Part III of this study covers the basic characteristics of a Stirling cooler based on a simplified Stirling cycle. Two different types of Stirling coolers—one with a piston and displacer, and the other with two-pistons—are described by a simplified isothermal model using Schmidt equations. Examples of calculation results are given to explain the optimum phase difference between the piston movement and the pressure wave of the working gas. The regenerator, as one of the critical components of cryocoolers, is analyzed in detail. Numerical investigations have been conducted to study the regenerator efficiency in terms of the geometry, materials selection, pressure ratio, and the phase between mass flow and pressure in the regenerator. Improvement in regenerator performance is discussed as related to minimization of the enthalpy flow within the regenerator.
We performed tensile tests at low temperatures from room temperature to 4 K for SUS 304L and SUS 316L in order to obtain basic data on the mechanical properties of materials to be used in a liquid hydrogen tank service. First we studied tensile curves and specimen heating during tensile testing from 70 K to 4 K, and then evaluated the ferrite contents of those alloys during tensile deformation from room temperature to 4 K. For both SUS 304L and SUS 316L, tensile strength showed a small peak around 10 K, and specimen heating decreased above 30 K as the environment temperature increased. Below 77 K, there was almost no clear influence of testing temperature on strain-induced martensitic transformation. However, for SUS 304L, the amount of ferrite content increased as the temperature decreased down to 233 K, and increased only slightly below 233 K. For SUS 316L, it increased as the temperature decreased down to 4 K, and increased steeply after 60% plastic strain above 243 K.