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

The characteristics of condensation heat transfer and pressure drop for refrigerant R-134a flowing in a horizontal small circular pipe that has an inside diameter of 2.0 mm were investigated experimentally in this study. The effects of the heat flux, mass flux, vapor quality and saturation temperature of R-134a on the measured condensation heat transfer and pressure drop were 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 coefficient averaging over the entire quality range tested here for the small pipe is about 10% higher. Moreover, we noted that in the small pipe the condensation heat transfer coefficient is higher at a lower heal flux, at a lower saturation temperature and at a higher mass flux. In addition, the measured pressure drop is higher for raising the mass flux but lower for raising the heat flux. Based on the present data, empirical correlation equations were proposed for the condensation heat transfer coefficient and friction factors. The results are useful in designing more compact and effective condensers for various refrigeration and air conditioning systems using refrigerant R-134a. (C) 1998 Elsevier Science Ltd. All rights reserved.