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Antonio Romanazzi. 3D CFD study of the ATLAS (UX15) ventilation system. 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
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Antonio Romanazzi 3D CFD study of the ATLAS (UX15) ventilation system
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
Main simplifications from CATIA model • 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 811370) Original CATIA model Simplified CATIA model The mesh has been generated in Star-CD
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
Ventilation in UX15 2 outlets total 60,000 m3/h 12 inlets, 60,000 m3/h total air at 17°C Argon extraction has not been considered The air flow is limited by UX15 installed equipments
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
Heat sinks Toroids: -4.8W/m2 Thermal screens: Fixed temperature 18 °C sectors 03 - 07
Wheels Heat generation Small Wheels: 1 kW per side BW EO: 3 kW per side 2 BW TGC: 12 kW per side Inner detector and Calorimeters: Adiabatic BW MDT: 1.5 kW per side BW TGC: 5 kW per side
Barrel Heat Generation Outer Layer Medium Layer Inner Layer The model is ready for computation
Computation 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. 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
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= -9000 W Inlet Temperature= 17 °C ∆Flow Energy Outlet average Temperature= 22.4 °C 112 kW Flow rate = 60.000 m3/h = 17 kg/s Cp= 1006 J/kgK
Results – Velocity MapsZ Sections from C to A side The average velocity in the model is about 0.1 m/s
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
Hot spots in sector 13 • 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 Surface with splitters and PADs in M and O layer
Heat removed by the screens: -94 W Descending flow Average temperature on the outside surface of the screen: 19°C Thermal Screens act on the flow pattern
Big Wheels MDT Air flow reduced in the big wheel’s gap
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. From 3D to 2D model
Sector 10 2D simulation on Chambers Sector 09 Sector 05 • 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 12
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. 2D models use
Results from 2D Models / Example Simulation Temperatures are corrected by 3D simulation average temperature (air reference temperature ). In this case from 20°C to 22°C.
Expected Temperatures on Muons Chambers at 0.1m/s Chambers position
Expected Temperatures on Muons Chambers at 0.1m/s Chambers position
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
2D model with the worst air velocity conditions Chambers position
2D model with the worst air velocity conditions Chambers position
Temperature dependence on air flow With a flow between 0.01 and 0.1 natural convection drives heat transfer
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.
Sect 04 Sect 06 Sect 02 Sect 10 Sect 12 Sect 14 Back to 0.1 vel Back to min vel
Sect 05 Sect 09 Sect 01 Sect 13 Back to 0.1 vel Back to min vel
Heat transfer on PAD 0.06m 0.5m Sreal > Smodel ∆Treal< ∆Tmodel P= α∙∆T∙S α≈1W/m2K 2400[W/m3]∙0.5∙0.06∙ L=1∙∆T∙(2 ∙0.5 ∙L) ∆T=P/(α ∙S)=70K
