1. Cryogenic Engineering, CERN, March 2004 Cryogenic Engineering CERN, March 8 - 12, 2004 Temperature reduction by throttling and mixing Temperature reduction by work extraction Refrigeration cycles: Efficiency, compressors, helium, hydrogen Cooling of devices

2. Cryogenic Engineering, CERN, March 2004 cold Process running by itselfProcess needing driving power Mankind had an intellectual difficulty with the production of refrigeration: We could not learn it from nature. The problem: One has to add energy to remove energy.

3. Cryogenic Engineering, CERN, March 2004 cold Where should the outside power be applied Solution: One needs an additional sytem: The refrigerator

4. Cryogenic Engineering, CERN, March 2004 Refrigeration cyle Refrigerant Method to increase pressure Method to reduce entropy Method to reduce the temperature Method to transfer the refrigeration Recuperation T-s Diagramm Flow Diagram

5. Cryogenic Engineering, CERN, March 2004 Tw Tc T S T S Tw Tc isentropic adiabatic Cooling power Widen the low-temperature end of the cycle as shown in the T-S diagram Work IdealReal  S1  S2 AB CD AB C D

6. Cryogenic Engineering, CERN, March 2004 Compressor and Aftercooler Purpose: Increase the pressure and reduce entropy Types of compressors Volumetric compressors: piston, screw Turbocompressors

7. Cryogenic Engineering, CERN, March 2004 Piston compressor Oilfree labyrinth piston compressors. Preferred by CERN until about 1980.

8. Cryogenic Engineering, CERN, March 2004 Screw Compressor Oil flooded screw compressor preferred at CERN since about 1985.

9. Cryogenic Engineering, CERN, March 2004 Screw compressor principle

10. Cryogenic Engineering, CERN, March 2004

11. Screw Compressor Installation

12. Cryogenic Engineering, CERN, March 2004

16. The four-stage LHC cold compressors 1 st stage Cold Compressor Cartridges of 2.4 kW @ 1.8 K Refrigeration Units IHI-Linde Cold compressor impeller

17. Cryogenic Engineering, CERN, March 2004 Isentropic Efficiency of Cold Compressors

18. Cryogenic Engineering, CERN, March 2004 Flow Compliance of “Mixed” Compression N2 N3 Stall line Choke line Volumetric P inter Flow P out (fixed) P inter P in (fixed) Hydrodynamic Volumetric For fixed overall inlet & outlet conditions, coupling of the two machines via P inter maintains the operating point in the allowed range N1 Flow (variable)

19. Cryogenic Engineering, CERN, March 2004 How to evaluate efficiency and to identify losses When discussing expanders, we shortly talked about reversibility In power engineering there is always a best method to do something, i. e. no unnecessary losses = reversibility Losses can be idebtified by the deviation from reversibility Comparison is the input power We have to give refrigeration a value in the scale of the input power Carnot ratio

20. Cryogenic Engineering, CERN, March 2004 The definition of exergy Minimum amount of work to produce refrigeration Exergy= Mimimum Power= Q*(T a -T 0 )/T 0 Minimum amount of power to change the state of a fluid from an initial state 1 to a final state 2: e 2 -e 1 = h 2 -h 1 + T a *(s 2 -s 1 )

21. Cryogenic Engineering, CERN, March 2004 Cycle for liquefaction of hydrogen The Exergy Mountains Prometheus (prehistoric) Minimum Power to obtainHeating or Cooling (W/W)

22. Cryogenic Engineering, CERN, March 2004 Specific exergy of cold copper and helium

23. Cryogenic Engineering, CERN, March 2004 Stored exergy in the cooled-down LHC

24. Cryogenic Engineering, CERN, March 2004 Helium is recovered from natural gas

25. Cryogenic Engineering, CERN, March 2004

27. Development of the size of helium refrige- rators and liquefiers in the last century.

28. Cryogenic Engineering, CERN, March 2004 C.O.P. of Large Cryogenic Helium Refrigerators

29. Cryogenic Engineering, CERN, March 2004

32. History of gas liquefaction

33. Cryogenic Engineering, CERN, March 2004 History of use of liquid hydrogen Hydrogen Bomb Heavy Water Commercial Supply Rockets Cold Neutron Source Bubble Chambers

34. Cryogenic Engineering, CERN, March 2004

36. Liquid Hydrogen Fuelled Rocket

37. Cryogenic Engineering, CERN, March 2004 BEBC (Big European Bubble Chamber at CERN)

38. Cryogenic Engineering, CERN, March 2004 Liquid Hydrogen Fuelled Car

39. Cryogenic Engineering, CERN, March 2004

40. Liquid hydrogen tank in car

41. Cryogenic Engineering, CERN, March 2004 Hydrogen

42. Cryogenic Engineering, CERN, March 2004 Future Large Scale Hydrogen Liquefier Expected Efficiency: 60 % of Carnot 7 kWh/kg LH2