Koichi Matsumoto

High Efficient two-Stage gm Refrigerator with Magnetic Material in the Liquid Helium Temperature Region

This paper describes experimental results obtained from a two-stage Gifford-McMahon (GM) refrigerator which uses a rare earth compound as a 2nd regenerator matrix instead of Pb (lead) matrix. The refrigeration capacity below 10 K for a conventional two-stage GM refrigerator is so small that the lowest temperature achieved is limited to the 8 K level. The purpose of this study is to improve the refrigeration performance in the temperature region below 10 K. The technical point is to use Er3Ni (Erbium-3 Nickel) as a 2nd stage regenerator matrix, because it has much larger volumetric specific heat than Pb below 15 K and has almost the same specific heat as Pb at higher temperature. The reciprocating speed was optimized to improve the refrigeration performance. Refrigeration capacity of 1 W at 6.59 K and no load temperature of 4.50 K were obtained from the Er3Ni regenerator. The refrigeration loss mechanism below 10 K is also discussed.

An Ericsson Magnetic Refrigerator for Low Temperature

An Ericsson magnetic refrigerator has been designed and built for research in magnetic refrigeration in the temperature range of 20–77 K. In this temperature range, both magnetic refrigerant and refrigeration cycle are different from those below 20 K. The main features of our magnetic refrigerator were as follows: magnetic refrigerant and regenerator material were made of ferromagnetic material and lead respectively, with the thermal conductivity of gaseous helium used to transfer heat between the magnetic refrigerant and the regenerator material. The initial experimental results are described in this paper.

Thermodynamic analysis of magnetically active regenerator from 30 to 70 K with a Brayton-like cycle

Abstract A magnetically active regenerator produces refrigeration without gas expansion because it makes use of the magnetocaloric effect. A magnetically active regenerator is equivalent to many cascading magnetic refrigerators. Analytical estimation of its performance is difficult owing to the complexity of the system. In the present paper, a model active regenerator with a Brayton-like operation cycle was analysed by numerical cycle simulation. DyAl 2.2 sintered compound which has a Curie temperature of 50 K was adopted as the magnetic regenerator matrix in the temperature range below 70 K. From the analysis, the model active regenerator was shown to have the potential of attaining a lowest temperature of 30 K from 70 K. The optimum operating conditions giving maximum refrigeration capacity are discussed and thermal efficiency is estimated.

INVESTIGATIONS ON THE POSSIBILITY OF THE RAl//2 SYSTEM AS A REFRIGERANT IN AN ERICSSON TYPE MAGNETIC REFRIGERATOR.

We investigated the Ericsson type magnetic refrigerators in the range below 77 K. This is the first report of experimental results of the refrigeration character, especially the magnetocaloric character of RAl2, where R is a rare earth atom.

Optimum structure of multilayer regenerator with magnetic materials

Abstract We investigated a layered structural regenerator (multilayer regenerator) with magnetic regenerator materials using a two-stage GM refrigerator. In this study we used Er 0.75 Gd 0.25 Ni which was expected to be placed in the high temperature part of the second regenerator. To confirm the effect of Er 0.75 Gd 0.25 Ni, the heat-exchange efficiency of the regenerator (regenerator efficiency) with Er 0.75 Gd 0.25 Ni, Er 3 Co and Er 0.9 Yb 0.1 Ni, which were in the volumetric ratio x: (0.5 − x): 0.5 (0 ≤ x ≤ 0.5) was calculated as a function of x by computer simulation. We found that the regenerator efficiency increased when x (i.e. the amount of Er 0.75 Gd 0.25 Ni) was increased and an optimum value of x was ~ 0.25. We then made two kinds of second regenerator: a triple layer regenerator with Er 0.75 Gd 0.25 Ni, Er 3 Co and Er 0.9 Yb 0.1 Ni, which were in the volumetric ratio 0.25:0.25:0.5, and a double layer regenerator with Er 3 Co and Er 0.9 Yb 0.1 Ni, which were in the volumetric ratio 0.5:0.5. We compared their refrigeration performances experimentally. With the triple layer regenerator, the lowest temperature was 2.60 K at the second stage and the maximum refrigeration capacity at 4.2 K was 1.17 W. These results were superior to those with the double layer regenerator.

Recent Progress in Magnetic Refrigeration Studies

After the 1985 Cryogenic Engineering Conference, two directions for the fundamental investigations on the magnetic refrigeration to expand the refrigeration range above ~15 K have been developed by our group. One is the improvement of the refrigeration characteristics able to refrigerate from ~20 K for the Carnot magnetic refrigerator and the other is the fundamental study of the Ericsson magnetic refrigerator. As for the former purpose, we used a new magnetic material, Dy3A15012, as the refrigerant in a reciprocating Carnot magnetic refrigerator instead of Gd3Ga5012. Consequentially, we succeeded in expanding the refrigeration range. As for the latter, we have established the method to make the refrigerant suitable for the ideal Ericsson cycle including two kinds of iso-magnetic field processes. Now, the investigation of the Ericsson magnetic refrigeration cycle and refrigerator is starting.

Analysis of Rare Earth Compound Regenerators Operating at 4 K

This paper describes the analysis of regenerators which consist of rare earth compounds. In a regenerative cycle refrigerator, refrigeration loss is larger than useful refrigeration capacity at liquid helium temperature, and the main loss is regenerator loss. The purpose of this paper is to establish a numerical calculation method which gives useful information for designing high efficiency regenerators. The model regenerator consisted of two regenerator compounds: Er3Ni, which is hot-side material, and another material such as ErNi2, Er0.75Dy0.25Ni2, ErNi, or Er0.9Yb0.1Ni. The regenerator efficiency was calculated for various ratios of the two materials. Regenerator efficiencies for various combinations of rare earth compounds are systematically discussed. The maximum regenerator efficiency was obtained at 4 K with the condition that Er3Ni was 45% and Er0.9Yb0.1Ni was 55% of the regenerator volume. Moreover, it was shown that a refrigerator with this optimized regenerator could achieve a 52% larger refrigeration capacity than one with an all-Er3Ni regenerator.

A new method of producing the magnetic refrigerant suitable for the ericsson magnetic refrigeration

A layer structural complex magnetic refrigerant, which is suitable for the Ericsson cycle, satisfying the Carnot principle, has been investigated. Above ∼ 15 K, since the thermal agitation energy and the lattice entropy increase considerably, the ferromagnetic material has to be used for the refrigerant in the magnetic refrigeration. However, the variation of the magnetic entropy of the ferromagnets is not appropriate to the Ericsson cycle in which the entropy difference ΔS J between two kinds of the isomagnetic field processes should be constant in the refrigeration range. In order to make the refrigerant having constant ΔS J mentioned above, we made the layer structural sintered material composed of four kinds of ferromagnets, ErAl 2.2 , HoAl 2.2 , (Dy 0.5 Ho 0.5 )Al 2.2 and DyAl 2.2 , and investigated its entropy experimentally. As the result, it is verified that the layer structural magnetic material is one of the most promising refrigerant for the Ericsson cycle.

Investigation of the Magnetic Refrigerant for the Ericsson Magnetic Refrigerator

In the temperature range above ~20 K, the Ericsson magnetic refrigeration cycle has to be adopted instead of the Carnot cycle, because the lattice entropy becomes no longer negligible as compared with the magnetic entropy. Moreover, in this range since the thermal agitation energy ~kT of spin also increases, the ferromagnetic materials have to be used for the refrigerant to obtain large entropy change enough to refrigerate. However, temperature variation of the magnetic entropy change of ferromagnetic material is not suitable for the Ericsson cycle. In the present paper we will give the answers to the following questions; (1) what kinds of ferromagnets must be used for the refrigerant? (2) what kind of method to compose the refrigerant using those ferromagnets is promising?

Surface Tension Maximum of Liquid 3He—Experimental Study

The surface tension of liquid 3He was measured as a function of temperature by means of the capillary rise method. Suzuki et al. [Europhysics Lett. 5, 333 (1988)] reported that the surface tension was almost temperature independent below 120 mK. Here we have examined it with greater precision and found that it has a small maximum around 100 mK. The surface tension increased with temperature from 35 mK and had a maximum of about 3×10−4 as a fraction of the surface tension at 0 K. It was found that the surface tension maximum can be attributed mainly to the T4 ln T variation which has been theoretically derived by Misawa on the basis of a local approximation for the entropy including Fermi liquid effect.