A new general correlation for frictional pressure drop during condensation inside horizontal micro-fin tubes

Experimental pressure drop data of condensation from present study and literature were collected to develop a new frictional pressure drop correlation for horizontal micro-fin tubes. The collected database contained 481 data points, covering nine refrigerants including CO2 at average saturated condensing temperatures ranging between 14 and 65 °C, with mass velocities ranging from 50 to 800 kg/m2 s, and average vapor qualities from 0.11 to 0.91. The hydraulic diameter of micro-fin tubes varied from 2.16 to 5.67 mm and was employed in the calculation of Reynolds number. The Fanning frictional factor was calculated by adopting the Churchill model with the empirically fitted relative roughness. Four existing pressure drop correlations developed for micro-fin tubes were evaluated by the database for condensation in micro-fin tubes. The correlation proposed by Cavallini et al. was the best prediction model among them, predicting 85.6% of the collected data points within the 30% error band. In addition, a new correlation based on the Martnelli parameter Xtt modified by incorporating the reduced pressure was proposed to predict the present database, which showed a good agreement. Finally, some corresponding experimental work was conducted for evaluating the reliability of the new prediction model.