Improvement of magnetic refrigerator performance by enhancement of helium condensation heat transfer

The authors have developed magnetic refrigerators for helium liquefaction from temperatures in the 15 K region. Condensation heat transfer enhancement is effective to increase refrigeration efficiency. An array of small fins (940 μm pitch) has enhanced condensation heat transfer 2.5 times as much as that for a flat surface. To apply this effect to magnetic refrigerators, GGG single crystal unit with fins (550 μm pitch) was demagnetized in 4.2 K atmospheric gaseous helium. Heat absorbed by the GGG crystal unit was 1.5 times as much as that absorbed by unit without fins. These results will be applied to magnetic refrigerators