Issues about the full scale thermosiphon (TSP )

1. Issues about the full scale thermosiphon (TSP ) D. Giugni Thermosiphon Review III, May 28th 2010 Thermosiphon Review III, May 2010

2. General • The R&D on the thermosiphon and the solution that we are discussing today aims to: • Replace the actual compressors system with a gravity driven system (TSP) that has no any mechanical active component in the main refrigerant loop. The complexity (chiller) is moved to the surface and the equipment disentangled from the C3F8 (see next slides for further comments). • Increase significantly the reliability solving the vibration problems and the associated failure modes: • Welds a/o mechanical failure in the compressors or in the surrounding piping • Sealing failure: leaks! • Compressor valve failures • Component failures (pressure gages, actuator etc). Thermosiphon Review III, May 2010

3. General (2) Following a staged approach, two are the “design” goals: • Provide a plant that replaces the compressors considering, as design baseline, the same thermodynamic parameters of the actual plant: • Pressure after the BPR (streamwise) < 800mbara (nominal 750) • Flow rate/Cooling power: 1.13kg/s | 62.4 kW • Provide a plant that can easily manage different fluid without requiring complex and tricky adaptations: • C3F8/C2F6 mixtures IMPORTANT NOTE Case (1) allows to solve the reliability problems only . It will be a vibration-free system BUT it will not be able to decrease significantly the evaporation temperature on the SCT boiling channel. In fact this is driven by the pressure drop in the exhaust lines before (streamwise) the BPR . Unfortunately this is “built in” the detector. The temperature gain is modest: ~4/5 C due to the slightly lower pressure after the BPR. Case (2) allows to decrease considerably the evaporation temperature. Compared to what we have now in the SCT the gain can easily be >> 10C as long the chiller can provide the required power at the requested temperature. Thermosiphon Review III, May 2010

4. Qualification path • The mini-TSP has validated the concept. We learned much and we convinced ourself that it can work. It gave us the confidence that the cost of the PX15 TSP is well justified. We rally want to proceed. • The PX15 TSP will provide us the ultimate thermodynamic parameters to design the full scale one. It allows to measure the time characteristics and performances with the C3F8 and mixtures. • Let us now look at what are the issues related to the full scale TSP. Thermosiphon Review III, May 2010

5. TSP (the big one) 200KW pixel 6 X SCT BPR PR Thermosiphon Review III, May 2010

6. Issues and arguments • Reliability Preliminary tests with the mini-TSP leads to think that the reliability of such a system is definitely very high. The PX15 TSP will provide the results on the long test run. • Cleanliness and tightness The technology of the system allows to reach very high standards: high vacuum flanges, SS piping and TIG welding. • Energy efficiency The COP of the TSP is intrinsically low. Most of the inefficiency is due to the need to warm up the feeding line to ambient temperature before sending the fluid into the detector (no insulated lines.). A compressor based system is more efficient since the condensation takes place above the room temperature and the fluid does not need to be re-heated again. Nevertheless I would like you to focus on the overall limited amount of power required: 200kW at the end of the detector life including a robust safety factor Thermosiphon Review III, May 2010

7. Issues and arguments (2) • Operational conditions: Start-up, recovery, etc Some important indications came out already from the mini-TSP test. • Indicative cool down time • Parameters to control for a stable operation • Procedure for the warm and cold re-start More solid indications will come from the PX15 TSP which is now required to tune up the design of the full scale one. However the preliminary results leads to exclude showstoppers. • Mixtures The tests with blends will go both on the detector side (blends test in SR1) and on the plant side (with the PX15 TSP). The first one, based on a compressor system, will let to evaluate the thermal performances of the blends in the actual detector structures. The second will allow to define the protocols for running the TSP with blends: monitor and control the mixture ratio. Thermosiphon Review III, May 2010

8. Issues and arguments (3) • Chiller This equipment is not a minor issue. A 200kW chiller @ -60/-70C with the required redundancy is a wide and costly installation (see next talk) ... but it is: • Industrial standard and rather common. • It is located on surface. Easy to access, to service and to repair. The specs on the chillers have been set to: • Replace the actual plant (no T evap decrease) 200kW @-60C • Decrease the evaporation T by >10 C (SCT request) 200kW @-70C The temperatures are meant to be the minimum temperature of the brine of the chiller. It has an headroom of few degrees. Potentially we might relax the spec using a direct evaporation in the condenser but it would not be favourable for potential contamination in case of failure of the heat exchanger. Actually planned to use C6F14. Thermosiphon Review III, May 2010

9. Issues and arguments (4) CHILLER (cont’ed) • The impact of such an installation on the surface has not been looked into details yet. • Plan foresees to come up with a lay-out within this year. Major aspects to evaluate are: • Size and space compatibility. • Redundancy level / reliability / maintenance plan. • Delivery time. • Cost vs. the various options. Mainly vs. the required evaporation T in the SCT boiling channel. • I know someone is sceptic but I do not really see what there is “a priori” wrong with such a system. • The size can be negotiated and the lay-out can be adapted to the morphology of the space available. • The plant cost can be reduced balancing it with the contamination risks (in HeX evaporation) • The technology is well proven and reliable. It is really industrial business. Thermosiphon Review III, May 2010

10. Conclusions • Not only TSP! As already said this group is looking at different solutions: • Increase the reliability of the actual plant ... • Centrifugal oil-free compressors (Turbocor, McQuay and others) • Fluid-dynamic in the high speed impellers is very dependant upon the fluid. Very difficult to predict and evaluate. Also potentially unsafe for the compressor. • Fluid-impeller tips impact is controlled by a deflection valve that must be optimized for the new fluid. • Motor cooling is an issue with different fluids (C3F8 and mixtures). we are hardly working on this, but it is not straightforward. • At the moment the TSP is the most advanced and developed solution to replace the actual system. Within 2010 the PX15 TSP will provide the final answers about chiller, reliability, mixtures and performances allowing us to design properly the full scale TSP. • So please, look at what we have now, trying to resist to drop what is not the “optimum” in favour of something that does not exist yet. Thermosiphon Review III, May 2010

11. Backup Slides Thermosiphon Review III, May 2010

12. C3F8 P-H for TSP