Method for transferring heat

A process for transferring heat from a heat source to a heat sink, said process comprising using as heat transfer medium a composition comprising:

• at least one fluorinated ether fluid free from functional groups (fluid (H-1)), wherein the fluid H-1 is a hydrofluoropolyether fluid (fluid (HPFE)) or a perfluoropolyether fluid (fluid (PFPE)) having a viscosity at 20° C. of less than 10 cSt;
• at least one functional (per)fluoropolyether (functional PFPE(1)) comprising recurring units (R1), said recurring units comprising at least one ether linkage in the main chain and at least one fluorine atom (fluoropolyoxyalkylene chain), and at least one functional end group selected from the group consisting of —COOH and —CONH2;
• and
• at least one functional (per)fluoropolyether (functional PFPE(2)) comprising recurring units (R1) as defined above and at least one functional end group selected from the group consisting of —COCF3 and its hydroxylated derivative —C(OH)2CF3.