1. TS/CV/DC CFD Team CFD Study of the L3 Thermal Environment Sara C. Eicher www.cern.ch/cfd

2. THE PROBLEM Sara C. Eicher www.cern.ch/cfd ALICE requires stringent temperature conditions for adequate operation of the sub-detectors. Previous CFD studies were carried out to investigate different ventilation strategies inside the L3 magnet (EDMS 528133). Updated values of the heat generated inside the L3 volume requires further simulations.

3. OBJECTIVES Sara C. Eicher www.cern.ch/cfd To investigate the temperature distribution in the volume enclosed by the L3 magnet for a given ventilation configuration and under different heat dissipation loads.

4. THE CFD MODEL Sara C. Eicher www.cern.ch/cfd Only the air volume enclosed by the L3 magnet is modelled. The sub-detectors are assumed thermally neutral. Heat dissipation prescribed as heat fluxes at the surfaces of the sub-detectors °Magnet thermal screen and door defined as heat sinks at 20°C Ventilation configuration: 2 inlets at the bottom and one single outlet at the top (EDMS 528133). °Specified flow rate 6000m 3 /h of air at 20°C 3D, transient, non-isothermal simulation Natural convection dominant mode of heat transfer: ~6 vol/h

5. GEOMETRY & MESH Sara C. Eicher www.cern.ch/cfd Mesh containing around 500,000 trimmed, non-uniform cells Three cases studied: 1. Reference Case – 7.1kW 2. Casestudy 1 – 13.5kW 3. Casestudy 2 – 15.3kW

6. RESULTS – TEMPERATURE FIELD Sara C. Eicher www.cern.ch/cfd Reference Case 7.1kW ° Temp HS = 29°C ° Aver. Temp top = 23-24°C

7. RESULTS – TEMPERATURE FIELD Sara C. Eicher www.cern.ch/cfd Casestudy 1 13.5kW ° Temp HS = 36°C ° Aver. Temp top = 25-27°C

8. RESULTS – TEMPERATURE FIELD Sara C. Eicher www.cern.ch/cfd Casestudy 2 15.3kW ° Temp HS = 40°C ° Aver. Temp top = 27-29°C

9. RESULTS – TABLE OF RESULTS Sara C. Eicher www.cern.ch/cfdParameter Reference Case Casestudy 1 Casestudy 2 Hotspot Temperature, °C 293640 Temperature Difference Across TPC, °C 1-26-76-7 Extractor Temperature, °C 232627 Heat into Magnet, kW 0.81.82.1

10. CONCLUSIONS & FUTURE WORK CFD simulations predict, in all three cases, that nearly all heat generated within the volume is taken out by the ventilation system. Temperature gradients are still not within the desired limits. The simulations indicate that mixing within the volume is quite poor with maximum velocities in the order of those found in natural convection. Next step: to investigate ways of improving the mixing and hence even out the overall temperature inside the L3 envelope. Sara C. Eicher www.cern.ch/cfd

11. RESULTS – COMPARISON PLOTS Sara C. Eicher www.cern.ch/cfd Casestudy 2 15.3kW Casestudy 1 13.5kW Reference Case 7.1kW

12. RESULTS – COMPARISON PLOTS Sara C. Eicher www.cern.ch/cfd Reference Case 7.1kW Casestudy 1 13.5kW Casestudy 2 15.3kW

13. NATURAL CONVECTION Sara C. Eicher www.cern.ch/cfd Fluid motion occurs by natural means such as buoyancy. Associated with low velocities (<1m/s). h strong function of velocity so h NC << h FC. Buoyancy is the force associated with the upward movement of a lighter fluid. Its proportional to density which is proportional to temperature. Larger  T → Larger F B → Stronger Conv. currents → Higher HT rate. Grashof number: ratio of buoyancy to viscous forces. q=h.A.(T w -T  )