Heat transfer characteristics of R410A–oil mixture flow boiling inside a 7 mm straight microfin tube

Two-phase heat transfer characteristics of R410A–oil mixture flow boiling inside a straight microfin tube with the outside diameter of 7.0 mm were investigated experimentally. The experimental conditions include the evaporation temperature of 5 °C, the mass flux from 200 to 400 kg m−2 s−1, the heat flux from 7.56 to 15.12 kW m−2, the inlet vapor quality from 0.2 to 0.7, and nominal oil concentration from 0 to 5%. The test results show that the heat transfer coefficient of R410A–oil mixture increases with mass flux of refrigerant–oil mixture; the presence of oil enhances the heat transfer at the range of low vapor qualities (xr,o < 0.4); while at high vapor qualities (xr,o > 0.65), the presence of oil deteriorates heat transfer, and the heat transfer coefficient drops off very sharply with the increase of nominal oil concentration and vapor quality at high vapor qualities. A new correlation to predict the local heat transfer coefficient of R410A–oil mixture flow boiling inside the straight microfin tube was developed based on local properties of refrigerant–oil mixture, and it could agree with 89% of the experimental data within the deviation of ±30%.