Fallingfilm

Falling-film is a type of heat-transfer and separation equipment used in chemical and process industries, in which a thin liquid film flows downward over a heated surface while vapor is generated. The liquid typically forms a continuous film on the outside of heated tubes or on flat plates, driven by gravity, and the resulting vapor is removed from the system. Falling-film configurations contrast with rising-film designs, where the liquid initially climbs the heated surface.

In operation, feed enters the evaporator and distributes as a thin film over the heating surface. Heat transfer causes rapid vaporization of the liquid in contact with the surface, while the liquid continues to flow downward as a film. The film thickness, flow regime (laminar or wavy), and surface area determine the heat-transfer coefficient and overall evaporation rate. Many installations employ single-effect or multi-effect arrangements to reuse vapor and save energy. Proper liquid distribution and surface cleanliness are important to maintain uniform film formation and avoid dry spots.

Applications are common in the concentration of heat-sensitive liquids, including fruit juices, dairy products such as milk and whey, sugar solutions, and other viscous or foaming liquids. Falling-film evaporators are valued for their gentle handling, relatively high heat-transfer coefficients for thin films, and suitability for viscous or fouling fluids. Limitations include sensitivity to poor liquid distribution, potential for fouling or pin cups on surfaces, and higher capital complexity compared with some other evaporator types.