The falling film evaporator is to add the liquid from the heat exchanger, through the liquid distribution and film forming device, evenly distributed into each heat exchange tube, under the action of gravity, vacuum induction and air flow, it becomes a uniform film flow down from the top. During the flow process, it is heated and vaporized by the heating medium in the shell side, and the generated vapor and liquid phase enter the separation chamber of the evaporator together. After the vapor-liquid is fully separated, the vapor enters the condenser to be condensed and collected. Falling film evaporators are mainly used in solvent recovery in biological, pharmaceutical, chemical and other industries, and can be used in multiple stages to achieve a higher energy efficiency ratio.