 x 18 mm Heating foils exactly cover this area Heat input to capillary @ max. power = 25 W/m from Feb 2010: Pixel test structure tested with blow system Information by Nick Lumb Lyon

13. CO2-FlascheCO2-Bottle 13Jennifer Merz Heat Exchanger Expansion Vessel Detector CO 2 Bottle Aachen: CO 2 Test System (I) 19cm 7.6cm 16cm 42cm Aachen

14. CO 2 Test System (II) Alu-Box  Vakuum zur Isolierung Bedien- fläche 14 Aluminium Box  Vacuum for Insulation Panel -4 x 6m stainless-steel pipes, 1.6mm inner diameter -Thermistors along pipes: measurement of temperature distribution -Simulation of uniform heat load, current through pipes (  Ohmic losses) Cooling Pipes Position on Pipe Detector Temperatur, °C CO 2 @ -20 g/min Heat Load: 60W No Vacuum Vacuum ΔT~1K Restriction Valves Aachen

15. Parallel Cooling Pipes (I) 15Jennifer Merz Parallel Cooling Pipes: -Needed because of space constraints -Dedicated measurements have to be done: high heat load  low mass flow -Restrictions necessary in each branch 80W 100W 120W 4 parallel branches L = 5,5m d i = 1,5mm ϕ = 3 g/s same heat load on all pipes Aachen  uniform temperature distribution with applied heat load

16. Parallel Cooling Pipes (II) 16Jennifer Merz 4 parallel branches L = 5,5m d i = 1,5mm ϕ = 3 g/s 3 pipes: 100W 1 pipes: 100-130W Heat Load on Pipe 2: 100W 120W 130W Aachen  uniform temperature distribution even if one pipe sees higher heat load -Measurements needed on what happens if one branch sees significantly higher heat load -Effect can be reduced by restrictions -Measurements so far with open restrictions

17. Organization 17Jennifer Merz -Convener: Hans Postema and Antti Onnela, both CERN -Recent decision: focus on phase-I activities (Pixel upgrade), “observe” these developments for phase-II -meetings during Tracker Week, last: October 2010 -meetings attended also by non-CMS people: ATLAS and LHCb, knowledge is very much shared between collaborations, Hans called it “open source style”

18. Implications for module design when implementing CO 2 cooling: -Small pipe diameters: mechanical support has to be guaranteed -Low temperatures: large temperature gradient between room and operating temperature: module parts have to stand thermal stress  thermal measurements on mechanical structures need to be done -Heat transfer coefficient of CO 2 dependent on many parameters: cooling contacts between pipes and heat dissipating devices has to be adapted  different sizes, shapes and materials should be investigated -Optimal pipe routing needs to be found Module Design 18Jennifer Merz  future contribution from Aachen

19. System Aspects 19Jennifer Merz Implications for system design when implementing CO 2 cooling: -Operation of parallel cooling branches under different conditions -Measurements with non-uniform heat load, simulating modules with different power consumption -Devices for flow and temperature/pressure control might be needed on/near module

20. Conclusions 20Jennifer Merz -CO 2 is promising coolant for the CMS tracker upgrade -Participating groups: CERN, Lyon and Aachen -So far good progress on “basic” (and important) measurements (heat transfer coefficient, pressure drop) -Measurement of thermal contacts, pipe routings need to start soon -Further investigation and measurements on parallel piping