The central circulation tube evaporator is also known as a standard evaporator. Its heating chamber is composed of vertical tube bundles, with a central circulation tube with a large diameter in the middle, and the other heating tubes with smaller diameters are called boiling tubes. Due to the large size of the central circulation tube, the heat transfer surface occupied by a unit volume of solution in the central circulation tube is smaller than that occupied by a unit volume of solution in the boiling tube. This means that the heating degree of the solution in the central circulation tube and other heating tubes is different, resulting in a lower density of the vapor liquid mixture in the boiling tube compared to the solution in the central circulation tube. In addition, the upward suction effect of the rising steam will cause the solution in the evaporator to form a solution that falls from the central circulation tube Circulating flow rising from a boiling tube. This cycle is mainly caused by the density difference of the solution, hence it is called a natural cycle. This effect is beneficial for improving the heat transfer effect inside the evaporator.

The steam generated in the heating chamber contains a large amount of liquid foam, which can be separated from the steam through self condensation or the action of a defoamer when it reaches a larger evaporation chamber. Usually, the defoamer is located at the top of the evaporation chamber. Boiling evaporation: Heating a solution to its boiling point to evaporate in a boiling state. The evaporation operations in industry are basically of this type.