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Cryocoolers: Thermodynamic Principle, Limitations, Vibration, and Noise

This article explores the introduction to cryocoolers, the thermodynamic principle behind their operation, the limitations of their cooling performance, and the issues of vibration and noise. It also includes a comparison of different cryocooler types and concludes with an overview of maintenance requirements.

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Cryocoolers: Thermodynamic Principle, Limitations, Vibration, and Noise

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  1. Contents • 1 Introduction to cryocoolers, • 2 The thermodynamic principle, • 3 Limitation of the cooling performance, • 4 Vibration and noise level, • 5 Comparison and conclusions.

  2. Introduction

  3. Introduction Generation of low temperatures using cryocoolers allows: - Independency of cryogenic liquids, - Flexibility (only electrical power), - Indipendent from orientation comparing to normal cryostats, - Low-maintenance (12,000 h). • Problems: • Mechanical vibrations, • Temperature oscillations, • Electromagnetic noise. Research and development of cryocoolers

  4. Cooling process: = × + j V V ( 1 cos )/2 0 C = + V V V 0 C W = × - × j p p ( 1 a cos ) m ò & = × Q ν p dV C Thermodynamic principle Position Piston VC Additional phase shift between p and VC is necessary. Tw Tc Regenerator temperature

  5. Thermodynamic principle Low temperature regeneration Active type of phase shifting using two needle valves at the warm end of the PT

  6. Limitation of cooling performance Limitations of the cooling performance Limiting factors to reach low temperatures: Refrigeration process: Volumetric heat capacity: with T CReg CFl , Pressure drop in the regenerator matrix, Incomplete heat transfer between fluid flow and regenerator, Residual heat loads.

  7. Volumetric heat capacity in J/cm3 K Comparison He – Standard materials Helium 1 MPa Helium 2 MPa Lead Stainless St. Bronze Temperature in K * Arp, Thermophysical Prop. 4He, R. Radebaugh, NIST, Boulder, WADD Technical Report NBoS.

  8. Rare earth compounds R. Radebaugh, NIST, Boulder

  9. Coaxial, Single-stage Pulse Tube Refrigerator Valve- unit Cooling capacity in W Pulse tube & Stainl. Steel + Lead εPb = 0.39 Stainl. Steel + Lead εPb = 0.43 Stainl. Steel mesh ε = 0.57 Cold tip temperature in K Cold tip Pein 6,2 kW, p=1,60 MPa. T. Koettig, et al., Advances in Cryogenic Engineering, Vol. 51A, (2006), pp. 35-40.

  10. Coaxial, two-stage Pulse Tube Refrigerator T. Koettig, S. Moldenhauer, R. Nawrodt, M. Thürk and P. Seidel, Two-Stage Pulse Tube Refrigerator in an Entire Coaxial Configuration, Cryogenics, 46 (2006), pp. 888-891. 0,1 m

  11. Coaxial, two-stage Pulse Tube Refrigerator Cold tip temperature 2nd stage in K Pel = 6.2 kW, pfill=1.60 MPa. Cold tip temperature 1st stage in K T. Koettig, et al., Cryogenics, 47, 2007, pp. 137-142.

  12. Mechanical vibrations and temperature oscillations Limitations of the cooling performance Vibration and noise level: • Mechanical vibrations at the cold head, • Temperature oscillations, • Electromagnetic noise.

  13. Pressure oscillations in a two-stage PTR

  14. Mechanical vibrations

  15. Mechanical vibrations and temperature oscillations Vibrations and noise level: • Mechanical vibrations at the cold head, • Temperature oscillations, • Electromagnetic noise.

  16. Temperature oscillations

  17. Temperature 2nd stage [ K ] Time Temperature oscillations T - sensor Lakeshore Cernox ΔT=± 200 mK at 5.7 K

  18. Mechanical vibrations and temperature oscillations Vibrations and noise level: • Mechanical vibrations at the cold head, • Temperature oscillations, • Electromagnetic noise.

  19. 300 K flange Stainless Steel Regenerator 1st stage Lead spheres Er3Ni Regen. 2nd stage HoCu2 Cold tip 1.5W@4.2 K Electromagnetic noise • Sources: • Driving or valve unit=>synchronous motor, • split configuration max. 2m connection lines! • Normal lead spheres as regenerator material, • Magnetic phase transision of the low temperature regenerator • material Er3Ni, HoCu2, ... ~ 20nT very near to the cold tip! • Signal with the operating frequency of • the cryocooler fmag~ 1.0 to 3 Hz and harmonics. • ! Persistent phase transition in the regenerator. • Radiopurity of all construction materials: Pb, Er, Ho!

  20. Maintenance Cryo-Coolers: Resume cryocoolers Advantageous of cryocoolers: • Simple device switch on/off, • Cryogen free , • Supervision at distance possible. Disadvantageous: • Very small cooling powers at 4.2 K (several plants required), • Cool down time of large cold mass may become (very) long, • Vibration (even if small), • Material problems. • Compressor: 12,000 hours • GM cold head 8,000 hours • PT Rotary valve: 12,000 hours

  21. Thank you for your attention

  22. Back-up slides Pulse Tube type cooler (SHI Sumitomo) • Nominal cooling power 1.0 W (4.2K) • Power consumption 7.5 kW • Water cooling Features: Lower vibration, improved reliability and lower cost compared with traditional Gifford McMahon and Stirling cryocoolers (However, still 1-3 microns vibration level)

  23. Back-up slides

  24. Back-up slides

  25. Back-up slides T=300 K

  26. Back-up slides Split-configuration of the valve unit and the cold finger Performance characteristic decrease a little bit !?

  27. Temperature oscillations in LHe

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