Heat transfer measurements were made in the post-CHF region of a boiling refrigerant under swirl flow conditions generated by twisted tape inserts inside of a vertical tube. The tube inside diameterswas 7.75 mm with a heated length of 3.66 m. Wall-superheats were relatively low below 60°C and the mass flux spanned the range of two previous investigations. Results are presented in a low mass flux range 214–425 kg/m 2 s and at a higher mass flux of 1001 kg/m 2 s. These tests represent the first reported that cover both of these mass flux ranges and significant differences were found in the data trends. The lower mass flux data were predicted by an existing heat transfer correlation equation while the higher mass flux data exhibited an increased drop-wall contribution to the heat transfer.