The condensation of vapours of binary immiscible liquids
Heat transfer data are reported for the condensation of steam-toluene and steam-trichloroethylene eutectic mixtures on 25.4 mm diameter oxidised copper and gold plated horizontal tubes. Data are also presented for the condensation of pure steam, toluene and trichloroethylene on the oxidised copper tube and the film heat transfer coefficients obtained agree to within ± 20% of the Labunstov form of the Nusselt equation. For the binary immiscible systems the heat transfer coefficients decrease as the temperature difference increases, with the oxidised copper surface giving higher coefficients than the gold. These differences are attributed to the two observed fundamental mechanisms of condensation, a channelling mode on the oxidised copper and a standing drop mode on the gold. Models based on the different mechanisms are proposed and predict the experimental results to within ± 20%. Finally it is postulated that the temperature dependent mutual solubilities affords an explanation of the formation of the large number of very small droplets observed during the condensation of these eutectic mixtures.