Two-phase condensation heat transfer coefficients of HFC-134a at high mass flux in smooth and micro-fin tubes

The two-phase heat transfer coefficients of pure HFC-134a condensing inside horizontal smooth and micro-fin tubes are experimentally investigated. Different from most previous studies, the present experiments are performed at high mass flux conditions. The test section is a 2.5 in long counterflow double tube heat exchanger with refrigerant flowing in the inner tube and cooling water flowing in the annulus. The inner tube is made from smooth or micro-fin copper tubing of 9.52 mm outer diameter. The test runs are done at average saturated condensing temperatures ranging between 30 and 40 degreesC. The mass flux are between 400 and 800 kg/m(2)s. The experimental results from both smooth and micro-fin tubes show that the average heat transfer coefficient increases with increasing average quality and mass flux, but decreases with increasing condensing temperature. The average heat transfer coefficient of micro-fin tube is 10 to 85% higher than that of the smooth tube. New correlations based on the data gathered during this work for predicting the condensation heat transfer coefficients are proposed for practical applications. (C) 2003 Elsevier Science Ltd.