It is widely used for petrochemical industry, chemical industry, pharmacy, fertilizer, paper making, aluminum industry, monosodium glutamate, brewage, sugar making and etc.

In the falling film evaporator, the liquid enters into the heating tube for heating by adopting the principle of siphon pump and flows into the separator. After that, the liquid and steam are separated and then return to the evaporator through the circulation pipe, and a closed circulation is formed. Therefore, this evaporator is also called external circulation evaporator. When it comes to the evaporator selection, if the evaporation is higher, the multi-effect device can be adopted to achieve the purpose of saving steam and reducing energy consumption.

The heating tube is composed of heat exchanging tubes. After it is preheated to reach or get close to the boiling point, the raw material liquid is introduced from the bottom of the heating chamber and is driven by the secondary steam that rises at a high speed. It will be evaporated while it flows along the interior wall of the heat exchanging tube. After it reaches the top of the heating chamber, the required strength is reached. The completed liquid will be discharged from the bottom of the separation chamber. The secondary steam produced will become the heat source of the next effect after foam, water drop and impurities are removed at the upper separation board. This evaporator is suitable for disposing thin solutions of higher evaporation, heat sensitive solutions or solutions easy to produce foam.

After being preheated, the raw material liquid enters into the heating tube through the bottom of the evaporator. The heating steam carries out condensation outside the pipe. After the raw material liquid is heated, it is boiled and vaporized. The secondary steam produced will rise at a high speed in the tube and drive the material liquid to flow upwards along the interior wall of the tube in the form of film and carry out continuous evaporation and vaporization with accelerated flow. The gas-liquid mixture will be separated after it enters into the separator. The completed liquid after concentration will be discharged from the bottom of the separator. This evaporator needs elaborate design and operation. That is, the secondary steam in the heating tube shall have higher speed and higher heat transfer coefficient to make the material liquid reach the preset concentration requirement when it passes through the heating tube only once. Generally, under the normal pressure, the speed at the outlet at the top of the tube shall be kept about 20～50m/s, and during the pressure relief operation, the speed can reach 100～160m/s.

The falling film evaporator is suitable for disposing solutions of higher evaporation, heat sensitive solutions of low viscosity and solutions easy to produce foam, but not suitable for solutions of high viscosity, solutions having crystalline precipitation and solutions easy to agglomerate.