Falling-film column

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.

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] Because 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.