Marangoni condensation heat transfer for binary mixture vapor at different vapor pressures

When a water-ethanol binary mixture vapor condenses on a vertical flat plate, the condensate film rises locally and creates many drops on the film. Many researchers called such a phenomenon non-film condensation, pseudo-dropwise condensation or Marangoni condensation. The purpose of this paper was to experimentally study the effect of vapor pressure on Marangoni condensation. At the same vapor speed u = 4 m · s^-1 and three different vapor pressures, i. e., 31.16 kPa, 47.36 kPa and 84.53 kPa respectively, the condensation processes of the vapors of water, ethanol and water-ethanol mixture on a brass block were studied and the variation of condensation mode was observed. The results showed that, at the same vapor concentration/speed and surface subcooling, the heat transfer coefficients of high vapor pressure were larger than those of low vapor pressure. Furthermore, at different concentrations, the vapor pressure had different effects on condensation. For water-ethanol mixture vapors of extremely high or low concentration of 22%, 51%, and 0.5%, 1%, the vapor pressure had little effect on the condensation heat transfer, but for mixture vapors of 5.1% and 9.83%, heal transfer coefficients increased obviously with the vapor pressure.