Flow boiling experiments for two new non-azeotropic, three-component refrigerant mixtures (HP80 and HP62) and R-502, the azeotropic refrigerant binary mixture they are replacing, have been carried. Comparative results show that local flow boiling heat transfer coefficients for HP62 are slightly larger that those for R-502 under the same test conditions while those for HP80 are on average slightly smaller. The heat transfer performances of the three fluids are accurately predicted by an existing flow boiling correlation modified here to include a nucleate boiling mixture correlation.