Marangoni condensation heat transfer characteristics on vertical surface with temperature gradients

Marangoni condensation heat transfer of water-ethanol mixtures on a vertical surface with temperature gradients were studied experimentally, and the variation of condensation modes was observed. The results show that the local heat transfer coefficients at different locations on condensing surface were different, and at the local position with greater temperature gradient the heat transfer coefficient was higher. When the ethanol vapor concentration (mass fraction) was at low range (0.5%, 1%), the heat transfer coefficient decreased with the increase of vapor-to-surface temperature difference. When the ethanol vapor concentration was higher, the characteristic curve was a nonlinear one with a maximum. The highest heat transfer coefficient existed at a ethanol vapor concentration of 1%. The heat transfer coefficient decreased with the increase of vapor concentration when the ethanol vapor concentration was more than 2%. Compared with the solutal Marangoni condensation, the present Marangoni condensation driven by concentration and temperature gradients had stronger heat transfer. The preliminary analysis also shows that, under the coaction of concentration and temperature gradients, the surface tension gradient on the condensate surface is greater, leading to the condensation heat transfer to be further enhanced.