Experimental investigation of two-stage active magnetic regenerative refrigerator operating between 77 K and 20 K

• The two-stage AMRR operated between 77 K and 20 K is attempted and tested.
• The AMR reached the lowest temperature of 24 K and the temperature span is 56 K.
• The refrigerator has inherent cooling effect by gas expansion at the pulse tube.

This paper presents an experimental investigation on a magnetic refrigerator operating between 77 K and 20 K. Since the magneto-caloric effect of typical magnetic refrigerant is concentrated in a narrow temperature region, four different rare-earth intermetallic compounds (GdNi2, Dy0.85Er0.15Al2, Dy0.5Dr0.5Al2, and Gd0.1Dy0.9Ni2) are utilized according to their favorable temperature regions. The magnetic refrigerator is composed of two stages each of that is made of two different porous active magnetic regenerators. Helium gas as the heat transfer medium in the magnetic refrigerator is shuttled similar to a GM type pulse tube refrigerator so that the overall cooling capacity is enhanced by gas expansion effect when both gas and magnetic expansions are properly coordinated. The approximate peak magnetic field of 4 T is provided for the internal region of the regenerators by the AC superconducting magnet which can fast ramp up to the maximum field for 3 s. The fabricated magnetic refrigerator reached the lowest no-load temperature of 24 K and the whole temperature span was approximately 56 K rather than 57 K. The cooling performance of the system is sensitive according to the load match between the first and the second stages in conjunction with helium mass flow rate distribution.