Heat transfer during reflux condensation of R134A in a small diameter inclined tube

Heat transfer coefficients for reflux condensation of R134a in a small diameter inclined tube are determined. The inner diameter of the tube is 7 mm and the length is 500 mm. Experiments are carried out at condensate film Reynolds numbers between 50 and 165 and at pressures between 0.67 MPa and 0.74 MPa. It has been found that the inclination angle has a strong effect on the heat transfer coefficient. At an inclination angle of about 45 degrees the heat transfer coefficient is increased by a factor of nearly 2 when compared with the heat transfer coefficient for reflux condensation in the vertical position. Existent correlations from the open literature do not agree well with experimental data for the small diameter inclined tube. A modified form of a semi-empirical correlation proposed by Wang and Ma is presented that predicts well the experimental data.