Condensation heat transfer and pressure drop of refrigerant R-134a in a small pipe

The characteristics of condensation heat transfer and pressure drop for ref rigerant R-134a flowing in a horizontal small circular pipe that has an ins ide diameter of 2.0 mm were investigated experimentally in this study. The effects of the heat flux, mass flux, vapor quality and saturation temperatu re of R-134a on the measured condensation heat transfer and pressure drop w ere examined in detail. When compared with the data for a large pipe (D-i = 8.00 mm) reported in the literature, the condensation heat transfer coeffi cient averaging over the entire quality range tested here for the small pip e is about 10% higher. Moreover, we noted that in the small pipe the conden sation heat transfer coefficient is higher at a lower heal flux, at a lower saturation temperature and at a higher mass flux. In addition, the measure d pressure drop is higher for raising the mass flux but lower for raising t he heat flux. Based on the present data, empirical correlation equations we re proposed for the condensation heat transfer coefficient and friction fac tors. The results are useful in designing more compact and effective conden sers for various refrigeration and air conditioning systems using refrigera nt R-134a. (C) 1998 Elsevier Science Ltd. All rights reserved.