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    The rising film evaporator is also called a climb film evaporator. It operates according to the principle of the siphon pump. According to the lift of the steam bubbles generated during the boiling process, the liquid and the steam flow in parallel, and at the same time, the amount of steam generated increases, thereby A flowing membrane is created on the wall of the tube, ie the liquid "crawls up". The parallel flow movement is ribbed to create a high degree of turbulence in the liquid. 

　　This type of evaporator is characterized by a long heating tube (about 5 to 7 M), but the temperature difference between the heating chamber and the boiling chamber must also be large. Otherwise, the energy of the steam flow is insufficient to transport the liquid and produce a climbing film. .

A：Material import

B：Condensate outlet

C：Condensate outlet

D：Concentrate outlet

E：Secondary steam outlet

　　 In the falling film evaporator, the liquid and the steam flow in parallel, the concentrated liquid is preheated to the boiling temperature, and the uniform liquid film enters the heating pipe through the liquid distribution device on the top of the evaporator, and flows downward at the boiling temperature. And partially evaporating, the gravity introduced by the downward movement is continuously strengthened by the cocurrent steam flow.

　　 In a falling film evaporator, it is extremely important to fully wet the liquid to heat the surface to face the trouble-free operation of the device. If the heating surface is not sufficiently wetted, local drywall and crusts will occur, and the bad condition is that the heating tube will be completely blocked. In critical cases, the wetting rate increases as the evaporator efficiency increases or divides, so the advantages of single pass operation should be maintained. In this mode of operation, the contact time of the liquid and the heating surface is almost constant, usually in the order of seconds.

　　 In addition to the tube size, the selection of a suitable liquid distribution device is important to achieve complete wetting. The following figures illustrate two liquid distribution devices. Due to the low amount of liquid in the heating tube and the fast flow rate, the product residence time is quite short, so that the heat sensitive material can be evaporated extremely gently.