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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 -30°C.

• 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

Sub cooling heat exchanger

Pressure regulators

Compressor Sub cooling evaporative unitBuffer tank

Condenser

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RAL Evaporative Cooling

AB

C

DE F

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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 speed=low mass flow=less 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- 20°C• 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