Effect of Tube Diameters on Marangoni Condensation Heat Transfer for Ethanol-Water Mixture Vapors

Marangoni condensation attracts much attention in recent years. This study focused on the effect of tube diameters on Marangoni condensation heat transfer in the case of ethanol-water mixture vapors. Several tube outer diameters, including 0.793 mm, 1.032 mm, 1.221 mm, 10.0 mm, and 20.0 mm, were chosen to indicate the phenomenon, as well as the vertical plate. The ranges of the tube diameters were from macroscale to microscale. The experimental results showed that for pure steam the heat transfer coefficients monotonically increased with the decrease in diameters. For the ethanol-water mixture vapors, the reduction effect of liquid thickness and the accumulation effect of condensate liquid jointly influenced the heat transfer. In the case of macrosurfaces, the promotion effect caused by diameter decrease played a dominant role, and the heat transfer coefficients increased with decreasing the diameters. In the case of microsurfaces, the negative effect of condensate liquid accumulation became active and was the dominant role. The heat transfer coefficients did not always increase with decreasing the diameters, and a critical diameter corresponding to the largest heat transfer coefficients existed.