Marangoni Condensation of Steam-Ethanol Mixtures

Principal investigator: Huasheng WANG

A very small concentration of ethanol (e.g. 0.05% - 0.1% in mass) in the liquid phase has been found to give significantly higher (3-4 times) heat-transfer coefficients than found with pure steam. The mechanism of the enhancement is attributed to the fact that for condensation of binary mixtures, where the less volatile constituent has the higher surface tension, the condensate film is potentially unstable and various ‘‘modes” of condensation are seen depending primarily on composition and vapour-to-surface temperature difference. The appearance of the condensate closely resembles that of dropwise condensation of a pure fluid on a hydrophobic surface. An ongoing programme of steam-ethanol mixtures condensation on horizontal tubes and bank of tubes at atmospheric and sub-atmospheric pressures is in progress.