1. Detector cooling system Update on UT cooling specifications and status of activities LHCb CO2 cooling meeting Simone Coelli For the Milano UT Group INFN Milano 1 Istituto Nazionale di Fisica Nucleare Sezione di Milano 18/3/2015

2. 2 temperature difference over any silicon sensor ∆T sensor max = 5 °C (as a goal) a constrain to limit both the sensor deformation due to thermal contraction and the relevant stresses induced by the cooling down silicon sensor maximum temperature for any sensor T sensor max = - 5 °C functional requirement for the sensor operation under the worst condition foreseen in the detector at the end of life ASICs read out maximum temperature should be under a temperature T ASIC max = 40 °C The electronics read-out ASIC chips are the most powerful local heating source in the detector, so that their temperature is the maximum figure present in the detector COOLING POWER DETECTOR DISSIPATED POWER total number of ASICs in UT detector: 4192 ASIC dissipated nominal power: 0,768 W ASICs estimated total power dissipation is 4192 * 0.768 W = 3220 W dissipation in power data flex-cables +10% Plus margins TOTAL COOLING POWER ~ 5 kW UT Detector thermal requirements

3. 3 FEA thermal simulation have been done on a variety of stave design hypothesis to check the thermal behavior and other requirements, several thermal contact materials studied Local support design last version (V.5) L-shaped ceramic stiffener PBN (Pyrolytic Boron Nitride) / AlN (Aluminum Nitride) phase-change removable glue interface CO2 boiling into cooling pipe Titanium C.P.2 O.D. 2,275 mm, th. 0,125 mm Pipe embedded in Carbon foam Allcomp K 35 Carbon fiber Faceplates TRACKER SENSOR SUPPORT STRUCTURE L-ceramic stiffener with slits Central stave inner region Snake pipe design and foam details Stave detail

4. 4 FEA thermal simulations T1, T2, T3 CENTRAL STAVE SENSORS Thermally critical special solution adopted carbon foam extension i.e. ANSYS FINITE ELEMENT ANALYSIS MODELS GENERAL (~90 %) SENSOR FEA thermal simulations to study and optimize the local temperature gradients from these simulation figures => input parameters to design the cooling system 8 ASICs read-out 4 ASICs read-out steady-state solid materials thermal conduction

5. 5 FEA thermal simulations sum up Temperature difference over the silicon sensor. ∆T sensor max = 5 °C Main effect: heat dissipated by the read-out ASICs create a thermal flux toward the sensor (colder) and produces a sensor hot spot The sensor hot spot give raise to the Temperature difference over the silicon sensor Effect driven by the local support design (use of conductive materials and geometric strategy) improvement of this ∆T is possible only working on the local stave structure. For the large majority of the detector the sensor temperature difference ∆T ~< 5 °C. The detector worst ∆T case is: central stave T3 sensor Having: 8 ASICs read-out sitting over the for power/data flex-bus The worst case for T3 in the central stave, for P.B.N. ceramic stiffener, thickness 0,5 mm, without slits, ∆T ~ 7 °C for the following considerations on the cooling system design With engineeristic safety approach The maximum ∆T could be rounded, with a margin on FEA calculations => ∆Tmax = 10 °C It’s not a true Temperature difference over any silicon sensor (and It’s probably the real limit of acceptability)

6. 6 FEA thermal simulations sum up Silicon sensor maximum temperature ∆T sensor max = - 5 °C The calculated thermal field shows that the coolest part of the sensor is a few degrees over the external cooling pipe temperature. The hottest part of the sensor is obtained adding the previously discussed ∆T over the sensor. Consequently the cooling pipe temperature is required to be, as a first approximation: T cooling pipe < T max sensor - sensor ∆Tmax Worst case T cooling pipe < - 5 °C – 10 °C  T cooling pipe < – 15 °C ∆T on titanium pipe wall The cooling pipe is I.D. 2 mm, ~ 0.1 mm thickness, Titanium pipe  the internal and external pipe temperature difference is negligible, for the thermal flux of interest in this configuration. internal convection temperature drop ∆Tconv CALCULATION WORK IN PROGRESS, FIRST ESTIMATES internal convection temperature drop is a function of the thermal flux on the internal surface of the pipe and of the heat transfer coefficient (H.T.C.). a maximum internal convection temperature drop comes from the central stave (max power and thermal load) snake pipe having ~100 Watt on a heated length of ~1.6 m (internal surface ~0,01 m2) The pipe mean thermal flux is in the range ~ 10000 W/m2 (= 1 W/cm2). H.T.C. for CO2 evaporating in the range of interest should be in the range of a value of ~5000 W/m2*K. ∆Tconv= thermal flux / HTC ∆Tconv= 10000 W/m2 /5000 W/m2*K= ~ 2 °C For safety, taking into account margins and waiting to do more refined calculations, a value of 5 °C can be used for an initial estimate. T fluid < T cooling pipe - ∆Tconv < – 15 °C - 5 °C  T CO2 inlet fluid < – 20 °C CO2 nominal cooling inlet temperature inlet temperature could be set putting a margin on this – 20 °C For example.. -25 °C/.. -30 °C To be decided, see next

7. 7 FEA thermal simulations sum up => T inlet fluid CO2 < – 20 °C. How much go under this threshold with colder CO2 need to be optimized! Going to lower temperatures: May have a benefit on the sensors working at lower T Have a detrimental effect on the thermal induced deformations and relevant mechanical stress. The mechanical “life” of the cooling components is mainly related to the: coolest temperatures in the system = max stress induced number of thermal cycles, between ambient temperature and minimum T NOTE inlet-outlet decrease of temperature is related to the stave pressure drop ∆Tin-out In the stave cooling pipe, due to the pressure drop along the channel, the evaporation temperature will decrease along the path. This is one of the parameters to be investigated in a real scale, precise mass flow rate test. If the calculation will be verified and tested on prototypes the requirement of Silicon sensor maximum temperature ∆T sensor max = - 5 °C May be satisfied using T inlet fluid CO2 < – 20 °C The outlet temperature will be lower, ∆Tin-out is not exactly known but has to be limited to 5 °C. The CO2 cooling system control probably will use the T set-point on the outlet common manifold, taking in account the ∆Tin-out that will be measured in the test.

8. 8 FEA thermal simulations sum up ASIC maximum temperature T ASIC max = 40 °C The cooling system adopted to maintain the sensor in the temperature range explained before, automatically will take the ASIC temperature in an acceptable range. From the F.E.A. simulation done, the ASIC temperature is expected to be, in the worst case, 20 °C more than the cooling pipe temperature. fixing the T cooling pipe < -15 °C expected ASIC max temperature is around T ASIC max < 5 °C. IMPORTANT NOTE All the consideration on the cooling system foresee that the system works in the correct evaporation regime with CO2 in full boiling into the stave cooling pipe channel and avoiding the dry-out condition with large margin (i.e. setting 30 % CO2 vapor fraction at the cooling pipe outlet) These working condition are set by: correct design of the inlet-outlet cooling connection and distribution system proper inlet temperature/hentalpy of the CO2 coolant from the cooling plant proper coolant mass flow-rate

9. 1 of 8 “Half-planes” Γ Γ Introduction: The detector thermal management The detector is made of 4 + 4 “half planes” Each with 8 or 9 parallel staves Each “half plane” has its inlet/outlet coolant connection Γ = CO2 coolant mass flow rate (g/s) “snake pipe” design

10. 10 Nominal stave coolant MASS FLOWRATE Nominal operation: Dissipated power Q = ~85 this is the central stave Outlet vapour fraction X = 30 % = ~0,3 Latent heat of vaporization CO2 (liq.=> vap.) H lv = ~280 kJ/kg  Calculated design mass flow rate Γ = Q / X * hlv = 85 W/(0,3*280) J/g = ~ 1 g/s Power Q Γ Γ h L h out, X UT detector one stave energy balance This is valid for both the 2 cooling pipe design under investigation: snake cooling pipe design 2 parallel cooling pipes

11. 11 cooling pipe design The 2 geometry options Snake cooling pipe 2 Parallel straigth pipes 8 central staves (C type) 60 staves (A,B type) 68 staves

12. 12 DESIGN OF THE COOLING SYTEM REQUIRES: INLET CO2 LIQUID SUBCOOLED BUT NEAR TO SATURATION h in = h liq OUTLET VAPOUR FRACTION X H lv := hentalpy difference liquid to vapour => see next slides X := outlet vapour fraction h out = hl + X * hlv => (h out – h in) = X * hlv Mass flow rate  Γ = Q / X * hlv This is the design massflowrate needed to extract a given power Q, using a boiling fluid from saturated liquid to a fraction X vapour phase Mass - energy balance General equations Power Q (W) Γ out mass conservation law Γ := mass flow rate (g/s) Γ in = Γ out Γ in energy conservation law h:= coolant hentalpy (J/kg) Q = Γ *(h out – h in) (kW = g/s * kJ/kg) Mass flow rate => Γ = Q / (h out – h in) h out, X h in Detector element dissipating power

13. 13 THE PURE CO2 SATURATION CURVE CORRELATES TEMPERATURE AND PRESSURE (INSIDE THE EVAPORATION CHANNEL) - 20 °C TO - 30 °C COOLING FLUID OPER. TEMP. => 10 TO 20 bar COOLING FLUID OPER. PRESSURE SU blow-off test 12-13 bar

14. 14 H lv (liq.=> vap.) = 280 kJ/kg H lv (liq.=> vap.) LATENT HEAT OF VAPORIZATION FOR CO2 FROM THE CO2 PRESSURE-HENTALPY DIAGRAM 10 TO 20 bar COOLING FLUID OPER. PRESSURE RANGE At 10 bar (- 40 °C) H lv= 320 kJ/kg

15. 15 Design MASS FLOWRATE for the central stave Nomilnal operation extimate: Dissipated power Q = 85 W Outlet vapour fraction X = 30 % = 0,3 Latent heat of vaporization (liq.=> vap.) H lv =280 kJ/kg => Calculated design mass flow rate Γ = Q / X * hlv = 85 W/(0,3*280) J/g = 1 g/s Power Q Γ Γ h L h out, X UT detector central stave energy balance Always valid Both using a 1 snake or 2 straight cooling pipes

16. 16 Central stave energy balance INLET = OUTLET MASS FLOWRATE in different cooling flow configurations Γ Γ Γ Γ Γ/2 Q = 85 W X = 30 % H lv =280 kJ/kg Coolant Mass flow rate always  Γ = 1 g/s Given the same boundary conditions Γ/2 Γ Γ

17. UT DETECTOR one half box UNDER INVESTIGATION USING ONE LONG CAPILLARY/MINIPIPE THAT IS A DISTRIBUTED PRESSURE DROP CONNECTING EACH STAVE PIPE INLET; EXTERNAL MANIFOLD DISTRIBUTED DELTAP The detector coolant distribution system goal is to give the correct flow distribution using balanced pressure drop in the circuit => THE DEGREE OF FREEDOM WE HAVE IN THE DESIGN IS IN THE INLET COOLING LINES (INTERNAL DIAM, LENGTH, ROUGHNESS) This sketch is to satisfy the “half panel” service modularity required

18. 18 Here shown the “snake pipe” design Half planes UTaX, UTaU with 8 staves Q = ~460 W X outlet= ~30 % H lv = ~280 kJ/kg Coolant Mass flow rate Γ = Q / X * hlv  Γ = ~5,5 g/s Γ Γ Half planes UTbV, UTbX with 9 staves Q = ~512 W X outlet= ~30 % H lv = ~280 kJ/kg Coolant Mass flow rate Γ = Q / X * hlv  Γ = ~6 g/s Half plane energy balance

19. CO2 cooling test Set-up proposal 19 The maximum power consumption of the ASIC chip, at the moment, is believed to be 0.768 Watt. this figure is here assumed to calculate the detector power and the needed cooling power. Sensor self heating negligible Power data Flex-bus power dissipation will be taken into account with a 10 % margin on the dissipated power READ-OUT ASICs are the main power source in the detector Starting assumption One of the 8 Half-plane POWER DISTRIBUTION SKETCH is shown in the next slide

20. 20 = 4 ASIC = 8 ASIC Nominal power 0,768 WATT/ASIC A (A)C B AA A A A 10 cm 5 cm 10 cm Half-plane POWER DISTRIBUTION SKETCH

21. 21 1* C 1* B C (1 Stave) = 82 W B (1 Stave) = 64 W A (7 staves) = 48 W 17 7* A EQ 48 30 14  Watt self heating margin included 17 14 17 14

22. GOAL: INVESTIGATION AND MEASUREMENT OF THE THERMO-HYDRAULIC PROPERTIES OF STAVE PROTOTYPES WITH CO2 COOLING UNDER REALISTIC OPERATIVE CONDITIONS TESTING SCALE (1:1) STAVE PROTOTYPES WITH CONTROLLED COOLANT CONDITIONS 1 - First step of this test will use a single dummy stave The test system foreseen is using a 2 PACL refrigeration unit, called TRACI, 1:1 test stave prototype Real titanium pipe Real geometry will be used in the dummy. Vertical flow Real heat load distribution will be simulated using heaters on the dummy. Nominal flow condition will be applied with accurate mass flow-rate measurement (Traci Coriolis) CO2 fluid temperature & pressure will be measured at the stave inlet and outlet using PT, TT identical to the TRACI trasmitters upward and downward flow conditions could be investigated for a single stave. 2 - two parallel staves. test power/fluid supply unbalance can be tested to investigate the behavior of the system.. 3 - a half panel with 9 parallel dummy staves test of power and fluid supply unbalance can be tested to investigate the behavior of the system limited by the TRACI cooling power Useful to test inlet/outlet cooling circuit manifolding/capillaries connection 4 – a half panel with 9 parallel dummy staves full power half plane cooling design demonstrator using a full scale prototype will use a half panel with 9 dummy staves Using cooling unit available at CERN cooling laboratory.. 22

23. Test set-up one stave thermo-hydraulic stave properties measurement 23 Test planned using TRACI PT NEEDLE VALVE TT SAFETY VALVE 110 bar SAFETY VALVE 110 bar PT TT PT Traci connection lines +Up to 30 Temperature probes TK Attached to the pipes externally to follow temperature behaviour

24. 24 DUMMY STAVES 20 W heaters 8 W heaters titanium pipe Real geometry

25. 25 DUMMY STAVES Model and production in progress Trying to simulate in the dummy real stave thermal behaviour Using «equivalent» thermal conditions I will shoe detils next mechanical-cooling meeting

26. Test system set-up status COOLING CIRCUIT Swagelok hydraulic components ordered with spares to build variants in house PIPES 10 Titanium pipes ordered and arriving (Sheffield-Cern- Milano) BENDING TOOL FOR SNAKE PIPE: some parts received fom Lancaster We’re working to realize the «central stave type C» Thanks to Ian Mercer Lancaster For the «bobbins and bending tool»! 26 status of activities and plans for this year

27. 27 BENDING TITANIUM PIPES Fit very well in the geometry mask

28. 28 box production in progress ENVIRONMENTAL COLD-BOX GOAL: environment as similar as possible as for the stave into the real UT box AIR TIGHTNESS TO GUARANTEE INTERNAL DEW-POINT Harmaflex INSULATION OR DRY-AIR (10ppmv) FLOW

29. Test system set-up status DAQ AND SENSORS Ordered a complete system with 5 PT, 5 TT, 30 TK + spare channels for additional meas. (flowmeter) 29 DAQ cRIO9066 Pressure trasmitter Swagelok component Labview acquisition T trasmitter

30. COBRA code INSTALLED SUCCESSFULLY (..beta release..) FIRST SIMULATIONS DONE USING «EVAPORATOR» SIMULATOR PROBLEMS (NO CONVERGENCE) FOUND IN SOME OPERATIVE CONDITION PROBLEMS USING THE VERTICAL GEOMERTY 30

31. COBRA CODE TRIAL SIMULATIONS LHCB UT SNAKE PIPE design CENTRAL STAVE 31 Approximation to use the code Power distribution is the total pover uniformly spreaded Over the full lenght of the snake pipe

32. COBRA CODE TRIAL SIMULATIONS LHCB UT SNAKE PIPE design CENTRAL STAVE 32 -40 °C sat temp +85 Watt Angle 0° horizontal Cooling flowrate 1 g/s

33. 33 -40 °C sat temp +85 Watt Angle 0° horizontal Cooling flowrate 1 g/s

34. COBRA CODE TRIAL SIMULATIONS LHCB UT SNAKE PIPE design CENTRAL STAVE 34 -40 °C sat temp +85 Watt Angle 90° VERTICAL => NO SOLUTION Cooling flowrate 1 g/s..WORK IN PROGRESS TO UNDERSTAND..