Droplet departure radii for Marangoni condensation

An oblique copper block, which created surface temperature gradient, was designed to experimentally study the effect of macroscopic temperature gradient on Marangoni condensation of ethanol-water vapor mixtures. The experiment was carried out under a wide range of concentrations (0%-50%). For each concentration, the experiment was performed at different velocities and pressures. During the experiment condensation photographs were shot. Dropwise condensation departure radii was studied based on these photographs under the condition of different concentration, vapor-to-surface temperature difference and vapor velocity. The departure radii of dropwise condensation closely depended on the above factors. The correlation for the maximum departure radii of condensate drops was obtained on the basis of the formula for pure water vapor with velocity and Marangoni effect caused by condensation surface temperature difference. The calculation results are in good agreement with the experimental measurement over large vapor-to-surface temperature difference, and its maximum error is 23%.