1 Antonio Romanazzi 3D CFD study of the ATLAS (UX15) ventilation system

2 Agenda The 3D model The 2D simulations of Muon chambers

3 Problem specification Three dimensional model of the UX15 cavern and the main components of the ATLAS experiment to analyze: Ventilation system of UX15 cavern Temperature map around the muon chambers Bi dimensional models of the muon chamber to study: Temperature profiles on the solid part of the chambers

4 Existing 3D CATIA models has been simplified before exportation to Star-CD. Simplifications: –Muon chambers are simplified regular solids (parallelepipeds) –All solid parts are considered “empty volumes” (no conduction) –HS structure are simplified to zero-dimensional porous buffers –No cables, no services –Cavern walls are considered as adiabatic (less than 1.5 kW/ EDMS ) Main simplifications from CATIA model Original CATIA model Simplified CATIA model The mesh has been generated in Star-CD

5 3D Model generation in Star-CD From CATIA geometry we retrieved the closed surfaces on which was produced a preliminary surface mesh The volume mesh was produced with a automatic meshing system The resulting model consists of about 12,000,000 tetrahedral and hexahedral cells (hybrid mesh) Fluid domine only Once the model is finished we define the boundary conditions

6 Ventilation in UX15 2 outlets total 60,000 m 3 /h 12 inlets, 60,000 m 3 /h total air at 17°C Argon extraction has not been considered The air flow is limited by UX15 installed equipments

7 Obstacles to the air flow HS/O Platforms: To simulate the grid effect, the platforms are modeled as porous material. Flexible chains: No thermal impact

8 Heat sinks Toroids: -4.8W/m 2 Thermal screens : Fixed temperature 18 °C sectors

9 Wheels Heat generation 2 BW TGC: 12 kW per side BW MDT: 1.5 kW per side BW EO: 3 kW per side BW TGC: 5 kW per side Small Wheels: 1 kW per side Inner detector and Calorimeters: Adiabatic

10 Barrel Heat Generation BOL [W]BOS [W]BML [W]BMS [W]BIL [W]BIS [W] PADs & Splitters18,46515,76011,7589, MDT electronics 3,900 2,741 3,447 Tot (75,785 W) 22,36519,66014,49912,3673,447 Outer Layer Medium Layer Inner Layer The model is ready for computation

11 Computation Development Model generation more than 10 months Run time ≈ 4 months over 12÷20 Openlab nodes Post processing and computing time more than 6 months Development time 1,5 years Set-up Buoyancy driven flow k-ε turbulent model/low Reynolds numbers SIMPLE solver Steady state simulation Openlab CFD cluster:20 4 CPU Intel Itanium 1.6 Ghz, running IA64 Linux.

12 Results show the overall energy balance of the caverne Big Wheels=45,000 W Muon Chambers= 75,785 W Muon Barrel 112 kW Thermal Screens= -94 W Coils= W Inlet Temperature= 17 °C ∆ Flow Energy Outlet average Temperature= 22.4 °C 112 kW Flow rate = m 3 /h = 17 kg/s Cp= 1006 J/kgK

13 Results – Temperature Maps Z Sections from C to A side

14 Results – Velocity Maps Z Sections from C to A side The average velocity in the model is about 0.1 m/s

15 Air stagnation in sector 5 between level M and O Recirculation between M and O layers in sect 05 No evident effect of experiment inclination on the flow … and this has an impact on the temperature field

16 Stagnation in sector 05 should be investigated

17 Hot spots in sector 13 Surface with splitters and PADs in M and O layer Highest temperatures are on BML and BOL of sector 13, positioned on the Splitters/PADs surface. For all other sectors temperature keeps below 30°C We suggest experimental measurements in this critical area

18 Thermal Screens act on the flow pattern Heat removed by the screens: -94 W Descending flow Average temperature on the outside surface of the screen: 19°C

19 Cavern temperature gradient leads Big Wheels EO one…

20 … and the Big Wheels TGC too

21 Big Wheels MDT Air flow reduced in the big wheel’s gap

22 From 3D to 2D model At this moment we have the “environmental” condition of the cavern. We want to obtain the detail of temperature on the solid. We can get this level of detail using 2D models.

23 2D simulation on Chambers 2D models Natural/forced convection Variable flow rate adjusted to the 3D model Variable orientation of chambers Same heat load of 3D model Air at 20°C PADs are modeled detached from the chamber (highest heat load section on the chamber) Material properties from study of Snezhinsk Institute Sector 05 Sector 09 Sector 10 Sector 12

24 2D models use Evaluate the temperature map on the muons chambers with the level of detail that would not be possible in the overall 3D simulation. Two conditions have been investigated: Inlet velocity equal to the average velocity of the air inside the muons chambers volume in the 3D model. Inlet velocity equal to the minimum velocity detected in the 3D model.

25 Results from 2D Models / Example Air reference temperature / Sector Tavg RPC [°C] Tmax RPC [°C] Tavg MDT [°C] Tmax MDT [°C] ∆Tx on MDT ∆Ty on MDT Tavg MDT electronics [°C] Tmax MDT electronics [°C] Tavg PADs [°C] Tmax PADs [°C]BOL 22°C / Simulation Temperatures are corrected by 3D simulation average temperature (air reference temperature ). In this case from 20°C to 22°C.

26 Expected Temperatures on Muons Chambers at 0.1m/s Air reference temperature / Sector Tavg RPC [°C] Tmax RPC [°C] Tavg MDT [°C] Tmax MDT [°C] ∆Tx on MDT ∆Ty on MDT Tavg MDT electronic s [°C] Tmax MDT electronics [°C] Tavg PADs [°C] Tmax PADs [°C] BOLBOLBOLBOL 22°C / °C / °C / °C / BMLBMLBMLBML 21°C / °C / °C / °C / BILBILBILBIL 20°C / °C / °C / °C / Chambers position

27 Expected Temperatures on Muons Chambers at 0.1m/s Chambers position Air reference temperature / Sector Tavg RPC [°C] Tmax RPC [°C] Tavg MDT [°C] Tmax MDT [°C] ∆Tx on MDT ∆Ty on MDT Tavg MDT electronics [°C] Tmax MDT electronics [°C] Tavg PADs [°C] Tmax PADs [°C] BOSBOSBOSBOS 22°C / °C / °C / °C / BMSBMSBMSBMS 20°C / °C / °C / °C / BISBISBISBIS 20°C / °C / °C / °C /

28 How to find point with the worst thermal conditions Temperature on MDT 3D model surface used to locate “critical” positions on Z axis. Velocity conditions retrieved from the 3d model and implemented in 2D. Lowest velocity value

29 2D model with the worst air velocity conditions Air reference temperature / Sector Tavg RPC [°C] Tmax RPC [°C] Tavg MDT [°C] Tmax MDT [°C] ∆Tx on MDT ∆Ty on MDT T avg MDT electronics [°C] T max MDT electronics [°C] T avg PADs [°C] T max PADs [°C] BOLBOLBOLBOL 22°C / m/s °C / m/s °C / m/s °C / m/s BMLBMLBMLBML 21°C / m/s °C / m/s °C / m/s °C / m/s BILBILBILBIL 20°C / m/s °C / m/s °C / m/s °C / m/s Chambers position

30 2D model with the worst air velocity conditions Air reference temperature / Sector Tavg RPC [°C] Tmax RPC [°C] Tavg MDT [°C] Tmax MDT [°C] ∆Tx on MDT ∆Ty on MDT Tavg MDT electronics [°C] Tmax MDT electronics [°C] T avg PADs [°C] Tmax PADs [°C] BOSBOSBOSBOS 22°C / m/s °C / m/s °C / m/s °C / m/s BMSBMSBMSBMS 20°C / m/s °C / m/s °C / m/s °C / m/s BISBISBISBIS 20°C / m/s °C / m/s °C / m/s °C / m/s Chambers position

31 Temperature dependence on air flow With a flow between 0.01 and 0.1 natural convection drives heat transfer

32 CONCLUSIONS Air stagnation in sector 05 should be investigated Presence of hot spots in sector 13 suggests experimental test to verify the phenomena Natural convection process leads the heat extraction form the muons chambers. RPC average temperature should stay under 25°C.

33

34 Sect 02 Sect 10 Sect 12 Sect 04 Back to 0.1 vel Back to min vel Sect 06 Sect 14

35 Sect 05 Sect 13 Sect 01 Sect 09 Back to min velBack to 0.1 vel

36 Heat transfer on PAD P= α∙∆T∙S α≈1W/m 2 K 2400[W/m 3] ∙0.5∙0.06∙ L=1∙∆T∙(2 ∙0.5 ∙L) ∆T=P/(α ∙S)=70K 0.5m S real > S model ∆T real < ∆T model 0.06m

37 BOL - Sector m/s

38 BOL – Sector m/s

39 BOL - Sector m/s

40 BOL - Sector m/s

41 BML – Sector m/s

42 BML - Sector m/s

43 BML - Sector m/s

44 BML - Sector m/s

45 BIL – Sector m/s

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47 BIL - Sector m/s

48 BIL - Sector m/s

49 BOS - Sector m/s

50 BOS - Sector m/s

51 BOS - Sector m/s

52 BOS – Sector m/s

53 BMS - Sector m/s

54 BMS – Sector m/s

55 BMS - Sector m/s

56 BMS – Sector m/s

57 BIS – Sector m/s

58 BIS – Sector m/s

59 BIS - Sector m/s

60 BIS – Sector m/s

61 BOL - Sector m/s

62 BOL – Sector m/s

63 BOL - Sector m/s

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65 BML – Sector m/s

66 BML - Sector m/s

67 BML - Sector m/s

68 BML - Sector m/s

69 BIL – Sector m/s

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71 BIL - Sector m/s

72 BIL - Sector m/s

73 BOS - Sector m/s

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77 BMS - Sector m/s

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80 BMS – Sector m/s

81 BIS – Sector m/s

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83 BIS - Sector m/s

84 BIS – Sector m/s