Quarter-wave pulse tube

► In a pulse-tube refrigerator, a long pulse tube changes the pressure–velocity phase. ► Changing this phase enables efficient addition of a second stage of refrigeration. ► The long pulse tube works well despite boundary-layer turbulence. ► The long pulse tube can be coiled compactly without penalty. In high-power pulse-tube refrigerators, the pulse tube itself can be very long without too much dissipation of acoustic power on its walls. The pressure amplitude, the volume-flow-rate amplitude, and the time phase between them evolve significantly along a pulse tube that is about a quarter-wavelength long. Proper choice of length and area makes the oscillations at the ambient end of the long pulse tube optimal for driving a second, smaller pulse-tube refrigerator, thereby utilizing the acoustic power that would typically have been dissipated in the first pulse-tube refrigerator’s orifice. Experiments show that little heat is carried from the ambient heat exchanger to the cold heat exchanger in such a long pulse tube, even though the oscillations are turbulent and even when the tube is compactly coiled.