Marangoni condensation of steam-ethanol mixtures using low-ethanol concentrations

Marangoni condensation heat transfer characteristics of steam-ethanol mixture were experimentally investigated using a horizontal smooth tube at atmospheric pressure. Results were obtained over a range of ethanol concentration, vapor velocity, and vapor-to-surface temperature difference. Ethanol concentrations by mass in the boiler when cold prior to start up were 0.001, 0.005, 0.01, 0.017, and 0.021%. The results indicate that maximum heat transfer enhancement of around 4 times was obtained at ethanol concentrations of 0.017 and 0.21%. Moreover, the point of maximum heat transfer shift ed from lower to higher vapor-to-surface temperature difference with increasing ethanol concentration. The condensate appearance changed from filmwise to the dropwise mode with increasing vapor-to-surface temperature difference. Photographs showing the condensate appearance are also included in the paper.