Experimental study on pool boiling heat transfer of R134a-oil mixture outside single horizontal enhanced tubes

In this study, heat transfer coefficients were experimentally determined for three horizontal enhanced tubes (E21, E22, E23) with R134a-oil mixture. The evaporation temperature was 10°C and 5°C, respectively and the water velocity inside enhanced tubes was ranged from 1.5 m/s to 3.5 m/s. The results show that compared with smooth tube the enhancement magnification of heat transfer coefficient inside E21, E22 and E23 is 3.703, 3.035 and 2.709, respectively. The heat transfer coefficients outside the tubes with the oil concentration of 100 × 10-6 increase by 3.7%-7.2% compared with those with oil concentration of 50 × 10-6 at the same water velocities and the evaporation temperature 5°C, while by 0.8%-10.9% at the evaporation temperature 10°C.