Pulse tube cooler

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A pulse tube cooler or pulse tube cooler (also known as pulse tube cooler ) is a refrigeration machine based on the principle of the Stirling engine . The advantage over the Stirling engine is that no mechanically moving parts are required near the cold heat exchange point. This makes very compact cooling heads possible and the minimum temperature that can be achieved is not limited by the mechanical frictional heat of these parts. Today, pure pulse tube coolers can reach temperatures of 1.3 K (= −272 ° C).

Applications

The areas of application extend over wide areas of industry, research, medicine and the military, where extremely low temperatures are required: liquefaction of gases, cooling of sensors, cooling of superconducting magnetic field coils, quantum computer circuits, superconducting circuits in mobile radio receiving stations, low-temperature experiments and space experiments. Thanks to their independence from cryogenic liquids, they are very well suited for outdoor use: in the military for cooling infrared sensors, for cooling optical sensors in space telescopes or for a future manned mission to Mars to remove the oxygen from the CO 2 of the Martian atmosphere before the astronauts arrive liquefy. In research, they can make cryostats independent of the supply of expensive cryogenic liquids such as liquid helium or nitrogen. They are used here as a direct precursor for further cooling steps such as 3 He-evaporative cooler, 3 He- 4 He-mixing cooler or paramagnetic Entmagnetisierungsstufen.

history

Fig. 1: The development of the temperatures reached by pulse tube coolers over the years. 1.2 K was achieved in a collaboration between two research groups from Gießen and Eindhoven. A superfluid vortex cooler serves as an additional cooling stage.

With the basic principle presented by WE Gifford and RC Longsworth in 1963, the BPTR ( Basic Pulse Tube Refrigerator ), temperatures of at least 124 K (= −149 ° C) could be achieved. Over the years, various research groups published variations with ever higher efficiency and lower minimum temperature. A variant of the OPTR ( Orifice Pulse-Tube Refrigerator ) type published in 1984 reached a temperature of 60 K. With another variant from 1990, of the DIPTR ( Double-Inlet Pulse-Tube Refrigerator ) type, and a series of two or three pulse tube coolers, the boiling temperature of helium could finally be fallen below (less than 4 K). A research group from Gießen achieved 1.3 K (2004) and together with a group from Eindhoven 1.2 K with an additional cooling stage (2005).

At the Walther-Meißner-Institut in Garching, a mixing cryostat with a pulse tube precursor succeeded in reaching a temperature of 4.3 mK in 2003 without the need to supply cryogenic liquids.

functionality

Stirling engine

The pulse tube cooler works on the principle of the Stirling engine with a regenerator . When operated as a heat pump, the piston of the Stirling engine in a cylinder periodically compresses and expands the gas contained therein, which initially causes a uniform periodic temperature fluctuation of the gas. So that a spatially directed heat transport occurs, on the one hand the gas is periodically relocated with a displacement piston so that the compression takes place at a different location than the expansion. On the other hand, in most Stirling engines the gas passes through a so-called regenerator, a gas-permeable material with a large heat capacity. This cools the gas in the compressed phase on the way to the cold end, absorbs heat itself, and thus warms the gas in the expanded phase on the way to the hot end. Both strategies ensure that on average one end is colder than the other. If the on average warmer end is kept at ambient temperature, the colder end can be used for cooling.

Pulse tube cooler

Fig. 2 : Structure of a pulse tube cooler in three historical stages of development. BPTR: Compressor, regenerator and the extended cylinder, the actual pulse tube, form the basic principle. OPTR: buffer volume connected via a nozzle for a time delay. DIPTR: additional bypass to increase the efficiency. The waste heat and the cold generated are dissipated at the warm (WTP1 + 3) and cold (WTP2) heat exchange points.

The pulse tube cooler avoids any moving parts, with the exception of the piston in the compressor, which is often located far away, which forces a periodic pressure fluctuation. The gas flowing in and out runs through a regenerator and flows into a so-called pulse tube, which is a replacement for the other moving parts of the Stirling engine. At the other end of the pulse tube, the air cannot escape or can only escape slowly. If one looks at a volume element of the gas in the middle of the pulse tube during the periodic compression, it moves back and forth relative to the immobile regenerator. The pulse tube thus acts like a piston and replaces the second movable piston or a movable regenerator and displacer required in the Stirling engine. However, heat transport only takes place if there is a temporal dephasing of the gas movement with respect to pressure or temperature. What is achieved mechanically in the Stirling engine, is achieved in the BPTR type in that the wall of the pulse tube absorbs heat and naturally releases it with a delay. The OPTR achieves a much greater time delay in gas movement when the pulse tube is connected to a buffer volume via a delay nozzle, which is filled and emptied with a certain inertia. In this way, the strategies of the Stirling engine are implemented without the disadvantage of mechanical parts that counteract the cooling due to frictional heat. The coldest point, which can be used for cooling, is located between the regenerator and the pulse tube if the warm heat exchange points are kept at ambient temperature by water or air cooling.

See also

  • Ranque Hilsch vortex tube for generating warm and cold air from a constant air flow, also without moving parts.
  • [1] wikibooks: Thermoacoustics (engl.)

Individual evidence

  1. ↑ Development of the Pulse Tube Refrigerator as an Efficient and Reliable Cryocooler (2000) (PDF; 1.2 MB)
  2. ↑ Pulse Tube Oxygen Liquefier (PDF; 508 kB)
  3. ^ WE Gifford, RC Longsworth: Pulse-tube refrigeration . In: Trans ASME . 1964, pp. 264-268.
  4. ^ WE Gifford, RC Longsworth: Surface heat pumping . In: Adv Cryo Eng . 11, 1966, pp. 171-179.
  5. ↑ EI Mikulin, AATarasov, MP Shkrebyonock: Low-temperature expansion pulse tubes . In: Adv Cryo Eng . 29, 1984, pp. 629-637.
  6. ↑ R. Radebaugh, J. Zimmerman, DR Smith, B. Louie: Comparison of three types of pulse tube refrigerators; New methods for reaching 60K . In: Adv Cryo Eng . 31, 1986, pp. 779-789.
  7. ↑ S. Zhu, P. Wu, Z. Chen: Double inlet pulse tube refrigerator: an important improvement . In: Cryogenics . 30, No. 4, 1990, pp. 514-520. doi : 10.1016 / 0011-2275 (90) 90051-D .
  8. ^ Y. Matsubara, JL Gao: Novel configuration of three-stage pulse tube refrigerator for temperatures below 4K . In: Cryogenics . 34, No. 4, 1994, pp. 259-262. doi : 10.1016 / 0011-2275 (94) 90104-X .
  9. ↑ N. Jiang, U. Lindemann, F. Giebeler, G. Thummes: A Hey pulse tube cooler operating down to 1.3 K . In: Cryogenics . 44, No. 11, 2004, pp. 809-816. doi : 10.1016 / j.cryogenics.2004.05.003 .
  10. ↑ IA Tanaeva, U. Lindemann, N. Jiang, ATAM de Waele, G. Thummes: Novel concepts or devices-superfluid vortex cooler . In: Advances in Cryogenic Engineering . 49B, 2004, p. 1906-13 .
  11. ^ Kurt Uhlig: “Dry” dilution refrigerator with pulse-tube precooling . In: Cryogenics . 44, No. 1, January 2004, pp. 53-57. doi : 10.1016 / j.cryogenics.2003.07.007 .

literature

  • Herbert Willem Gerrit Hooijkaas: Miniature Stirling-Type Pulse-Tube Refrigerators . Dissertation. 2000 ( tue.nl [PDF]).