An experimental study of frictional pressure drop characteristics of R410A-oil mixture flow boiling inside straight and C-shape horizontal enhanced tubes was performed. The test tube was an internally spiral grooved tube with the outer diameter of 7.0 mm. Experimental parameters included evaporating temperature 5℃

mass flux from 200 kg·m-2·s-1 to 400 kg·m-2·s-1

heat flux from 7.56 kW·m-2 to 15.1 kW·m-2

inlet vapor quality from 0.1 to 0.7

and oil concentration from 0 to 5%.The test result showed that frictional pressure drop of R410A-oil mixture flow boiling inside straight and C-shape enhanced tubes increased with increasing oil concentration and mass flux. New correlations of frictional pressure drop for R410A-oil mixture flow boiling inside the straight enhanced tube and C-shape enhanced tube were developed respectively based on the mixture properties. The new frictional pressure drop correlation for the straight enhanced tube could agree with 97% of the experimental data within deviation of ±10%

and the frictional pressure drop correlation for the C-shape enhanced tube could agree with 95% of the experimental data within deviation of ±15%.