Regenerator Loss Measurements at Low Temperatures and High Frequencies

Abstract

We report the design of an experiment characterizing the loss mechanisms in a regenerator operating with a cold end temperature between 10 and 20 K, and in a frequency range of 30–60 Hz. The regenerator is designed as part of a two-stage pulse tube system, incorporating 400-mesh stainless steel screens and 100-micron lead shot in the first and second stages respectively. The sinusoidal pressure wave generated by the linear flexure-bearing compressor provides an average pressure of 2.5 MPa and a pressure ratio of 1.4. Flow rates at both the warm and cold ends of the regenerator are measured as well as the pressure and temperature at the ends and intermediate locations. A laminar flow element has been designed to measure flow at the warm end, while the pressure oscillation in a cold reservoir permits calculation of the flow rate at the cold end. A cold inertance tube provides the desired phase shift. Loss measurements on the regenerator alone are achieved without the use a pulse tube by anchoring the intermediate and cold end temperatures to the first and second stages, respectively, of a Gifford-McMahon cryocooler. Loss mechanisms including conduction, radiation, PV degradation, and regenerator ineffectiveness will be measured as a function of cold end temperature and frequency. The experimental apparatus allows future measurements to be taken of the pulse tube losses in the same temperature and frequency range.