Superfluid Stirling Refrigerator Research Articles

Design, construction, and performance of plastic heat exchangers for sub-Kelvin use

The ultimate temperature and cooling power of both the superfluid Stirling refrigerator (SSR) and the 3He– 4He dilution refrigerator depend largely on the efficiency of their counterflow heat exchangers. This efficiency is limited mainly by the Kapitza boundary resistance at low temperatures. The usual method of overcoming this problem has been to increase the surface area of the heat exchangers. A different approach is to make the heat exchangers out of materials that have low Kapitza boundary resistance such as plastics. This article describes the design, construction, and performance of plastic heat exchangers that have been successfully used in our SSRs. Specifically, the paper includes a detailed description of our heat exchangers, step-by-step instructions on the construction of a plastic heat exchanger, and simple calculations of the performance of the heat exchanger under typical SSR operating conditions.

Experimental Evaluation of a Single Stage Superfluid Stirling Refrigerator Using a Large Plastic Recuperator

This paper describes the low and high temperature experimental performance of the second single stage superfluid Stirling refrigerator (SSR) to use a plastic recuperator. This SSR has a total internal volume of 96.6 cm3 and uses a Kapton recuperator which has 12.10 cm3 devoted to recuperative heat transfer. Operating from a high temperature of 1.0 K and with 1.5% and 3.0% 3He–4He mixtures, this SSR achieves a low temperature of 291 mK and delivers net cooling powers of 3705 μW at 750 mK, 977 μW at 500 mK, and 409 μW at 400 mK. Cooling power versus cold piston temperature for various frequencies of operation and for two piston stroke configurations are also provided. These results are non-dimensionalized and compared to the Schmidt model of a regenerative Stirling refrigerator and the adiabatic model of a recuperative Stirling refrigerator. The SSR was also operated from high temperatures between 1.0 K and 2.0 K. This SSR achieves low temperatures of 412 mK, 620 mK, 1.069 K, and 1.459 K operating from high temperatures of 1.2 K, 1.4 K, 1.6 K, and 1.8 K respectively. This high temperature performance is compared to the theoretical performance of the SSR using a phonon–roton gas model.

A Simple Model for a Superfluid Stirling Refrigerator at High Operating Temperature

The superfluid Stirling refrigerator (SSR) is a Stirling machine that uses the ideal gas behavior of the 3 He Component of a 3 He- 4 He mixture to provide cooling at temperatures below 2 K. The design of SSR's to date has used the Schmidt model to predict the performance of a given machine. Unfortunately, the Schmidt model does not account for the phonon and roton excitations present in 4 He component of the mixture. These excitations significantly change the performance of the SSR. An analytical model of the SSR that accounts for the phonon and roton excitations is presented. High temperature SSR experimental data is also presented and found to compare well with the model.

Experimental performance of a single stage superfluid Stirling refrigerator using a small plastic recuperator

The experimental performance of the first superfluid Stirling refrigerator (SSR) to use a plastic recuperator is reported. This SSR is a single stage machine, has a total internal volume of 83 cm3, and uses a 3 cm3Kapton heat exchanger. Operating from a high temperature of 1.0 K and with a 1.5%3He–4He mixture, this SSR achieves a low temperature of 344 mK and delivers net cooling powers of 1.86 mW at 750 mK, 358 μW at 500 mK, and 97 μW at 400 mK. Cooling power versus cold piston temperature for various frequencies of operation and for two piston stroke configurations are provided.

Uniform temperature cooling power of the superfluid Stirling refrigerator

Uniform temperature cooling power of the superfluid Stirling refrigerator

High-temperature cooling power of the superfluid stirling refrigerator

Uniform temperature cooling power measurements of a superfluid Stirling refrigerator are presented for3He-4He molar concentrations of 5.9%, 17% and 36% and for temperatures between 0.37 K and 1.4 K. The results are compared to an ideal Fermi gas model and to a more general thermodynamic model. The Fermi model agrees well with the 5.9% concentration data; however, the more elaborate model is needed for higher concentration mixtures.

Measurements and modelling of recuperator for superfluid Stirling refrigerator

Measurements and several methods of modelling of a recuperator for use in a dual superfluid Stirling refrigerator are discussed. The models are also applicable to non-superfluid machines. The heat capacity of the fluid entrained in the recuperator is essential for its efficient operation if the piston motions are sinusoidal.

The superfluid Stirling refrigerator, a new method for cooling below 0.5 K

A new sub-Kelvin refrigerator, the superfluid Stirling cycle refrigerator, uses a working fluid of 3He- 4He mixture in a Stirling cycle. The thermodynamically active components of the mixture are the 3He, which behaves like a Boltzmann gas, and the phonon-roton gas in the 4He. The superfluid component of the liquid is inert. Two refrigerators have been built, and temperatures of 340 mK have been achieved.