In the present article the recent developing process on the new application of high entropy magnetic materials in the He temperature range will be shown. First, the theoretical basis of these applications will be explained briefly and the necessary condition for selection of the magnetic materials will be discussed. Then, the several experimental results, such as the temperature dependences of the specific heat, in some promising Er compounds, Er3Ni, ErNi, ErNi2-DyNi2 etc., will be shown. In order to show clearly the present stage of the magnetic regenerator material investigation, we will show several results which verify the effectiveness of the magnetic regenerator materials obtained from refrigeration experiment using the GM refrigerator. Moreover, it has been made clear that the regenerator characteristics depends largely on the structure of the regenerator which contains several kinds of magnetic regenerator materials. Therefore, as an example, the experimental result of regenerator characteristics in the double layer type magnetic regenerator, in which Er3Ni powders are piled up on the ErNi powders, will be shown. Lastly, on the basis of the above experimental results, the development of the magnetic material application to regenerator in future will be discussed.
Procedures to measure critical parameters such as the critical temperature, Tc, the upper critical field, Hc2, the critical current, Ic, and the AC loss in practical superconductors are described. The criteria and factors which influence the evaluation of the parameters are briefly discussed. The importance of the holder in the 4 probe method which supports the sample against the Lorentz force is emphasized from the view point of strain effect. The magnetization method to measure the AC loss of a multifilamentary wire is described in detail.
Discussed are energy conversion and energy flux accompanied to oscillations of viscous fluid. The energy conversion per unit volume is shown to be ρm(∂T/∂p)S«p⋅dS/dt»+«u⋅∇p» for a small cycle, for which variations of pressure p and entropy S are small. ρm is time average of the density, u is the velocity and ∇p is the pressure gradient. « » indicates double operations of spatial average over crosssectional area of flow-channel and time average. «u⋅∇p» is a negative quantity corresponding to dissipation due to viscosity of fluid. The average of energy flux is shown to be enthalpy flux ρm«H⋅u» approximately, in the case that the velocity u and the mass flux «ρ⋅u» are small and the wave length is long. ρ and H are variations of the density and the enthalpy respectively. The enthalpy flux for small cycle is shown to be summation of heat flux and work flux: ρm«H⋅u»=ρmTm«S⋅u»+«p⋅u» where «p⋅u» is the work flux and ρmTm«S⋅u» is the heat flux. Final discussions are on the energy conversion, the work flux and the heat flux of adiabatic reversible small-cycle, isothermal small-cycle, polytropic small-cycle, isobaric small-cycle and isochoric small-cycle.
In order to discuss small cycles for different r collectively, the energy conversion and the energy flux are studied in a Lagrange system having an average velocity ‹u›r. In the beginning discussed are quasistatic small cycles for which variations of entropy are homogeneous in the flow channel, and later discussed are general small cycles for which variations of entropy aye inhomogeneous in the flow channel. Introducing a distribution function of velocity 1-fν and a distribution function of entropy fα and using their average over the cross-sectional area χν≡‹fν›r and χα≡‹fα›r, the work source W is, neglecting terms more than 4th order of p and (∇Tm)‹ξ›r; W=Wprog+Wstand+WP+Wν; Wprog≡β(∇Tm)FSχα′‹p⋅‹u›r›t; Wstand≡-β(∇Tm)FSχα″ω‹p⋅‹ξ›r›t; WP≡(KT-KS)FSχα″×ω‹p⋅p›t; Wν≡«u⋅∇p»; where FS is a measure of entropy exchange between solid wall and oscillating fluid. The work flux is I=‹p⋅‹u›r›t and the heat flux is, neglecting terms more than 3rd order of p and (∇Tm)‹ξ›r; Q=Qprog+Qstand+QD; Qprog≡-βTmFSg′‹p⋅‹u›r›t; Qstand≡-βTmFSg″ω‹p⋅‹ξ›r›t; QD≡ρmCP∇TmFSg″ω‹‹ξ›r⋅‹ξ›r›t; where g≡‹fα(1-fν+)/(1-χν+)›r=g′+ig″ and superscript+indicates complex conjugate of quantity without the superscript.
A superconducting model rotor had been constructed and a pair of test coil in the rotor was replaced after the preliminary test. The normal zone propagating velocities and the minimum propagating current were measured on this new test coil. These experimental results were compared with the caluculated results by Dresner's equation. The rotation speed dependence in experimental results were measured and well explained theoretically by Dresner's equation. The normal zone propagating velocities at the downward of helium flow were measured and the temperature rise of the conductor due to hot helium flow from upward were found out.
A Vuilleumier cooler has the potential advantages of long-life operation with low mechanical vibration, and hence, it is expected for cooling spaceborne IR sensors. This paper describes the results from an endurance test and also causes of the cooler performance degradation. In the endurance test, it has been operated in an atmospheric environment for over 13, 000h. Cooling capacity was 1.6W at 80K at the beginning of life and it decreased to 0.8W at the end of life. After the test, the cooler was disassembled to investigate how the performance degradation had happened. We found that both crankpin bearing of a cold displacer and crosshead pin bearing of a hot displacer were broken. It is believed that cold head volume was reduced by former bearing breakdown and indicated work was reduced by later bearing breakdown. Both bearing failures brought cooler performance degradation.
A linear motor car using the diamagnetism of a high Tc superconductor has been manufactured. In this model the track is constructed by Sm-Co permanent plate magnets magnetized perpendicularly to the plane. The car is comprised of Tl based superconductor with a critical temperature of 120K. When it is cooled by liquid nitrogen down to 77K, it becomes superconductive and levitates above the magnet track by the repulsive forces due to the diamagnetism. The levitating car moves smoothly along the track by applying traveling magnetic field by the propulsion coils which are layed at uniform intervals on the magnet track. According to 3-phase AC operation, the propulsion coils generate a traveling magnetic field and the car runs with the slip to the synchronous speed. As a results, we think that the driving mechanism is similar to induction motor. Because there are eddy current paths due to the grain boundary normalized in the superconductor.