Interfacial heat transfer coefficients of various vapors in direct contact condensation

Interfacial heat- transfer coefficients h_i for the direct contact condensation of a vapor on a liquid film of similar chemical composition were measured at various saturation pressures for the following substances: water, carbon tetrachloride, methanol, n-pentane, methylene chloride, Freon-113, 1,1-dichloroethane and carbon disulfide. Carbon disulfide was also condensed on a film of water. A wetted sphere with a laminar film was employed for these measurements. It was found that the relative magnitude of the interfacial resistance 1/h_i was appreciable compared with the overall average resistance and varied in the range 10-80%. Consequently the condensation coefficients α were found to be much lower than unity, varying between 0.001 and 0.06. For water, carbon tetrachloride and methanol, the exponential decrease of α with increasing saturation temperature was in agreement with theoretical predictions. Further understanding of the condensation mechanism of immiscible vapors on water was obtained by comparing the present results for interfacial heat transfer coefficients with those obtained for direct contact condensation of immiscible vapors on a water film. It seems that the condensation mechanism of n-pentane and Freon-113 on water is associated with nucleation phenomena. On the other hand, when methylene chloride, carbon disulfide and 1,1-dichloroethane are condensed on water, the mechanism is different. A continuous film of these substances is probably formed on the water surface so that the vapors condense as if on a liquid film of similar chemical composition.