Thin film or wiped film evaporators are used to separate a mixture of liquids having different boiling points. It is also used to increase the concentration of liquids.

Principle of Operation
The liquid feed is distributed on the heated wall of the evaporator to form a uniform thin film with the help of suitable configuration of blades. The volatile component or the component with lower boiling point gets evaporated and is vacuumed out of the evaporator, while the component with higher boiling point flows down the wall and is collected at the bottom. The vapours are passed through a condenser and collected separately.

Operating Features
The heat transfer in thin film evaporator is very quick and efficient, thus demanding lower surface area and heat input as compared to other types of evaporator. Due to high vacuum distillation and very short residence time the thin film evaporator are suitable for handling wide range of heat sensitive, high boiling and viscous feeds. Due to low rotor speeds in the range of 100 to 150rpm, the horse power requirements are very low. To reduce the pressure drop between the evaporator and condenser, the internal condensers can be provided to achieve short path distillation. The thin film evaporators are designed to handle various products with operating pressures up to O.1torr. Liquids with viscosities above 2,00,000cps can be handeled in these evaporators.