Both falling film evaporator and rising film evaporator belong to the category of thin film evaporator, and they have significant differences in multiple aspects, including working principle, structure, operation mode, applicable materials, and performance characteristics.

      1、 Working principle

      Falling film evaporator: The liquid is added from the top of the heating chamber, and under the action of gravity, it forms a film like descent along the inner wall of the tube and evaporates. The concentrated liquid enters the separator from the bottom of the heating chamber and is discharged from the bottom, while the secondary steam overflows from the top. Due to the consistency between the flow direction of the secondary steam and the flow direction of the feed liquid, it can promote the downward movement of the feed liquid and form a thin film.

      Rising film evaporator: The liquid material enters the heating tube from the bottom and quickly vaporizes after being heated and boiled. The steam rises rapidly inside the tube, and the liquid material is driven by the high-speed rising steam to form a film like rise along the tube wall and continue to evaporate. Gas and liquid separate at the top, secondary steam overflows from the top, and the completed liquid is discharged from the bottom.

    II. Structure and Operation

      Both are structurally similar, including heating chambers, evaporation chambers (or separation chambers), etc., but the inlet and outlet positions of the feed liquid are different.

      The falling film evaporator requires the inner wall of each tube to be wetted by the liquid and continuously have the liquid flow slowly to prevent dry wall phenomenon.

      The rising film evaporator relies on high-speed rising steam to drive the liquid to form a film like rise.

      3、 Applicable materials

      Falling film evaporator: suitable for heat sensitive materials, it can effectively prevent materials from denaturing or decomposing due to high temperature during the evaporation process. But it is not suitable for materials that are prone to crystallization, scaling, or have high viscosity.

      Rising film evaporator: suitable for solutions with large evaporation capacity, heat sensitivity and easy to produce foam. However, it is not suitable for materials with high viscosity, easy crystallization or scaling.

      4、 Performance Characteristics

      Falling film evaporator: high heat transfer coefficient, less prone to scaling, low energy consumption, and low operating costs. In addition, due to the natural flow of the liquid under gravity, the operation is relatively stable.

      Rising film evaporator: Due to the high-speed rise of steam, the material liquid can form a film like rise, resulting in high evaporation efficiency. However, compared to the falling film evaporator, its operational stability may be slightly inferior.

      In summary, falling film evaporators and rising film evaporators each have their unique advantages and applicable ranges. When choosing which evaporator to use, it is necessary to comprehensively consider factors such as specific material properties, evaporation capacity requirements, and operational stability.