Comparison of three adjustable inertance tubes

Inertance tubes are widely used to adjust the phase angle between the mass flow and pressure wave at the cold end of pulse tubes for the purpose of improving their performance and optimizing their efficiency. However, the phase shift mechanism is sensitive to the dimensions of the inertance tube, such as diameter and length. In order to investigate the phase shift mechanism of an inertance tube, this paper describes three different inertance tubes for which the length or diameter or both can be adjusted while the cryocooler is operating. The distributed component model is used to analyze the performance of these three variable inertance tubes. In the calculation, the diameter varies from 4 mm to 14 mm while the length changes from 1 m to 4 m, variations that can provide a large phase angle shift from -75 to 60 , along with acoustic power values ranging from 50 W to 4000 W. Also, the figure of merit for an adjustable inertance tube is defined and discussed to find a good way to have a sensitive phase shift while maintaining a constant acoustic power.