CO 2 return pressure drop budget and pipes from PP2 to tracker

1. Georg Viehhauser CO2 return pressure drop budget and pipes from PP2 to tracker

2. Do we have to watch the return line pressure drop? • Evaporation pressure set by accumulator • Remote in USA15 → need to offset return line pressure drops • Coolant temperature at pump given by condenser temperature • Needs to be lower than accumulator temperature (sub-cooled) for pump operation • In LHCb VELO system this is ΔT=15°C because of temperature control on primary heat sink • Finally, design evaporation temperature is -35°C and there is hard limit at around -55°C (CO2 freezing) • Put all this together: • Evaporation temperature at start of evaporator: -35°C • Evaporator and return line pressure drop equivalent to 10°C • Suggested split: 3°C+3°C+3°C evaporator/patch pipes to PP2/pipe PP2-USA15 (ΔT=3°C equivalent to Δp~1.3bar) • Accumulator at -45°C • Condenser at -50°C (sub-cooling ΔT=5°C) 2PACL Return line pressure drops

3. Health warning • Warnings: • All predictions depend on power (=mass flow) assumptions. These have large unknowns attached. Typically will look into worst case, with all safety factors included. • All numbers are from calculations, which need to be verified experimentally. Typically the highest pressure drops from different calculation methods have been used. • Calculations are for straight pipes, missing bends, fittings, etc.

4. Evaporator Driven by power in circuit • Strip stave: 5.12W/module + 10%(powering) + Psensor (short: 24 modules, long: 32 modules) • Pixel layer 3/4: 0.3W/cm2 + 10%(powering) + Psensor (48 4-chip modules) • Two cases: nominal and incl. safety (as before and ×2 for Psensor) + Δx (vapour quality difference): given by design. Assume here xin = 0, xout = 0.5 + allowed ΔT in evaporator: ΔT=3°C + 2-phase fluid dynamics calculations Range of diameters for different models NB: Models predict HTC from 5-6kW/m2K (start of strip stave) to 13-15kW/m2K (end of strip stave), or 7-8kW/m2K (start of pixel stave) to 16-19kW/m2K (end of pixel stave).

5. Pipes from detector to PP2 • Depend on manifolding, power per stave (different types), service organisation etc… Here only an indication of a plausible set of pipe dimensions • Looking at barrel strips, assumed manifolding 1:35 at PP2, approximately 1:4 inside tracker • Manifolding must take different mass flow in different systems into account, plus the overall service organization • Assume 1/16 service modules → 7 short and 8 long strip staves (layout dependent) per SM • Assume 2×2 and 1×3 short strips (at 230W/stave this is 690W, or 4.4g/s maximum (Δx=0.5) in manifold), and 1×8 for long strips (at 65W/stave this is 520W) • So, worst case is 1×3 manifold with 4.4g/s total flow. • Single stave flow to internal manifold: 3mm ID, 2.2m long (maximum from service module drawings): frictional Δp = 0.3 bar • Triple stave flow to end of service module/ITk: 5.65mm ID, 0.75m long (maximum from service module drawings): frictional Δp = 0.02 bar • Triple stave flow to PP2: 5.65 mm ID, 10m long (estimated, conservative as routing not yet known): frictional Δp = 0.33 bar • Total frictional Δp = 0.65bar • But: potentially hydrostatic pressure drop: for Δh = 5m Δp = 0.54 bar (pure liquid), so together Δp = 1.2bar, which is compatible with pressure drop budget. • NB1: Not all the diameters used here are compatible with standard diameters • triple flow pipe is for ¼”, but single pipe flow is not • There are advantages in standard dimensions, therefore might want to go to different ID (slightly smaller for OD3 (if final flow per stave is lower), or larger for OD4 (if maximum flow as used here) • NB2: For pixels flow in outer stave is potentially higher so OD4 might be required anyway, for long strips/EC petals flow most likely lower, so smaller ID possible

6. Where should be the joints? • Baseline is all welded connections inside tracker • Final in situ joint between staves and SMs by orbital TIG welding • Programme to verify that this is ok with electronics is under way – so far no indication that there is a problem • Programme to understand welding with different materials (Ti) and thin walls under way. Ti welds with 200μm seem no challenge, so that should be the target. • To facilitate this joint without requiring high precision in pipe end position plan to weld in short, intermediate pipe (~100mm), tailored in situ. So, two weld joints per connection. • Other welds inside could be any technology (also laser or EB) • First detachable joint on SM/ITk end: preferred industrial connector (e.g. VCR, ⅛” for feed, ¼” for return) • To save material and maintain weld joint simplicity all internal pipes will be Ti (pipes from ITk to PP2 st/st, so material break within VCR connection) manifolds Stave Service module OD ⅛”, t200? OD ?,t200 OD ?,t200 OD ?,t200 Capillary ID 0.65,t? OD ?,t200 OD ¼”, t400 OD 3 or 4, t200 OD 3 or 4, t200 OD 3 or 4, t200 OD 2.2 or close, t120 or 100 TE Final orbital TIG weld joints (with short patch pipes) QAed in situ VCR ¼” ⅛” TIG, EB or laser welded QAed before installation

7. Pipes – USA15 to PP2 • Exercise: Take LHCb VELO system (2kW)… • LHCb VELO: inner feed pipe (ID4, OD6), outer concentric return pipe (ID13, 55m long, mass flow typ. 12g/s, min. 5g/s) • … and scale to future ATLAS system (20kW): mass flow ×10, 100m (estimated) • Maintaining pressure drops • Feed: monophase (easy): 10.5mm ID for 0.12kg/s • Return: 2-phase (x~0.3-0.4) • LHCb: eq. diameter 11.5mm → calculate Δp=0.08-0.13 bar (different models) • Future system: Same pressure drop for eq. diameter of 31-34mm • My current estimate: • 1 Concentric pipe, inner feed pipe with ID12, OD14, and concentric outer return pipe with ID38, OD 42? per station (total 10 off) • Insulation • LHCb has 25mm Armaflex, probably not sufficient for ATLAS phase II (colder), but overall OD~100 probably not unrealistic • Other insulation technologies (vacuum insulation) might require less space. • In any case, return line pressure drop dominated by hydrostatic pressure (LHCb VELO: ~1bar), so routing is important. • These calculations come with the usual health warnings - need to be verified experimentally… • The introduction of 10 new pipes of OD100 appears possible • If concentric pipes with these dimensions are not feasible can have separate feed/return pipes (cold) and HEX at PP2 (probably more space required there) 7

8. Conclusions • Even with CO2 we have to be very careful with the evaporator + return line pressure drops • Available is a pressure drop equivalent to 10°C • Suggest to split this 3°C+3°C+3°C for evaporator/pipes to PP2/pipes to USA15 • A plausible set of pipe diameters has been discussed – should help guide various service studies • Final dimensions might be slightly different • Things we need to understand better: • Stave power, • Manifolding, • Service organization • Pipes on calorimeter endflanges (insulation, space, etc.)

9. Further material

10. Example: short strip stave (1.2m)

11. Example: short strip stave (1.2m)

12. Example: short strip stave (1.2m) Flow pattern map in Evaporator Evaporator

13. Example: short strip stave (1.2m)