HEAT AND MASS-TRANSFER IN WATER AMMONIA FALLING FILMS AT SMOOTH AND ROUGH TUBES

The present paper studies the water/ammonia film falling down along evaporation tubes. Heat and mass transfer coefficients with smooth, sandblasted, knurled and spine tubes were measured and compared to values found in literature. The experiments cover the laminar-wavy flow range and the concentration range between 45 and 70 weight percent of ammonia. Compared to other working mixture pairs the mass transfer with smooth tubes is clearly higher in the water/ammonia film. The heat transfer, however, does not vary substantially compared to the values of the other liquid mixtures. Knurling the wall improves primarily the heat exchange. But only a direct disturbance of the gaseous-liquid interphase did result in a considerably accelerated mass transfer through the film.