Heat transfer characteristics of refrigerant-oil mixtures flow boiling in a horizontal C-shape curved smooth tube

Two-phase heat transfer characteristics of R410A-POE oil mixture and R22-mineral oil mixture flow boiling inside a horizontal C-shape curved smooth tube with an outside diameter of 7.0 mm and a curvature ratio of 60 were investigated experimentally. The test results show that the curvature of C-shape curved smooth tube deteriorates the flow boiling heat transfer, and the ratios of the heat transfer coefficients in C-shape curved smooth tube to those in straight smooth tube for R410A-oil mixture and R22-oil mixture are within 0.46-0.74 and 0.74-0.90, respectively. A correlation to predict the heat transfer coefficients of refrigerant-oil mixtures flow boiling inside C-shape curved smooth tube was developed based on mixture properties of refrigerant-oil, and it could agree with 96% of the experimental data within a deviation of +/- 20%. (C) 2010 Elsevier Ltd and IIR. All rights reserved.