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Concept
Pulse tube refrigerator
Summary
The pulse tube refrigerator (PTR) or pulse tube cryocooler is a developing technology that emerged largely in the early 1980s with a series of other innovations in the broader field of thermoacoustics. In contrast with other cryocoolers (e.g. Stirling cryocooler and GM-refrigerators), this cryocooler can be made without moving parts in the low temperature part of the device, making the cooler suitable for a wide variety of applications.
Pulse tube cryocoolers are used in industrial applications such as semiconductor fabrication and in military applications such as for the cooling of infrared sensors. Pulse tubes are also being developed for cooling of astronomical detectors where liquid cryogens are typically used, such as the Atacama Cosmology Telescope or the Qubic experiment (an interferometer for cosmology studies). PTRs are used as precoolers of dilution refrigerators. Pulse tubes are particularly useful in space-based telescopes such as the James Webb Space Telescope where it is not possible to replenish the cryogens as they are depleted. It has also been suggested that pulse tubes could be used to liquefy oxygen on Mars.
Figure 1 represents the Stirling-type single-orifice pulse-tube refrigerator (PTR), which is filled with a gas, typically helium at a pressure varying from 10 to 30 bar. From left to right the components are:
a compressor, with a piston moving back and forth at room temperature TH
a heat exchanger X1 where heat is released to the surroundings at room temperature
a regenerator consisting of a porous medium with a large specific heat (which can be stainless steel wire mesh, copper wire mesh, phosphor bronze wire mesh, lead balls, lead shot, or rare earth materials) in which the gas flows back and forth
a heat exchanger X2, cooled by the gas, where the useful cooling power is delivered at the low temperature TL, taken from the object to be cooled
a tube in which the gas is pushed and pulled
a heat exchanger X3 near room temperature where heat is released to the surroundings
a flow resistance (often called orifice)
a buffer volume (a large closed volume at practically constant pressure)
The part in between X1 and X3 is thermally insulated from the surroundings, usually by vacuum.
Official source
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