"Mixed" pattern condensation of multicomponent mixtures

"Mixed" pattern condensation, in which drops, streaks and a few patches of a continuous film simultaneously form the condensate, was investigated by condensing binary mixtures of methanol-water and methanol-ethanol and ternary mixtures of acetone-methanol-water onto a gold-plated copper surface. Photographs of the condensate showed the following patterns relative to the temperature difference T_∞ - T_w : filmwise, filmwise-streakwise, streak-wise, streakwise-dropwise and dropwise. The observations demonstrate the following general trends: (a) The condensation pattern of mixtures which form a stable film with respect to the Marangoni effect (acetone-methanol) is always filmwise. (b) The condensation pattern of mixtures forming an unstable film (methanol-water, acetone-methanol-water) changes from filmwise to dropwise. depending on T_∞ - T_w and the composition of the mixture. At large temperature differences or as the composition approaches that of a pure component, filmwise condensation is predominant. At small T_∞ - T_w, streakwise-dropwise and dropwise condensation occurs. (c) In all cases the gas side resistance increases with decreasing T_∞ - T_w. (d) Mixed pattern condensation enhances the condensation flux as compared to filmwise condensation by as much as a factor of 4.