RAL Evaporative Cooling

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RAL Evaporative Cooling

• UK-V Meeting, RAL
• Wednesday 30th January
• Julia Easton
• Talk given by Richard Apsimon

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RAL Evaporative Cooling

• Evaporative cooling system for testing ATLAS
  structures here at RAL
• You have to cool 132 modules on a disk
• The unit uses C3F8 refrigerant and should
  provide about 500W of cooling at -30C.
• The same plant will be used for disk and barrel
  cooling units.
• We will also need a cleaning plant that will
  circulate heated refrigerant liquid through the
  pipes.

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RAL Evaporative Cooling

Condenser
Pressure regulators
Sub cooling heat exchanger
Compressor
Sub cooling evaporative unit
Buffer tank
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RAL Evaporative Cooling

B
A
E
F
D
C
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RAL Evaporative Cooling

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Evaporative Cooling Cycle

• Vapour is compressed pseudo-isentropically from
  1.5 to 9 bar (A - B)
• Vapour is condensed at constant pressure,
  returning to the liquid phase. (B - C)
• It is then sub-cooled, using another evaporative
  system. (C - D)
• Pressure reduced at constant (ish) enthalpy by
  throttling. (D - E)
• Heat removed from stave by evaporating the
  refrigerant (E - F)
• Finally, there may be some heating (at constant
  pressure) to ensure that no liquid returns to the
  compressor. (F - A)

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Evaporative Cooling in Practice

• We are aiming to take full advantage of the
  latent heat of vapourisation of the liquid
  refrigerant.
• Measure the temperature at the inlet to the
  staves, the evaporation temperature, and at the
  end of the staves.
• The temperature difference across the staves
  tells us if we have too much or too little
  refrigerant flow through the system. This flow
  is currently regulated by hand at the inlet to
  the capillaries.
• A rise in temperature between F and A tells us
  that there is no more liquid to evaporate.
• A PID controller varies the compressor speed and
  sets the inlet pressure to the compressor to
  maintain the evaporation pressure

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Some facts

• All components are standard.
• The compressor is oil-free and can work at low
  speed without overheating too much. (Low
  speedlow mass flowless cooling)
• The system cost SFr23000 and capacity could be
  doubled with a 2nd compressor. There is room to
  fit one.
• One compressor needs 3 l/min cooling water at
  around 15- 20C
• An 8 litre buffer tank is used, this allows
  cooling over long distance.
• The frost free freezer, to house the
  sub-cooling was bought in Germany. Not available
  in UK, France or Switzerland
• C3F8 is expensive! Smallest cylinders are 60kg
  and cost 30/kg
• Due to their high global warming potential and
  long atmospheric lifetimes, PFC are now included
  in the Kyoto Protocol framework. Therefore COSHH
  risk assessments.

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Some other points

• Need suitable scales to weigh the cylinder 100kg
  x 50gm
• Also need an oil free vacuum system. We are
  buying a turbo- molecular pump with scroll
  backing pump.
• Cooling units need cleaning. CERN use GALDEN SV90
  from Ausimont. This also costs 30/kg but it
  comes in 7kg packs.
• Julia thinks this should be preceded by a
  degreasing agent, IPA
• The benefit of having a unit built at CERN is
  that you only pay component costs, manpower is
  free. They should have a reasonable level of
  expertise, since they have built a few systems.
• For more information, contact Julia Easton or
  Lewis Batchelor