EXPERIMENTAL STUDIES ON THE CONDENSATION HEAT TRANSFER OF A HORIZONTAL COPPER TUBE WITH HYDROPHOBIC SURFACE

Dropwise condensation of steam occurs on a horizontal copper tube treated with a fluorination modification technique. Experiments were conducted to measure the condensation heat transfer of steam on a horizontal copper tube. The condensation heat transfer performance was systematically investigated across a wide range of subcooling temperatures and vapor velocities, with corresponding droplet dynamics behaviors visually observed. The maximum condensation heat transfer coefficient of the modified surface reaches 6.6 W/(cm<sup>2</sup> °C) at a subcooling temperature of 4.8°C and a vapor velocity of 0.76 m/s, whereas the coefficient on the Nusselt curve under the same subcooling is only 1.8 W/(cm<sup>2</sup> °C), which is attributed to the high efficiency of droplet condensation. Field-emission scanning electron microscopy (FESEM), energy dispersive X-ray spectrometer (EDS), surface roughness measurement (SRM) instrument, and X-ray diffraction (XRD) were employed to analyze the morphological structure and composition of the modified copper surface. Microscopic results demonstrate the novel fluorination modification technique, which creates Cu<sub>2</sub>O nanostructures on the copper surface in an atmosphere containing fluoride. The modified copper surface and tube exhibit excellent hydrophobic characteristics, with average contact angles of 120° and 112°, respectively. Hydrophobic surfaces facilitate dropwise condensation, leading to improved condensation heat transfer performance. The influence of vapor velocity, subcooling temperature, and Jakob number on the condensation heat transfer properties of the modified surface was analyzed. The degradation in condensation heat transfer characteristics is closely associated with increases in both subcooling temperature and the Ja number. The fluorination modification technique provides an effective approach to wettability control, enhancing condenser efficiency, and broadening industrial applications.