Studies on heat-transfer film coefficients inside a horizontal tube in falling film evaporators Original Research Article

The effects of liquid load, tube diameter, evaporation boiling point, condensation temperature difference and steam flow velocity on the heat-transfer film coefficients inside horizontal tubes were studied. The experiments were conducted with various operation parameters. In fact, if there is little shear stress on the film surface, it affects film thickness and blocks the condensate flowing inside the tube, but it is not strong enough to make the condensate to be ring flow. We defined the shearing Reynolds number in order to describe the effect of this small shear on the film of condensate. Using a regression of the experimental data, the models of condensation heat-transfer coefficient were built. According to the literature, some theoretical models cannot be used to explain why condensation heat-transfer coefficients increase gently with steam flow velocity. Our models of condensation heat-transfer coefficient can be used to explain this problem. These results provide a basis for further developing the high efficiency heat-transfer process and novel evaporators.