Cooling: CEDAR PMT & Electronics

Tim JonesLiverpool Group

PMT Array Cooling 2

Overview• Cooling System Parameters– Estimate Power Loads• Active components• Extraneous heat sources

– Develop methodology for exploring cooling system parameter space• Flow rate• Pressure drop• Pipe bores

• Control and Monitoring– Strategies– Implementation

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PMT Array Cooling 3

Cooling System Parameters• Working document - “Specifications for the

Cooling System for the NA62 CEDAR Kaon Tagger”

• Considers 2 sides as being separate sub-systems– Chiller/Heater– Interconnect pipe-work– Internal pipe-work, etc..

• System specification driven from a desired inlet-to-outlet bulk temperature rise

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PMT Array Cooling 4

Considerations• Desired temperature rise

and total power defines the mass-flow;– 1g/s cools 4.2W for 1C

• Mass flow, density and tube bore defines volume flow and velocity.

• Velocity defines Reynolds Number.

• Reynolds Number defines pressure drop and HTC

• HTC defines tube wall temperature

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PMT Array Cooling 5

Power Estimate (half unit)• FE

– 32 PMTs per array– 4 arrays per cooling circuit connected in series– 0.5W per PMT– 16W per PMT array, 64W for four arrays on one side

• Environment– Box dimensions 1.2(h) x 0.6(w) x 0.3(d).

• Area of 5 sides = 2.16sq.m

– Box insulation k=0.05 W.m-1.K-1

– Wall thickness 50mm– Assume external wall is at 30C and internal wall is at 20C– Power = 0.05 x 2.16 x 10 / 0.05 = 22W

• Total Power– 64 (FE) + 22(env) = 86W [Round this to 100W cooling power]15/03/2011

PMT Array Cooling 6

Pipe-work Geometry• External Interconnect– Flow and return lines 7m long with a bore of

12mm

• Internal– Heat exchanger: heated length 0.5m per array– Interconnect: 4m in total– Bore: sensible choices might be 4, 6, or 8mm

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PMT Array Cooling 7

System Properties• Volume Flow– Inversely proportional to desired temperature rise– Independent of tube bore– Flow = 1.54/T lpm

0 0.5 1 1.5 2 2.5 30.1

1.0

10.0

100.0

Inlet-to-outlet Temperature Rise (deg C)

Volu

me

Flow

Rat

e (lp

m)

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PMT Array Cooling 8

System Properties• Pressure Drop– Depends on fluid velocity (strong dependence on

tube bore)

0 0.5 1 1.5 2 2.5 30.00

0.01

0.10

1.00

10.00

4mm6mm8mm

Inlet-to-outlet Temperature Rise (deg C)

Tota

l Pre

ssur

e D

rop

(bar

)

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PMT Array Cooling 9

Draft Chiller Requirements

T rise 0.5deg C 0.25deg C 0.10 deg C

Bore 4mm 6mm 8mm 4mm 6mm 8mm 4mm 6mm 8mm

Flow 3.09 3.09 3.09 6.17 6.17 6.17 15.43 15.43 15.43

Pressure 3.52 0.55 0.17 11.8 1.83 0.57 58.8 9.13 2.83

• Tabulate Flow and pressure for different bores of the internal pipe work and desired temperature rise

• Chiller Specifications (preliminary web-trawl)

Model Power Flow (lpm @ 0 bar) Pressure (bar)Fryka DLK 402 380W @ 30C 4 0.15Grant RC350G 350W @ 20C 15 1.60 (@1 lpm)Neslab Thermoflex 900/P2 900W @ 40C 12.5 (@4.1 bar) 7 barJubalo FC600S 600W @ 20C 15 1.2Cole-parmer WU-13042-07 250W @ 20C 21 0.8Lauda WK 502 600W @ 20C 10 (@1.5bar) 2.2

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PMT Array Cooling 10

Chiller Parameters• Cooling Specification– Cooling Power (W)– Flow Rate (lpm)– Maximum Pressure (bar)

• Control– Set-point stability– Heater Power (W)– PID / remote control– Control Temperature (internal / external)

• Alarm signal (low flow, low level, ….)15/03/2011

PMT Array Cooling 11

Monitoring• DCS Monitoring

– ELMB (ATLAS) – quote from ELMB128 User Guide• “It should be usable in USA15 outside of the calorimeter in the area of

the MDTs and further out. This implies tolerance (with safety factors) to radiation up to about 5 Gy and 3·1010 neutrons/cm2 for a period of 10 years and to a magnetic field up to 1.5 T.”

• Automated reading, archival & presentation in central DCS

– Inputs• 128 floating input (2 wire) channels• Can be configured for DCV, Ohms…• Can be used in pairs for 4-wire RTD (PT100)

• DSS– Detector Safety System

• High level alarms relating to safety ONLY• Independent of DCS15/03/2011

PMT Array Cooling 12

Control• Issues

– Maintain the PMT arrays at a given temperature– Minimise the heat transfer between the box and the CEDAR

• Options1. Monitor the temperature of the PMT array and manually adjust

the set point of the cooling unit so that the global temperature of the electronics box is close to the CEDAR (hydrogen). Provide sufficient thermal insulation to minimise coupling between box and CEDAR.

2. Additionally, control the temperature of the cooling fluid using a feedback loop such that the temperature difference between the electronics box and the CEDAR is minimised. Provide sufficient thermal insulation to minimise coupling between box and CEDAR (hydrogen).

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PMT Array Cooling 13

Thermal Interfaces

• Heat Paths– Nitrogen enclosure/beam pipe/CEDAR– Environment/Support Tube/CEDAR– Environment/beam pipe/CEDAR

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PMT Array Cooling 14

Option 1

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PMT Array Cooling 15

Option 2

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PMT Array Cooling 16

Comments• Option 1:– Likely to need greatest number of interventions to

adjust Chiller PID controller– Needs Chiller with in-built heater– Needs high precision chiller set-point & stability

• Option 2:– Highest cooling power requirement– Need to develop fault tolerant PLC /heater sub-system

• We would most likely implement option 1 first as a prototype system before moving to option 2

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PMT Array Cooling 17

Further Thoughts about the Nitrogen Enclosure

• We want to optimise the nitrogen enclosure as follows:– Separate the 8 octants to enable the electronics in each to be

accessed without compromising the nitrogen environment of the others;

– Separate nitrogen feeds to each to enable faster flushing;– Minimise outlets to reduce sealing and gas-leakage problems by

routing cooling pipe-work externally;– Assure a nitrogen atmosphere close to the quartz windows.

• We envisage a cylinder, coaxial with the beampipe, as part of the support structure, with gas flow to the enclosures surrounding electronics in each octant. All will be enclosed within an insulated, protective cover.15/03/2011

PMT Array Cooling 1815/03/2011