An experimental study on the performance of boiling heat transfer of R123 outside a single horizontal tube was conducted with three doubly-enhanced tubes (No.1，No.2 and No.3)with different geometries at saturation temperatures of 12℃and 10℃ respectively. Tube No.1 was Turbo-B type of Wolverine

and tube No.2

3 also belonged to this type with a minor difference in the tip of the fin. Wilson plot technique was used to separate the boiling heat transfer resistance from the total thermal resistance. It was found that under the same conditions

the in-tube convective heat transfer coefficients of the doubly-enhanced tubes were 2.8—3.1 times of that of the smooth one

and the boiling heat transfer coefficients of R123 were generally lower than those of R22. The thermal resistance analysis reveals that the thermal resistances of the water side and refrigerant side were of the same order for most of the tubes.With the increase in heating water velocity

the thermal resistance of the inner water decreased and that of the refrigerant increased. To further enhance heat transfer

the augmentation of the inner side and the outer side was equally important.