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Falling-film columnA falling-film column (or wetted-wall column) is a kind of laboratory equipment used to achieve mass and heat transfer between two fluid phases (in general one gas phase and one liquid phase). It consists of a vertical tube-shaped vessel: the liquid stream flows downwards through the inner wall of the tube and the gas stream flows up through of the centre of the tube.[citation needed] Description In the most common case, the column contains one liquid stream and one gas stream. The liquid forms a thin film that covers the inner surface of the vessel;[1] the gas stream is normally injected from the bottom of the column, so the two fluids are subjected to a counter-current exchange of matter and heat, that happens through the gas-liquid interface.[citation needed] Sometimes, the same equipment is used to achieve the co-current mass and heat transfer between two immiscible liquids.[2] ApplicationsBecause they are easy to model, falling-film columns are generally used as laboratory equipment, for example to measure experimentally the values of transport coefficients.[1] A significant experiment was carried out in 1934 by Edwin R. Gilliland and Thomas Kilgore Sherwood that used a falling-film column to study the mass transfer phenomenon between a liquid phase and a gas phase, obtaining an experimental correlation between the Sherwood number, Reynolds number and Schmidt number.[3] Falling-film columns are not used at industrial scales, because they have a low surface area and liquid hold-up[definition needed] compared to other gas-liquid contactors (e.g. a packed column or a plate column).[citation needed] References
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