Influence of regenerator void volume on performance of a precooled 4 K Stirling type pulse tube cryocooler

• Behavior of 4 K regenerator at high frequencies is investigated theoretically and experimentally.
• Effect of regenerator void volume on the performance of the 4 K SPTC is studied.
• The first and second precooling powers are obtained.
• Cold inertance tube at 10 K is used as phase shifter.

Stirling type pulse tube cryocoolers (SPTC), typically operating at 30–60 Hz, have the advantage of compact structure, light weight, and long life compared with Gifford–McMahon type (1–2 Hz) PTC (GMPTC). The behavior of flow and heat transfer in the regenerator of a 4 K SPTC deviates from that at warmer temperatures and low frequencies. In this paper the behavior of 4 K regenerator at high frequencies is investigated based on a single-stage 4 K SPTC precooled by a two-stage GMPTC. The 4 K SPTC and the GMPTC is thermally coupled with two thermal bridges. The 4 K SPTC uses a 10 K cold inertance tube as phase shifter to improve phase relationship between mass flow and pressure. The regenerator void volume is an important factor that significantly influences the heat transfer between regenerator matrix and working fluid helium, pressure drop along the regenerator, and phase shift between mass flow and pressure. In this paper, influence of regenerator void volume on the performance of the 4 K SPTC with different operating parameters including operating frequencies and average pressure is studied theoretically and experimentally. The first and second precooling powers provided by the GMPTC are obtained which are important parameters to evaluate the efficiency of the whole 4 K system with precooling. The results of the regenerator void volume are given and discussed in normalized form for general use.