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Refrigeration and cryogenics

Refrigeration and cryogenics. Zakład Kriogeniki i Technologii Gazowych Dr hab. inż. Maciej Chorowski, prof. PWr. Methods of lowering the temperature. Isentropic expansion Joule-Thomson expansion Free expansion – gas exhaust . Gas isentropic expansion with external work.

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Refrigeration and cryogenics

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  1. Refrigeration and cryogenics Zakład Kriogeniki i Technologii Gazowych Dr hab. inż. Maciej Chorowski, prof. PWr

  2. Methods of lowering the temperature • Isentropic expansion • Joule-Thomson expansion • Free expansion – gas exhaust

  3. Gas isentropic expansion with external work

  4. Gas isentropic expansion with external work Drop of the gas temperature: Entropy is a function of pressure and temperature S= S(p, T) Total differential must be equal to zero: Differential effect of isentropic expansion msshows the change in temperature with respect to the change of pressure:

  5. Gas isentropic expansion with external work We know from thermodynamics We get where: b is coefficient of cubical expansion

  6. Gas isentropic expansion with external work For the ideal gas: After integration

  7. Piston expander

  8. Cryogenic turboexpander

  9. Isenthalpic – Joule-Thomson - expansion • When gas, vapour or liquid expands adiabatically in an open system without doing any external work, and there is no increment in velocity on the system reference surface, the process is referred to as throttle expansion. • In practice, this process is implemented by installing in the gas stream some hydraulic resistance such as throttling valve, gate, calibrated orifice, capillary, and so on.

  10. Isenthalpic – Joule-Thomson - expansion

  11. Isenthalpic – Joule-Thomson - expansion Temperature drop inIsenthalpic – Joule-Thomson - expansion Enthalpy is a function of pressure and temperature: h= h(p, T) Total differential must be equal to zero: Differential throttling effect μh:

  12. Isenthalpic – Joule-Thomson - expansion

  13. Isenthalpic – Joule-Thomson - expansion

  14. Free expansion (exhaust)

  15. Free expansion (exhaust) • Adiabatic process • Non equilibrium process – gas pressure and external pressure are not the same • Constant external pressure (pf= const.) • External work against pressure pf

  16. Free expansion (exhaust) Final gas temperature: I Law of Thermodynamics where: u0, uf – initial and final gas internal energy v0, vf – initial and final gas volume

  17. Free expansion (exhaust) For ideal gas: We get:

  18. Comparison of the processes for air

  19. Cryogenic gas refrigerators

  20. Heat exchangers Recuperative Regenerative

  21. Comparison of coolers

  22. Refrigerators with recuperative heat exchangers Joule – Thomsonrefrigerators

  23. Examples of miniature Joule-Thomson refrigerator

  24. Claude refrigerators

  25. Stirling coolers

  26. Stirling cooler

  27. Stirling cooler In Stirling refrigerator a cycle consists of two isotherms and two isobars Stirling cycle is realized in four steps : • Step 1-2: Isothermal gas compression in warm chamber • Step 2-3: Isochoric gas cooling in regenerator • Step 3-4:Isothermal gas expansion with external work • Step 4-1: Isochoric gas heating in regenerator

  28. Stirling split cooler

  29. Stirling cooler with linear motor

  30. Efficiency of Stirling cooler filled with ideal gas Work of isothermal compression Work of isothermal expansion Heat of isothermal expansion

  31. Stirling cooler configuration:

  32. Stirling cooler used for air liquefact-ion

  33. Stirling cooler used for air liquefaction

  34. Two stage Stirling refrigerator

  35. Gifforda – McMahon cooler

  36. Gifforda – McMahon cooler Four steps of McMahon cycle: • Filling . • Gas displacement • Free exhaust of the gas • Discharge of cold chamber Efficiency of McMahon cooler:

  37. McMahon refrigerator

  38. Combination of McMahon and J-T cooler, 250 mW at 2,5 K

  39. Pulse tube – free exhaust

  40. Scheme of pulse tube cooler

  41. Development of pulse tube coolers Gifford, 1963, rather curiosity that efficient cooler Kittel, Radebaugh, 1983 orifice pulse tube Dr. Zhu et. al., 1994, multiply by-pass pulse tube

  42. Comparison of Stirling and orifice pulse tube cooler

  43. Pulse tube cooler for 77 K applications Weight:2.4 kgDimensions (l x w x h):11.4 x 11.4 x 22 cmCapacity:2.5W @ 65KUltimate low temperature:35KInput power2kW

  44. Pulse tube

  45. Two stage pulse tube

  46. Pulse tube configuration

  47. Adiabatic demagnetization of paramagnetic

  48. Paramagnetic salts

  49. Magnetic coolers

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