CFD Simulations of a Novel “Squirt-Nozzle and Water Bath” Cooling System for the RFQ

CFD Simulations of a NovelSquirt-Nozzle and Water Bath Cooling System for the RFQ

Vacuum Pump FlangeVacuum Flange Coolant ManifoldWater Baths Milled Into VanesPotentially Bolted TogetherTuner & Coupler PortsVanes

Vane Cut-BackVane EndWater Bath Shaped to Follow Vane Cut-BackTuner & Coupler PortsO-Ring Joint to Mount to End Wall

Temperature vs. Input PowerOuter WallVane Tip

Total Heat Load on Walls = 1 MWWater-bath Heat Transfer Coefficient = 3000 W m-2 K-1 Thermal Solver SolutionTemperature / CReally need to directly cool the vane tips!

Squirt Nozzles

Squirt Nozzle InsertedSquirt Nozzle HTC: 0 Wm-2K-1Input Power: 500 kW

Water bath HTC: 1000 Wm-2K-1Tuner, Coupler & Vacuum Port HTC: 3000 Wm-2K-1Input Power: 500 kWVariation with Squirt Nozzle HTC

Are these HTCs Achievable?Water bath HTC: 1000 W m-2 K-1Squirt Tube HTC: 3000 W m-2 K-1

How to Manufacturea Squirt Nozzle

Squirt Nozzle Design 1

Squirt Nozzle Design 11.64 mm bore1.0 mm-thickwalls4.0 mm channelTapers up to6.0 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 2Objectives:Ease of manufactureBased on tried and tested designsMore symmetrical flow patternAnalytically predictableHigh water velocity and HTCs at vane tipSensible mass flow rate and pressure drop

Squirt Nozzle Design 2Minor Vane as designed with bath milled into it.

Squirt Nozzle Design 2Cover bath with an inlet/outlet plate.

Squirt Nozzle Design 2Make 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 2Close up of baffle.

Squirt Nozzle Design 2Mill a 5mm square channel along the baffles length.

Squirt Nozzle Design 2Mill up the side as well.

Squirt Nozzle Design 2Top view, with finished channel carried up to inlet/outlet hole in cover plate.Note: baffle could be any shape, so overhang on end is not necessary.

Squirt Nozzle Design 2View into bath in the vane.

Squirt Nozzle Design 2Drill 7mm diameter hole down into vane toward its tip.

Squirt Nozzle Design 2Fit 6mm outer diameter tube into hole to make the squirt nozzle.

Squirt Nozzle Design 2Side view of squirt nozzle inserted into vane.Hole drilled only as far as will allow a minimum of 1mm clearance all round.

Squirt Nozzle Design 2Underside of baffle where squirt nozzle will be inserted.

Squirt Nozzle Design 2Drill 6mm diameter hole into baffle. I.e. same O.D. as squirt nozzle.Nozzle will be brazed into this hole. Drill 1cm deeper than nozzle will extend.

Squirt Nozzle Design 2Nozzle inserted into vane and baffle.

Squirt Nozzle Design 2Need a way to fill inside of nozzle and allow water to leave the outside, but keep these areas physically separate.

Squirt Nozzle Design 2Close up of where nozzle will eventually go in the baffle. See also the milled channel to the right.

Squirt Nozzle Design 2Mill another block out to allow water flowing around outside of nozzle to recombine before proceeding down main channel.

Squirt Nozzle Design 2Nozzle now needs a way to be filled from the inside.

Squirt Nozzle Design 2Drill 5mm diameter hole in to meet the 1cm gap left at top of nozzle. Mill inlet channel to meet this hole. Nozzle inner can now be filled.

Squirt Nozzle Design 27mm6mm0.5mm62mm

Squirt Nozzle Design 2Cover PlateBaffleVaneSquirt TubeTube Inserted 1cm into Baffle and Brazed in PlaceWaterFinal flow path of water: Inlet Nozzle inner Bottom of nozzle Nozzle outer Recombine Proceed along vane length.

Predicting andSimulating the Flow

Flow Equations Used

Main Structures UsedCoaxial Squirt Nozzle:Total flow length through outer annulus is 7 cm. Hydraulic diameter of annulus, DH = Do Di = 7 6 = 1 mm.For estimated flow velocity in annulus of 5 m/s, this gives:p 0.34 Bar Re 5,500 HTC ~ 30,000 W m-2 K-1Inlet and outlet Holes:Pipe diameter of 1 cm Flow area of 0.79 cm2.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 T ~ 8C. Square Cross-Section Milled Main Flow Channel:Hydraulic diameter of 5 mm square pipe is same as circular pipe DH = 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:p 0.09 Bar Re 13,000 HTC ~ 11,500 W m-2 K-1

Water Flow Velocity4.96 m/s1.98 m/s0.039 kg/s in & out

Total Pressure Difference = 0.43 BarP = 0.04 BarP = 0.39 BarWater Pressure

11,000 W m-2 K-139,000 W m-2 K-1Water Heat Transfer Coefficient

Copper Temperature

Water Flow StreamlinesColoured By Water Temperature

Review of Results

PropertyEstimated ValueANSYS CFD ValueMass Flow Rate0.047 kg/s (2.82 L/min)0.039 kg/s (2.34 L/min)Water VelocityNozzle5 m/s4.96 m/sMain Channel2.4 m/s1.98 m/sPressure DropNozzle0.34 Bar0.39 BarMain Channel0.09 Bar0.04 BarTotal0.43 Bar0.43 BarHeat Transfer CoefficientNozzle~ 30,000 W m-2K-1 39,000 W m-2K-1Main Channel~ 11,000 W m-2K-1 11,000 W m-2K-1Average Water Temperature Rise8 C7 C

Nozzle Misalignment

Potential IssuesFitting a 6mm tube into a 7mm hole with equal 0.5mm gap all round is difficultDoes misalignment affect flow?Does it change nozzles 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 holeWorst Case Misalignments

Scenario 1: Position Offset

Scenario 2: Angle Offset

Main Cooling ChannelAlong the Vane Length

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

Replace Distributed Channels With One Large Water BathBath milled into vane from air sidePlate bolted on to cover the bath and allow water in/outBaffle shaped to leave 2-3mm gap around edges of bath so the water flow is properly directed

One channel per quadrantThree channels per quadrantOne bath per quadrantOne directed-flow bath per quadrant

One channel per quadrantThree channels per quadrantOne bath per quadrantOne directed-flow bath per quadrant32C29C34C31C

Three channels per quadrantOne directed-flow bath per quadrantA water bath with directed flow achieves very similar copper temperatures to a normal multiple-cooling-channel layoutNovelSimpleEffectiveBUT: 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?

SummarySquirt nozzle idea borrowed from ISIS & SNSTried and tested designWhole system is outside vacuumEasy to machine, maintain or modifySimulated flow rates, HTCs etc match predictionsRFQ is well cooled at full RF powerBut is it good enough from beam dynamics POV?Nozzle misalignments dont affect performanceFlow through different main channels testedDirected bath performs as well as many channels

Questions?

Extra Slides

Flow Velocity (m/s)

Water Temperature (K)

Heat Transfer Coefficient for Different Sized Pipes127 l/min!11.8 l/min0.012 l/min0.07 l/min1.5 l/minHTC / Wm-2K-1Turbulent Flow

CFD Mesh Used

Eigenmode SolverSurface H-Field Results

Structural DeformationLongitudinal Displacement / mmVertical Displacement / mmVanes move toward each other by ~30 m. Walls move outward by ~150 m.Vane ends move toward end wall by ~300 m.

Frequency Shift vs. Input Power

CFD Simulations of a Novel “Squirt-Nozzle and Water Bath” Cooling System for the RFQ

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