Visualization study of the influence of non-condensable gas on steam condensation heat transfer

Abstract

This paper experimentally investigates the influence of non-condensable gas on water vapor condensation heat transfer on an isothermal vertical aluminum plate in an air mass fraction range of 0.05–0.5. A high-speed digital camera was employed to capture real-time images of water vapor condensation in non-condensable gas under different wall temperatures and air concentrations. The experimental results showed that the condensation modes varied with surface subcooling and air concentration. Four condensation modes were observed in the experiments: drop, drop-streak, film, and streamlet. Under identical air concentrations, the condensation mode varied from the fine drop and film mode to the larger drop-streak mode; the condensation drop diameters departing the plate became obviously bigger, the drops fell off the plate more quickly, and the heat transfer coefficients decreased gradually as surface cooling increased. Under identical surface cooling conditions, the condensation drops grew and fell off more quickly when the air mass fraction was low, the condensation drops irregularly varied from drop, drop-streak, to ribbon stream, and the condensation had a tendency to spread out. The heat transfer coefficients decreased with the increase of the air mass fraction. The heat transfer coefficient declined greatly under a lower air mass fraction (5–10%), while it declined slightly under a higher air mass fraction (40–50%).