ABSTRACT
In most industrial applications the cooling fluid and the condensing vapor are physically separated: condensation is realized on the dividing wall. An intermediate situation is represented by direct contact condensation, where the cooling liquid is in contact with the condensing vapor; the liquid phase is usually finely dispersed or stratified. There are different heat transfer situations, depending on the geometry and on the cool surface characteristics. The surface wettability and its orientation may determine two basic different condensation modes: with separated drops on the wall, or with a continuous liquid film. Flowing vapor exerts friction drag on the liquid film at the interface due to the momentum transfer of vapor molecules condensing on it. When the flow of liquid is determined by the shear action of vapor, it is suggested that the same approach for the computation of the heat transfer coefficient inside horizontal tubes be adopted, with appropriate values for the constants of correlations proposed for that situation.
