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 degrees 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 (x(r,o) 0.4); while at high vapor qualities (X-r,X-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%. (C) 2007 Elsevier Ltd and IIR. All rights reserved.