Condensation heat transfer of steam on vertical micro-tubes

In this paper the condensation heat transfer of steam on vertical micro-tubes was investigated. Experiments were carried out under various vapour pressures and vapour velocities. Four tubes with different diameters, 0.608 mm, 0.793 mm, 1.032 mm and 1.221 mm, were included. The results showed that, with the increase in vapour-to-surface temperature difference, condensation heat transfer coefficient decreased monotonously, as well as that by Nusselt's Equation on vertical surface. With the decrease in tube diameter, the condensation heat transfer coefficient decreased monotonously. As the curvature effect on heat transfer, the experimental values of condensation heat transfer coefficients were higher than the predicted values by Nusselt's Equation. The difference of condensation heat transfer coefficients between different tubes was obvious. It indicated that the effect of tube diameters on condensation heat transfer for micro-tubes was significant, and should be attached great importance. With the increase in vapour pressure and vapour velocity, the condensation heat transfer coefficient increased. A new correlation for condensation heat transfer of steam was proposed considering the effect of tube diameter and vapour velocity. For 95% of the data, the deviation between the predicted values and the experimental data is in the range of ±20%.