The falling film evaporator is particularly used in application, when the driving force between heat transfer medium and liquid is small.
In a falling film evaporator with separate vapor body and heat exchanger the liquor is fed into the top liquor chamber of the heat exchanger where it is distributed to each tube.
The liquor accelerates in velocity as it descends inside the tubes because of the gravity and drag of the vapour generated by boiling. Liquid is separated from the vapour in the bottom liquor chamber of the heat exchanger.
Concentrated liquor is discharged from the bottom liquor chamber and cone bottom of the vapour body.
Evaporation occurs inside the tubes of the falling-film evaporator. The unit can used to concentrate the same non-salting liquids concentrated in rising-film evaporators, and it is suitable for concentrating more viscous liquors.
The retention time for liquor in this evaporators is less than that for a rising-film evaporator. The combination of short liquid retention time and the ability to operate at a low dT makes the falling-film evaporator ideal for concentrating the most heat-sensitive materials.
