Experimental study on condensation heat transfer of water-ethanol vapour mixtures inside inclined tubes

Marangoni condensation is a new way to form dropwise condensation mode, which has significant potential applications in the industrial field. However, condensation with binary mixtures inside tubes, which can achieve pseudo-dropwise condensation mode is limited. This study experimentally investigated the heat transfer characteristic of water-ethanol vapour mixtures inside inclined tubes with an inner diameter of 21 mm. Experiments were conducted at inclination angles of 0 degrees, - 10 degrees, and - 30 degrees, vapour mass fluxes of 10.81, 16.22, 21.62, and 27.03 kg center dot m- 2 center dot s- 1, coolant flow rates of 1000 and 1800 kg center dot h- 1, and thermal differentials from 15 K to 60 K. The results demonstrated that pseudo-dropwise condensation mode can be formed in the condensation of waterethanol vapour mixtures inside macro-scale tubes. As vapour mass flux increased, flow regimes transformed from stratified-droplet to wavy-droplet flow. The heat transfer coefficients increased with the increase in coolant flow rates. When the coolant flow rate increased from 1000 to 1800 kg center dot h- 1, condensation heat transfer coefficients in four segments increased by 38.12%, 11.75%, 24.51%, and 9.67%, respectively. The thermal transfer increased with inclination angles in the first condensation segment. Additionally, heat transfer was found to be increased with vapour qualities. These findings provide valuable insights for optimizing heat transfer processes in nuclear systems, where precise control of condensation dynamics is essential for safe and efficient operation.