The Gifford low-frequency pulse-tube
A revealing introduction to the pulse-tube comes from the inventors (Gifford and Longsworth 1964):
... recently a number of very useful refrigeration devices have been built which involve different portions of the gas proceeding through a very different series of operations. Later, in the context of the practical Stirling cycle: ... you find that significant fractions of the working gas do not perform the same operations.
These assertions imply acceptance that functioning depends on the ‘autonomy’ of individual fluid particles - a pocket of gas is first compressed, then transported to a new location where some of the heat of compression is transferred to the enclosure. The same pocket is then re-expanded and transported back to its original location where it takes in heat on cooling towards the earlier temperature. In practice the phases merge, but the cycle of merged phases undergone by one parcel of gas is generally distinct from that undergone by another. Operation is not dependent on direct exchange of thermal energy between adjacent working fluid parcels.
The inventors’ observation that ‘the effect, which occurs in many places, is frequently ignored ...‘ may have been apt at the time of writing, but has been overtaken by subsequent events: Feulner (2002) has independently observed and recorded a marked axial heat pumping effect in the tubular exchangers of a motored Stirling engine.
Perversely, the original inventors ...