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What Is a Falling Film Evaporator?

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  • Written By: Lakshmi Sandhana
  • Edited By: Lauren Fritsky
  • Last Modified Date: 27 November 2016
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A falling film evaporator is a device used in industries to evaporate temperature-sensitive substances and obtain concentrates of those substances under controlled conditions. They find application in several industries such as dairy, paper and chemical. Falling film evaporators can also be used if the pharmaceutical and food fields.

The heat-sensitive liquid to be processed flows downwards in a thin film along the walls of the heating tubes, which is why it is called as a falling film evaporator. The liquid substance is heated to boiling temperatures if necessary, before being allowed to enter the head of the evaporator. Once it enters the head, it flows downward through the inside surface of the heating tubes.

Steam is applied to the outside surface of the tubes. The liquid evaporates without coming into direct contact with the steam. In the next phase, the concentrated liquid and the steam vapor enter a separator. The liquid is collected and released through a pump.

A falling film evaporator is used to concentrate substances that have a tendency to leave behind residues due to condensation. They are very carefully designed to allow the liquid to flow evenly down the surfaces of the tubes and require proper wetting of the heating surfaces for the process to go smoothly. If the surfaces aren’t properly moistened, then incrustations and dry patches could occur, which would hinder the whole process.

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They are the most commonly-used evaporators in many industries when it comes to concentrating heat-sensitive liquids. They are used in the diary industry to concentrate milk and skimmed-milk without incurring any heat damage. Fruit and vegetable juices are also concentrated with the aid of falling film evaporators.

It is a challenge to concentrate these substances since certain elements in the juices that affect the flavor are lost during the evaporation process. Juices also contain small solids, which are left behind in the evaporation process. These solids stick to the surface of the tubes and will either burn or cause spoilage. This problem is avoided by controlling the system so that the fluid circulates at high rate insides the tubes. Sometimes the flavor of the juice changes as it becomes more concentrated, so a little raw juice is introduced into the concentrate to ensure that the flavor remains the same.

It is possible to get consistent liquid concentrates with the help of a properly-designed control system. A falling film evaporator has a very high degree of sensitivity to change in parameters like feed rates and energy supply. It can be operated with extremely low temperature differences between the liquid to be processed and the heating medium. This characteristic allows a falling film evaporator to be used in multiple configurations in many industries.

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