Abstract: A thin-film evaporator comprising a vertical drum (1), a supply line (4) that is arranged in the upper region of the drum (1) and is used to supply a medium to be evaporated, a heating jacket (3) arranged on the periphery of the drum and forming vapours, a discharge line (20) for discharging the residue left in the lower end of the drum, and a condenser (11) supplied with a coolant, for increasing the separating capacity and optionally for performing chemical reactions, is characterized in that an inner device (24) influencing the action of the thin-film evaporator is provided in the path of the vapours from the heating jacket (3) to the condenser (11).