DIRECT CONTACT CONDENSATION OF DILUTE STEAM/AIR MIXTURES ON WAVY FALLING FILMS

Abstract Condensation from air-steam mixtures on falling water layers is investigated experimentally and theoretically. The thin film flows on the inner surface of a 5cmi.d. vertical pipe. This film is wavy turbulent while the gas phase is kept saturated with steam. Experiments are conducted with the gas mixture effectively stagnant, compared with the fast moving liquid film. Measurements are also made under a mild vacuum applied on the gas phase. Heat transfer coefficients averaged over the entire length of the condensing surface, tend to increase by decreasing the liquid flowrate, by increasing the steam fraction, and by applying a mild vacuum on the gas phase. However, for the cases examined, there is a liquid flowrate above which the heat transfer coefficient becomes almost constant. Numerical predictions are made for a fully developed turbulent film using an eddy diffusivity model. The results indicate that for a system with a large amount of noncondensable gases-as in this study-the temperature prof...

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