1. CERN Cryolab CO 2 cooling for pixel detectors Investigation of heat transfer Christopher Franke, Torsten Köttig, Jihao Wu, Friedrich Haug TE-CRG-CI

2. 2 Content: Objectives of the study Objectives of the study Test setup Test setup Measurement conditions Measurement conditions Investigation tube diameter Investigation tube diameter Summary Summary

3. Objectives of the study Experimental verification of 2-phase CO 2 flow regimes and stability criteria of CO 2 flow in minichannels suitable for cooling of the upgraded pixel detector of CMS. Establish a rather comprehensive experimental database in the range of relevant mass flux and heat flux α = f(x,q,G,T sat ). Validation of existing correlations for heat transfer coefficient and pressure drop. If necessary, adapt exisiting correlations to the database at the range of interest.

4. 4 Test setup 8 Cooling cycle schematic and log(p)-h diagram

5. 5 Test setup Piping and Instrumentation Diagram

6. Operating temperatures -40°C to -5°C Mass flow up to 1.5 g/s Heat flux at test section up to 30 kW/m² Tube diameter (test section) up to 2.0 mm Design pressure of the setup 100 bar Cooling power Pulse Tube Cryocooler 150W@225K Insulation vacuum 5 ⋅ 10 -5 mbar Test setup

7. 7 flow direction Stainless steel Stainless steel Length of the actual test section (heated part) Length of the actual test section (heated part) l = 0.15 m Inner diameter d i = 1.4 mm Inner diameter d i = 1.4 mm Wall thickness s = 120 μm Wall thickness s = 120 μm Max. heat flow Q TS = 30 W Max. heat flow Q TS = 30 W

8. 8 Test setup

9. 9

10. 10 Measurement conditions 1. Saturation Temperatures: Change in saturation temperature causes a change of the fluid properties which on the other hand influence the flow pattern and heat transfer coefficient respectively! Following fluid properties are used for calculation: Desity ρ (liquid and gas phase) Desity ρ (liquid and gas phase) Dynamic viscosity η (liquid and gas phase) Dynamic viscosity η (liquid and gas phase) Surface tension σ (liquid phase) Surface tension σ (liquid phase) Latent heat of vaporisation h LV Latent heat of vaporisation h LV Proposed temperature levels for measurement: ϑ Sat [°C] -5-10-12-15-20-25-30 T Sat [K] 268,15263,15261,15258,15253,15248,15243,15

11. 11 Measurement conditions 1. Saturation Temperature: temperature in °C surface tension in N/m ΔT = 25 K Δσ = 5,4E-3 N/m

12. 12 Measurement conditions 2. Mass flow (density): Change in mass flow m and mass flow density G respectively influences the flow pattern which on the other hand determine the heat transfer coeffincient! Proposed mass flow (density) steps for measurement: G [kg/m²s] m [mg/s] 75132,5 150265,1 300530,1 450795,2 6001060,3 7501325,4 9001590,4

13. 13 Measurement conditions 2. Mass flow (density):

14. 14 Measurement conditions 3. Heat flux test section: Change in heat flux and influences the quality factor where dryout occure. Proposed heat flux levels for measurement: Q TS [W] q TS [kW/m²] 0,50,66 0,751,00 1,01,33 1,251,99 2,03,89 4,15,44 There are 2 theoretical heat flux thresholds: 1. Onset of nucleate boiling q ONB = 1 kW/m² (VDI Wärmeatlas) 2. Critical heat flux q crit = 794 kW/m² (S.S. Kutateladze) Q TS [W] q TS [kW/m²] 7,09,28 10,013,26 20,026,53

15. 15 Measurement conditions 3. Heat flux test section:

16. 16 Measurement conditions Due to CMS requirements of 150W@5.5m (4.1W@0.15m) at - 12°C, tube diameter 1.4 mm the following measuring plan is proposed. 7x 9x 4 (7) 0,05 ≤ x ≤ 1 Δx ≈ 0,025 = 252 (441) cases T Sat [K] 268,15 -263,15 261,15 -258,15 253,15 -248,15 243,15 Q TS [W] 0,5 0,75 1,0 1,25 2 4,1 7,0 10,0 20,0 G [kg/m²s] 75 150 300 450 600 750 900

17. 17 Investigation tube diameter

18. 18 Investigation tube diameter

19. 19 Investigation tube diameter Inner diameter (average)lowhigh Sample 1 1,4201,3971,442mm Sample 2 1,4331,4101,455mm Sample 3 1,4211,3971,445mm Average (1,2 & 3) 1,424mm Wall thickness (average)lowhigh Sample 1 119,9118,4121,3μm Sample 2 115,4114,3116,4μm Sample 3 117,8117,2118,4μm Average (1,2 & 3) 117,7μm Inner diameter Wall thickness

20. 20 Summary ➡ Test session for 1.4 mm inner diameter tube in horizontal orientation (according to CMS requirements) ➡ This results an outcome of 252 (441) cases α = f(x) ➡ Good database for comparison with existing flow maps ➡ Good database for comparison with existing calculation models for heat transfer coefficient ➡ Extensive commissioning and validation of the setup