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PMT Array Cooling
Tim
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
15/03/2011
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
15/03/2011
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
15/03/2011
PMT Array Cooling 5
Power Estimate• 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 40C and internal wall is at 20C– Power = 0.05 x 2.16 x 20 / 0.05 = 47W
• Total Power– 64 (FE) + 47(env) = 107W15/03/2011
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: 4, 6, 8mm
15/03/2011
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)
15/03/2011
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
)
15/03/2011
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
15/03/2011
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– Control the heat transfer between the box and the CEDAR
• Options1. Control the PMT array temperatures such that the global temperature of the
box is close to the CEDAR. Provide sufficient thermal insulation to minimise coupling between box and CEDAR.
2. Monitor the CEDAR temperature and control the temperature of the PMT arrays such that the temperature difference between the box and the CEDAR is minimised.
3. Control the PMT array temperatures such that the global temperature of the box is just below the CEDAR. Provide an ACTIVE thermal enclosure between the box and the CEDAR and control the temperature on the CEDAR side to minimise heat flow.
• Need more engineering input to define interfaces between CEDAR and box15/03/2011
PMT Array Cooling 13
Thermal Interfaces• For Option 1 and Option 3 - need to consider
Thermal Interfaces– Option 1: Passive thermal interfaces between PMT
array box and CEDAR• Control of thermal exchange between box and CEDAR
would have to be through adjusting the set-point on the chiller PID
– Option 3: ACTIVE Thermal Interfaces between PMT array box and CEDAR• Control of thermal exchange between box and CEDAR
would be through regulation of the power to the heaters o the active thermal enclosure.
15/03/2011
PMT Array Cooling 14
Thermal Interfaces
• Heat Paths– Box/beam pipe/CEDAR– Box/Support Tube/CEDAR (is steel the right material?)
• NB– Option 3 heat generated on CEDAR side of thermal enclosures will need to be
absorbed by the cooling system15/03/2011
PMT Array Cooling 15
Option 1
15/03/2011
PMT Array Cooling 16
Option 2
15/03/2011
PMT Array Cooling 17
Option 3
15/03/2011
PMT Array Cooling 18
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
• Option 3:– Chiller may not need in-built heater– May allow low precision chiller set-point & stability– Complete segmentation of control sub-systems– Needs detailed engineering analysis / design & manufacture of active
thermal enclosure15/03/2011