M. Battistin (EN/CV/DC) 28 th May 2010

1. Detector Cooling Project III Thermosiphon Workshop-Back-up solutions to the ATLAS ID Thermosiphon: centrifugal compressors M. Battistin (EN/CV/DC)28th May 2010

2. Centrifugal oil free compressors • A market survey has been launched last summer to identify alternative compressors to Haug ones: • Labyrinth • Membrane • Oil free screw • Three main lines of investigation are now active: • Turbocor oil free magnetic bearing centrifugal compressor • McQuay oil free magnetic bearing centrifugal compressor • Another oil free gas bearing centrifugal compressor • The three possibilities are and will be investigated. All of them give some concerns.

3. Turbocor project • The most promising alternative to HAUG compressors is centrifugal compressors: • full oil free solution • high power density (one single machine could make the work the ID cooling needs) • High rotation speed (48 krpm) leads to an almost vibration less system • The cost of one of this compressor is about half of the Haug one. • Positive feed-backs form the market after about 10 years of industrial applications on fridge systems (mainly HVAC industry). “it is extremely reliable!!” • Hermetic compressor system guarantee high leak-tightness of the process. Mandatory feature to manage the activated fluid we will have in some year.

4. The Turbocor solution on paper • First calculations show that the smallest Turbocor compressor TT-300 (the one we have now) could manage 90% of the flowrate required by ATLAS ID cooling. Larger compressors are available from Turbocor (TT-400 and TT-550) and McQuay(from 1000 kW). • Discharge pressure will be most probably limited to 7-8 bara. The surface condensation will allow to gain the other 8-9 bar needed to feed the detector. 15th April 2010

5. Turbocor qualification process • Turbocor compressor has been designed to handle R134a, the standard fluid for refrigeration industry. This technology is less then 10 years old and is progressively conquering the market now. • Main parameters to consider for fluid change; • Compressor cooling: apparently R134a @ ≈+4°C, R218 @ ≈ -40°C? • Corrosion problems? • Material compatibility problems? • Control issues: shall we (you) modify the internal code? • Shaft forces check; • Critical components in case of fluid change; • Detailed Test Procedure; • The test of the compressors foresees many phases with different fluids (R134a, C3F8, blends) and will take many months to reach the full qualification. • The support of the design team would be extremely important… or even fundamental: what is the guarantee of a try and error process?? • Danfoss-Turbocor never answered… • We shall qualify this compressor with our gas (R218 = C3F8) • We have bought a test bench (see picture). • The system has been modified to test the compressor performances (new piping, pressure regulator and flow meter). • A test area has been set-up in SMI2 (close to 298). • Test procedure • No support from Turbocor • A list of problems:

6. …McQuay answered • McQuay compressors use the same technology of Turbocor. • The design offices worked together to develop Turbocor in ‘90. • McQuay launched more recently a series of larger compressors (more than 1 MW) using this technology. • McQuay Europe is qualifying this machines for the European power (50 Hz – 400 V) now. • We were searching for support from the design team: • Meeting with McQuayEurope in Rome on 22nd of April 2010. T. Watson (Chief Engineer of McQuay USA) and L. Paolella (General Manager of McQuay Europe). • T. Watson is verifying on paper the feasibility of this project. • The “stone-wall” condition could critical and could limit the maximal performances of the machine. • The control of the machine should be most probably modified: L. Sorabella (control specialist of McQuay could help on this point). • Meeting with Padova University on 26th of May (two days ago). Prof Zilio and Prof. Cavallini. • We are defining a three partners collaboration and identifying one resource dedicated to the compressor qualification project working in strict collaboration with CERN, McQuay (Italy and USA) and UniPadova. • Phone conference to be organized soon. P Stall Stone wall m’

7. Gas bearing oil free compressor • “It will be possible to design for above mentioned parameters as a one machine 1.2 kg/s which will be based on following components: • High speed asynchronous motor 33 kW / 65 000 rpm (rotor: diameter 66.6 mm, active length 105 mm, materials: heat treated carbon steel, Cu, Ti), stator: outer diameter 160 mm, air cooled. • Fully dynamic self acting radial & axial gas bearings (materials: Al alloy, heat treated carbon steel, graphite composite) • One stage working stage containing blades impeller D=68 mm / 65 000 rpm (material: Al alloy, outer body of the spiral case carbon steel) • Pressure body - galvanized carbon steel or Al alloy • Frequency converter (FC)” • We are organizing a technical visit to the supplier in the next 2 weeks. • Question marks: • Is that a brand new design? • Is the company solid enough (Haug II)? • We will start debugging it in few years? • …

8. Compressors project conclusions • Only centrifugal compressors give oil free guarantee and size • We have a Turbocor machine but we don’t have Turbocor support • We could have McQuay support but we don’t have McQuay machine • Many experts already warned us on the most critical points of the qualification process. • We need to identify one resource, already expert in turbomachinesthat could work 100% on this project in collaboration with CERN and the other partners.