| abstract |
(57) [Summary] [Problem] To provide a working medium for a refrigerator, which improves the lubricity of a refrigerant / oil mixture and greatly improves the reliability of the refrigerator. A mixed oil (B) of isobutane (A), a naphthenic mineral oil or a paraffinic mineral oil (1), and a polyol ester (2), wherein the polyol ester (2) in the mixed oil (B) The mixing ratio is 5 to 70% by weight, and the viscosity at 40 ° C. of the mixed oil (B) is 7 to 2 Working medium for refrigerators of 5 mm 2 / s. |