EXPERIMENTAL STUDY ON COOLING CHARACTERISTICS OF A MAGNETOCALORIC DEVICE WITH TWO DIFFERENT TYPES OF MAGNETIC REFRIGERANTS

摘要

Magnetic refrigeration is a cooling technology based on a magnetocaloric effect, which is a temperature-changing phenomenon caused by the entropy change of magnetic refrigerants exposed under magnetic field alterations. Recently, it is commenced to apply for a room temperature region, as the magnetocaloric device does not use any F-gases that greatly influence global warming. In this paper, we have developed a renewed rotational type of magnetocaloric device with a simple component formation as well as an uncomplicated control system. The system is composed of a permanent magnet circuit which has 0.96 Tesla of its magnetic flux density at the gap center, a rotational disk which has circumferentially aligned 12 cells for magnetic refrigerant particle packed beds, and its casing that guides and controls the fluid flow through each packed bed cell, a circulating pump, and a rotation control unit. Both gadolinium and gadolinium alloy particles are applied as the magnetocaloric refrigerants and distilled water as the heat transfer fluid. An experimental study has been conducted to obtain cooling characteristics of the magnetocaloric device operation using three types of magnetic refrigerants such as gadolinium, gadolinium-dysprosium-alloy, and their hybrid type. The following operating parameters: the flow rate of heat transfer fluid, the rotational frequency and the temperature of inlet and outlet of heat transfer fluid are examined. As a result, the relationship between the rotation frequency and the flow rate to obtain the maximum temperature span between the inlet and outlet of the magnetocaloric device has been indicated. In addition, both the flow volume and flow rate of heat transfer fluid greatly affect the heat transfer between the fluid and the types of magnetic refrigerant particle packed bed through the rotation of the disk. Also difference of the magnetic refrigerant type and the inlet temperature affects the maximum temperature span between the inlet and the outlet temperatures and the coefficient of performance (COP) of the system.