1.64 mm bore 1.0 mm-thick walls 4.0 mm channel Tapers up to 6.0 mm channel
Comments on Design 1 ProsCons Narrow cone protrudes and hence cools v. close to vane tip Nozzle separated from baffle can be easily replaced if broken Separate nozzle & baffle means either can be modified later Bolted-on nozzle would have a bit of play if slightly misaligned Hollow cone v. hard to make Tapered channel v. hard to drill Proximity to sides of vane 1mm hole could easily get blocked, eroded or misaligned Overly complicated water flow pattern around baffle
Squirt Nozzle Design 2 Objectives: Ease of manufacture Based on tried and tested designs More symmetrical flow pattern Analytically predictable High water velocity and HTCs at vane tip Sensible mass flow rate and pressure drop
Squirt Nozzle Design 2 Minor Vane as designed with bath milled into it.
Squirt Nozzle Design 2 Cover bath with an inlet/outlet plate.
Squirt Nozzle Design 2 Make a baffle, attached to the cover plate, to completely fill the bath. Note: baffle can be any shape we like to direct the water.
Squirt Nozzle Design 2 Cover Plate Baffle Vane Squirt Tube Tube Inserted 1cm into Baffle and Brazed in Place Water Final flow path of water: Inlet Nozzle inner Bottom of nozzle Nozzle outer Recombine Proceed along vane length.
Main Structures Used Coaxial Squirt Nozzle: Total flow length through outer annulus is 7 cm. Hydraulic diameter of annulus, D H = Do – D i = 7 – 6 = 1 mm. For estimated flow velocity in annulus of 5 m/s, this gives: Δp ≈ 0.34 Bar R e ≈ 5,500 HTC ~ 30,000 W m -2 K -1 Inlet and outlet Holes: Pipe diameter of 1 cm Flow area of 0.79 cm 2. If inlet velocity = 0.6 m/s Mass flow rate = 0.047 kg/s = 2.8 L/min. If power removed per channel = 1,562 W Water temperature rise ΔT ~ 8°C. Square Cross-Section Milled Main Flow Channel: Hydraulic diameter of 5 mm square pipe is same as circular pipe ∴ D H = 5 mm. For constant mass flow rate in all sections, expected flow velocity ≈ 2.4 m/s. For total milled length = 0.5 m, this gives: Δp ≈ 0.09 Bar R e ≈ 13,000 HTC ~ 11,500 W m -2 K -1 m. m. DHDH DoDo DiDi DHDH
Water Flow Velocity 4.96 m/s 1.98 m/s 0.039 kg/s in & out
Total Pressure Difference = 0.43 Bar ΔP = 0.04 Bar ΔP = 0.39 Bar Water Pressure
11,000 W m -2 K -1 39,000 W m -2 K -1 Water Heat Transfer Coefficient
Water Flow Streamlines Coloured By Water Temperature
Review of Results PropertyEstimated ValueANSYS CFD Value Mass Flow Rate 0.047 kg/s (2.82 L/min)0.039 kg/s (2.34 L/min) Water Velocity Nozzle5 m/s4.96 m/s Main Channel 2.4 m/s1.98 m/s Pressure Drop Nozzle0.34 Bar0.39 Bar Main Channel 0.09 Bar0.04 Bar Total0.43 Bar Heat Transfer Coefficient Nozzle~ 30,000 W m -2 K -1 ≈ 39,000 W m -2 K -1 Main Channel ~ 11,000 W m -2 K -1 ≈ 11,000 W m -2 K -1 Average Water Temperature Rise 8 °C7 °C
Potential Issues Fitting a 6mm tube into a 7mm hole with equal 0.5mm gap all round is difficult Does misalignment affect flow? Does it change nozzle’s ability to cool? Does it make a large pressure difference? In short, what are the tolerances?
Tube offset in position relative to hole in vane Resting flush against one side of hole Tube offset in angle relative to hole in vane Resting against both sides of hole Worst Case Misalignments
Other RFQs use many channels! Indian SNS: Six per quadrant American SNS: Four per quadrant Chinese SNS: Five per quadrant HINS (FNAL): Three per quadrant
Replace Distributed Channels With One Large Water Bath
Bath milled into vane from air side Plate bolted on to cover the bath and allow water in/out Baffle shaped to leave 2-3mm gap around edges of bath so the water flow is properly directed
One channel per quadrant Three channels per quadrant One bath per quadrant One directed-flow bath per quadrant
One channel per quadrant Three channels per quadrant One bath per quadrant One directed-flow bath per quadrant 32°C 29°C 34°C 31°C
Three channels per quadrant One directed-flow bath per quadrant A water bath with directed flow achieves very similar copper temperatures to a “normal” multiple-cooling-channel layout Novel Simple Effective BUT: There is always a variation of temperature (and hence copper expansion) along the vane length. How does this affect local E-fields? How does it affect beam dynamics? Do vane modulations complicate temperature distribution? What amount of growth is acceptable?
Summary Squirt nozzle idea borrowed from ISIS & SNS –Tried and tested design Whole system is outside vacuum –Easy to machine, maintain or modify Simulated flow rates, HTCs etc match predictions RFQ is well cooled at full RF power –But is it good enough from beam dynamics POV? Nozzle misalignments don’t affect performance Flow through different main channels tested –Directed bath performs as well as many channels