Recently, in order to actualize the magnetic refrigerator in the high temperature region from 4K to room temperature, several investigators in Japan and USA have studied the problem of the magnetic refrigerants, the refrigeration cycles and the new type of magnetic refrigerators. In this review successive to the previous one by Ohtsuka the current works of those are introduced. This paper consists of the following four parts: 1) First, in order to make clear the direction of the investigation for the magnetic refrigerator, operations and physical charactor of the magnetic refrigerator by Brown are discussed precisely and it is pointed out that investigations on the magnetic refrigerant, heat exchange between the regenerator and refrigerant, and the thermal analysis of the fundamental magnetic refrigeration cycle are important. 2) Next, current investigations on two types of magnetic refrigerants, which have the large applied magnetic field dependence of the magnetic entropy change caused by its considerable increase of internal field near Tc and the rotation of the large magnetic anisotropic substance in the magnetic field, are cited and the origin of these phenomena is explained physically. 3) Then, we describe the investigations of heat exchange between the magnetic substance and heat transfer gas and of the thermal analysis of the refrigeration cycle. 4) Last, for examples of new types of magnetic refrigerators, rotational-cooling magnetic refrigerator by Barclay and regenerative magnetic expander (RME) by Barclay and Steyert are introduced.
Acousto-thermal and thermo-acoustic effects in tubes are discussed in terms of fluid mechanics. A fluid in a tube is assumed to be an ideal gas and basic equations of fluid mechanics are linearized. Averaging over the tube cross-section makes the problem into one-dimensional one. At first the discussion proceeds without viscosity and it becomes clear that thermal conductivity of gas play an important role. After that viscosity is included and effects of finite viscosity are discussed. Results obtained explain some qualitative features of experiments. Limitation of this linearized theory is also discussed.